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1987 TBI 2.8, gas mileage?

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Old 11-30-2012, 01:51 AM   #1
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1987 TBI 2.8, gas mileage?

Hey everybody, new to the forums, I have an 87 S10, with 4x4, 4 speed auto, gutted cat and slightly oversize tires (Like maybe P225 R70 when its supposed to be P215 R65, or something like that, can't remember right now). I am getting about 11 miles to the gallon city, this seems unreasonably low. I just changed the oil and the plugs and wires recently. The truck smells like it runs rich, and is worse when it is first started. So basically I was hoping someone could pitch in any ideas which could help the mileage, thanks in advance for the help.
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Old 12-01-2012, 12:47 AM   #2
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Re: 1987 TBI 2.8, gas mileage?

My old 92 2.8 2wd got around 21 mixed driving getting beat every gear. Idk what my 93 gets I just picked it up & haven't drove it much but I'm expecting the same out of this one too.
Old 12-01-2012, 03:33 PM   #3
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Re: 1987 TBI 2.8, gas mileage?

Hmm alright, just putting my summer car away for the winter now, when I get some garage space maybe I'll check on the wheel bearings and maybe replace the O2 sensor, hopefully that will help.
Old 12-06-2012, 01:08 AM   #4
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Re: 1987 TBI 2.8, gas mileage?

Well I put Seafoam in the oil and gas as the label said, and that seemed to quiet down the tick some, but I drove it on the highway for the first time in a while and it seemed very down in power, it was fine in getting to 65, but I had to fight it to get it past there. Seems like the truck really lacks low end torque too, and always hesitates when I get on the gas from a stop. Any suggestions on what to try to fix this hesitation problem? Distributor maybe? Any help would be greatly appreciated, thanks.
Old 12-06-2012, 01:49 AM   #5
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Re: 1987 TBI 2.8, gas mileage?

I sure as hell hope you don't still have that Seafoam shit in the oil! That will wipe your bearings right out of the engine quick! It could also free up enough sludge in the engine to clog up the oil passages if there was a substantial amount of sludge inside to begin with. So, first thing you want to do is pray that you didn't hurt the engine.......second thing I'd do is change the oil.........and don't run a p.o.s. Fram filter either! Stick with Wix.
Old 12-17-2012, 12:46 PM   #6
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Re: 1987 TBI 2.8, gas mileage?

I generally get 18-19 city and 21-22 highway, but I took a trip the other day to look for a used car for my wife. I. Didn't rev over about 2000 rpm and didn't go over 65 on the very flat Florida interstate. I can't believe this myself, but I got 26.6 miles per gallon!!!! wow! I know exactly how much gas was in the tank because it ran out of gas right after I left my house and I coasted 1/2 mile into the gas station. I put in exactly 3.00 gallons and then drove 79.9 miles looking at cars, then ran out of gas pulling into my driveway..26.6!!! (it's still out o gaz, my lawn mower can is empty...)
That kicks ass for a 2.8 with almost 200K miles. I have a 92 2.8 5 speed with gutted cat, glasspack muffler, new stock ACDelco plugs, 10 year old wires, new cap n rotor, 235/60-15 cosmetic performance tires, stock rear end (i think 2.73) and run regular unleaded gas from cheapest store I can find. Something to check out....My truck was a basket case before I rebuilt the whole fuel system (rebuilt T.B.I., new fuel pump, filter, sending unit, pressure washed fuel tank.) bad mileage, very unreliable. been great since fuel system overhaul. Years ago I had a 91 S10 Durango 4.3 5 speed and it got 16-18 on the highway. it really sucked gas but was sooo strong it was barely controllable. No one ever used 1st gear till the truck had over 90k miles on it. When I had to put a clutch in it I found out it had 4.11 gears in the rear and a special transmission with lower gearing (original factory). The transmission was called a "MY2" i was told by chevy parts counter dude it was part of the Durango towing package. It would roast the tires in 1st and second gears, 3rd would yelp and would chirp the tires @72 mph going into 4th geat on dry pavement!!
But it did have quite an appetite when you stomped it, I think around 12 to 14mpg.
Check your transmission model and rear gearing, if your setup is similiar to my old 91 then you may never get over 17 or 18 with a 4x4 even if it's running great.
Old 12-17-2012, 12:52 PM   #7
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Re: 1987 TBI 2.8, gas mileage?

