Losing Fuel Pressure when parked

socalfiver · Post by **socalfiver** » Wed May 02, 2012 3:03 pm

I've noticed that most of the cars at the salvage yard retain fuel pressure in the injector hoses, even though some have not run for years.

My car loses fuel pressure after being parked for about 20 minutes. It has no trouble starting, but cranks for a few seconds to rebuild pressure then starts right up. Runs perfect, no other fuel issues besides taking about 4-5 seconds to start after being parked. Maybe 8 seconds if it's cold outside.

Where is the fuel pressure most likely going? I've entertained all sorts of ideas, like leaky injectors and bad fuel pumps. Has anyone had this problem before, and is there a place I should check first?

Eric Q · Post by **Eric Q** » Wed May 02, 2012 4:06 pm

In my E23, the mechanic diagnosed the culprit as leaky fuel injector seals.

socalfiver · Post by **socalfiver** » Wed May 02, 2012 4:30 pm

The Fuel Injector Seals go between the intake manifold and the injectors themselves. I replaced them about 18 months ago when I did a valve job.

Injector seals might cause slow starting by allowing outside air into the manifold and changing fuel/air ratio, but my problem is low pressure within the fuel rail after the engine is turned off. Fuel pressure is fine with the engine running.

Thanks for the input!

-Ted

Blaise · Post by **Blaise** » Wed May 02, 2012 4:35 pm

socalfiver wrote:The Fuel Injector Seals go between the intake manifold and the injectors themselves. I replaced them about 18 months ago when I did a valve job.

Injector seals might cause slow starting by allowing outside air into the manifold and changing fuel/air ratio, but my problem is low pressure within the fuel rail after the engine is turned off. Fuel pressure is fine with the engine running.

Thanks for the input!

-Ted

I have no measure the pressure on my car, but it does crank a bit before starting. I figured the fuel pressure was just building.

Everything is new, except for the fuel pump.

socalfiver · Post by **socalfiver** » Wed May 02, 2012 5:15 pm

Maybe the check valve in the fuel pump is my culprit. I replaced my fuel pump about a year ago with one salvaged from an e28, but the problem persists.

wkohler · Post by **wkohler** » Wed May 02, 2012 6:43 pm

socalfiver wrote:Maybe the check valve in the fuel pump is my culprit. I replaced my fuel pump about a year ago with one salvaged from an e28, but the problem persists.

That's my bet.

Put one of these in:

16 14 9 068 988

Well, I did a quick search and they appear to have gone NLA. Essentially, plumb in a check valve in front of the fuel pump. They make some that have NPT threads, so you'd just get a couple 3/8" barbs and you're good to go.

Blaise · Post by **Blaise** » Wed May 02, 2012 7:00 pm

Keep us posted.

Falkenberg · Post by **Falkenberg** » Thu May 03, 2012 3:26 am

Also the pressure regulator might be a bit leaky.

Robert Bondi · Post by **Robert Bondi** » Sun May 06, 2012 5:19 pm

I've got a an elec fuel pressure gauge among my extra gauges.

Fuel pressure is retained for hours after cranking or running. Reading is obtained on the hose feeding the rail in the same place where I have a second, spin-on fuel filter. Normal pressure is about 30 psi.