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4.3L misfires only at cruise - rich condition.

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Old 11-07-2007, 10:28 PM   #1
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4.3L misfires only at cruise - rich condition.

I have a 1999 Blazer 4.3L with new intake gaskets, new head gaskets (runs extra good, no oil in the coolant, and no coolant in the oil). The engine idles perfect, starts great. New spark plugs, wires, cap, rotor.

When driving down the road at light throttle (cruise), the engine will misfire and shutter. Under hard acceleration the engine smooths out and runs excellent with normal power. The shutter happens at light throttle either hot or cold and gets slightly better when it is warm.

The engine is getting horrible fuel economy and the spark plugs were checked and they were very dark (too rich).

The error code says Catalytic converter, however the converter was just changed about 6 months ago. A shop recommended changing the EGR valve, but the engine is super clean with only 110,000 miles on it and I don't think it is the EGR valve causing the rich condition and the misfire/shuttering.

Please help!!!!
Old 11-07-2007, 10:37 PM   #2
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Re: 4.3L misfires only at cruise - rich condition.

I have the same problem with the same conditions, but only 47000 miles...Jeff
Old 11-09-2007, 03:16 AM   #3
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Re: 4.3L misfires only at cruise - rich condition.

need to check the distributor gear for excessive wear. it's a common problem.
Old 11-11-2007, 12:43 PM   #4
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Re: 4.3L misfires only at cruise - rich condition.

Dont go with the EGR, Here is a post made to a earlyer thread.

Help Missing!!!!!!!!!

I have a 1996 4.3 Vortec 5 spd with 120,000 miles, The only mods is a piped cat. About 5,000 miles ago i started to feel a sort of studder and miss in the morning when going from 2nd to 3rd gear @ 2,000 to about 3,000 rpms. But for the last 1,000 miles it has done it all the TIME in all gears.....I know theres a TSB for the timing chain but i know 100% that it is not the problem. About 2,000 miles ago the fuel pump went out and it has been replaced as well as the EGR valve and fuel filter. It also had a tune up not to long ago with plugs, plug wires, cap and button. If it is in neutral or under heavy accel it wont do it. Just the other day i got tired of it and unplugged the mass air flow and the sensing sensor in front of it, to see if it would effect it. After i unplgged it it completly stoped for about 60 miles and then started doing the same thing again. While using a snap on scan tool no abnormal voltages can be seen. The only code that was shown befor the mass was unplugged was Random Missfire. If you have any ideas to what this could be please post gettin pretty disperate and low on cash.

Im pretty sure we are havin the same problem, i checked the cam No Play at all and everything seems rock solid, I put a new muffler ant tip on it like 500 ago and its already coated in a thick black soot (RICH AS HELL!!!) Im puttin it in my guarge today and pullin the disturbutor out so i will get back to you.

PS im not advising the EGR yet...I got it a discount cuz i work at a GM Dealer at 180 bucks and well it did the same dam thing and not alowed a return after use so bad idea if your on a thin wallet.
Old 11-12-2007, 06:55 AM   #5
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Re: 4.3L misfires only at cruise - rich condition.

i have the same problemon my 01 4.3 with 39,000 miles. feels likes its bucking unless i give it alot of gas. and im getting worse gas milage than my 4 cylinder with a full load. someone help please.
Old 11-12-2007, 12:42 PM   #6
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Re: 4.3L misfires only at cruise - rich condition.

I have this problem occasionally, except my mileage is completely normal. It only happens after a cold start and lasts til it warms up for a couple minutes. I'm thinking its just my cheap duralast cap and rotor. I think moisture is the culpret.
Old 12-10-2007, 07:00 PM   #7
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Re: 4.3L misfires only at cruise - rich condition.

I solved my issue. turns out it was a bad distributor cap. It have a bunch of corrosion on the inside terminals and the rotor. This was replaced only 6 months prior. I put new units on and the truck drives perfect. Might want to check this out...Jeff
Old 02-13-2008, 07:22 AM   #8
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Re: 4.3L misfires only at cruise - rich condition.