How many miles on your truck? Oh, wait, You have a carburetor, you poor soul....I haven't owned anything with a carb (except my boat that needed a carb rebuild) in 20 years or more. It may need a carb rebuild...
Old 12-21-2012, 12:04 PM   #8
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Re: 1987 TBI 2.8, gas mileage?

If it's running rich, why not try adjusting the carb a bit?
Old 12-29-2012, 11:16 PM   #9
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Re: 1987 TBI 2.8, gas mileage?

Sorry all, forgot about this thread. Just filled the S10 after replacing fuel injectors and got 11.6 mpg. Yuck. Its a TBI, not carbed, and now it doesn't seem like its running rich. I think I need to check the timing, I don't know where else to turn. On an unrelated note I'll be replacing tranny fluid soon, the pan gasket is leaking a little bit. By the way, truck has 799xx miles, not high mileage at all. Thanks for any more input, open to any suggestions
Old 01-02-2013, 01:06 AM   #10
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Re: 1987 TBI 2.8, gas mileage?

With out going back through all of the posts above; have you replaced the O2 sensor? They're pretty cheap; and should be replaced every 60,000 miles.....at least that's what the Haynes manual states for my 2.5. That could possibly be why it's running rich.............that, and/or your egr valve or map sensors are crap. A good mechanic can test the MAP sensor for you (or MAF on your engine?). I found that changing my fuel filter twice a year made a huge difference in gas mileage too; and I burn through a lot of fuel......so, I didn't think it really needed to be changed more then once a year. It helps keep the fuel pressure up where it's suppose to be.
Old 01-18-2013, 12:56 AM   #11
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Re: 1987 TBI 2.8, gas mileage?

Hello all, haven't updated this in a while, wanted to see where my gas mileage would go with more driving, and the results aren't great. More of the same. About 12mpg last fill. Realistically I think I should be getting about 16mpg, as I do a lot of short trips, and have 3.73 gears. As stated earlier, it still smells like it runs rich, has a kind of "lawnmower" smell to it, according to a friend :P .Where would the O2 sensor be located on these? I feel dumb for asking, but I just looked at the exhaust pipe, and didn't find anything. I looked on the Y-pipe, after both exhaust manifolds dump together, and before the place my catalytic converter would be, but didn't see anything. Also will be changing the transmission fluid soon, pan is leaking bad, if the forecast showed a day without lows below zero I would get it done...
Old 01-18-2013, 11:37 AM   #12
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Re: 1987 TBI 2.8, gas mileage?

My 87 blazer with a 3 inch bl and 31 inch tires got around 18 with the 2.8 auto and 3.73 gears. It never had a cat on it and i removed the A.I.R. pump.

After the 3.4 swap i did get it to the low 20s even with 300lbs of bumpers.

My 2wd 91 reg cab gets mid to high 20s but its a 5 speed.
Old 01-18-2013, 02:19 PM   #13
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Re: 1987 TBI 2.8, gas mileage?

86 2wd Jimmy 2.8, with a manual 4 speed gets around 20 in the city. But I don't drive aggresively at all. It also easily passes emissions.
Old 01-18-2013, 04:19 PM   #14
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Re: 1987 TBI 2.8, gas mileage?

That hesitation sounds just like the problem I had. It was too retarded on the timing. Bumped it up a few from 10 and its gets up and goes. Also ran cooler after I adjusted the air fuel mixture screw.
Old 01-19-2013, 05:18 AM   #15
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Re: 1987 TBI 2.8, gas mileage?

Quote: Originally Posted by greasemonkeys10
That hesitation sounds just like the problem I had. It was too retarded on the timing. Bumped it up a few from 10 and its gets up and goes. Also ran cooler after I adjusted the air fuel mixture screw.
He never said anything about a hesitation. And he's Throttle Body Injected.
Old 01-20-2013, 04:42 PM   #16
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Re: 1987 TBI 2.8, gas mileage?

