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No Spark off Coil

XJZ

NAXJA Forum User
Location
SF Bay Area
So here I go again....

Now I have no spark coming off the coil. Do other sensors keep the coil from doing it's thing? Just changed the CPS. Could it be the MAP sensor? TPS? What else would keep the coil from sparking?

OR.....it it just the coil itself? Is there a way to check it (don't have any meters, etc.) Jeep will check it for $100-seems rediculous. Also if it is the coil, is it best to replace it with the factory coil, or after market, I remember a post that sais you are probably better of with the stock coil and that there's little to no advantage with an after market such as the MSD, etc. Also are there better places than the dealership to purchase.

Any and all comments much appreciated.

TIA.
 
heres what you do. get a test light, very cheap you can get a pretty good one for like 6 bucks. all it is (if you dont know) is a a pick witha light bulb in the handle and a cord coming out that ends with a clip. clip the lead on the negative side of battery turn key on check both wires on coil . it will probably be easier to unplug it. one wire should have battery positive voltage with key on(light bulb lights up, duh).Now switch the clip to the positive terminal and probe the other wire (the one that didnt have power) have a buddy crank the motor while you probe the other (non hot) wire. The test light should flash on and off. If you have both power and a pulsating ground (negative) the coil should spark. If you have both but no spark , bad coil, go to CarQuest and get one just whatever one they have it is fine.If you dont have a hot wire with the key on check your fuse, it will be labeled engine igition or something similiar, it will probably be in the under-hood realy box.if you dont have a pulsating ground you probably need a crankshaft position sensor.if thats the case let me know ill clue you in more later.forget the othere sensors on the engine they dont really mean squat to your igition. Good luck bro, dont zap yourself- Aaron
 
I have a 1990 XJ 4x4 4.0. Last year my ignition switch went out, I replaced it but it still wouldn't get the engine to turn over (but it would provide power to the gauges?). So I added the typical horn-type push button switch to spin the motor over.. That was ok for a while then one day my ignition decided to not spark anymore. After replacing the rotor, distributor cap, plug wires, coil & ICM I STILL had no spark!!!!!!!!!!!!!!!

After reading a few of the MANY post here concerning XJ's that have ignition problems, I decided to look for the CPS. While looking, I discovered a vacum hose that was disconnected. It ran right across the top of the valvecover...

I cut the frayed end off and traced out to where it was supposed to go. From what I'm told, it went to the MAP sensor.

Anyway, I plugged it back on and decided what the hell? and tried to start it. No shit, after 5-10 seconds the damn thing started! How the hell a vacum hose has anything to do with spark not coming out of the coil is beyond me but then again I have never claimed to be an expert...

Just something to think about...

RDX
 
It might be the distributor pick up assembly. It was on my jeep when I had a similar problem. Not sure what model year your jeep is but you might want to check.
 
OK....next question;

When this thing first started having problems and it would die after idling for x amount of time, I pulled a plug on the firewall assuming in was the connector for the CPS. After reconnecting this plug it would start up again (It's not the connector for the CPS, I just changed the CPS. DOH!), but this was only temporary, work a few times, then not at all. It would also run very rough, with slight backfire. Is this the connector for the MAP sensor and would a bad MAP sensor cause a no spark at the coil? I'm heading out to the garage to follow the wires.

Thanks for all the input.
 
in a weird sort of way, *it can*-but its highly unlikey.
the MAP itself`s MAIN useage is to tell the ECU just how much fuel it needs(which is why we have adjustable MAP sensors-XJs are lean from the factory)-

BUT-
the output voltage from the map to the ECU can also affect-
injector pulse (time of squirt)
spark timeing (got spark, just wrong time for it)
idle speed ( which I doubt)
EGR flow rate (because of low vac signal)
the upshift light (always wondered if this was actually true)
O2 heater relay (another doubtfull thing)

thats out of the manual- but again, its some highly unlikely stuff in my real world experience.
get a volt/ohms meter-test that sucker.
 
I'm used to working on Harley's and older cars with "normal" engines and electrical systems...

After owning this XJ since 2000, I disavow all knowledge of ever thinking I knew how to work on mechanical items... My 1990 XJ seems to prove me wrong 8 out of 10 times.

RDX
 
This afternoon I stopped by the local O'Reilly's autostore to pick up a CPS since I've also been having spontaneous spark / no-spark coming out of my brand new coil / ICM /wires /dist & rotor /etc... I figured better safe than sorry (stranded).

The parts guy could not find a Crankshaft Positioning Sensor anywhere in the computer for a 90 XJ 4.0.

Tonight I read my Haynes Manual cover to cover, especially the wiring diagrams for the 1987-90 4.0L inline six-cylinder models. It list no CPS for this year but on the next page it shows the 1991 and later 4.0L inline six cylinder and there is the CPS right next to the Sync sensor and Distance sensor.
Am I missing it or what?
The manual seems to skip over the 1990 XJ allot.

Was 1990 XJ the bastard step-child or what?
 
The parts guy could not find a Crankshaft Positioning Sensor anywhere in the computer for a 90 XJ 4.0.

Tonight I read my Haynes Manual cover to cover, especially the wiring diagrams for the 1987-90 4.0L inline six-cylinder models. It list no CPS for this year but on the next page it shows the 1991 and later 4.0L inline six cylinder and there is the CPS right next to the Sync sensor and Distance sensor.
Am I missing it or what?

I know I'm 4 weeks late but the CPS is often refered to as the "Engine Speed Sensor"
 
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