Intermittent Fuel Pump problem

**drogers302** · 09-17-2009, 11:35 AM

I have a 1999 Chevrolet Suburban, K1500 with 170,000. Replaced the fuel pump and filter 6,000 miles ago. I replaced it with a new factory GM pump. 6 weeks ago, I began having problems with the fuel pump not consistently engergizing. Only have problems at start up. Never while driving or idling. I have replaced the ignition switch, fuel pump relay - numerous times, new terminal connections in the fuse block where the relay resides. It doesn't matter if the engine is hot or cold. All the other electrical accessories work. The vehicle will crank over, but sometimes the pump just won't energize. Any ideas? I am at a loss. What role does the computer play in this?

**MrShorty** · 09-17-2009, 11:10 PM

I'm not exactly sure how the relay and the oil pressure switch interact, but the PCM would be responsible for closing the relay -- especially at startup. Get a wiring diagram and a voltmeter and see if the relay is closing. If you can get at a connector between the relay and the pump, see if the pump is getting power when it doesn't "energize."

When you replaced the pump, did you replace the wiring harness? Most new pumps come with a new harness, or at least should recommend that you replace the harness.

Don't forget to check the ground for the fuel pump. If the pump has a good ground, and is getting power, and still doesn't run, then the pump itself is almost certainly bad. If the pump doesn't have a good ground or is not getting power, locate and repair the break in the wiring.

**vncj96** · 09-18-2009, 06:48 AM

So if you put the key in and turn the ignition on without actually starting the truck the fuel pump doesnt kick in and you dont hear the humming?? On old Chevy such as yours, it may sound crazy, but one way to check if it is actually the pump or not is if the truck doesnt start, have a buddy crawl underneath and while you crank again have him whack the middle of gas tank with a hammer. If it turns over it should just be the pump. My fuel pump went on the fritz and was able to do this a couple times untill I could make ge the fuel pump replaced, once its running you shouldnt have any problems just on start ups.