RAH

I am working on my brothers 98 xj limited. It all started with a new crank sensor. I have tested everything and replaced crank sensor several times, and a new distributor. The problem I am having is a misfire at 2k rpm and a real erratic crank signal at the pcm. I have scoped the sensor and I am getting a good sin wave at idle and as the rpms increase the signal degrades to small peaks. I will post up more info if anyone wants to read that much, but its alot. thanks in advance

Cherryokee

Sounds like your crankshaft position sensor is working properly. It stands to reason that signal amplitude diminishes (slightly) with frequency (RPMs). Pardon the seemingly dumb questions but were the wires, cap and rotor replaced with the distributor or did you re-use the originals? What of the camshaft position sensor - original or replaced? Is the coil in good shape? The primary coil resistance should be between 1-1.25 ohms and the secondary coil resistance should be between 11.3-15.3 Kohms - and oh yeah, check the coil ground too.

RAH

All of that has been replaced. Plugs,wires,cap,rotor,complete dist., coil, I even replace the pigtail to the coil because the insulation was peeling off.

Cherryokee

Needle in a haystack. Don't get lost in the detail. Drive it. If it's a real issue then it will reveal itself in time. If it ain't broke then don't fix it.

RAH

It misfires so bad that i can't drive it. Its misfiring when the crank signal is messing up so i know it has to be related. I've check fuel pressure, timing chain stretch, made sure the the flywheel wasn't bent. if i put the original ditributor back in and it drives great. but the check engine light comes on setting a cam crank correlation code.

Cherryokee

It's clear that you know what you're doing so I won't say anything about firing order (whoops, I said it didn't I?). One last dumb question: Does the 0 degree timing mark on the damper line-up with the pointer and does the rotor correspond when the #1 piston is at TDC?

CodeXJ

Good call on the firing order. I know several people who've gotten a plug or two mixed up.

RAH

checked and recheck firing order. even had someone else check firing order just to make sure. will double check the timing mark though

mccauley84

Im haveing the same d%$@ problem on my 98xj i replaced the cps and now its mis firering between 2000 and 3000 rpm went through everything and replaced what needed to be and still running like crap really getting frustrated with it.

kimcrwbr1

with a screwdriver handle tap and wiggle all the connectors erratic faults are usually wiring/connector related. Clean the connectors with elect cleaner and apply dielectric grease when putting them together. I am voting for a corroded or dirty connector usually female ends.

RAH

New symptom. We were checking the timing today. At idle its sitting at 12deg. If you slowly raise the rpm the timing advances to approx. 28 deg. then when you get right at 1800 rpm, the timing jumps 113deg.

kimcrwbr1

Have you checked the TPS on mine the timing advances in direct relation to the butterfly and it did not throw a code. Have you checked the timing chain pull the dist cap and turn the crank clockwise then ccwise while watching the rotor how far can you turn the crank until the rotor moves. The crank sensor is for timing and the cam sensor is for pulse width of the injectors and they have to be in sync which takes you to the timing chain/gears check for slop in the chain. I just did the timing set in mine also I was able to pull the damper without removing the radiator still a biotch. I believe the TPS and map is what adjusts the spark using throttle position and vacuum as a referance to advance or retard the timing. GL

RAH

There is very little movement in the crank till the rotor moves. I will check the tps voltage

RAH

I think you may have something there. I'll check that tom.

kimcrwbr1

I was reading as the rpm raises the crank sensor advances the timing as the throttle opens it changes the pulse of the injectors the vacuum also changes the pulse. I am guessing if the tps is not giving the correct reading will not be in sync with the crank or rpm. same with the map sensor. your crank and dizzy check out then it has to be in the tps/map system