92 Engine Hot - no fuel pressure

martinf · #1 (**permalink**) 10-11-09, 09:56 PM

All,

Thanks for your help in the past. I've got a tough one here & hope someone has seen before and can point me in the right direction.

92 Deville. When engine is cold (i.e. overnight), the engine will start almost instantly when the key is turned. After driving around (engine hot), I can turn off the engine, and from 0 to 10 min or so, restart with no trouble.

The issue comes when the car is off for ~1hr (after a good warmup). The car needs ~10 sec or so of start before it catches. I have checked the FPR, and no visible gas is coming from the unit during idle, or after.

I purchased a fuel pressure tester, and confirmed that the fuel pressure is zero during the 'trouble spot' (Key on, engine off) - but jumps right to ~45 when cold.

I switched the horn relay with the fuel pump relay, in hopes that that would help isolate - unfortunately, same issue.

Anyone have a good suggestion?

_Thanks in advance!

Martin

**Ranger** · #2 (**permalink**) 10-11-09, 10:29 PM

Failing (intermittent) pump. replace it. My '92 ran fine WOT when cold. Once it (pump) warmed up it would fall flat on it's face at WOT.

martinf · #3 (**permalink**) 10-12-09, 09:25 PM

Thanks for the quick reply Ranger. I forgot to mention (although it's probably obvious) no codes are present.

The strange bit about the system is that it only 'acts up' after its been off for a while (~1hr). Overnight, it's just fine. Also odd, if I shut down and restart within 10 min or so - it jumps back to life. Would a failing pump care how long it's been off?

I did plug the fuel pressure gauge back in after the hour wait - and could watch as the fuel pressure 'gradually' came back up when the starter was engaged - almost like the motor was pressurizing the line...

Is there another signal that must be 'true' before the relay is commanded on?

-Thanks again,

Martin

**Ranger** · #4 (**permalink**) 10-12-09, 09:37 PM

Fuel pumps die in different ways. Your comment "could watch as the fuel pressure 'gradually' came back up when the starter was engaged" sounds like proof that the pump is weak. I believe it should come up to pressure almost instantly. The pump should energize at key on and if not cranked in 2-3 seconds it shuts down until cranking begins, but 2-3 seconds is enough to pressurize the system. It should hold that pressure even if the pump shuts down.

martinf · #5 (**permalink**) 10-14-09, 08:56 PM

The odd bit is - why only weak when the car's been off for an hour? When cold, the fuel pressure immediately jumps to 45 - no starter involved...

I test drove it a bit, a few WOTs when warm, and didn't detect any hesitation. Seems to run perfect - once it's running...

I thought I read in another post that if the relay is bad, the oil pressure would somehow build the fuel pressure. Seems like my case - but again, only when off for ~1hr..

Cold=OK, immediately after shutdown (<10min)=OK

Ghost in the system??? *grin*

-Thanks again for all your help,

Martin

**Ranger** · #6 (**permalink**) 10-14-09, 10:06 PM

Quote:

I thought I read in another post that if the relay is bad, the oil pressure would somehow build the fuel pressure. Seems like my case - but again, only when off for ~1hr..

True, if the relay fails, then the oil pressure switch will power the pump after 8 psi (I think) oil pressure is built up. That does not sound like your case unless the relay is intermittent. Not sure if that is possible, but swap it out and see if the problem goes away.

martinf · #7 (**permalink**) 10-22-09, 09:21 PM

Well, it was worth a shot. Bought a new relay for the fuel pump, double checked the fuze, and had it fail after the 1hr wait...

Ironically, the car started perfectly this morning (cold) - and drove beautifully on the freeway to work (several WOT tests.) Drive home was also uneventful. Let her sit for an hour, and it was back to the 20sec starter operation before it would engage.

Will try again after an hour with the fuel gauge connected. If it repeats the past error, there will be no pressure on keyOn/EngineOff - but only build up slowly as the starter cranks...

Will report back - but will also start shopping for a fuel pump. Guess I shouldn't be too grumpy after 18 years and 230k miles on the original...

_Thanks!

Martin

martinf · #8 (**permalink**) 11-20-09, 07:35 PM

It's been a few weeks - but I wanted to report back to the group that the fuel pump was indeed the problem.

Ranger, you had it from the start!

I guess the issue that really got me was the 1hr 'cooldown.' After thinking a bit, it makes sense - the pressure was OK at cold - once warm, the pump was failing. Immediate restarts were OK since the pressure was still at the rail. After ~1hr, the pressure had dropped - but the pump was still warm. No luck with restart. Overnight, the pump cools, and the pressure is good again.

-Thanks again Ranger,

-Martin