HELP WITH 4.OL TIMING ON A 89 XJ

hey guys im about to go off the deep end on my jeep its a 89 with the good old renix computer system and i cant get the timming right and i can get close but once you rev the motor to and beyond 2grand its starts missing and the ocassonal backfire if anybody can help me ill be so happy ill just filp out i had this jeep for about 6 months and it had a miss in the motor well i found a lifter that wasnt in the hole and the pushrod was tighten down on the block so it didnt reck the motor as soon it ran but it was missing all the time and i couldnt figure out what was wrong with it. i have check my timming chain and sprocket and thats all new and the dots line up where they are soposed to at tdc so HELP ME PLEASE!! thanks much!

Could be your Crankshaft Position Sensor. Research it. Apparently it can cause problems in higher revs.

You need to re-index the distributor. The distributor does not line up on #1 cyl when the crank is at #1 TDC. Instead when the crank is at TDC, move the distributor 1 tooth AHEAD. The XJ should run like a champ after you do this.

if you haven't messed with the distributor, yes, try the CPS.
mine cut out at 3800 rpms..

mattbred said:

Could be your Crankshaft Position Sensor. Research it. Apparently it can cause problems in higher revs.

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i really dont think its my cps because its brand new and ive try tdc with out taken the value cover off do i need to take that off to get the most accurate tdc? thanks for all the help

alright well i tried to time the motor like slo sho said and i still can get the to run right i can rev it up to about 2500rpms and then its starts stumbleing and missing and if i floor it it will just backfire at me and thats all it will do PLEASE HELP!!

Mine did the same thing. Pull the crank sensor. If it wasn't put in correctly the flywheel will hit it. Seriously, pull it and look at it.

Did the one tooth move change the engine problem any?

If not, there are many posibilites to check or recheck in addtion to the CPS. Start with the plug wires, rotor and cap. Are any plugs wires criss crossed? any HV leaks to ground under heavy load, high RPM (try looking under the hood after dark, lights out, look for a spark to ground). EGR valve / solendoid might be messed up.

Not enought fuel flow passed a certain RPM to maintain pressure.

I even had your exact problem when I attached my TPS and O2 sensors to the harness back wards (my harness clips are old, warn, and allow one to connect the sensor backwards). Damn think ran, but ran like yours.

You might also check your grounds under the hood.

I can't prove it, but I suspect many week CPS sensors get replaced early when clean grounds, solid ground wire connections might have allowed them to work properly, longer.

Ecomike said:

You might also check your grounds under the hood.

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x2, that business gave me the EXACT PROBLEM after an engine swap on a 87 XJ about 10 years ago! You cannot go wrong by cleaning up your ground connections anyways, you'd be amazed at how much better things will respond