2001 RWD still getting bad gas mileage - S-10 Forum
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post #1 of 58 Old 04-14-2019, 04:37 AM Thread Starter
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2001 RWD still getting bad gas mileage

After replacing my fuel spider, plugs, fuel filter, MAF, fan clutch and many other parts, I'm still getting pretty terrible mileage from my 2001 RWD. Not sure what could be causing it. I'm not getting any codes, and the truck seems to run fine. I was able to get 317 miles per tank every time with my old S10. Seemed consistent no matter how I drove. This truck, however, was a mess when I got it. Pretty much everything was trashed. I'm wondering if there's something I missed. Pretty much the only stock part of the fuel system left is the pump, and it tested as holding pressure. Fires the truck up on the first shot every time, so if it's going bad it would surprise me.

What are some other things that could cause bad mileage, without tripping the check engine light?

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post #2 of 58 Old 04-14-2019, 07:36 AM
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Re: 2001 RWD still getting bad gas mileage

What is bad mileage ? What drive train rear end? What kind of driving? Winter- summer?
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post #3 of 58 Old 04-14-2019, 11:45 AM
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Re: 2001 RWD still getting bad gas mileage

You need to give us more info on the truck. Like said above, motor, trans, rear gears, tire size all play a role in it.

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post #4 of 58 Old 04-14-2019, 02:11 PM
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Re: 2001 RWD still getting bad gas mileage

The fact it's an S10 with a 4.3 enters in also. They don't get the kinda of mileage a Honda with a 2.nothing does.
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post #5 of 58 Old 04-14-2019, 03:40 PM
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Re: 2001 RWD still getting bad gas mileage

If you don't drive it like you stole it, and the tune is in order, 4.3's will get respectable milage for what they are.

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post #6 of 58 Old 04-14-2019, 04:36 PM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

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Originally Posted by lilbowtie View Post
What is bad mileage ? What drive train rear end? What kind of driving? Winter- summer?
To me, any mileage that's worse than what I was getting previously, since it's a lot of the same equipment swapped onto the new truck. I want to be able to get about 300 miles in before the low fuel light comes on. Right now I'm getting closer to 200 miles per tank. I'll have to watch it more closely over the next week to see what it averages with its new MAF.

I don't know much about the rear end. It's a RWD truck, with drum brakes on the back. It looks like the rear end from the old truck, but I can't be sure if they're the same model.

Driving conditions are summer and fairly dry. I live in the Southern part of the US. I do a lot of highway driving, and a fair amount of idling in traffic. None of this ever effected the old truck.
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post #7 of 58 Old 04-14-2019, 05:07 PM
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Re: 2001 RWD still getting bad gas mileage

I did a 268 mile round trip yesterday in the wife's Blazer2. I just filled and calculated...19mpg. Frfeeway speeds were between 65-75. I won't complain about that.

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post #8 of 58 Old 04-14-2019, 08:36 PM
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Re: 2001 RWD still getting bad gas mileage

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To me, any mileage that's worse than what I was getting previously, since it's a lot of the same equipment swapped onto the new truck. I want to be able to get about 300 miles in before the low fuel light comes on. Right now I'm getting closer to 200 miles per tank. I'll have to watch it more closely over the next week to see what it averages with its new MAF.



I don't know much about the rear end. It's a RWD truck, with drum brakes on the back. It looks like the rear end from the old truck, but I can't be sure if they're the same model.



Driving conditions are summer and fairly dry. I live in the Southern part of the US. I do a lot of highway driving, and a fair amount of idling in traffic. None of this ever effected the old truck.
Look in your glove box and get the rpo code for the gears. What size tires?

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post #9 of 58 Old 04-15-2019, 01:57 AM
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Re: 2001 RWD still getting bad gas mileage

Do you have the ability to view the trucks fuel trim numbers in the live data stream? If something is causing poor fuel economy, there is a good chance it would be reflected in the fuel trim numbers.

You could check the coolant temp sensor as well, these will generally cause a vehicle to run excessively rich when they go bad and often times won't set any codes. Often times they will give a reading of -44 degrees when they go bad, but not always. After the truck has been sitting overnight, look at the coolant temp on the scanner (don't start the truck first), it should show very close to what the ambient air temperature is.