Fuel injected 87 Blazer crate 3.4l 700R4 4.11 rear end 4x4 With 4.3 Thottle body 4.3 injectores and bored intake

On way to beach with about 1,000 pounds of luggage (and we took two vehicles at that) with tires at 32 or so PSI (I had Hitch cooler carrier There was so much weight over the rear axle that I could hardly control the steering on the highway) And I obtained 22mpg with 93 octane.

At the beach (was 4x4 beach only beach driving 7 miles to our house by way of one road which was the sand on the ocean) 20 psi in tires 4x4 half the time got 15 mpg

On way back from beach forgot to put air in tires and got 18 miles to the gallon

Around town I get around 15.5
Old 01-22-2013, 02:18 AM   #17
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Re: 1987 TBI 2.8, gas mileage?

Actually I did mention a hesitation, and timing will be checked when the temperatures get back into double digit degrees F. Just changed transmission fluid and gasket, finally have a truck that doesn't leak a drop of anything at least. Hopefully a timing adjustment will get me back to where I need to be. Good news is the truck starts great, even started yesterday morning when temperatures were as low as -10F and it sat outside. Anyway, I'll update next time I fill up, or when I adjust the timing, whichever comes first. Thanks for the input from all.
Old 01-22-2013, 12:06 PM   #18
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Re: 1987 TBI 2.8, gas mileage?

Your calculations may be off......

When i first got my dime, it had original black stamped steel 14"wheels with 195/70-14 tires on it. I upgraded to 15" Blazer rims but could only afford 2 new tires at the time. My dad gave me 2 good tires he had laying around. I put them in the back because they were so much taller than the new ones in front. The rear tires were 235/75-15 . My speedo and odo were way off because of the change in total outside diameter. the truck actually went 1.22 miles for every 1 mile on the odo. and the speedo was only accurate at exactly 31 mph. ( I checked using my Garmin GPS12XL i have for my boat.) the faster i went, the more it was off. you mentioned 4X4, got big tires? How far are you really going?

My truck now has 235/60-15 tires( 70's/80's camaro/firebird size) all the way around and the speedo and odo are accurate. The total outside diameter is the same as the original 195/70-14 tires. if you change to a taller or shorter tire (total outside diameter), you need to change your speedometer gear to match for accurate readings.
Old 01-22-2013, 06:12 PM   #19
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Re: 1987 TBI 2.8, gas mileage?

Thanks for the suggestion baddad, but I have accounted for this too, I usually add 10 miles on every fill to account for the inaccuracy, giving it the benefit of the doubt. When I drove it home from the seller when I bought it (~200 miles), my father followed me in his car, and my odometer was off 10 miles. So I have that covered too, thanks for the suggestion though.
Old 01-22-2013, 10:49 PM   #20
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Re: 1987 TBI 2.8, gas mileage?

Sorry, I must have missed the hesitation part.

Speedometer/odometers are off by a percentage, not miles per hour.
If that was true your speedometer wouldn't read zero when you are stopped.
Basically, the faster you go, the more of a speedometer error you will be getting. The more miles you drive, the greater the odometer error.
What is supposed to be your original tire size, and what do you have on there now?
Old 01-23-2013, 10:29 PM   #21
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Re: 1987 TBI 2.8, gas mileage?

Door sticker says it wants 195/75R15, currently has 205/75R15. Oh and I borrowed a timing light from a friend, and I tried to check timing, but ran into three questions. First, is cylinder #1 on the driver or passenger side!? In my Chilton it says front drivers side plug, but I've also read in other threads that it is passenger side front. (Sorry if these are dumb questions, I've never dealt with timing before). Also, when I shined the light at the timing marks, there were maybe 5 or 6 teeth I could see, and the outer two were deeper than the rest, but what do these teeth represent in respect to the line? Like a certain amount of degrees? And finally, where is the bolt on the distributor to turn it? Sorry for all the questions, my handy Chilton has been useless and generic in answering, and sadly I've searched the forums with no success. Again, please excuse my noob-ness. Thanks all.
Old 01-26-2013, 01:18 AM   #22
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Re: 1987 TBI 2.8, gas mileage?

