I out driving my 1991 vette on Friday, had driven about 2 miles and I lost power. It would not restart, I coasted to the side of the road. After sitting for 3-4 minutes, it starts but won't run unless I have my foot pressed halfway down, I let it die as I have to shut the hood. It barely restarts and suddenly clears up. I headed back home, after about 1 mile it started to act up again, like it was missing, bogged down with too much fuel. I kept it in 2nd hear and with my foot pressed halfway into the gas pedal. It was blowing black smoke out the exhaust. The instant MPG was reading 2, going about 40 mph. Pulled into the garage and and it was incredibly hot, white vapors coming from the back of the engine. Next day, I read the code of H21 (TPS too high) and the knock sensor code. I am assuming the root cause was the TPS code and the drive home with too much fuel being pumped through the engine triggered the knock sensor code. That same morning it fired up, ran rough and less than a minute later it acted the same way stalled out. I could not get it to re-fire. I tried to follow the Air Idle reset in this forum, but could not get the engine to fire. It acted as if it was going fire for a few seconds, then nothing. I could smell fuel as if it was flooded. I bought a new TPS and installed. Nothing, could not get the engine to fire. Any thoughts...could the computer be the problem? Any help much appreciated!

 

ALWAYS include the year vette you are asking help for, C4's are not all made exactly alike!!!!!!!!!!!!!
Measure the fuel pressure on the shrader valve at the end of the right side fuel rail. It should be 35-42 psi. After you shut the ignition off, the pressure should hold for a long time. If it drops rapidly, then you likely have one or more leaky injectors which are flooding your engine and the cure is to replace the injectors. I would also use a noid light (available at parts stores) or make one with an LED and a 240 ohm series resistor, both available from Radio Shack. Place the light across several unplugged injector wires and crank the engine. You should see the light pulse during cranking. If it stays on continuosly you could have a defective computer. The homemade noid light requires plugging in the wires to the socket with the correct polarity, try it the other way if it doesn't pulse during cranking.

 

JFB offered some good suggestions, I will toss one of my own out there. Remove the vacuum line from the fuel pressure regulator and check it for raw fuel, a broken diaphragm will cause flooding such as you describe too, and inspection requires no tools except for your eyes and nose. Good luck.

 

Sorry, the year is a 91. Thanks for the help will give it a shot this week.

 

Sounds like you have a injector shorting out or hanging open which will cause a no start or bad running condition try disconecting one injector at a time and see if it will start. This might help you narrow it down. Your 91 has Mul-Tects and when they fail it can happen very fast.

 

Went to Autozone last night and borrowed the noid light set. I disconnected all the injectors at once and tested each harness. The all blinked as I started it. Funny thing, it actually acted as if it was going to fire up / start from all the excess fuel from the previous day. I also checked the resistance on the injectors and they all read 15.8 to 15.9 ohms. Thanks for the help and will test the fuel pressure in a few days.

 

Your test with the noid light and ohm test of the injectors does not rule out a stuck open injector as suggested by JFB and Floridamale, injectors can fail mechanically even if the coil checks good.
Your testing does verify ECM operation and rules out a shorted harness, the fuel pressure test may help isolate a stuck open injector.

 

ohm your injectors ,my bet is on them !
if you have faulty injectors ...don't sweat and get a cool set from
http://www.fuelinjectorconnection.com
Jon's the best !!!!!

 

You guys are not going to believe this, but I am not getting ANY pressure at the shrader valve. Based on what I experienced with the black exhaust I am speechless. I hooked up the guage and only no reading ... I followed the instructions of turning on for 2 sec for the fuel pump to pressurize, then if not enough pressure turn off for 10 sec and repeat. I did this numerous times and nothing. I unhooked the guage and manually with my finger released the valve and got maybe a thumb size amount of gas come slowly out...nothing with 40 psi behind it I don't know how to explain the gas smell after trying to start it previously, maybe it is just a little gas in vapor phase is easily detectable. Any other thoughts on what I could be missing?????

 

Wanted to summarize the Root Cause of my problem. One last piece of info to share, I could get the car to run on Carb Cleaner with the injectors unplugged. The fuel pressure was low but not the problem and ended up replacing the fuel pump for fun. I had it towed into the Chevy dealer and they could not connect with the computer consistently. They replaced the computer (parts/labor for $400) and it fired up!!!! There was also a miss and it was traced to 2 injector harness tips being bent because of the numerous times I had removed the injector harness in prior troubleshooting. Thanks for all the tips everyone provided.