Tough trouble

[r2142]

I am at my wits end. I own a 1997 C1500 Silverado extended cab and I have just rolled past 210k miles. I wish to keep the truck since I cannot find the money to buy a new one so I have been repairing and replacing as necessary, which brings me to my issue.

 

I have owned the truck for 3 years and bought it at 160k miles and at the time it had some issues with it in the engine as it didn't idle just right and it choked up on hard acceleration so I replaced all the usual and got my power back but the truck always had a bit of a stumble that never went away. I replaced nearly every part that deals with ignition and timing and got to the point this January that I had enough money to pay someone to rebuild an engine for me and pulled the original engine and dropped in the new one (rebuilt).

now the fun part, the stumble issue showed up in the new engine as well. I have paid two different shops to diagnose and bother cannot find the issue in why it is misfire. The kicker, is all the misfires occur in just the front of the engine in cylinder 3 (the worst) and 2 and 4. The other cylinders do not misfire and the miss is visible at idle and can be felt at any throttle while driving.

The parts from the old engine were transferred to the new engine

normally I would have assumed the issue was in the spider injector but it passed leak down test flawlessly.

 

One more issue is it would seem that the computer is trying to cut fuel and the truck is running slightly lean.

 

I am currently considering that even though the EGR test passes it may be possible that there is something wrong with it opening too far and messing with the front cylinders.

 

Any assistance anyone who has an idea would be greatly appreciated.

Thanks in advance

[sdog4127]

This is a mass airflow engine. An easy test I used to do to check for a contaminated MAF was to unplug the MAF so the VCM sees a fault and ignores the MAF signal, then relies on MAP sensor calculations for fuel strategy. I would than test drive and make sure both upstream O2 seniors can max out to 900mv or so when accelerated at full throttle. If O2s do not go wide open rich under acceleration you have a fuel delivery problem. If sensors max out rich you know that you have adequate fuel delivery and you need to look at other inputs causing the lean misfire, most likely the MAF. If O2s cannot go max rich under WOT acceleration with MAF plugged in it is likely your MAF is vontzminared or faulty.

An exhaust back pressure check on both banks is very important in this scenario, as back pressure will cause erratic operation and higher than normal manifold pressure and thus erratic misfires.

 

Just some more thoughts.. Hope it can help.

[Jsdirt]

Didn't know that existed - that's the way to go right there! That spider assembly has got to be the biggest steaming pile of engineering in automotive history.

 

Surprised they didn't located it inside the oil pan ....

[Jsdirt]

Yeah, it's definitely all the bolt on electronically controlled stuff causing the issue. This I don't doubt for a second.

 

Had similar misfiring issues with a '00 Jimmy. Spend THOUSANDS trying to get the thing to pass MA emissions, and get the damn check engine light to go out. After the P0300 saga, I parted the truck. I took the engine, stripped all the electronic crap off it, and threw it in my '89 S10 Blazer. Installed a new intake, carburetor, and HEI ignition system. Thing never ran better! Drove it for 5 winters like that, and sold it running just as good as ever. Body was rotting away to nothing, otherwise would've kept it.

[Blueballs]

What about replacing the throttle body gasket or check the runners in the intake? If the runners in the intake are all carboned up (like an egr does) that could cause it. Or warped heads at those cylinders or even a cracked block?

 

Sent from my XT1565 using Tapatalk

[Jsdirt]

 

 

This should work.

 

 

http://www.truckmodcentral.com/forums/f36/well-ill-damned-wifeys-burb-alive-how-kind-18288/

 

Ahh, that worked - thanks!

 

Looks like that's the same thing I did to my buddy's Tahoe. Thought it was a completely different design eliminating the spider for some reason.

 

I still can't get this POS to run on more than 6 cylinders .... My buddy has been driving it like this for almost 2 years now, lol.

 

 

[Jsdirt]

Personally, I think the E3s are a waste of money. One electrode works fine - anything more is just a marketing gimmick.

[r2142]

Took to another dealer with a good reputation and they say it is the Injection Spider may be faulty but I am not going to give them $1100 for something I can do for $400

[r2142]

Why is it important for 1,2,7,8 in first?

[Jsdirt]

One of the worst GM designs in history, besides the diesel 350 of the 70's-80's.

[Jsdirt]

I don't understand what you're asking here ...

[r2142]

EGR didn't solve the issue

[diyer2]

OEM plugs IMO.

[grampadirt]

I did the MPFI upgrade on my wife's '99 GMC Suburban almost five years ago,best thing I ever did for it.The local dealership diagnosed the CFI fuel control module under the upper plenum took a crap.It's really not that hard to do.

[grampadirt]

I did a ''how to'' thread on another site,it may help shed some light on the MPFI upgrade.

 

http://Well I'll Be Damned,Wifey's Burb Is Alive(How To,Kind Of)

 

 

 

btw I'm dirtyoldman there

[Jsdirt]

NGK's are cheaper. Same exact plug too.