What about a fuel leak? Have you checked for leaks, particularly around the filler neck and all the connections in the fuel lines? What about those drum brakes... are they dragging? That would reduce economy as well.

All that said, it would help to know what the actual calculated fuel economy is. Fill the tank full, till the pump stops itself and do not overfill the tank. Reset trip odometer when you fill up. then drive until its almost empty, fill the tank full again. Take the number of miles driven (as seen on trip odometer) and divide that by the number of gallons you put in on the second fill up. It would be much easier to say there is or isn't a problem if we knew the trucks actual calculated fuel economy.
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post #10 of 58 Old 04-15-2019, 10:27 PM
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Re: 2001 RWD still getting bad gas mileage

Someone may correct me if I am wrong but wasn't there 2 different capacity tanks for S-trucks over the years? Maybe this truck you have now has the smaller tank compared to your last one.
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post #11 of 58 Old 04-15-2019, 11:04 PM
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Re: 2001 RWD still getting bad gas mileage

You can check tank capacities at the GM Heritage site. For the most part, they ranged from 18.5 to 19 gallons.

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post #12 of 58 Old 04-16-2019, 10:46 PM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

Thanks so much for the responses, lots of good info. I always suspected my tank was about 19 gallons in the old truck. The new one appears to be identical.

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Originally Posted by thebadwrench View Post
Do you have the ability to view the trucks fuel trim numbers in the live data stream? If something is causing poor fuel economy, there is a good chance it would be reflected in the fuel trim numbers.
I've been meaning to get an adapter so I can plug my laptop in. Otherwise I'll have to take it to a shop. That's a last resort.

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You could check the coolant temp sensor as well, these will generally cause a vehicle to run excessively rich when they go bad and often times won't set any codes.
I didn't even know it had one, so this is good info. I might try swapping the CTS from my spare engine that I saved from the old truck. It had no problems as of the last time I drove it. I've been meaning to change the coolant anyway.

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What about a fuel leak? Have you checked for leaks, particularly around the filler neck and all the connections in the fuel lines? What about those drum brakes... are they dragging? That would reduce economy as well.
I already put new drums on it. The old ones were pretty bad. And I'm fairly sure it doesn't leak fuel. There's no gas smell, at least. No drips or anything, and I've spent a fair amount of time under it cleaning off all the mud from the previous decades of this truck's life.
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post #13 of 58 Old 04-17-2019, 06:49 PM
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Re: 2001 RWD still getting bad gas mileage

Figure out your real fuel mileage, rather than just saying X amount of miles before the light comes on.


1. Go to the gas station and fill up your tank until the pump clicks off. Don't "top it off". Reset your trip meter.
2. When you're low on fuel, go back to the gas station (preferably the same one) and fill up again the same as step 1.
3. Look how many miles are on your trip meter. Divide it by the number of gallons the pump is showing. That is your fuel mileage.
4. Report back to this forum and post your results so we have an idea of what you're talking about.
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post #14 of 58 Old 04-17-2019, 07:02 PM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

Alright, I've refilled the tank today. I put 14.90 gallons in, and the trip was at 167 miles when I reset. We'll see how it does when I fill up again. When I filled up today, the needle was well under the quarter tank mark but not entirely on E. Close enough to make me nervous. I realize now that all those years when I was driving until the fuel light came on, I was probably nearly bone dry in the tank. Very dangerous to do in my city, I don't know if I have the nerve to drive like that again. I live in a place where there's a good chance I can die if my vehicle breaks down. I'm also not entirely sure this new truck has a working low fuel light. But could it really have had three to four gallons left in it with the needle as low as it was?

I guess we'll see after this next tank burns through.
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post #15 of 58 Old 04-23-2019, 01:33 AM
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Re: 2001 RWD still getting bad gas mileage

I know my fuel light comes on when there's about 8-10 Liters left (aprox. 2-2.5 gallons) I have a bad habit of running it past the E line...... I've gotten good at guessing how much gas will fill my tank based on how far I drove with the light on lol. Not that I would ever recommend it but you might be surprised how far you can go with the low fuel light on.
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post #16 of 58 Old 04-23-2019, 02:33 PM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

Ok, the results are in. I was able to drive the truck 233 miles before filling up. The low fuel light came on, and the truck was sputtering as I pulled into the station. I was only able to put in 14.825 gallons, which confuses me. Shouldn't the tank be bigger? Because I filled up with roughly this much before. So I guess my tank is only 15 gallons or so? I know the truck was just about on fumes today.

