greasemonky

hi my xj started runing really sh**y so i fixed the egr valve, new knock senser, fixed vacume leaks, adjusted tps, checked spark plugs, new cap and plug wires 2 months ago and i cant figure it out so any help whould be great!!!!! it is runing really rough at idle

captainwoot

check your fuel pressure/delivery, how about a compression check?

tjwalker

I agree. Verifying proper fuel delivery should be done early in the troubleshooting process.

You will need a fuel pressure gauge; no shortcuts.

At an idle, you should have 31 psi. Then disconnect the vacuum line leading to the fuel pressure regulator (be sure the line is pulling good vacuum and is NOT wet with fuel), and after disconnecting that line, the pressure should jump to approx. 39 psi.

A compression test is a good "snapshot in time" of the internal condition of your engine and is never a bad idea. For the 4.0, you should have 120-150 psi, with no more than a 30 psi variation between cylinders.

Here is a link to testing other things on your RENIX (1990) XJ. Good Luck!

http://www.lunghd.com/Tech_Articles/...iagnostics.htm

89Laredo

Oxygen sensor? A renix will really run like crap with a bad oxygen sensor.

greasemonky

i had found 2 fuel injectors that wear leaking i cleand them up reinstaled them with new o-rings and still no change.i dont have the tools to check fuel presure yet also i did replace fuel filter and pump not that long ago. can you take the o2 sensor out and clean it with out hurting it?

greasemonky

compresion is good around 140 on all 6 cylinders

Trisler57

Have replaced the o2 sensor on ur exhaust? My 93 Cherokee had the same problem and that was my solution

greasemonky

i just did another compresion test and now no comperesion on the #3 and 90lbs on #1. what the hell i am really hoping its the valves!!!!!!!!!!!

tjwalker

Did you try performing a WET compression test (adding a small amount of oil to the cylinder) after the DRY compression test?

That can help you isolate whether this is lower end or top end problem.

greasemonky

yea i did!!!!pulled the head and i can see through the exhaust valve in the #3 side and a lot of carbon build up on the #1! no damage to the cylanders they look great!!

freegdr

did you clean the iac motor

freegdr

also check intake/exhaut manifold mounting bolts very comon problem the get loose over time/ dasket shrinking oi guess i had a slight stumble in mine found these loose sat snug them up problem solved the very back ones by the fire wall were loose sprayed sarb cleaner along mounting area to find leak

tjwalker

I think he found his problem........