Hey guys,

Please allow me to share in this aggrevation. I get same code P0300. I have replaced dist. cap, plugs, wires and egr valve. I have a 2001 blazer 4.3L w/92,000. miles. As mentioned by someone else My blazer seems to hesitate at real low speed. If I stomp on the gas there seems to be no problem. The problem only exists in the morning. Problem seems to go away when the engine is warmed up. The EGR valve was expensive don't bother with that.

I am thinking maybe even though the parts were replaced perhaps they were faulty. But Probably not seeing I am not the only one with the problem. Maybe it is time to trade it in.!!?

Anyone know if I decide to deal with the annoyance will the problem get worse? Will I cause more damage by not fixing it?

Any help will be greatly appreciated.
thanks,
Very respectfully,
Tony SMith
Old 02-13-2008, 07:27 PM   #9
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Re: 4.3L misfires only at cruise - rich condition.

i bet its the distributor gear same problem here tried that and it fixed it i was so happy that was the most annoying thing ever especially if u got exhaust
Old 02-13-2008, 07:51 PM   #10
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Re: 4.3L misfires only at cruise - rich condition.

Has anyone thought about the oxygen sensors?
Old 02-14-2008, 09:40 AM   #11
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Re: 4.3L misfires only at cruise - rich condition.

i'm pretty much having the same problem except my plugs looked alright. i changed the cap and rotor about a month ago the problem went away for awhile now its back. i noticed there was some loosness with the rotor is there supposed to any freeplay? could it be the fuel injection spider? i have a 98. also it will not shift into fourth gear for a little while.
Old 02-14-2008, 01:18 PM   #12
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Re: 4.3L misfires only at cruise - rich condition.

The rotor shouldn't have more than 1/2" of play. Even that's a little much. Your shifting problem is probably something unrelated. Check your trans fluid.

How well-sealed is the cap? Maybe moisture is getting in there. Sometimes my cheap cap would get moisture in there and after a cold rain it wouldn't start til it dried out.
Old 02-14-2008, 03:36 PM   #13
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Re: 4.3L misfires only at cruise - rich condition.

Is anyone pulling codes? All your posts about poor mileage ^ are because your engine is running rich, unburned fuel is getting all over your o2 sensors and plugging up your cat converter as well. That low rpm misfire could be a fouled o2 sensor telling your engine to dump more fuel. It also could be any fouled sensor for that matter. post up your codes
Old 02-14-2008, 09:45 PM   #14
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Re: 4.3L misfires only at cruise - rich condition.

the shifting problem only happens when the sputtering and misfires are going on.
Old 02-16-2008, 02:55 PM   #15
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Re: 4.3L misfires only at cruise - rich condition.

po146
po300
po713
please help!
Old 02-17-2008, 10:10 PM   #16
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Re: 4.3L misfires only at cruise - rich condition.

PO146 OXY sensor no activity- Bank 1 sensor 3

PO300 is random misfire

and I think the po713 is a trans temp sensor?

Start with that oxygen sensor and see if that fixes the other problems
Old 02-17-2008, 11:53 PM   #17
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Re: 4.3L misfires only at cruise - rich condition.

So most of these were solved in the distributor?
Old 02-17-2008, 11:59 PM   #18
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Re: 4.3L misfires only at cruise - rich condition.

i have no cat, so what should i do as far as the o2 sensor?..where to get it and all
Old 02-18-2008, 09:07 AM   #19
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Re: 4.3L misfires only at cruise - rich condition.

There are multiple O2 sensors in your fuel injection system. Figure out which one bank 1 sensor 3 is and replace that one. Your post cat sensor should have nothing to do with how your truck runs and having misfires.

I'm in class right now, so I'll let you do the reading on this one:
http://www.aa1car.com/library/o2sensor.htm
Old 02-18-2008, 09:27 AM   #20
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Re: 4.3L misfires only at cruise - rich condition.

After reading through that it looks like the bank 1 sensor 3 may be your post-cat sensor. Since you have no cat, that one is ruled out of the problem.

