1991 Chevy S-10 1991 S-10 no start when hot

Tiny
SNAGGS
  • MEMBER
  • 1991 CHEVROLET S-10
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 227,000 MILES
Reading through some of the other forums, this is the one that helped me best. 1991 s-10 4.3L will start when cold but will not start hot. Fuel is not injecting into the throttle body. Tried bypassing the fuel pump relay and no sucess. Read another post about checking resistance on the ect sensor. That was within range. Could this be a low oil pressure problem? Has good oil pressure when running (have to spray fuel into throttle body while cranking to get started) but how can I test the oil pressure switch? I don't want to condemn the ICM just yet but that's my next step
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Sunday, October 17th, 2010 AT 6:25 PM

9 Replies

Tiny
RASMATAZ
  • MEMBER
There's nothing wrong with the ICM-did you check power at the fuel pump connector gray wire?

Its take 4 psi of oil pressure to close the oil pressure switch to power the fuel pump constantly-
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Sunday, October 17th, 2010 AT 7:03 PM
Tiny
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Truck will run if you spray quick start or throttle body cleaner into it then start. Starts cold, not easily, but never starts hot. Pump is not priming the injectors but runs fine when truck is running. Kind of embarassing popping the hood everytime to get it started. I checked the fuel pump relay, and bypassed it and nothing happened. Power to the pump is ok, is there a prime circuit anywhere?
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Tuesday, October 19th, 2010 AT 9:46 AM
Tiny
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Could be the computer is not getting an input signal such as ignition reference signal to synchronize the injectors -also check the fuel pressure if its with specs and the fuel pump and oil pressure sending unit
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Tuesday, October 19th, 2010 AT 1:40 PM
Tiny
SNAGGS
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Threw a service engine light today. Actually stayed on this time. Ecm has been replaced. Gonna swap out the oil switch and try that. Otherwise I'm thinking the icm is not recognizing the crank. Might try to grab one of those too. What pins do you connect to display the code in the dash?
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Tuesday, October 19th, 2010 AT 10:06 PM
Tiny
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Jumper A to B
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Wednesday, October 20th, 2010 AT 5:43 AM
Tiny
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Jumped A to B and got a code 12. 3 different ICM's 2 different oil pressure switches and still the same problem. ECT sensor resistance is in spec. Sick of waiting 2 hours before I can restart my truck lol. I understand the 12 code is just an ecm code. A friend said it should flash 12, then codes, then 12 again?
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Wednesday, October 20th, 2010 AT 8:26 PM
Tiny
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Do you hear the fuel pump when you turn key to run if so-Check the fuel pressure if its within specs, If not check fuel pump fuse and fuel pump relay
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Wednesday, October 20th, 2010 AT 8:30 PM
Tiny
SNAGGS
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I never could hear the pump run. Not even with my head by the tank. Relay I just bought so we'll see if that works. Thanks for all your help! Truck still starts cold, and I drove it all over for 3 hours today without shutting off. Pretty sure the pump is ok. Know the resistance spec for a ckp sensor?
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Thursday, October 21st, 2010 AT 6:05 PM
Tiny
RASMATAZ
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If there's a problem with the CPS I don't think you'll be able to drive for 3 hrs-It will prevent the engine from starting-To my understanding you don't have a CPS
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Thursday, October 21st, 2010 AT 7:35 PM

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