It seems like replacing the CTS did improve economy. I also replaced the EGR valve. Are there any more things that would rob economy and performance? The truck drives normal on surface streets, but seems to lag somewhat in the top end. It's like there's a flat spot in the acceleration above 70 mph. I might try swapping the throttle position sensor and cleaning the throttle body out.
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post #17 of 58 Old 04-23-2019, 06:06 PM
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Re: 2001 RWD still getting bad gas mileage

Your tank is 19 gallons...thought I said that already...

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post #18 of 58 Old 04-23-2019, 06:47 PM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

You did, but clearly it's not taking 19 gallons. There's no way that tank had more than a gallon in it when I filled up today. There's no certainly way I still had 4.17 gallons in there. If that gas station had been even a few hundred feet down the block I wouldn't have made it.
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post #19 of 58 Old 04-23-2019, 08:19 PM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

I might have solved the mystery of the missing economy and acceleration, since the truck gave a p0420 this evening after a long drive. I can't decide if I want to go ahead and put a new cat in there, or first try the trick I saw on Youtube of putting a gallon of paint thinner in the tank. Though I'm fairly sure it would be a waste of time, as that trick appears to be for cats that are dirty, not plugged up as I suspect mine to be.
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post #20 of 58 Old 04-23-2019, 08:30 PM
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Re: 2001 RWD still getting bad gas mileage

You're right...it is a trick. Just get another cat, or have one welded in.

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post #21 of 58 Old 04-24-2019, 12:54 AM
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Re: 2001 RWD still getting bad gas mileage

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Ok, the results are in. I was able to drive the truck 233 miles put in 14.825 gallons,
15.74 MPG isn't really out of line for a 4.3 automatic that has a bunch of miles on it. Not spectacular, but close to normal for your average S10.
I know there are guys who are meticulous about maintenance and drive like someones Granny that get over 18, but that's not your average 4.3 S10 or driver either.
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post #22 of 58 Old 04-24-2019, 01:32 AM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

We'll have to see, but I think the rest will probably clear up once I replace the cat. Having it plugged up must not be doing me any favors on fuel economy.
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post #23 of 58 Old 04-24-2019, 03:02 AM
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Re: 2001 RWD still getting bad gas mileage

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Ok, the results are in. I was able to drive the truck 233 miles before filling up. The low fuel light came on, and the truck was sputtering as I pulled into the station. I was only able to put in 14.825 gallons
Your fuel economy is right on par with what an S-10 with the 4.3L usually gets. For comparison, my blazer averaged 14-16 and on rare occasion I might see 17-18. I actually managed 21mpg on one tank, not sure how I managed to do it though.

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You did, but clearly it's not taking 19 gallons. There's no way that tank had more than a gallon in it when I filled up today. There's no certainly way I still had 4.17 gallons in there. If that gas station had been even a few hundred feet down the block I wouldn't have made it.
Most any car out there, when it runs out of gas... the gas tank will still have at least 2-2.5 gallons of fuel, sometimes more, sitting in the bottom of the tank that the pump can't reach. 4 gallons isn't out of the question either, especially if the pump isn't sitting quite right in the tank because some yahoo didn't orient the pump correctly when they put it in. I'm just mentioning that as a possibility.... there's absolutely no need to go and pull the tank to check for that though. Was just sayin

My Blazer had a 17 gallon tank and very rarely did it ever take more than 14 gallons if it was on or even below "E".
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post #24 of 58 Old 04-24-2019, 08:34 PM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

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there's absolutely no need to go and pull the tank to check for that though. Was just sayin
Is there a way to tell if I've got the OEM fuel pump in there, without dropping the tank? I'd love to know if it's some ancient part that's about to fail, or a brand new made in China part that's about to fail. I suspect it may have been replaced, because the truck has like 250k miles on it. If it's an OEM pump, it's on its last legs. My old truck made it 213k with the OEM pump, and I suspect that might be in the upper threshold of these thing's lifespan.
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post #25 of 58 Old 04-24-2019, 09:51 PM
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Re: 2001 RWD still getting bad gas mileage

Pretty much any of the s10 and blazer replacement pumps nowadays require the old pump connector to be removed and a new one installed, which comes with the pump. If you can get your hand up there, you may be able to feel around and see if you feel where this splice has or hasn't been done. A mirror would work too. At 250k I'd be really surprised if it had the OE pump still. They're usually toast long before that point.
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post #26 of 58 Old 04-24-2019, 10:30 PM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

Good advice. I'll check that out the next time I'm under it. I'll need to get started soaking my catalytic converter bolts now so I can get them loose by the time the new assembly ships to me.