Seeing as how you only have a misfire code, but no other O2 sensor codes I'd go ahead and check your distributor. Clean the connections with some WD40 and the inside of the cap too. Replace it firmly and wait about 10 minutes before you fire it up. If you want any troubleshooting help shoot me a PM and I'd be willing to come help you out in person.
Old 02-19-2008, 03:31 PM   #21
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Re: 4.3L misfires only at cruise - rich condition.

it wouldn't hurt to check your coolant temp sending unit. if it's junk, it might be telling the engine it's not warm and dumping in too much fuel.
Old 02-19-2008, 10:50 PM   #22
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Re: 4.3L misfires only at cruise - rich condition.

Running a little rich wouldn't cause a misfire bad enough to throw a code. And if the temp sensor wasn't reading, that code would be thrown too.
Old 09-30-2008, 01:15 PM   #23
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Re: 4.3L misfires only at cruise - rich condition.

Im having the same problem. Shutters and misfires at slower cruise speeds especially while shifting from 1st to 2nd. And when it rains the truck wont start at all... wont even run on starting fluid.
Old 09-30-2008, 03:15 PM   #24
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Re: 4.3L misfires only at cruise - rich condition.

Since your symptoms are identical to the ones described in this thread, try the above recommended solutions with the distributor cap.
Old 09-30-2008, 06:52 PM   #25
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Re: 4.3L misfires only at cruise - rich condition.

This probably wont help you all but I just went through a little fuss with the 4.3 in my 06 express at 45K miles. Symptoms started as random stumble/surge on idle. The motor would near die and then surge back to life. The motor also seemed to idle up and down while the A/C was on, going from low to near choke style idle every 10-20 seconds. The problem got worse and began to miss under low acceleration and clear up with heavy gas pedal. It would throw a code that would auto clear after so long of driving without a problem. I could never get it checked since it cleared after I got off work.

For a while I thought bad gas since the problem cleaned up after a major system cleaning but it returned less than 2 days later. It also acted up more in the rain which led me to believe it was a electronic issue.

The answer to my problem was the TPS (throttle position sensor). If you have a multi meter they arent to hard to test. There are some write ups on the proper procedures online if you search for them. I didnt need to test for mine since I finaly got a code reader and it told me the problem (after 3 days of waiting to throw a code again... it threw one three times a day up until I got the reader!!). I think the target values for it should be .45V at no throttle and 4.00V at WOT.

Mine had developed some dead spots in the lower throttle areas which caused fuel delivery to be shakey at idle and mild pedal. It also caused hard shifts. I could tell it was about to do it to me if I was slowing down and the trans started to downshift hard while coming to a stop. As soon as I replaced it my motor began to run fine, the trans shifts smoothly and the gas mileage improved from 15.5 MPG average to 18 MPG average.

If it is the problem the unit is only 30 dollars at autozone and takes about 10 minutes max to replace.
Like I said though it may not help anyone here but its worth thinking about or getting the multimeter out and taking a look. Mine could mess up and not throw a code. If the abnormal operating levels in the TPS dont occur long enough the computer wont throw a code.
Old 10-01-2008, 10:05 AM   #26
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Re: 4.3L misfires only at cruise - rich condition.

Good info Fawien. The 06 4.3's have distributorless ignition systems, so that obviously wasn't the culpret.

Normally, on older 4.3's an aftermarket cap is the problem. A little spray with WD40 and a good seal will usually fix the problem but if it doesn't this is a good thing to check.
Old 10-02-2008, 10:36 PM   #27
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Re: 4.3L misfires only at cruise - rich condition.

Quote: Originally Posted by BudRacing
The 06 4.3's have distributorless ignition systems, so that obviously wasn't the culpret.
So what does the distributor on my 06 4.3 do?
Old 10-02-2008, 10:47 PM   #28
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Re: 4.3L misfires only at cruise - rich condition.

I thought after 05 they switched to an individual coil setup? I'm looking for the answer but can't find anything.
Old 10-02-2008, 10:58 PM   #29
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Re: 4.3L misfires only at cruise - rich condition.

I can say for sure mine has one. I had my head hovered over it while I lay in the floorboard changing the TPS. Autozone lists a replacement for it as well.



Thats the cap it uses.
Old 12-28-2008, 10:50 AM   #30
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Re: 4.3L misfires only at cruise - rich condition.

