JGA

Hi

Any help appreciated.

Car cold - Key on, engine not running
- 52 psi
- pressure leaks down slowly after a few minutes

Start car - at idle till normal temp
- 60 psi steady
- does not drop off

My Haneys manual quotes 55 to 60 psi key on, engine not running, so 52 psi looks a little low. Also, the manual states it should hold steady. My pressure definatley leaked off.

Also, pressure raised to 60 with car at idle. Manual states it should drop 3 to 10 psi at idle. My pressure went up 8 psi.

I tried the key on test, engine not running again after the engine had wormed up. It read 52 psi and then climbed to 54 psi slowly, which is the opposite of when it was cold, when it dropped off.

I plan to replace the fuel filter next weekend.

Is the above normal? Am I misunderstanding my manual? Should the test only be done when the engine is worm? I am thinking, filter, regulator or leaking injector.

Thanks JA

oange ss

iTrader: (50)

look for 58 psi while driving, everything sounds normal.....dont take info in that Haynes manual as gospel

DrkPhx

iTrader: (15)

It should be between 55-60 psi with the ignition in the ON position. If the pressure leaks 5 psi or more in 10 minutes it could be the fuel pressure regulator or leaking injectors.

To check the fuel pump check valve, relieve the pressure down to 10 psi with the ignition ON. If it leaks 2 or more psi in 10 minutes, the check valve is bad.

Make sure you are measuring the pressure at the rail and make sure the gauge is tightly secured to the rail to eliminate false readings.

JGA

Hi
It's a proper fuel injection pressure gauge connected to the Schrader valve with a GM adaptor and I am quite sure it was not leaking. It leaked down from 52 to 46 in about 2 or 3 minutes. I did not wait for 10 minutes. However this was cold. When the engine was hot it actually increased pressure sligjtly, but again I did not wate very long.

I am assuming the next step is to verify the pump check valve and regulator? If these are Ok, then look at the injectors?

Thanks JA

DrkPhx

iTrader: (15)

Check the injectors for obvious leaks first. What year car is this?

JGA

Hi

Its a 98 and it seems to runs fine. However, I had poor dyno numbers recently (245 HP with headers and K&N induction) so I am starting to look into some of the simpler things I can check now. I hope to get Autotap soon.

When you say check the injectors first are you talking about external leaks from the fuel rail/manafold o-rings onto the outside of the intake manifold, or internal into cylinder? Sorry I am a newbe.

Also, is the regulator also in the fuel tank with the pump, or out front at the manifold?

Thanks I appreciate the help.

JA

DrkPhx

iTrader: (15)

Autotap will help take the guess work out of diagnosing you problems and it's always nice to see what going on in your engine.

The 98's have the fuel pressure regulator located inside the gas tank, which are metal (99 up are plastic), which are a PITA to drop. Bascially you would have to replace the fuel pump assembly. That should be your last resort.

Look for external leaks by all the injectors. Turn the ignition in the ON position so the pump is working but the engine is not on. Usually you can smell raw gas when this is the case. What kind of dyno was it?

JGA

Hi

Mustang

I just had a look at the injectors, manifold and fuel rail and everything looks tight. There is no leakage anywhere.

I purchased the car from a dealer and still have 1 year left on the warrantee. It is 250 deductable and a 1200 limit. I think I might consider taking it to the local corvette shop. I risk the diagnostic time (about 1 hour labor) if nothing is realy wrong with the fuel system, but if it is a pump or regulator, I can get it done quickly and right for 250. It looks like you have to drop the rear end and pull the tank to replace apump. What a joke that is.

The car runs fine, but it does feel flat at higher RPM, especialy after it shifts. The 2nd, 3rd shift feels like the engine disapears for about 5 seconds and then revs up very slowly. The A/F on the dyno was fine at about 13.1.

DrkPhx

iTrader: (15)

It could be the fuel pump. D0 you hear a hissing sound from the the rear when the car is at operating temp when it's hot outside? The shift lags you are referring to is actually Torque Management which pulls several degrees of timing at WOT on every shift. Don't feel so bad about your dyno numbers, mine did 298 rwhp bone stock on a Dynojet 248C model which dyno higher than the less common Mustang dyno. How many miles on the car?

JGA

Hi

45K, cylinder compression is almost perfect.

I agree I don't want to get carried away on somthing if it is in my head.

Thanks for the input.

JA