There are two options for people in my situation. I can either order a whole new cat and pipes that connect to the manifold, or I can saw the old cat out and bolt in a cheapo replacement with some sleeve brackets. I've decided to order the option that includes the new downpipe, and also order new O2 sensors while I'm at it. I want to be on an even footing with those sensors and not have the thing look like crap by having to use those brackets and some aftermarket thing.

Do you think I will be able to DIY the swap? I've already gotten 5 of the 9 bolts loose. There's one stubborn bolt on the driver side donut and the three on the flange behind the cat. As I mentioned, I won't bother trying to unseat those ancient O2 sensors. I want all new all around. Then I'll probably get the emissions tested right now to make sure it passes. It was sold to me with fraudulent inspection certification, so who knows how that will go.
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post #27 of 58 Old 04-25-2019, 03:54 AM
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Re: 2001 RWD still getting bad gas mileage

I don't know what your skill level is so it's hard for me to say if you'll be able to DIY. It is a job that a mechanically inclined individual should be able to complete at home. That said, nuts and bolts for exhaust components tend to be a bit stubborn and sometimes take some patience. If you don't have a MAP gas torch, you might want to get one. If the nuts wont break loose, heat em with the torch (when heating be VERY careful of surrounding areas... collateral damage to wiring is never fun). Those downpipe to manifold nuts can be a real sometimes. Occasionally I'll just cut the stud with the seized nut off with a cutoff wheel, right at the flange. Then I'll use a stud puller to remove the remainder of the stud from the manifold once the downpipe is out, replace the stud with a new one.

O2 sensors usually aren't too difficult to remove. They have anti-seize on the threads when they get installed and if you make sure the exhaust is warm, they often times break loose easier than you might think. Not always though.

If the emissions certificate presented to you was forged, there is probably a reason for it i.e. it wouldn't pass. With any luck maybe it'll pass with the new cat though. Did you buy it from an individual or a dealer of some kind?
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post #28 of 58 Old 04-25-2019, 11:29 PM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

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If the emissions certificate presented to you was forged, there is probably a reason for it i.e. it wouldn't pass. With any luck maybe it'll pass with the new cat though. Did you buy it from an individual or a dealer of some kind?
I got this truck from a mechanic who bought bought it from an auction. I had previously hired him to work on another truck, which he ruined. He basically gave me this one since he got in way over his head trying to fix the other one. He passed it off as being a runner and sent me on my way. I could tell it had a lot of problems but was just ready to be done with the guy. I was able to use the emissions test he presented with the vehicle at time of sale to get it titled, even though it was giving EVAP codes from day one.

Since then I've replaced the fuel spider, fuel filter, power steering pump, alternator, serpentine belt and tensioner, power steering lines, radiator, water pump, fan clutch, EVAP solenoid and pigtail, MAF, throttle body, spark plugs and wires, airbox and door gaskets. I also had to hire a shop to do my control arms and ball joints. Everything else I did myself. I'm currently struggling to get the secondary steering shaft removed so I can swap in a better one I found that has less slop in it. I have no idea why mine is being so stubborn, when the one at the junkyard I practiced on came right out. But whatever. I'll have a few days to mess with it while I wait on the cat to arrive.
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post #29 of 58 Old 04-26-2019, 12:14 AM
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Re: 2001 RWD still getting bad gas mileage

Sounds like a soap opera in the making.
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post #30 of 58 Old 04-26-2019, 09:29 PM
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Re: 2001 RWD still getting bad gas mileage

My 94 with a rebuilt motor and brand new exhaust (everything beyond the Y pipe), AC on half the time, and a little bit of highway driving on my way home is getting right at 16 mpg.


I recently replaced my (one) oxygen sensor also. Had to use a pipe wrench to get it out.