This post is probably late in the game but I have / had the same exact Radom Miss at Cruise Only (55+ MPH) that I could stop by accelerating. Truck is a 2000 GMC Sonoma 4.3. Now with lots & lots of miles (185K miles).
I think I am now on to something after almost 2 years dealing with it. It all started about 4 months after I installed new intake gaskets (The DexCool Nitemare). About 4 months after the intake gasket repair the random miss started. Although it would clear after about 30 miles. I since replaced both O2 sensors, fuel pressure regulator (Fuel pressure was ok at idle highway speeds), EGR Valve, MAF Sensor, Map Sensor, Ambient Air Temp Sensor, plugs, wires. About 1 year ago I did replace the distributor cap & rotor, but the miss came back after a couple months. I then replaced the ECM with no success. I recently left it with a reputable repair shop (Against my better judgement) for a week to see if they could find this intermittent miss with no success. I figured I would just drive it till it blew up missed continuously so I could find it. This last week we got some pretty wet weather and the miss became constant at all speeds. So for chits and giggles I again replaced the Cap & Rotor and the miss went away. So now is my next question. Why did the cap & rotor fail so quickly?? Below is a couple pics of the original OEM rotor & cap that failed 6 months after the intake gasket install and another of the 1 year old cap. I turned the rotors up side down inside the cap so the gap between the rotor contact & cap contact can be seen. IS THIS NORMAL or wear?? Next question is looking at the close ups of the contacts it looks as if the arcing is on the side of the contact instead of directly infront. Might the distributor timing / position be wrong causing this premature wear or the cam gear as another poster mentioned???








Last edited by GeneP; 12-28-2008 at 10:51 AM.
Old 12-28-2008, 11:18 AM   #31
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Re: 4.3L misfires only at cruise - rich condition.

Gene P check the dist gear. Supermumble, same thing, my 99-4.3 was exactly the same as yours with 50 something grand on it. I changed wires 3 times. Finally after reading some threads in this forum I went deeper. Low and behold the dist gear was worn only on one side. I replaced the gear and it has been flawless since. There is a thread on it in here somewhere. It is "runs like a wet ignition" Good luck.
Old 12-28-2008, 12:15 PM   #32
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Re: 4.3L misfires only at cruise - rich condition.

I also have this problem in my 2000 Blazer with 111,000.
My question is, can I change just the gear or do I need a new distributer?
Old 12-28-2008, 12:34 PM   #33
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Re: 4.3L misfires only at cruise - rich condition.

Quote: Originally Posted by Zed
I also have this problem in my 2000 Blazer with 111,000.
My question is, can I change just the gear or do I need a new distributer?
I just checked AutoZone online. They list 3 different gears but Oversized (0.009, 0.012, & 0.015)?
What is actually oversized & how do I figure which one? These are MSD Bronze fancy lookin ones.
A reman distributor from AutoZone lists $109 Plus a $88 core charge..


Many Thanks,
Gene
Old 12-28-2008, 12:43 PM   #34
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Re: 4.3L misfires only at cruise - rich condition.

Well need a new cap & rotor for sure (GeneP). You have to handle the cap and rotor very gently. It needs to be perfectly clean and moisture free when it's reassembled. Not even finger grease is good.

Last edited by Vash; 12-28-2008 at 12:46 PM.
Old 12-28-2008, 01:47 PM   #35
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Re: 4.3L misfires only at cruise - rich condition.

Quote: Originally Posted by GeneP
These are MSD Bronze fancy lookin ones.

Many Thanks,
Gene
Leave those Bronze MSD gears alone for anything short of a weekend warrior. They wear very quickly and you will get erratic timing in no time. I used to change them all the time in my rustang due to wear. I would say if you use them check them at every regular oil change and prob replace every other one. Of corse type of oil pump, oil thickness,ect can help wear them quicker as well. I would go for a OEM gear and it should have a roll pin through the gear/shaft to remove the gear. Some are a real challenge and not worth the effort to save a few $$$ over a reman unit it they are reasonable price wise.

