When I finished my heads/cam swap, my car fired right up and everything seemed kosher, except it ran like crap and had under par throttle response of course due to the stock PCM. All gauges worked properly, throttle body worked, engine would shut down immediately when turning the ignition off.
Along with heads and cam (torquer v3, 231/234 .643/.598, 112lsa) I added LT headers, off-road X-pipe which deleted the rear O2 sensors. Also added LS6 intake, CAI, 42lb injectors and LS6 valley cover.

I sent the PCM off to get a basic tune in hopes it would make the car mobile. When I got the PCM back the car had the following problems: engine would start idle very poorly for a short time then die out or it starts and dies out immediately. No longer has any throttle response, TB butterfly does not operate anymore when pushing down throttle pedal. When the engine does run, it stays running even after turning the ignition off and physically taking the key out. So the motor won't turn off until it dies out. Oil pressure gauge and fuel gauge does not work. Temp gauge automatically maxes out. Tach doesn't work properly. When the engine is at an idle, approx. 500-800 rpm, the tach reads 4000-5000 rpm.

I sent the PCM back to the tuner and informed them of the issues. They reflashed the PCM, sent it back to me and it still has the same problems. Why would all these problems occur? Please comment with any ideas or advice what is going on with my PCM.

Thanks, any help is greatly appreciated.

 

My guess is that you have loosened or damaged something in the harness that plugs into the ECM. Make sure you are plugging the two connectors all the way in. Look over the connectors to see if there are any obvious wires that have pulled out or may be grounded. Try disconnecting your battery for ~30 minutes, verify your ECM connectors and properly seated, and then try to restart.

 

When that many things go wrong--it usually is NOT tune related-- but rather due to something in the -re-installation of all your mods----Sounds like you missed a ground---or left something unplugged
You have SO many mods all at once--A mail order tuner would still have a difficult time trying even to get it to run for awhile--
You need to sort out all the electrical issues 1st before trying to attemp to tune it---tach--fuel gauge--temps-oil pressure gauge--these are most likely all related to one thing being wrong
once this is corrected then with you mods the 1st thing will being trying to get it to run and stay running when cold--
Most important make sure he scaled your injectors correctly--and they are tuned for a 4 BAR fuel system--(58 PSI)
Typically a modded engine like yours will need an adjustment in the "open loop normal" fuel table to get it to start--cold or warm
The stock tune commands a way to rich mixture---on my 98 the commanded start AFR is in the 13.75 range--I had to lean it way down in the start-up fuel areas to 16.12 to get it to start nicely--
Mail order tunes are nice but as you stack on the mods it takes several attempts to get the tune "RIGHT" That's the drawback--the $$ you save is lost in the several back and forth shipping of the ECM--In hindsite it would have been better to spend the $ if you could and take it to a local tuner once---and be done---

 

What you gentlemen are suggesting makes sense, if the car didn't run fine before the tune. When I got done with the build, the car ran (with stock injectors) via feathering the gas and EVERYTHING worked perfectly fine on the stock tuned PCM. Motor ran long enough to get up to operating temp. Absolutely nothing was touched between the time I pulled the PCM, getting it tuned, to plugging it back in. The tuner shipped the 42lb injectors with the PCM and it was calibrated for those injectors while it was out. I checked the connectors prior to plugging it back up, all looked good. Then I installed the injectors. No ground wires get disconnected when swapping injectors, only injector connections, coilpack connections, TB and MAF connections. All plugged back in ok.

The tuner I have doing this mail order tune is the tuner that is going to dyno tune it. The purpose of this mail order tune is to get the car mobile/driveable. And the purpose of that is because the tuners shop is 80 miles from where I live and its a $300 tow.

 

Tuner did notice there was a mishap in the tune that caused the issues. After the tuner corrected the issue the car fired up and ran perfect. Motor ran smooth as butter, nice and quiet. All gauges working and good throttle response. I let the car idle and get up to operating temp. When I jumped into the car to take for a cruise, it dies. Car would start, run like crap shortly and die out. Checked the fuel pressure at the rail and it read about 11 to 14 psi. Car started and pressure quickly dropped to 9-10 then it would die. Obviously the problem. To me the issue must be a bad fuel pump and/or filter. My question, where is the fuel pump located and how to replace it?

 

I believe it's in the tank, inserted from the top. I've not done a Vette, but have others and it's a royal pain & not something you want to do unless you're sure. I'd look for another reason in line first, I think. I'd disconnect the fuel line and connect a hose or a way to let it pump into a clean container and see if it's pumping steadily, and if there's any debris getting through. As others have said, it could also be a bad ground and/or the pump isn't getting enough voltage. Also ask in the C5 Tech section, this section is more for Tuners, even though that's where your ailments started... Good luck!

Best regards,
...z

 

Unless you have a late 03 to 04, the pump is located in the bottom of the driver's side tank. Pretty easy to get to and change. MUCH easier than the late 03-04!!

Remove the driver's side rear tire. Remove the shield covering the backside of the tank, and you'll see the sending unit staring you in the face.

 

Thanks for the replies. Going to replace the fuel filter/regulator first then the pump if needed.