Don't know what you mean by "secondary steering shaft", but my gearbox had some slop in it. You can adjust it by loosening the lock nut and turning the hex-head screw on the top of the gearbox. Just be careful not to tighten it too much.
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post #31 of 58 Old 04-27-2019, 02:20 AM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

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Don't know what you mean by "secondary steering shaft"
The steering shaft is in two pieces and is collapsible in the case of a front end crash. This is so you don't get speared by the shaft as it pushes through the firewall, like what used to happen on cars in the old days. On the S10/Blazer, it just folds up instead. Detaching the bolt from the end of the shaft allows it to telescope back, and is necessary for removing the motor mount on the driver side and also the manifold iirc.

These trucks still have sloppy steering after turning that bolt in the box, because they have a rag joint at the end of that secondary shaft. Even when new they aren't as tight as something with u-bolts, like a Jeep. In fact, the shaft from a late model Grand Cherokee will fit on an S10 with very little modding. I chose not to do this mod because I like the sloppy steering when it isn't so bad. You can shimmy the wheel back and forth at highway speed ever so slightly to slow down without using brakes. This is without the vehicle swerving noticeably at all. At least that's how it worked on my old truck once it got a few miles. It saves a lot of gas if I do it right.
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post #32 of 58 Old 05-01-2019, 12:39 PM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

I need advice from anyone who has purchased a catalytic converter new. The one I ordered arrived, but it's very obviously been used. There's exhaust residue in the pipes, and on the outside as well. Did these jerkoffs sell me a used cat? I watched a few videos on Youtube and every cat unboxing I saw didn't show any soot like these pipes have. Is it normal to get hands dirty just by touching the outside of the pipes?

https://www.s10forum.com/forum/attac...316473&thumb=1

https://www.s10forum.com/forum/attac...316475&thumb=1

https://www.s10forum.com/forum/attac...316477&thumb=1

https://www.s10forum.com/forum/attac...316479&thumb=1

https://www.s10forum.com/forum/attac...316481&thumb=1

I'm concerned the item I received might have been an RMA repackaged as new.
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post #33 of 58 Old 05-01-2019, 12:43 PM
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Re: 2001 RWD still getting bad gas mileage

Where did you get it from?

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post #34 of 58 Old 05-01-2019, 02:07 PM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

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Where did you get it from?

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From an ebay seller. He claims it shipped directly from the manufacturer, which was Catco.
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post #35 of 58 Old 05-01-2019, 02:47 PM
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Re: 2001 RWD still getting bad gas mileage

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From an ebay seller. He claims it shipped directly from the manufacturer, which was Catco.
He definitely lied. Return that and try again. Did the shipping documents say it was shipped directly from Catco? Or was the first scan on the tracking where your seller lives/does business? Check the routing on the tracking number.

I've never gotten a used cat from RockAuto, Amazon or any locla parts store. I can't say I would consider getting one on eBay.
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post #36 of 58 Old 05-01-2019, 08:40 PM
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Re: 2001 RWD still getting bad gas mileage

I'll just reiterate, my '01 4.3 Xtreme, with rebuilt engine last year, pulled just at 20 MPG on a 5 hour round trip on the highway, 65-70 mph.


Around town which is usually what I do, I get about 14.5 MPG.


3.42 rear gears, 235/60r16 tires (27.10" tall)



I'm a little older, so I am not concerned about going as fast as I can between stoplights. I drive like a normal person should. I like my ticket free license and low insurance rates.
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post #37 of 58 Old 05-01-2019, 08:59 PM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

The docs say it was sent from NC. I have no idea where Catco is located, their site doesn't make it clear.

I'm having an impossible time getting this new cat to even go in. It's like there's no way to do it without taking the transmission crossmember out. I've also broken a bolt for the downpipe, so now I have to take the passenger side manifold off to see if I can fix it. I have an extra manifold from another 4.3 motor, but it's from a 2000, and is different slightly from my 2001, which has some sort of extra connector tube running off the front held on by two 14mm bolts.
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post #38 of 58 Old 05-01-2019, 09:11 PM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

There were a lot of things affecting my mileage, but I think I might have found the heart of the problem. This old cat I pulled is totally clogged. A bunch of what looked like cement poured out of it when I got it out of there.

https://www.s10forum.com/forum/attac...316489&thumb=1
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post #39 of 58 Old 05-01-2019, 10:08 PM
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Re: 2001 RWD still getting bad gas mileage

I wouldn't mess with it. Send the new/old one back and take it too an exhaust hop and weld in a Magnaflow cat. I was going to replace the cat on the wires Blazer2, but once I got under it and looked...no thank you very much.

