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]

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

[Blueballs]

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.

[r2142]

Broke down and decided to take to a dealership they wasted time and time money to not solve the problem. They ran an injection cleaning motor vac with slight improvement but not solved.

[r2142]

Does anyone have a suggestion for my next step

[sdog4127]

IAC in my opinion should never cause a misfire or poor idle issue unless it is holding idle below desired RPM. I wouldn't just throw parts at it at this point. Need to know facts of what is happening (easier said than done, I know!!!). As far as aftermarket spark plugs... I am a huge proponent of using factory parts. Give it what it was born with, that is how it was engineered and designed to run optimal in all applications. I would not recommend paying the price for E3 or any "performance" spark plug as you are just changing the variables further.

I haven't offered any real advice to remedy your situation, but I would stick to GM only parts until you iron this problem out.

 

great luck!!!!

[Jsdirt]

Need to find someone who specializes in drivability issues on OBD-II vehicles. Sounds like the local shops aren't that well versed in that particular repair segment.

[r2142]

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.

[r2142]

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?

[Blueballs]

I have been following performance magazines and I'm an ex certified mechanic. Use AC Delco plugs exactly what came I. The truck. The only time they should be changed to something different is if you are adding nitrous, a supercharger, a turbocharger, or decking the heads to I crease compression. Otherwise, the stick plugs made by the manufacturer that they came from the factory with will always perform the best.

 

It has been proven many times having more electrodes to have spark jump the gap to doesn't help. Even with MSD it will only fire to one electrode at a time so the others are useless until the others burn out. Save your money and go with AC Delco!!

[r2142]

Has anyone ever tried diagnosing the harness? Is there a pin-out for the ECU that I could maybe look for a short or a ground? I really think with all the parts that I have changed that something is wrong with the wire harness.

[Jsdirt]

Yikes man .... don't EVER yank a battery terminal on anything built after 1995 while it's running! Just asking for trouble. Too many delicate electronics on these things, and you've got enough trouble here!

 

 

Checking the harness is the best way to diagnose this, since you've already replaced parts - check for continuity or voltage at the computer. Check every wire going to the device - need good 5v reference, ground, and signal return. You'll need a good, and CORRECT wiring diagram, or you'll yank all your hair out in frustration. Check for 5v reference on a few different sensors to make sure that's ok. Helps having a scan tool with a graphing feature to check operation if the unit runs on a PWM signal.

 

This type of work makes me nuts. Hope you discover something!

[r2142]

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

[r2142]

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

[Jsdirt]

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.

[Jsdirt]

That link brought me right back this thread .... just FYI.