Fuel Pump Prime Issue...
Fuel Pump Prime Issue... For the past month or so, nearly every time i put my ignition on (9 times outta 10) The fuel pump relay will click. Which is fine, but after it stops it clicks again to reprime the fuel pump. Ive checked over all the wires and cant find anything wrong. I went out to my tuner and he had a problem reading my ECU so im thinking there might be a problem with my harness. But the car runs and drives great. Where should i look first ? Thanks
Have you let the car sit awhile at all? or near a field where a mouse could have gotten in the engine bay? There is a place where the wires run from the computer and harness into the cab that is located right behind the computer it has MANY wires and Ive read a few times that mice can wreck Havoc there?
Have you let the car sit awhile at all? or near a field where a mouse could have gotten in the engine bay? There is a place where the wires run from the computer and harness into the cab that is located right behind the computer it has MANY wires and Ive read a few times that mice can wreck Havoc there?
Yup... and then again, and again, and again... on a rarity itll stop after the first time, sometimes after twice or 3 times. All the rest of the time it just continuously pulses
I've never seen that..try a different PCM if you can..
The reason I say that is because what controls that priming is a 12v wire coming from the PCM to the 86 pin on that Relay. When you turn the key it goes hot for 3 sec, then should shut off, then power back on when you start the car.
I don't think it's a wiring issue.
Just find a '94 or '95 PCM from a Fbody, it doesn't even have to be tuned..you aren't trying to start the car, just checking prime.
The reason I say that is because what controls that priming is a 12v wire coming from the PCM to the 86 pin on that Relay. When you turn the key it goes hot for 3 sec, then should shut off, then power back on when you start the car.
I don't think it's a wiring issue.
Just find a '94 or '95 PCM from a Fbody, it doesn't even have to be tuned..you aren't trying to start the car, just checking prime.
Don't know if you've checked it yet,but try checking the ignition switch on the steering column my would do this sometimes when my wires were all jacked up down there causing the switch to slowly go out.
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I've never seen that..try a different PCM if you can..
The reason I say that is because what controls that priming is a 12v wire coming from the PCM to the 86 pin on that Relay. When you turn the key it goes hot for 3 sec, then should shut off, then power back on when you start the car.
I don't think it's a wiring issue.
Just find a '94 or '95 PCM from a Fbody, it doesn't even have to be tuned..you aren't trying to start the car, just checking prime.
The reason I say that is because what controls that priming is a 12v wire coming from the PCM to the 86 pin on that Relay. When you turn the key it goes hot for 3 sec, then should shut off, then power back on when you start the car.
I don't think it's a wiring issue.
Just find a '94 or '95 PCM from a Fbody, it doesn't even have to be tuned..you aren't trying to start the car, just checking prime.
I have not, im not entirely sure where it is. Ill check shbox right now for that thanks
I didnt even think of that. but nothing else goes on or off, the dash lights stay constant and so does auxiliary power.
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Ill check it out tomorrow. Even tho i doubt its that. Ill check the relay, the ECU and the wiring tomorrow hopefully 
if the piece ofmetel inside the relay got to hot at some point and melted it so it can touch just enough to turn it on and off repediatly. I see this on A/c relay when people hot wire them or try and bypass something else the clutch will short cycle like low on freon and the system will be full. take the relay apart and its melted in a way it can still pass current and wont switch off causeing it to turn on and off over and over again.
if the piece ofmetel inside the relay got to hot at some point and melted it so it can touch just enough to turn it on and off repediatly. I see this on A/c relay when people hot wire them or try and bypass something else the clutch will short cycle like low on freon and the system will be full. take the relay apart and its melted in a way it can still pass current and wont switch off causeing it to turn on and off over and over again.
Here is a quick test. Remove the relay. Rig a test lamp to the relay "coil" terminal and ground. Put it where you can see it from inside the car. Cycle the key and see what the relay is getting. I'd bet it getting the "turn on" signal from the PCM. Why is another problem. (If you do this and do not see the pulsing at the coil terminal, it might be problem that will only show up with the relay in, I'll explain if needed. Put a small wire in the "coil" hole and push the relay back in and test it again.) It could be getting some stray signal telling it the engine is cranking. I doubt the ignition power from the key switch is intermittent, if it was the engine would die and all kinds of PCM controlled stuff would also be intermittent. If you want to test that, a test light on the "PCM IGN." fuse will show it. It's also on the "A" terminal of the ICM. on the driver's side head right in front.
Basic trouble shooting is the way to go. Don't start chasing everyone's guess you'll just waste time.
Al
I dont do it when key off BC the PCM supplys voltage.
I was just saying to check the relay, It does supply power to the fuel system.
I also agree with proper diag, i post that more than anything else that diag will solve the issue not guessing. I have seen wierder things happen in a circuit and i just suggested checking the relay. Is that the issue IDK not in front of me to check it over. You ALWAYS check the easy stuff first. Fuses,relays, plugs.....
I was just saying to check the relay, It does supply power to the fuel system.
I also agree with proper diag, i post that more than anything else that diag will solve the issue not guessing. I have seen wierder things happen in a circuit and i just suggested checking the relay. Is that the issue IDK not in front of me to check it over. You ALWAYS check the easy stuff first. Fuses,relays, plugs.....
Staging Lane
Joined: Nov 2006
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I've been trying to figure out a similar problem with my car. Once you turn the key on, the pump cycles on, but never shuts off after the prime until you shut the car off. Is there a parameter in the PCM that can change that? Or do you think its a relay problem?
