Fuel delivery

90

Asked by Apr 18, 2014 at 08:59 PM about the Chevrolet C/K 1500

Question type: Maintenance & Repair

I have a 1990 Chevy 1500 that will not get fuel. I replaced the fuel pump relay as well as the 20 amp in line fuse. I have power clear through to the pump but the pump will not turn on. I checked the ground, it is good. I dropped the tank applied 12 volts to the pump and it pumps fuel and the truck starts. As soon as I plug it back into the harness which does have power the pump will not work. Any suggestions?

27 Answers

390

Check the voltage on the plug.while someone is trying to start the truck

90

8.5 volts with switch turned on and while trying to start it.

1 out of 1 people think this is helpful.
390

That's your problem there your pump is 12v should be getting above 12. Did you test the ground also

90

Yes, ground is good. Even ran a temp wire from battery to pump to make sure. If I am only getting 8.5 volts then where am I losing power? Where do I even begin to check? Possible ECM fault maybe?

3 out of 3 people think this is helpful.
390

You need to do a fuel pressure test on the line

1 out of 1 people think this is helpful.
390

Possible or maybe a brake in the wire.check fuseable links make sure there are good

3 out of 3 people think this is helpful.
90

Ok I will check them in the morning and let you know where I stand. Thank you very much for your input and entertaining my ignorance.

915

also check your main bus fuse in your panel under the hood, also here is a common one you can do on your own. unplug the map sensor and disconnect the battery for the 30 minute period to reset the computer. then reconnect map sensor and battery and see what happens.

3 out of 3 people think this is helpful.
90

Ok, I'll try that also. Thanks.

1 out of 1 people think this is helpful.
390

No problem.

16,905

the pump needs 12v. You have resistance somewhere. Check the relay connections

11,855

Electricity is fun if you can understand it. Finding a short is really hair pulling, short of replacing the entire wire. Use a volt meter to see if your getting a 12 volt draw when trying to start the engine. If everything up to the fuse box is good, it is after it leaves the fuse box and connects to the pump. Will the pump operate if there is a block in the gas line? Check the filters.

2 out of 2 people think this is helpful.
90

Ok, I checked all grounds, all are good. Re-set computer tested voltage at the pump and have 8.5 still with switch on and 13.1 while cranking but the pump still will not kick on. The pump still does work when I hook 12 volts directly to it. I hooked a new pump to the harness and it will not kick on until you try to crank the motor nothing when the switch is turned on. I am completely lost here, I have voltage where I should and ground where I should. Whats next?

3 out of 3 people think this is helpful.
90

Fuel lines and filter are free, I hook 12 volts directly to the pump and it fires right up.

11,855

I'm not familiar with the new computer hook-ups to all things electrical in the newer cars. Is there a chance the line goes through a computer module that is not sending the correct voltage and or signal to the pump the work? If you directly hook it up by by passing everything and it works, than it stands to reason when the key is turned on and the engine is cranking, there should be power to the unit and it will work. Hook a line from the tank to the frame, independent of the wiring to the pump. Perhaps the ground from the tank is not strong enough to complete the circuit. If the pumps works by hot wiring it, does not when re-connected to the correct wires, than there is either a backward connection, ground is hot, hot is ground, or the circuit is not being complete. Read the instructions on the new fuel pump and make sure it is wired correctly, it is the fuel pump replacement for your year and make of truck. Be careful as your dealing with a tank of gas, and stray sparks can cause intense heat if it goes wrong. Th9nk of electricity as water running. To get to where you want it to go, the valves must be open. In DC circuity, there must be a complete circuit back to the battery, and that is through ground.

16,905

There resistance somewhere. Check the power before and after the pump relay. Ive seen the connectors and the relay develop resistance and bring the voltage down. Also bad grounds and any connector

11,855

Ever consider the replaced pump relay may be bad? Re-check all the connections on the relay, spray them with either acetone or WWD-40 and hit them with a clean toothbrush to clean all the contacts. It sounds like your dropping voltage somewhere. If the voltage is low, the motor/pump may not have enough juice to function. If your not versed enough in checking for this, my next suggestion is to find a garage that specializes or has someone that is knowledgeable in car electrical issues.

90

The pump and relay are getting the 12 volts needed. I am well versed in using a multi meter and reading schematics, that's why I am seeking advice from someone that may know of something I am overlooking.

1 out of 1 people think this is helpful.
11,855

I goggled 1990 Chevy fuel electrical and got a diagram, I'll try to add it to the picture part.

4 out of 4 people think this is helpful.
11,855

The diagram came through. Hope that helps.

2 out of 2 people think this is helpful.
915

Check the map sensor. everything has to go through the map sensor before going into the main board

2 out of 2 people think this is helpful.

I've got the same problem changed the pump fuel filter both of them and pulled the gas lines off to try and get fuel out of them and nothing but will try y'all methods in the mornings thanks

20

I have seen this happen and it was the ignition switch and or the cable in the steering column. They could start the suburban priming it but it wouldnt turn the pump on initially. Check voltage while pump is plugged in at the plug. Check while turning key etc key check all wiring and connections for resistance dropping the voltage. See if can prime and start and stays running. No dealership was smart enough to find this. Rob Sandera The peoples choice for President

2 out of 2 people think this is helpful.

Is fuel pumps will not deliver pressure unless oil pressure is registered from the sending unit behind the intake. If the ECM or PCM whatever you want to call it does not register fuel pressure it will not allow the fuel pump to turn on. If you crank the motor and see no oil pressure on the gauge then you know that is your problem

fuel pumps will not deliver pressure unless oil pressure is registered from the sending unit behind the intake. If the ECM or PCM whatever you want to call it does not register fuel pressure it will not allow the fuel pump to turn on. If you crank the motor and see no oil pressure on the gauge then you know that is your problem

20

Hi 304brad38: I also own a 1990 chevy 1500K. Had the same problem. After three weeks of no driving and extensive research on my year and model, the problem was with the oil pressure sensor (OPS) located on the block just below the carb. As soon as the new OPS was installed the engine fired up like a champ. The OPS is a safety mech mandated by Feds for safety during front end collisions. When the OPS goes bad or fuel source is shut down, look first at the OPS for it just may be your villain.

20

Hi 304brad38. I had the same problem with the same truck. After three weeks of no driving, I found my solution. The culprit was my "oil pressure sensor" aka OPS. Truck engineered to shut down fuel supply after head on collision, Fed mandated. However, the draw back to this design is when the OPS is defective or wears out, you're dead in the water because the OPS controls the fuel pump. After installing a new OPS, varoom! old girl fired up like the space shuttle. Fuel flows like great now. Talk about being mad. All the time I spent trying to figure out the problem, finally decided to spend the effort and research the cause. check it out my friend; it's the OPS.

2 out of 2 people think this is helpful.

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