ive have a 1991 xj 4.0 and im having a problem with it staying running. the fuel pump went out on it. I replaced the fuel pump and now it will start but wont stay running. It will stay running if i hold the throttle at 3000 rpms it will stay running. I took the iac out and cleaned it. Im not sure if its staying stuck or not. But if i spray throttle body cleaner in at idle it will run as long as i keep spraying some in. Im not sure what direction to head into.

 

Check the fuel pressure. if you fix something and a new issue arises, it is most likely related to what you did when fixing it. Make sure all your fuel lines are ok also.

 

change out fuel filter, possibly replace fuel pump relay

also that little white ceramic "thingy" (a.k.a. resistor) which is bolted up to the side firewall near the brake booster and brake master cylinder, make sure the wires to it are good condition, and if its cracked or broken replace it.

jes my 2 cents sir!


cpnwrench

 

I changed he fuel filter less than a year ago and I have 37 psi. Accroding to all data I should have 35. I will chech the resistor tomorrow. I was wondering if anyone ever had a problem with the fuel pressure regulator.I did a vacuum test on it and it held.

 

ttt

 

It sounds like you still have a fuel delivery problem.

For an 87-90, you should have approx. 31 psi at idle. Then disconnect the vacuum line leading to the fuel pressure regulator and the pressure should jump to approx. 39 psi.

Also, be darn sure that the vacuum line LEADING to the fuel pressure regulator is pulling good vacuum!

Don't discount the possibility of having installed a faulty fuel pump; it happens more than you think. It isn't an Airtex is it? If it is, the chance of it being faulty just went up big time. I don't use any of their products because of the history of reliability issues with them.