I also had a new Recon reman 4.3 I put in my s10 Blazer about 12 years ago(yes I'm old) and I had the same prob after 10k miles and found out they had reused the stock single row timing chain and it was so sloppy it almost ate through the sides of the chain cover in 2 spots.(wow I was mad). I used that chance to put a Eddy performer + cam and springs,eddy dual row chain, and shave the heads 30 thou. Man that woke it right up.

Best of luck to you
Eric
Old 12-28-2008, 03:25 PM   #36
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Re: 4.3L misfires only at cruise - rich condition.

Welp,
Figured it would be easiest to just go ahead and replace the complete distributor. Here's the wear I found on my gear:

Oh, and the brand new cap I installed yesterday looked almost as fried as the one it replaced.

Old 12-28-2008, 06:40 PM   #37
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Re: 4.3L misfires only at cruise - rich condition.

I bought a new gear from G.M. It was just easier. GeneP My gear looked just about the same. Good Luck!!
Old 12-28-2008, 08:50 PM   #38
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Re: 4.3L misfires only at cruise - rich condition.

Got A part number?
Old 12-29-2008, 09:47 AM   #39
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Re: 4.3L misfires only at cruise - rich condition.

I shoulda mentioned the original cap & rotor replacement did correct the intermittent miss fire but only for a month or so which is why I did not think it originally fixed the problem. This 2nd time another new cap & rotor again fixed it but for how long wasn't known. From what I've seen so far is that the fried or prematurely failed cap & rotor is a result of something else, like the distributor gear. So now the whole distributor is replaced and it is running good for now. What is so strange is how I could predict when it would start to miss then smooth out 35 miles later.

Thanks Again
Old 12-29-2008, 03:17 PM   #40
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Re: 4.3L misfires only at cruise - rich condition.

i am having the same problem on a 98 sonoma and cap,rotor, plugs,wires, fuel filter been replaced not too lng ago.....scanned it for codes and found that a p0300 multiple misfire code was set but not check engine light and it doesnt illuminate any more with key on engine off....weird....oh well....i am assuming it is the gear on the dizzy....anybody got pn# for oem dizzy gear. if so post em ....oh yeah it is a 98 sonoma with a 5 speed.....when i pull the gear out i will post pics of what i find....if anything good...
Old 12-29-2008, 04:02 PM   #41
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Re: 4.3L misfires only at cruise - rich condition.

oh yeah rock auto has some decent prices on dizzy gears and full dizzy assy. they also offer a full aluminum dizzy....any one had experience with those ?
Old 12-29-2008, 04:19 PM   #42
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Re: 4.3L misfires only at cruise - rich condition.

ACDelco Gear Kit, Distributor ShaftPart Number: 10457356
This is the number that I used. Came up to about 60 some dollars.
Old 12-29-2008, 07:05 PM   #43
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Re: 4.3L misfires only at cruise - rich condition.

thanks for that pn# i also wanted to add i am kind of not wanting to fix mine seing as i can get 380-395 miles out of a tank on my truck now....lol pretty good for a 4.3 with 135,000 miles....
Old 01-04-2009, 07:25 PM   #44
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Re: 4.3L misfires only at cruise - rich condition.

Quote: Originally Posted by supermuble
I have a 1999 Blazer 4.3L with new intake gaskets, new head gaskets (runs extra good, no oil in the coolant, and no coolant in the oil). The engine idles perfect, starts great. New spark plugs, wires, cap, rotor.

When driving down the road at light throttle (cruise), the engine will misfire and shutter. Under hard acceleration the engine smooths out and runs excellent with normal power. The shutter happens at light throttle either hot or cold and gets slightly better when it is warm.

The engine is getting horrible fuel economy and the spark plugs were checked and they were very dark (too rich).

The error code says Catalytic converter, however the converter was just changed about 6 months ago. A shop recommended changing the EGR valve, but the engine is super clean with only 110,000 miles on it and I don't think it is the EGR valve causing the rich condition and the misfire/shuttering.

Please help!!!!
Seems like this random misfire issue is becoming more common with the 4.3.
I've got everything new, including a new billet dizzy with a little over 4,000 miles on it and I experience the same issues.
Random misfires only happen when truck is warm (not cold or hot) and has been driven under 6 ish miles. Misfires completely goes away once at normal operating temp. Cap/Rotor looks good, wires are new. No codes are being thrown, no freeze frame data is available with code reader. VCM is basically not seeing this issue.

