Why sould the fuel cut off after 10 to 20 seconds at idle

40

Asked by Apr 27, 2016 at 06:53 PM about the 1988 Chevrolet C/K 3500 Silverado Extended Cab LB

Question type: Maintenance & Repair

1988 Chevy 454 Dually.  TBI .  New distributor. new Delphi fuel pump (11.5 psi)  Fresh gas.  Eliminated the air pump.   Engine would keep running if I feathered the throttle when I had only 6 psi on old pump.  Now it starts fine, runs for 10 to 20 seconds and fuel shuts off every time.

9 Answers

4,575

air temp sensor may be at fault~ https://www.google.com/? gws_rd=ssl#q=1988+Chevrolet+C%2FK+3500+air+temp+sensor

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I don't think that's it. The air temp sensor checks out. About 5 amps to it and there is a good ground. I did a temp check and the ohms dropped as I increased the temp. Any other Ideas? When the engine stalls, the injectors stop immediately. No stumble. As if the electricity or the gas is suddenly cut off. It does it at dead idle and when I am feathering the throttle.

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40

Sorry "5 volts to it" Long day.

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When I turn the ignition on, the fuel pump runs for a few seconds and stops if I do not start the engine. What keeps the pump running when I do start the engine?

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4,575

not to question your methods....how in the world... never mind...most times the system ground has corrosion...providing a less then reliable voltage to the ECU...you'd think a check engine light would appear...but not for reduced voltage...batteries will last 10 years before they stop accepting a charge...and with reduced voltage perhaps the ECU is "poopin- out" on ya~ just New battery and perhaps New battery cables to assure the full 30 amps to the chassis/frame and to the engine (second cable) both must be free of corrosion to avoid reduced voltages...(which is what may be the cause)~

4,575

actually can guess the starter (key switch) contacts may be worn...there is a fuel loop with your TBI...thankfully the pressures are not as great~ but to keep running after OFF is selected tells me there is a problem with the starter keyswitch...might go away once the proper grounding to the frame and engine are done right!~

40

Battery and cables are new and they are grounded well to the new heads. No rust or corrosion. The alternator charges at about 13.8 at 2000 rpm with all accessories on. I did not check the amperage. I have done a lot of the usual systems checks but I do not know how the TBI system is supposed to function. I understand the fuel pump is supposed to run for a short time to put adequate pressure to the lines and TBI. I do not know how power is maintained to the fuel pump after the engine has started. Or how to troubleshoot the electrical that controls the fuel pump. If you are wondering. Checking the air temp sensor is like checking a thermostat. Hold it so the tip is in water. As the water warms the resistance should drop from about 1.2 at chill to about .3 at about 180 degrees. A temperature controlled rheostat.

4,575

well a wire...that changes resistance when cold~...from what I understand/have seen...but 1988 technology with TBI seemed like a can...which may have to study a schematic to understand how this relates to fuel control...bet is a simple ECU function~ need the schematic to help you solve your problem...am limited to guessing at the solution...sorry it's slightly beyond my capability...I was a mechanic from 1993-1998....so as useful as a dial-phone...but still know a thing or two...thanks for your help~

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I thank you for your help. I started getting my ASE certs when 50 years ago as a hobby. Have not done anything in the last 20+ years. Though I understand the theory, I lack the hands on experience with injection systems to do any practical troubleshooting. I found the air temp sensor testing on YouTube and was amused at it's simplicity to maintain the air/fuel mix. So far I have not been able to find a schematic to show which circuits control the fuel pump operation at what times. The fact I could keep it running by feathering the throttle when I had low fuel pressure has me baffled, unless there might be a problem with the new ECM or a loose wire that just wants to drive me nutz. Tomorrow I will continue to pick the brains of those of you that know more than I. I appreciate your input and hope you might be able to help me solve my issues.

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