You're only 2.3% off. Shoot, the difference between new tires and old tires is probably that much. If you're really worried about it, take it to a speedometer shop and have it calibrated.

Passenger side front is number one for a 2.8

As far as teeth go....I think you're referring to the timing tab by the crank. The deep valley is zero, each tooth is four degrees with the valley in between is two degrees.

The bolt for the hold down clamp for the distributor is a pain in the ass to get to. It's way in the back, by the firewall, and you can sort of get to it from the passenger side. The coil packs get in the way. I think it's a fifteen mm...
Old 01-26-2013, 10:30 PM   #23
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Re: 1987 TBI 2.8, gas mileage?

RNLance, you sir are a genius. Just set the timing, the PO had timing set at 0 degrees, maybe they set it to 10 without disconnecting the EST, but whatever, bumped it back to 10 degrees advanced (with brown/tan wire disconnected), and the thing runs like a champ, so smooth, more power, AWESOME. Thank you all, hopefully this will be cure to all of my problems, it seems like it will be. Thanks.
Old 01-27-2013, 09:15 AM   #24
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Re: 1987 TBI 2.8, gas mileage?

Quote: Originally Posted by RNLance
Sorry, I must have missed the hesitation part.

Speedometer/odometers are off by a percentage, not miles per hour.
If that was true your speedometer wouldn't read zero when you are stopped.

My speedo didn't move till I was up to 8 0r 9 mph...
Old 01-28-2013, 11:56 AM   #25
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Re: 1987 TBI 2.8, gas mileage?

You're welcome.


Quote: Originally Posted by 87Durango
RNLance, you sir are a genius. Just set the timing, the PO had timing set at 0 degrees, maybe they set it to 10 without disconnecting the EST, but whatever, bumped it back to 10 degrees advanced (with brown/tan wire disconnected), and the thing runs like a champ, so smooth, more power, AWESOME. Thank you all, hopefully this will be cure to all of my problems, it seems like it will be. Thanks.
Old 01-28-2013, 11:57 AM   #26
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Re: 1987 TBI 2.8, gas mileage?

I don't know how that would be possible with a cable speedo.


Quote: Originally Posted by baddad71
My speedo didn't move till I was up to 8 0r 9 mph...
Old 01-28-2013, 12:33 PM   #27
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Re: 1987 TBI 2.8, gas mileage?

BTW, it wasn't me that suggested to check your timing, it was GreasemonkeyS10.
I just helped out a bit.
Old 01-29-2013, 12:14 PM   #28
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Re: 1987 TBI 2.8, gas mileage?

Quote: Originally Posted by RNLance
I don't know how that would be possible with a cable speedo.
The cable isn't attached directly to the speedo pointer. Its attached to a wheel that spins faster (where the vss gets signal) and it creates a magnetic field that picks up the pointer and moves it. That field gets weak it can take awhile or cause the bouncing problem some of us have had. The fix is to swap clusters and hope the "new" one is in better shape.


I just use a GPS for my speedo and odometer for gas figures. Way more accurate.
Old 01-30-2013, 12:38 AM   #29
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Re: 1987 TBI 2.8, gas mileage?

You know, I have that problem. Truck has 280,000 miles on it. I just assumed the reduction box at the trans was acting up, and never explored it more than that. Good info...
I hate taking that cluster out...every time I do more chunks of green plastic fall off. I actually had to bypass the connector and hardwire my cluster...almost nothing was working because the connector had broken.




Quote: Originally Posted by neo71665
The cable isn't attached directly to the speedo pointer. Its attached to a wheel that spins faster (where the vss gets signal) and it creates a magnetic field that picks up the pointer and moves it. That field gets weak it can take awhile or cause the bouncing problem some of us have had. The fix is to swap clusters and hope the "new" one is in better shape.


I just use a GPS for my speedo and odometer for gas figures. Way more accurate.
Old 02-03-2013, 06:38 PM   #30
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Re: 1987 TBI 2.8, gas mileage?