So, let's throw out a hypothesis and see what you guys think.

We know that when the vehicle is first started and is working it's way up to normal operating temperature, the VCM is running in "open loop" mode.
The O2 sensors have not heated up and the Cat. has not warmed up yet. The base fuel map is being used to operate the engine and most controls are not being used to control the air/fuel ratio etc...
Once the O2 sensors and Cat. have heated up and all other parameters have been met, the system goes into "closed loop" and the air/fuel ratio will be adjusted (fuel trim) for lean/rich conditions based on the free oxygen in the exhaust stream (It gets deeper with short term/long term fuel trims but thats for another class).

Where I'm going with this is, could we be experiencing some anomalies (read that random misfires) when the system is transitioning from open loop to closed loop???

I've pulled my hair out on this one and cannot find the smoking Gun.

All of the ASE tech's PLEASE jump in here...

Bill.
Old 01-04-2009, 07:53 PM   #45
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Re: 4.3L misfires only at cruise - rich condition.

Bill,
I was thinking the same with my random miss fire 1st running open loop then closed loop but couldn't get anybody to tell me what the program was.But my miss fire didn't start till I got 5 miles down the road or within 1 mile of reaching 60 MPH once on the interstate. Any initial temperature, summer or winter didn't make any difference. My miss fire was also when under very light load at 60+ MPH (Like when just lifting). It then cleared but at almost the exact place 25 - 30 miles down the highway. I could drive 400 miles the rest of the day & it ran perfect, till the next day. My new stuff included 2 O2 sensors, MAF, & MAP sensors, fuel pressure regulator (Even though pressure was OK), & 2 computers, Plugs, wires, and even a cap & rotor (The 1st time the cap & rotor didn't fix it so I figured something else was wrong). I even soaked the motor with a water hose including a pressure wash hose and still no miss during normal operation. I left the truck with a very reputable wrench for a week to drive it daily who couldn't find the problem although he could feel the miss. Almost 2 years of this crap until just last week when weather got pretty ugly & it started it's usual miss fire, but this time it did not straighten out after a 50 mile drive. It actually missed so bad I wondered if I would make it home. Then finding what I posted in my pictures and replacing the cap it seems to fix it. Just what I been waiting for to make it easier to find the problem. I then after reading about the distributor gear went ahead and replaced the whole distributor. No miss this past week & 200 miles so I think its fixed after almost 2 years and about $1000 in parts & aggravation.
Old 01-05-2009, 09:47 AM   #46
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Re: 4.3L misfires only at cruise - rich condition.

Quote: Originally Posted by GeneP
Bill,
I was thinking the same with my random miss fire 1st running open loop then closed loop but couldn't get anybody to tell me what the program was.But my miss fire didn't start till I got 5 miles down the road or within 1 mile of reaching 60 MPH once on the interstate. Any initial temperature, summer or winter didn't make any difference. My miss fire was also when under very light load at 60+ MPH (Like when just lifting). It then cleared but at almost the exact place 25 - 30 miles down the highway. I could drive 400 miles the rest of the day & it ran perfect, till the next day. My new stuff included 2 O2 sensors, MAF, & MAP sensors, fuel pressure regulator (Even though pressure was OK), & 2 computers, Plugs, wires, and even a cap & rotor (The 1st time the cap & rotor didn't fix it so I figured something else was wrong). I even soaked the motor with a water hose including a pressure wash hose and still no miss during normal operation. I left the truck with a very reputable wrench for a week to drive it daily who couldn't find the problem although he could feel the miss. Almost 2 years of this crap until just last week when weather got pretty ugly & it started it's usual miss fire, but this time it did not straighten out after a 50 mile drive. It actually missed so bad I wondered if I would make it home. Then finding what I posted in my pictures and replacing the cap it seems to fix it. Just what I been waiting for to make it easier to find the problem. I then after reading about the distributor gear went ahead and replaced the whole distributor. No miss this past week & 200 miles so I think its fixed after almost 2 years and about $1000 in parts & aggravation.
Glad your new Dizzy seems to have fixed your issue.