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post #40 of 58 Old 05-01-2019, 10:22 PM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

I made the wrong choice when I decided to buy the complete cat with downpipe included. It's too hard to get it back into the truck without a lift because of the bend in the pipe and that crossmember. But I don't have enough to take it to a shop, so it's DIY or nothing. I'll probably send this new thing back and buy the cat that doesn't have a downpipe already welded to it. Then I can cobble something together with the existing pipes and some sleeve brackets. What I should have done to start. But first I have to fix the broken manifold bolt. I'm trying to pull the manifold so I can cut the broken bolt off and drill a hole for a new one to go in.
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post #41 of 58 Old 05-01-2019, 11:43 PM
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Re: 2001 RWD still getting bad gas mileage

Just gut your old cat and be done with it, the anti fouler will keep the rear O2 happy. The whole job will only cost you a couple bucks
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post #42 of 58 Old 05-02-2019, 12:41 AM
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Re: 2001 RWD still getting bad gas mileage

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Just gut your old cat and be done with it, the anti fouler will keep the rear O2 happy. The whole job will only cost you a couple bucks
Have you considered he may have emissions/inspections, or maybe he's environmentally conscious.

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post #43 of 58 Old 05-02-2019, 12:44 AM
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Re: 2001 RWD still getting bad gas mileage

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The docs say it was sent from NC. I have no idea where Catco is located, their site doesn't make it clear.
Catco should be from AP Exhaust Products, Inc., 300 Dixie Trail Goldsboro, NC 27530.
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I'm having an impossible time getting this new cat to even go in. It's like there's no way to do it without taking the transmission crossmember out. I've also broken a bolt for the downpipe, so now I have to take the passenger side manifold off to see if I can fix it. I have an extra manifold from another 4.3 motor, but it's from a 2000, and is different slightly from my 2001, which has some sort of extra connector tube running off the front held on by two 14mm bolts.
That sounds like it's from an Astro van, and has AIR ports on the front of the manifolds. I've never seen the AIR system on an S10 or Blazer, although it could be on some years I guess.

You can use a stud from that in yours, or put a blocking plate on the AIR fitting and use the manifold.
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post #44 of 58 Old 05-02-2019, 06:22 AM
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Re: 2001 RWD still getting bad gas mileage

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Have you considered he may have emissions/inspections, or maybe he's environmentally conscious.
Or likes the idea of having an exhaust system that is legal in the US.
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post #45 of 58 Old 05-02-2019, 07:44 AM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

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Catco should be from AP Exhaust Products, Inc., 300 Dixie Trail Goldsboro, NC 27530.

That sounds like it's from an Astro van, and has AIR ports on the front of the manifolds. I've never seen the AIR system on an S10 or Blazer, although it could be on some years I guess.

You can use a stud from that in yours, or put a blocking plate on the AIR fitting and use the manifold.
My S10 definitely has an AIR pump. I noticed it the first day I owned the thing. I'd love to delete it but I'm not sure if the truck will run without a check engine light if I do.
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post #46 of 58 Old 05-02-2019, 01:55 PM
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Re: 2001 RWD still getting bad gas mileage

It cost me $30 to hand my new Ebay MagnaFlow cat to the exhaust shop, have them cut out the old one and weld the new one in. His only requirement was he kept the old cat. As someone who has made and installed a new Y pipe/cat assembly in my truck with out the right equipment, I highly recommend taking it to a shop.

As far as mileage goes, once you get the exhaust fixed, there should be an improvement. My '03 RCSB V6 5 speed is getting just over 19 mpg right now with 50/50 city/highway driving. It has dropped about 1 mpg in the last 2 years or so, but it does have 240K on it. I bought it new, and am meticulous about preventative maintenance (obsessive, probably spend too much), which I believe has helped in the long run. I do however drive it "enthusiastically". On the other hand, I will keep it in 5th gear during steady drives of 35 mph or higher. It has plenty of torque to drive at 1,500 or lower.

