: 1996 Deville hard start and fuel pressure specs



jeffst
08-22-08, 12:55 PM
My 96 Deville has trouble starting after the car has sat overnight. It takes an excessive amount of engine cranking to get it to run. Once running, it runs and drives is fine. If I stop and restart the car after a few hours it has no problem. It seems to have trouble after sitting for about 12 hours. I connected a gauge to the fuel rail and it reads 30-32 psi with the engine off and key turned to accessory. I can hear the pump run. It also reads the same pressures when it is at idle. I left the gauge connected overnight and in the morning it was reading 0. Again I turned the key to accessory to get the pump to run and it showed 30 psi and then droped to about 25 psi. I turned the key off and ran only the fuel pump a second time which then brought the pressure up to 30 psi. I have checked the vacuume line at the regulator and there is no fuel coming out of the regulator. I have read several posts on this site with similar problems and to check fuel pressures.

What is the correct fuel pressure when the key is turned to accessory and only the fuel pump runs?
What are the correct fuel pressures at idle ?
Should the pressure drop to zero after the car sits overnight?
Do I need to replace the fuel pump even though I can hear it run and it brings the pressure back up to 30?

Any help in solving this would be much appreciated.:D

Ranger
08-22-08, 05:19 PM
The correct fuel pressure is 45-50 psi. It should not leak down, but many do. There is a check valve in the pump that should prevent that. Yours may be bad. The pump only runs for 2-3 seconds at key on if the engine is not cranked. You might try key on for 2-3 seconds and then do it again 1 or 2 more times to build pressure in the system. If that does not help, it may be time for a new pump. On the other hand, the pump itself may just be getting weak as well as the check valve leaking.

The other possibility is an injector leaking down overnight. The procedure for checking it is in the Tech Tips section.

aamusls06
08-22-08, 07:08 PM
The correct fuel pressure is 45-50 psi. It should not leak down, but many do. There is a check valve in the pump that should prevent that. Yours may be bad. The pump only runs for 2-3 seconds at key on if the engine is not cranked. You might try key on for 2-3 seconds and then do it again 1 or 2 more times to build pressure in the system. If that does not help, it may be time for a new pump. On the other hand, the pump itself may just be getting weak as well as the check valve leaking.

The other possibility is an injector leaking down overnight. The procedure for checking it is in the Tech Tips section.


I don't mean to hijack, but me and this guy is having the same problem. I checked psi and I'm exhibiting the exact same symptoms. Would this also cause a slight rough idle and miss?

Ranger
08-22-08, 09:00 PM
It could if the fuel pressure is low enough. Have you pulled the DTC's?

jeffst
08-23-08, 09:51 AM
Thanks for the info. I suspect the pump is weak. Even if the car is running and I give it some gas the fuel pressure does not go past 35 or 36 psi. I usually try the key to accessory a few times to try and prime the system but it does not seem to help. I think the injectors are designed to work with certain fuel pressures and if it is not there it will have problems. Was the fuel pump a common problem on the late 90's Cadillacs? I remember replacing it in my 91 Chev truck but it just quit one day without any indication it was on its way out.

Ranger
08-23-08, 11:44 AM
Not REAL common, but certainly not uncommon. Sounds like the pump is your problem.

aamusls06
08-23-08, 07:54 PM
I'm at 32 psi idle with no codes....sucks....that pump is like 240.00 for the complete assembly.

aamusls06
08-25-08, 01:54 AM
Would bad injectors drop the fuel pressure?

Ranger
08-25-08, 12:05 PM
I doubt it, unless they were ALL stuck open (very unlikely).