Just getting back to what seems to be a life long project,.........
Replaced fuel pump, filters, regulator, etc. with fairly inexpensive but new parts. Installed a pressure gauge under hood at fuel rail input. After warm up, pressure stays a constant, but low 28-30 PSI until the motor is shut off. Then it increases to about 36 PSI and stays for awhile. Engine idles at a smooth 1350 RPM in Park/Neutral and drops to a rough but running 750 RPM in Drive/Reverse, sitting still.
I've tried adjusting idle speed and air/fuel mixture and cleaned/checked all intake hardware that I know of.
At the risk of being redundant, any ideas on where to go next?
Thanks, Jim

 

Does the engine reach normal operating temp or is the thermostat stuck open? I wonder if it's getting too much fuel. It seems to be stuck in warm-up mode with the auxilliary air valve staying open. Did you check the gap between throttle and throttle body for 0.002" gap? I'm only thinking of the idle situation here, I don't see how low pressure in the fuel rail could cause the 1350rpm idle.

How does this sound everyone?

 

Thank you for the quick reply. The throttle body .002 has been checked but it is probably time to recheck as I have not been successful so far. The engine does get to operating temp and I am not sure about the aux air valve. Would the idle drop so much in drive if that was stuck open?
Also, if the vacuum controls the pressure regulator, is there some way to adjust to get higher fuel pressure? Another question might be why the pressure increases when the engine is shut off?
I appreciate the input.
Jim

 

I think that your fuel pressure is just fine. It drops a bit as the engine runs, because the injectors are opening and closing. I'd leave that alone and look elsewhere.


1350 RPM at idle is more than a tad fast for any engine. And, a bit weak as it drops a lot when in gear!!


To me it suggests a vacuum leak of some considerable proportion.


Find on line or here, a vacuum line diagram and start checking them. At the intake source, clamp or plug each and observe engine performance. Under the intake and towards the rear is a hidden spigot that can break.


And, don't forget the throttle butterfly valve shaft. if it is a sloppy fit, vacuum will leak there. Most noticeable at idle.


The biggest vacuum draw is the brake booster. A failed one way valve can be disconcerting.


And, check the vacuum reserve tank, on the fire wall under the brake booster on LHD cars.


I've forgotten if you've checked compression values. Weak cyliders can cause ths idle issue.


And, valve clearance.


The basic stuff.


Good luck on the sleuthing.


Happy New Year to all.


Carl

 

Thank you for your input. The cold weather has sent me in other directions but will reply on your suggestions ASAP.

Jim

 

Your fuel pressure looks OK to me. The fuel pressure regulator is based on a spring loaded diaphragm and passes fuel back to the supply tank to maintain a pressure in the fuel rail. This spring is compensated by the other side of the diaphragm being connected by a pipe to the inlet manifold. So manifold pressure, ( actually a part-vacuum), influences the fuel rail pressure.

 

Does your vehicle stall out eventually in idle? Im having the same issues with my 82 xj6, it starts up everytime but stalls eventually and if it does run it dies quick when put into gear. Im in Ohio and its pretty cold here now