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r2142

Tough trouble

Question

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

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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

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

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Was referring to the cross post and he said it was important to run injector 1,2,7,8 first. Just asking for clarification as to why

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The engine is a rebuilt and I seen the issues with the missing prior to the new engine. It is a different engine than the original so that should eliminate the warped head or cracked block

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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.

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Have you checked fuel psi and volume. Because the misfires are on front cylinders they are higher on the fuel rail and will be more susceptible to low pressure/air in fuel rail. The original SCPI (Spider) unit is very particular with fuel pressure. The poppet valves need around 60 psi to unseat the balls from their seat in the nozzle. Only a few psi low and they simply won't spray fuel. So you can have a pump in a normal port injected engine that would work ok, but with the SCPI setup it won't spray fuel or just dribble.

Best advice based on all the things you have done/tried is to convert this truck to the port injector setup as previously suggested by other folks in this thread, and to take a serious look at your fuel pump and filter. Misfires have also been known to be caused by plugged cats as well so be sure your exhaust back pressure is in check. - again, these are things that should have all been checked when you took the problem to the dealer. These Vortecs are actually really simple engines, they just have a "cough, cough...unique" fuel system. I would make sure you can make minimum 60psi running fuel pressure and it should spike beyond 100 if you pinch off the return line. If not you need to replace your pump.

HTH

-Shawn.

 

 

Sent from my iPhone using Tapatalk

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I did check the fuel pressure and replaced the pump a month ago it was down to 48 psi. Not sure how I was even able to start the truck.

So I replaced the spider injector set for the second time now and instead of echlin I used AC Delco and I did notice a difference in the power afterwards. I still having a little bit of an issue with it missing so I have read that the O2 sensors can cause some of it so next item to replace unfortunately my truck has two of each upstream and downstream so it is expensive. Replacing because I drove the truck after the Injection Spider was changed and the O2 sensors were uneven on the banks at a steady rpm and load and they voltage was all over the map from high to low.

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Don't worry about the downstream o2's - they have zero effect on how the engine runs. They are 100% emission only sensors - just tells the computer you didn't sawzall the cats out of the exhaust.

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I totally agree with Jsdirt! The downstreams are useless unless the cat is clogged. I can't remember off the top of my head but does that engine have a MAP or MAF sensor?? Either of those could be clogged/dirty. Also, have the vacuum hoses ever been replaced as dry rotted vacuum hoses cause all sorts of issues. You can also take a bottle of throttle body/carb cleaner and with the engine running spray around as many gaskets as possible to see if any of them are leaking. A stumble or fast rev of the engine will tell you if the gasket is leaking. Clogged fuel filter or dirty throttle body/throttle position sensor will cause that issue as well.

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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.

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Have replaced the upstream O2 sensors and have cleared up most of the issue with the missing. The code scanner no longer shows p0300 and the emissions are now green instead of red. I have one more part I am going to replace and that is the idle air control as it appears to have been stuck open.

 

Oh on a side note, has anyone ever used the E3 plugs instead of the stock AC Delco and what are your results?

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

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OEM plugs IMO.

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NGK's are cheaper. Same exact plug too.

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