Vehicle starts, shuts off almost immediately

UGLYKIDMOE

MEMBER
1995 CHEVROLET 1500
4.3L
6 CYL
4WD
MANUAL
100,000 MILES

Starts but after a few seconds shuts off. To me it seemed like a fuel issue. Replaced: fuel filter, fuel injectors, distributor cap, rotor, ignition module, TPS (throttle position sensor), ECM (electronic control module). Error code is 22 (low voltage from TPS to ECM). Jump the TPS reference signal (five volts over voltage) wire to the TPS output wire (sending signal back to ECM to check that this wire is not broken) I then receive an error code of 21 (over voltage) so TPS wires appear to be okay. Once I restart the truck (and it shuts off) the error code reverts to 22. Totally confused and lost, any help would be greatly appreciated. Thanks in advance.

7 Replies

WRENCHTECH

MECHANIC
20,758 POSTS

Use a noid light bulb and test for injector pulse?
Also try this, disconnect the oil pressure switch and see what it does.
I have had a few of those with a shorted oil pressure switch which takes voltage away from the fuel pump when pressure builds up.

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Saturday, April 21st, 2018 AT 2:28 PM

UGLYKIDMOE

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4 POSTS

Thanks for the reply. Have not picked up a noid, but observed injectors while buddy started vehicle, both worked fine. I will look into the oil pressure switch. At this point I am convinced it is the TPS (although brand new). In checking the TPS plug I get a five volt signal at the reference wire, but when I check the signal wire at idle I have less than 0.2 volts (should be minimally 0.49 volts) and when I open the throttle to wot I does not even reach 0.3 volts (should be over 4.0 volts by that time).

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Saturday, April 21st, 2018 AT 4:02 PM

WRENCHTECH

MECHANIC
20,758 POSTS

Although there is some sort of issue there, I do not think it is your main problem. The TPS would have to go full throttle before the engine started to go into clear flood mode and shut off the injectors.

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Saturday, April 21st, 2018 AT 4:05 PM

UGLYKIDMOE

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4 POSTS

Thanks again. Just so I am clear, my understanding is that any signal back to the ECM from the TPS that is under 0.49 volts (minimal idle voltage) essentially is telling the ECM to not fire the fuel injectors. From idle to wide open throttle I never see voltage over 0.30 volts, still way below what is required to fire the injectors hence my error code 22 - low voltage. What am I missing? Sorry for my lack of knowledge, just trying to learn. :)

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Saturday, April 21st, 2018 AT 4:38 PM

WRENCHTECH

MECHANIC
20,758 POSTS

No, that is not true. The only time the injectors are completely shut off is in clear flood mode, which is full throttle with the engine off. That reading will lean the mixture slightly but will not shut the engine off. Some of them can be adjusted for minimum voltage.