When you get the known issues figured out, the thing you need to remember is your new truck isn't the same as your old one. There are variances and tolerances that can effect the gauges, not to mention how the vehicle is treated throughout it's life. My first two cars were both Oldsmobile Cutlass Cieras, the first a 1986 and the second a 1989. When I bought the second one I couldn't figure out why it had a gas can in the trunk. The next day when it ran out of gas at 1/8 tank I realized why. Even my current truck's gas gauge will vary. Over the life of my truck when I fill the tank I can drive between 30-100 miles before the needle will move. The distance will change when ever I reset the the computer to clear a CEL.

In my opinion you need a larger sample size to determine your trucks gas mileage, maybe 4-5 fill ups at least. Something to consider when filling up is how consistently your truck will top off at the pump. When filling my '96 the pump would shut off and I would be 2 gallons short of full. Every time. My '03 when new was completely different and when the gas pump would shut off, it was full. Now with age, I have to hold the nozzle just right or it will shut off before full.

Basically, you're on the right path by fixing the known issues, just realize the results are not always clear. You may have to temper your expectations to circumstances a little.
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post #47 of 58 Old 05-03-2019, 01:26 AM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

I've gotten the manifold back in. Upon closer inspection, I think it will be okay. The part of the bolt that broke was the unthreaded end part. Only a few threads were lost. I nearly had the damn thing off when it snapped. I've test fitted the old downpipe and it appears there's enough clearance to thread the bolt on. So fingers crossed on that.

I might have to end up using this cat, just because the truck is being pressed back into service. Another one of my cars had the cat go out on it today. Luckily it's just an old 90's car and not emission tested any more. She will be getting a visit from kindly old Doctor Sawzall. The truck is ready to fire now that I've got its plugs back in. I'm hoping it will finally run like its supposed to run, even if it can never be the truck my other truck was. This will be as close as it gets.

If I choose to keep the Truck's newish cat, I'll probably just chop the downpipe to get it in there and apply a butt clamp to put it back together. That seems like the easiest way to get it back on the road. I don't want to risk damaging the motor by driving it however far I would have to go to find a reputable shop in my area. Or risk getting pulled over for noise violation.
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post #48 of 58 Old 05-03-2019, 09:00 PM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

Finally, my truck can breathe again. I just took it on a test drive, and I can confirm that this is more or less what one of these is supposed to drive like. It accelerated easily onto the highway and in the top end.

But now for the problems, and there are a few. First, this cat was definitely not a direct fit for an S10. Not even close. The downpipe was totally the wrong size for the driver side. Passenger side went on beautifully, and the broken bolt was no issue. I used a Walker 2.5 butt connector from Summit Racing, and the cut I made between the passenger downpipe and the cat turned out great. Appears to be a perfect seal.

As stated previously, the driver downpipe is a no go. What I've done is reuse the old pipe from that side, but with a new donut gasket. However they don't quite fit. I think I can get another butt connector to fit over it and seal everything up.

But the real problem is the check engine light came on again. It's giving codes p0134, p0154 and p0155. Those are all O2 sensor circuit codes. It's not seeing the new O2 sensors I plugged in. I'll probably get back under there tonight and plug the old sensors in. I must have gotten an entirely bad batch, if all three aren't showing up.

https://www.s10forum.com/forum/attac...316505&thumb=1

I'll be driving out to Summit again tomorrow to see if they can offer something to patch that downpipe.
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post #49 of 58 Old 05-04-2019, 08:12 AM
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Re: 2001 RWD still getting bad gas mileage

IIRC, the O2 sensors have a fuse of their own.

One blown fuse can create those three codes. Check that, and if the fuse is blown, check the wiring to make sure you don't have bare wires exposed somewhere.
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post #50 of 58 Old 05-04-2019, 10:09 AM Thread Starter
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Re: 2001 RWD still getting bad gas mileage

I forgot about the fuse. I'll check that first. And if there is a bare wire, it's got to be the passenger side downpipe. There's no lead on that wire harness for some reason. It's super short, and the cable has a hard time plugging in. Plus it's right on the frame. I'm going to go get a pigtail and O2 sensor from the junkyard and wire them together to make an extender, even if that wire is fine.
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