My 99 GMC truck needs a miracle

[Redrocket1045]

Originally Posted by mudseeker

like i stated before, we need the freeze frame data to make an educated guess at what the problem might be. it could be as simple as a bad EGR. an EGR that is open at idle can cause a stumble/stall condition. it needs to be put on a tech2 and components tested. i've had an EGR that would go wide open when the computer commanded anything more than 40%. requested values and actual values need to be compared to find your problem.

You're correct about the egr. It causes what you stated but another good egr valve was tested and - no improvement. Here's what has been either replaced or a known good part tried. Also - checked all fuses.
MAP sensor
TPS
coolant temp sensor
knock sensors
O2 sensors
AIS motor
throttle body
ECM
crankshaft sensor
cam position sensor
new catalytic converters

[Redrocket1045]

Well guys - with no new leads to go on and that I'm just fed up with this problem, I've decided to remove all mods. The truck will be put back to stock except the headers and cats. In the next couple of weeks, I'll be pulling off the Powerdyne supercharger, the 39lb green giant injectors and the SLP 1.85 ratio rockers. I plan to sell them all - including the custom Diablo Sport programmer. I'm just waiting on the pigtails I ordered to replace the EV-6 pigtails that were required with the green giants. Thank you all for your input.
After this - I will be able to shift some time and start some mods on my '09 Sierra Denali

[stumpuller454]

well, i hope it cures your problem............. sad to see though!

[Sneakysportsman]

What type of compressor is it. If it is a twin screw, the teflon on the screws may not be pressurizing enough. Or if it is a snail drive the fins may be worn out. Check the boost.

[Redrocket1045]

Originally Posted by Sneakysportsman

What type of compressor is it. If it is a twin screw, the teflon on the screws may not be pressurizing enough. Or if it is a snail drive the fins may be worn out. Check the boost.

It's the snail drive type and the fins are excellent. What puzzles me is why do I have to accelerate the engine to 2000 rpms and hold it there for 30 seconds or so - and then it clears up. It acts like if a switch was turned on cause it goes from 2000 rpms to 3100/3200 rpms. If I just start it up and let it idle - it will try to die but manages to idle at approx. 400 rpms or so and misses like c*ap - sluggish with no response .
I've been at this since late January and it has been a biotch .

The only consolation is that I have my modded '07 Vette and my stock(but not for long) '09 - 403hp Sierrra Denali to drive.

[Redrocket1045]

Hey guys - I just had a brain far*. What would happen if any of the lead wires going to the injectors touch together. I know I rosin core soldered each wire and then wrapped each one with electrical tape. I know I should have used heat shrink tubing but I didn't. Remember - it's been 4 1/2 years and approximately 24,000 miles later. But just - what if the tape burnt or toasted off and a wire or two are touching another wire or grounding out? Could this be the problem?

[Sneakysportsman]

The injectors only fire when grounded. There should always be 12 volts at the injector. And the ground side of each injector lead goes back to the ECM to a driver that grounds the injector to make it pulse.

[Redrocket1045]

Originally Posted by Sneakysportsman

The injectors only fire when grounded. There should always be 12 volts at the injector. And the ground side of each injector lead goes back to the ECM to a driver that grounds the injector to make it pulse.

I'm just trying to think outside the box. Just - what if a wire is grounding out intermitently. Could that cause a "false" signal to the ECM - thereby pulsing more and therefore dumping an excess of fuel? I can't start working on the truck till next week so I guess only time will tell.

[scavanger]

I think unlike my L98 vette your injectors pulse indivigually . If you had and intermitten short on the ground wire it might pulse.Or if shorting on the 12 volt supply side it might screw up the ECM and not fire any of them for an instant. I know on an L98 each bank pulses.If you get a short in one of the injectors or wire it may not fire any of that bank. Don't remember if you checked your injectors. Check the ohms on your injectors , think somewhere between 12 and 16 ohms. Just a place to start.

Scav.

[Redrocket1045]

Originally Posted by scavanger

I think unlike my L98 vette your injectors pulse indivigually . If you had and intermitten short on the ground wire it might pulse.Or if shorting on the 12 volt supply side it might screw up the ECM and not fire any of them for an instant. I know on an L98 each bank pulses.If you get a short in one of the injectors or wire it may not fire any of that bank. Don't remember if you checked your injectors. Check the ohms on your injectors , think somewhere between 12 and 16 ohms. Just a place to start.

Scav.

Thanks, Scav - I'll check the resistence and see if they're within specs.