Well I am back, with some not so great news. 13mpg, even after fixing the timing. UGGHHHH! I'm sure someone knows where the O2 sensor is located? I can't seem to find one on my exhaust piping, and that might help to replace it. As usual, thanks for the reply, and by the way mine has 3.73 gears. Oh and one more thing, it still seems like it just gets choked at higher rpms, like when you get out of the torque band, fuel filter maybe? Thanks all.
Old 02-06-2013, 12:46 AM   #31
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Re: 1987 TBI 2.8, gas mileage?

It's toward the back side of the drivers exhaust manifold, under the steering shaft.



Mine chokes out too. I don't think these engines were ever intended to rev very high.
Old 02-10-2013, 01:12 AM   #32
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Re: 1987 TBI 2.8, gas mileage?

Alright cool, thanks for that picture Lance, that will be helpful if I decide to change the O2 Sensor, might not, seems like the gas mileage has been better this tankful. Will update after I fill up again, probably next week.
Old 02-10-2013, 06:38 PM   #33
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Re: 1987 TBI 2.8, gas mileage?

Not sure about your 87 model, but in my 92 the O2 sensor is in the exhaust Y pipe just ahead of the catalyst converter--- passenger side.


Bonestock
Old 02-12-2013, 10:24 AM   #34
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Re: 1987 TBI 2.8, gas mileage?

same here^

It should be in the same location if your truck is equiped with it.

I get 20-24MPG depending on how bad i stomp the piss out of it. Expecting roughly the same after my motor swap to the 3.4
Old 02-14-2013, 12:10 AM   #35
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Re: 1987 TBI 2.8, gas mileage?

Well mine is like Lance's, I just changed out the O2 sensor, the old one looked pretty bad, hoping for improvement with the new one. I'll be filling up again soon so I'll restart the trip hoping for better results. Surprised me that I didn't have to do anything drastic to get the old O2 sensor out, just turned it with a cheater bar and got it off. Thanks for the input all.
Old 02-14-2013, 01:04 AM   #36
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Re: 1987 TBI 2.8, gas mileage?

Gotta help.
Probably something I should do too.
Old 02-15-2013, 12:50 AM   #37
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Re: 1987 TBI 2.8, gas mileage?

Well I just filled up again, 13mpg. With probably 30 of the 170 miles in 4 wheel drive, and about 20 miles of it with the new O2 sensor. Maybe the old O2 sensor was bad after being run for so long with the timing being off by 10 degrees for who knows how long. Hopefully things will be better next time at the pump. I'll update at a later time, thanks all.
Old 02-15-2013, 10:42 AM   #38
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Re: 1987 TBI 2.8, gas mileage?

Have you run any fuel system cleaner thru that?
How's the air filter?
Old 02-16-2013, 01:51 AM   #39
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Re: 1987 TBI 2.8, gas mileage?

I did run seafoam through the motor oil and gasoline (put about a capful in the oil, as per instructions, and put the rest in the fuel) and have also used Lucas fuel treatment. I purchased the air filter when I got the truck back in August, and has about 1,500 miles on it and still looks clean. Maybe it could be my coil not giving enough energy to my spark plugs for a strong spark? Although the O2 sensor did help, and I'm going to wait until my next fill up to throw more money at it, but I'm always baffled at how unbelievably slow this thing is, really fights me when I try to get to 70 on the highway. Thanks again for all the input, I really do owe you all for the ideas.
Old 02-19-2013, 10:28 PM   #40
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Re: 1987 TBI 2.8, gas mileage?

Let my father use it for a trip, so he filled it up, got 16mpg, lot of highway, up here in the midwest cold. With 3.73 gears, that's no surprise on the highway, so maybe its better now. I'll keep updating with gas mileage and others. Thanks all.
Old 02-19-2013, 11:25 PM   #41
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Re: 1987 TBI 2.8, gas mileage?

Keep working with it, little things add up.
Tire pressure, how you drive, etc.
Old 03-04-2013, 10:56 PM   #42
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Re: 1987 TBI 2.8, gas mileage?

Back again, 14.5 mpg, a little better, but the weather was also a little warmer too.
Old 03-10-2013, 05:50 PM   #43
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Re: 1987 TBI 2.8, gas mileage?

