Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Welcome to ThirdGen.org!
Welcome to ThirdGen.org.
You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, at no cost, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, join the ThirdGen.org community today!
Fuel pump cycles on & off with key off,warm engine
Hi
Please help.
I just spent 2 years restoring my '88 GTA, first day on the road then... after an hour long drive I heard a hissing noise under the tpi plenum with engine off & still hot (sounds like air leak) then noticed the fuel pump was running.
Fuel pump would cycle on & off about 5 times then stayed on.
Re: Fuel pump cycles on & off with key off,warm engine
That's odd. I've heard of fuel pump relays sticking closed (on) and continuing to run the pumps, but never cycling on and off and finally staying on.
There's 2 ways to get power to the fuel pump (assuming no weirdo wiring issues). Fuel pump relay (firewall near the brake booster) and the oil pressure sending unit (screwed into the block just above the oil filter). When the pump is continuing to run after shut-off, unplug one and then the other- see which one kills the pump when it's unplugged.
Re: Fuel pump cycles on & off with key off,warm engine
Thanks, I'll check that out.
Does the pump have to maintain a constant pressure when car is shut off?
gurgling sounds coming from tpi plennum I've never heard before
Pump won't shut off at all now.
No change when relays at the brake booster are unplugged but have yet to try oil pressure sender.
I know it sounds strange but I'm at my wits end...By the way no wiring changes & low mile car.
Thanks...Larry
Last edited by crazylarry; 04-29-2009 at 10:26 AM.
Re: Fuel pump cycles on & off with key off,warm engine
When you shut off the key the pump stops and the line pressure bleeds down eventually. There's a check valve built into the system somewhere (in or near the pump itself, I believe). Some hold onto that residual pressure like a pit bull, some bleed down almost immediately when the pump shuts down. Either way, doesn't matter. There is no pressure sensor on the fuel lines- nothing on the car "knows" how much pressure is in the lines, and so has no way of "reacting" to it.
Re: Fuel pump cycles on & off with key off,warm engine
Thanks again.
I took the car into a shop for a manditory emissions test today & told them the problem only to get a call later saying that the pump seemed to be working fine???
For the last 24 hrs it would not shut off at all. I left the car at the shop to see if it is still ok in the morning.
This scares me because it will act up again at the worst possible time I'm sure.
I'm wondering about that oil pressure sender???
Thanks