I'm still puzzled on my end. The billet Dizzy I put in less than 4,000 miles ago was a really good unit from Rock Auto with brass Cap lugs, so I can't imagine this is the problem. If it was, the problem should exist all the time, not just within that small magic window that the misfires occur.
I also have the MPFI conversion done so I can't blame it on the old poppet valves.
I may try and run the truck for a couple of days with my OBD2 scanner plugged in and set on "live data". Maybe something will pop up during a misfire incident.
Just another nagging issue with the ol' mule.
Old 01-05-2009, 05:41 PM   #47
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Re: 4.3L misfires only at cruise - rich condition.

Quote: Originally Posted by blanz
Glad your new Dizzy seems to have fixed your issue.

I'm still puzzled on my end. The billet Dizzy I put in less than 4,000 miles ago was a really good unit from Rock Auto with brass Cap lugs, so I can't imagine this is the problem. If it was, the problem should exist all the time, not just within that small magic window that the misfires occur.
I also have the MPFI conversion done so I can't blame it on the old poppet valves.
I may try and run the truck for a couple of days with my OBD2 scanner plugged in and set on "live data". Maybe something will pop up during a misfire incident.
Just another nagging issue with the ol' mule.
Well, the old bitch decided to pop me with a CEL today for the first time.
P0302 (Misfire on cylinder 2).
Cleared the code.
We'll see if I get a repeat on cylinder 2 or if it goes random as I'm expecting.
Old 12-30-2009, 04:34 PM   #48
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Re: 4.3L misfires only at cruise - rich condition.

Yea i have the random multiple misfire too. I am not running rich, but studers in the lower RPM and gets crappy gas mileage. I replaced the cap, rotor, wires and plugs about 20,000miles ago, and ran fine for those 15,000 miles, and it started back up, Replaced it all again, and it took care of it for a wile longer, and it started doing it again a few weeks ago. So i decided to get a new distributor. I got the Summit Racing one that they offer. I installed it for Christmas, and its runs great, but its pulling a code. Its a crank and cam position sensor timing corolation problem. Called Summit Racing's tech line and spoke to a Tim there "who by the way is an ASS And useless to talk to." He gave me dumb guesses that it had something to do with those sencors going bad befor i had done the Distributor. telling me that i did not fallow instructions and disconnect a brown wire up under the dash and adjust the timing with the distributor. He was dumb

Any ideas?????????????????
Old 01-03-2010, 07:15 PM   #49
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Re: 4.3L misfires only at cruise - rich condition.

My 4.3 has the same symptons described in this thread. It first started out doing it intermittently but now does it ALOT and has thrown the p0300 code
  • Plugs and wires were replace back in May.
  • Coil, rotor, and cap were replaced last month.
  • Pulled the plugs (which can be a PITA b/c of how slammed the Blazer is) two weeks ago and they look fine, normal wear and tear, gap is still set.

I'm in the process of buying an X-Runner as a daily so I can get this issue figured out and start working on the Blazer, making it a project. Looks like I'll pull the dizzy out and take a look at the gear.
Old 01-04-2010, 12:24 PM   #50
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Re: 4.3L misfires only at cruise - rich condition.

Quote: Originally Posted by Jeffgoodtime
Yea i have the random multiple misfire too. I am not running rich, but studers in the lower RPM and gets crappy gas mileage. I replaced the cap, rotor, wires and plugs about 20,000miles ago, and ran fine for those 15,000 miles, and it started back up, Replaced it all again, and it took care of it for a wile longer, and it started doing it again a few weeks ago. So i decided to get a new distributor. I got the Summit Racing one that they offer. I installed it for Christmas, and its runs great, but its pulling a code. Its a crank and cam position sensor timing corolation problem. Called Summit Racing's tech line and spoke to a Tim there "who by the way is an ASS And useless to talk to." He gave me dumb guesses that it had something to do with those sencors going bad befor i had done the Distributor. telling me that i did not fallow instructions and disconnect a brown wire up under the dash and adjust the timing with the distributor. He was dumb

Any ideas?????????????????
what year is your truck? also what is the Summit racing distributor part number? you may have to do a case relearn on your truck with the new distributor...
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