Fuel Pump or ECM?

[Lodogg2221]

Sombody please help! My truck has had starting troubles for a few weeks now. Cranks for a while before start. Also no pump noise on key on, I relieved the pressure in the line, and still the pump would not cycle. Today it refused to start at all. After running thru the checks in the Haynes manual, I resorted to pulling the ecm fuse. After 10 min, put it back in and turned the key, and the pump ran fine. Truck started right up. So is it the pump or ECM? I can get the pump for about $330 with lifetime warenty, or the ECM for about $150. Guess which I want it to be? Anyway, I need to have it up and running reliably by Thursday. Thanks in advance.

[maxwedge]

You haven't diagnosed either problem , what is this truck, what engine, year! You need to get a fuel press gage on this and see what the pump output is, also there are relays and circuits involved in the pump operation.

[Lodogg2221]

Originally Posted by maxwedge

You haven't diagnosed either problem , what is this truck, what engine, year! You need to get a fuel press gage on this and see what the pump output is, also there are relays and circuits involved in the pump operation.

Whoops. 98 K1500 5.7. Kinda hard to check pressure if the pump wont run isnt it? I got it here, but doing the same thing. Not pumping. And as I said in my earlier post, I have checked as per the manual, relays and circuits, except at the pump, but which must be good because it works sometimes, while sitting or running. If there was a short, it would run intermitantly, same with loose connection.

[777stickman]

Originally Posted by Lodogg2221

Whoops. 98 K1500 5.7. Kinda hard to check pressure if the pump wont run isnt it? I got it here, but doing the same thing. Not pumping. And as I said in my earlier post, I have checked as per the manual, relays and circuits, except at the pump, but which must be good because it works sometimes, while sitting or running. If there was a short, it would run intermitantly, same with loose connection.

"but which must be good because it works sometimes,.."?? Isn't that the same thing as "intermittent"?? OK, the ECM B fuse is a 20a fuse that powers the fuel pump through the fuel pump relay. The relay is controlled by the VCM (Vehicle Control Module). 1st thing is replace the ECM B fuse!!! 2nd thing is check the wiring connector at the tank for corrosion or what ever. 3rd thing is replace the fuel pump relay. I wouldn't replace the VCM unless it's the last resort!!..........Steve

[Lodogg2221]

Did the 1st thing, and the 3rd thing, gonna do 2nd tomorrow, after I get the bed loose. Also from what Ive been hearing from people who've been dealing with these trucks a while, its most likely the pump. Besides, Im gonna be so close, and its got 139000 on it now, and the pump cant last forever can it......we shall see.....

[777stickman]

Originally Posted by Lodogg2221

Did the 1st thing, and the 3rd thing, gonna do 2nd tomorrow, after I get the bed loose. Also from what Ive been hearing from people who've been dealing with these trucks a while, its most likely the pump. Besides, Im gonna be so close, and its got 139000 on it now, and the pump cant last forever can it......we shall see.....

While you're there, check for 12v on the gray wire for about 2 seconds when the key is turned to the "run" position. That will tell you that there's power through the relay to back there.

[Lodogg2221]

Thanks for the replies, but seems its fixed. I replaced the pump on advice from two mechanics based on symptoms, and also the relay, though it tested ok, just because it was cheap, the pump sure wasnt! But it now idles a bit smoother, though I cant tell if it actually runs better (ran good before).....but it does run! And no fluctuation in the sound pitch of the pump while running like before.

[backyardmec]

Originally Posted by 777stickman

"but which must be good because it works sometimes,.."?? Isn't that the same thing as "intermittent"?? OK, the ECM B fuse is a 20a fuse that powers the fuel pump through the fuel pump relay. The relay is controlled by the VCM (Vehicle Control Module). 1st thing is replace the ECM B fuse!!! 2nd thing is check the wiring connector at the tank for corrosion or what ever. 3rd thing is replace the fuel pump relay. I wouldn't replace the VCM unless it's the last resort!!..........Steve

HI im haveing something going on with my truck like this need help please
I have a 88 GMC C3500 5.7 TBI 1ton drw box truck and im not get power to the ECM-B fuse im get 12v to the ECM1 fuse with key on like the book say im geting 0.01v to the ECM-B fuse and the same to the fuel relay and pump I put a new pump and relay and ECM in and trying to go with the book on the wiring but the colors are not the same please help me I need this truck soon to move my self and family thank you for you time