I've been putting 650 to 800 miles per week on my 92 2.8 TBI 5 speed and noticed that I get my best gas mileage between 75 and 80 mph on flat ground(23.5 to 24.5 mpg). if i'm doing 65 to 75 the engine isn't revving high enough to make enough torque to power the overdrive effieciently. I end up pushing the pedal down more and use more gas and end up getting 21 to 23 mpg. I have no idea what gears are in my rear diff. Weather makes a difference? I'm in florida and it's usually either warm or hot. mid 50's is freezing here.
Old 03-11-2013, 09:42 PM   #44
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Re: 1987 TBI 2.8, gas mileage?

I am wondering if that throttle body needs to be rebuilt. You can get the kits for them for under $50 on rock auto. Mine has 244K, and has never been rebuilt. Also try replacing the cap/rotor if you are having any power issues. Lastly, clean the vacuum port at the TBI unit for the MAP sensor. Use some carb and choke, etc. to clean that port. I chased, for years, a running issue and it turned out that this port was plugged with carbon. You may be stuck in 4x4 mode. Is this a manual transfer case or electronic? If you are dragging the front diff, that will drop some MPG's.
Old 03-18-2013, 08:37 PM   #45
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Re: 1987 TBI 2.8, gas mileage?

Yeah that's a good point, temperatures have been low here, so fluids are naturally soupier, especially on short trips. I wish I could go 75 - 80, but with the oversize tires, I'd be doing 85 - 90 haha. Tried the vacuum line you suggested, thanks for the try, but no dice. Maybe it does need a rebuild, I'll have to look into that this summer maybe. Manual T-case by the way, definitely not stuck in 4x4. Thanks for the input all, getting around 15mpg lately.
Old 04-20-2013, 10:59 AM   #46
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Re: 1987 TBI 2.8, gas mileage?

15 really isn't too bad for your setup. after you drive it for a while you should start to feel that "happy place" for effeicency, not power, where your motor, trans, and rear ( or both) diff find just the right rpm's.

In my light, empty, 2.8 5 speed, 3.42 rear, on flat ground on the interstate, it's in the mid to upper 70's motor turning around 2500 to 3000 rpm's

My Chrysler 300M 3.5L 24Valve likes the mid 70's around 2500 rpm's it gets 28 mpg in that zone. it averages 22 to 24 daily

In my 04 explorer 4.6 V8 auto with 4.01 rear, the "happy place" was in the low 60's with the motor spinning around 1800 rpm's and it got in the 18 to 20 on it's best trip ever. average was closer to 14

In my 92 Dakota reg. cab, long bed, 5.2 Auto, 4X4, with 4.11 rear, the happy place was about 53 mph with the motor turning around 1800 rpm. and that truck never saw 16mpg in it's 218K mile life. it averaged around 12 commuting through the suburbs of Tampa 5 years ago. when it was in 4 wheel drive the mileage dropped to single digit numbers.....that really throws off your averages!
Old 04-22-2013, 12:04 AM   #47
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Re: 1987 TBI 2.8, gas mileage?

I get what you mean, my sweet spot is too high for where I need it, mines probably 70 on the speedo, which is actually 76ish. MPGs have been consistent 15's as of late, and now I'm working on getting it ready for next fall, as I will be taking it with me to college, 5 hours away, so I'm working on stuff like brakes, saving the engine work for this summer when I'll have more time.
Old 04-22-2013, 02:45 AM   #48
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Re: 1987 TBI 2.8, gas mileage?

I would rebuild the TBI and put new injectors. Look at your spray patterns to see what they look like
Old 04-22-2013, 10:53 PM   #49
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Re: 1987 TBI 2.8, gas mileage?

Spray patterns are good, had issues with the injectors maybe 4 months ago and replaced them. A TBI rebuild is planned for this summer, along with valve cover gaskets and maybe rockers, MAYBE, long way away yet, debating doing it or not.
Old 04-23-2013, 09:24 AM   #50
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Re: 1987 TBI 2.8, gas mileage?

Rebuilding a TBI is cake man. Compared to building a carburetor? Nothing to it.
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