tbrown206

So I have a 1990 xj with a 4.0. It wont start but it will turn over I have replaced neutral safety switch crank sensor and starter relay switch. Can figure why it wont start im getting gas and im getting spark. Does anyone have an idea what may cause this.

Thanks

BuckB91XJ

Did you check for gas at the test port on the fuel rail? And if so did you just check that fuel squirts out or did you check it with a hand held gauge? I'm asking this because when my Fuel Pump crapped out it had enough pressure at the test port to shoot across my garage but, when I finally tested it with a gauge my fuel pressure was not enough to make my Jeep run. Swapped out the fuel pump and it ran like new.

tbrown206

I checked that fuel squirted out not with a gauge. Where do I put the gauge to check and how much pressure is it suppose to have?
Thanks

BuckB91XJ

You will thread the hose from the gauge right onto your fuel rail test port. The pressure on my 91 4.0 is supposed to be 30+-1psi. Anything else is out of spec and your FP is bad. It says how to do the test in the Jeep cherokee Haynes Manual.

tjwalker

You need 31 psi of pressure for the engine to start (verify with a gauge)

You also need a strong, blue, snapping spark. Yellow/orange/white indicates a weak spark, which may not be strong enough to start the engine. If you have weak spark, test your ignition coil for primary and secondary resistances with a meter and a manual.

Your problem is likely one of the above.

freegdr

also need injector pulse

tbrown206

Ok so I've put a new fuel pump and coil in today and still no luck. Many more suggestions.

tjwalker

1. Test the QUALITY of the spark

2. Test for injector pulse (with a noid light)

3. Test fuel pressure with a gauge just to be sure (even though it has a new pump)

Test your way to a solution here. Don't throw parts at it. Terribly inefficient and becomes expensive quickly!

SeriousOffroad

Use some needle nose vise grips to pinch off the rubber fuel return line from the FPR and then try starting it.