norway_xj

hi , i got a 1991 xj 4 liter ho . the fuelpump have jumping voltage/fuelpresure.

anyone have had this problem ? anyone have wiring diagram for the fuel system ?

cruiser54

Could have a bad ground. It's located up behind the spare tire and it's trim panel.

http://cruiser54.com/?p=249

peep

Agree, 1st check the ground.
Connector for your power delivery is ahead of axle driver side, area below the rear seat.
Check the connector and the wire quality back to the tank. Next check under rear seat in the cab and forward to insure the wire quality (no pinch, no cut)
Not sure if your 91 still has the Relay (passenger side, on wheel well, just behind battery on my 89, with the nest if wiring above the ignition coil).
Does your 91 have a balast resistor, driver side fender beside the air box.
Hopefully you find just a rusty or loose ground and resolve quickly.

cruiser54

Yes. 91 has a ballast resistor. Great idea to check voltage going into and out of it.
And, it can be bypassed.;

peep

Thank you Cruiser for the pic, pics are always best.
(Seems my brother in law (A Team member of the computer a hole squad) has abused my computer again !@$% and my pics files are messed up). Every time he visits. !@#$#$%
I dislike locks and passwords. I think next visit; I'll just taser him at the front door and sit him in a chair with a turkey sandwich to blubber and drool till it's time to go home.

cruiser54

I like your style and share your sentiments.

norway_xj

Thanx guys . that helped some . found a bad balast resistor, jumped it . tested the connectors on the fuel pump . they are OK . the engine works OK when cold , but it's getting worse when hot . then it dies. I can take of the ignition and start up.. Then it works fine for a minute...

cruiser54

Perhaps your fuel pump is failing.

norway_xj

I will test the fuel pressure tomorrow n let u know

peep

I've had three pumps fail, each was intermittent in the last of the life. Two died of old age and long use. The third was only 2 weeks old, Had to thump the fuel tank to get it to kick on, if your lucky just long enough to make it home.
Keep your fuel filter in good condition. If your tank is rusting internally it is hard on the pump life and metal sediment can clog the filter quickly.
I carry a spare resistor. Your Jeep will never fail if you have a spare part. You can run with the resistor jumpered. It may also reduce the life of the pump. The pumps get full voltage during staring, then the relay sends operating volts supply thru the resisted curcuit. The resistor provides for approx 11V to the pump (all the pump needs) when your alternator may be putting out in excess of 13V.
If you can get a pressure value, that would assist analysis.

norway_xj

I'm at it right now. Found a crack in the exhaust manifold. Shouldn't be a problem ? Fuel pressure is 33psi when idle cold engine.

norway_xj

So I drove around with the fuel pressure gauge. And the fuel pressure drops when I put the pedal to the floor... Should indicate a bad fuel filter .... I will try a new one as fast as I can get one

cruiser54

You have a fuel delivery issue. Could be a bad hose internally on the fuel module, low voltage to the fuel pump, bad fuel pump, poor ground for the fuel pump.

norway_xj

New filter ... Looks OK now ��

cruiser54

Please clarify.