Mechanics

LEAN CONDITION FUEL PRESSURE

Jaguar XJ8

I have a 2001 jaguar XJ8 4.0 V8 with only 38,000 miles. The check engine light is on and also periodically get the limited performance message. The OBDII code indicates a lean condition. I cleaned the MAF sensor and the check engine light stayed off for about 30 miles. Also periodically the engine runs rough for a minute or two on a cold start then runs fine. Fuel pressure may also be an issue but the Jaguar dealer flat out refuses to tell me what the pressure should be. Does anyone have a suggestion and does anyone know the fuel pressure spec?

Thx Mike
Avatar
Mslaton
September 15, 2007.




Regulated fuel pressure should be 43.5psi You did not post the codes, so I can't help much with that, but check also for vacuum leaks, or unregulated air getting past the MAF, any holes in the air duct?

Merlin2021
Sep 15, 2007.
Thx for the reply. The first time we checked the codes were P0171 and P0174. After changing the fuel filter (which was pretty bad) we got only the P0174 code. Fuel pressure at idle is running arounf 33 lbs and after you rev it up a let it go back to idle it settles in at approx 31 lbs. Can't detect any vacuum leaks thus far and no leaks in the air duct.

Tiny
Mslaton
Sep 18, 2007.
Pressure is a bit low! Also check the ECT, this acts like the choke during warm up - lean to rich.

Merlin2021
Sep 18, 2007.
Hello the fuel pressure should be 35 psi at idle. 33 is just a little low. Pull the vacum line at the regulator.
It should go up around 5 psi to 10 psi. You may have a vacum leak at the intake. Use carb cleaner and spray at base of intake at the cylinder heads and see if the idle changes let me know how it goes.

Tiny
Fstranger302
Sep 20, 2007.
Hi there. Yep - that's what it does when I disconnect the vacuum line. It goes up to 45 psi. Is this normal or does it indicate a vaccum leak? I haven't tried the carb cleaner trick yet.

Tiny
Mslaton
Sep 21, 2007.
Hi there. Yep - that's what it does when I disconnect the vacuum line. It goes up to 45 psi. Is this normal or does it indicate a vaccum leak? I haven't tried the carb cleaner trick yet.[/Quote: 267bcd41e0] yes this is normall. The fuel pressure is fine for your car. This will not tell you if you have a vacum leak. Try the carb cleaner. If it does not change, you may have to take the car to the dealer and have it smoke tested to find the vacum leak let me know please if this helps

Tiny
Fstranger302
Sep 21, 2007.
Hi there. Yep - that's what it does when I disconnect the vacuum line. It goes up to 45 psi. Is this normal or does it indicate a vaccum leak? I haven't tried the carb cleaner trick yet.[/Quote: c73f6ca9f1] yes this is normall. The fuel pressure is fine for your car. This will not tell you if you have a vacum leak. Try the carb cleaner. If it does not change, you may have to take the car to the dealer and have it smoke tested to find the vacum leak let me know please if this helps[/quote: c73f6ca9f1]

Hi again. Turned out to be the air sensor. Aslo your suggestions on the wind noise were the right areas to check. Both the mirrors and the door seal on one side was the culprit.

Another question - just the other day I had a situation where I got a 'gearbox fault' (or something similar )popped up on the message center and the transmission started shifting HARD. Also a couple of other messages came up saying ACS and another saying TRAC not available. In addition the ABS light came on. This has happened twice and then goes away. The only common condition was at both times I had been driving slow for a mile or so.

This happened once on my Ford pickup but never happened again.

Any clues?
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Tiny
Mslaton
Oct 6, 2007.

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