Total loss here.... cranks, intermittent starting
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Joined: Dec 2013
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Model: Cherokee
No. The starter circuit is not related to the ignition circuit.
When the PCM is happy with the Cam/Crank relationship and RPM while the motor is cranking, it initiates ignition (spark) by providing ground to the ASD relay (control side) - this together with the ignition switch being in the Start or Run/On position will provide the positive required at the same ASD relay (control side) this will close the relay and allow 12v positive to the ignition coil. The PCM further controls ignition (spark) by pulsing a ground to the ignition coil which receives a constant 12v from the ASD relay (and ASD fuse), but the timing and pulsing of the ground at the ignition coil comes directly from the PCM.
So, some likely candidates for missing spark are a faulty ignition coil, failed Crankshaft Position Sensor, a failed Camshaft Position Sensor, faulty ignition switch, or failed ASD relay (and of course, this includes the wiring these things depend on). These aren't the only possibilities, but the more common ones.
When the PCM is happy with the Cam/Crank relationship and RPM while the motor is cranking, it initiates ignition (spark) by providing ground to the ASD relay (control side) - this together with the ignition switch being in the Start or Run/On position will provide the positive required at the same ASD relay (control side) this will close the relay and allow 12v positive to the ignition coil. The PCM further controls ignition (spark) by pulsing a ground to the ignition coil which receives a constant 12v from the ASD relay (and ASD fuse), but the timing and pulsing of the ground at the ignition coil comes directly from the PCM.
So, some likely candidates for missing spark are a faulty ignition coil, failed Crankshaft Position Sensor, a failed Camshaft Position Sensor, faulty ignition switch, or failed ASD relay (and of course, this includes the wiring these things depend on). These aren't the only possibilities, but the more common ones.
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Model: Cherokee
i have, I was suspicious of the NSS as well but from what I’ve read that would cause a no crank issue as well. Mine will crank for days but no spark only when it’s warm though. From cold iron it’ll always start. It’s the heat or possibly vibration that causes this issue. Once it’s fully warmed up there’s less than a 5 percent chance it’ll start again until it’s cooled down.
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Joined: Dec 2015
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From: Syracuse, NY
Year: 1996
Model: Cherokee (XJ)
Engine: 4.0L
yea I’ve been doing research non stop and I’ve become more suspicious of the camshaft position sensor. I’ve already replaced the crankshaft position sensor, once with an autozone one and then again with a mopar one because the symptoms are so similar to a CPS. But that doesn’t seem to be the problem. I always thought if you tested for spark at the ignition coil and you don’t get any then you can rule out the distributor as the issue. Now I’m realizing the pickup coil, or camshaft position sensor, Is located in the dist. And talks to the ECU to give the ok for spark. Gunna pick one up tomorrow and see if that does the trick. I’m also going through the entire wiring system the best I can tomorrow. Also, wouldn’t a failed ignition switch stop it from cranking as well? If not maybe that’s my issue. I gotta look into that more. I swapped the ASD relay with a known good one so that’s not my issue and the ignition coil is new. I’ll let you all know what I find. Thanks for the input!
So in your case, if the 12v from the ignition switch that goes to the ASD relay was bad, it could cause the symptoms you have. Cranking would still work, but no ignition.
You are right in that if the coil is not getting positive voltage, the problem is usually between the PCM, ASD, and coil. The distributor comes after the coil.
You are also right that the cam sensor pickup is under the distributor rotor, and if it is not working properly the computer will never ground the ASD relay and ignition won't happen. Its a simple, and relatively cheap part, and sometimes they come apart and the magnetic pickup gets battered into a few pieces. Its worth taking a look, for sure.
On a 97, according to the FSM it appears that both the Dark Brown (DB) and Black Orange (BK/OR) wires (circuits A21 and A22 respectively) should be energized when the ignition is in the RUN position. DB being for both start and run, while BK/OR being only for run. Popping the trim around the steering wheel and putting a test lamp to the ignition switch connector is pretty straight forward.
Last edited by jordan96xj; Jan 21, 2019 at 10:56 PM.
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From: Groton, MA
Year: 1995
Model: Cherokee(XJ)
Engine: I6 4.0L
I would think that a failure in the ignition switch for the "On" would also cause the standard startup functions to fail to happen as well - in short, fuel pump priming and gauge light check. If/since the fuel pump prime occurs on each turn of the key, it's a good sign that the root cause is not the ignition switch.
I think the fact that you had crap under the cap is strong argument for considering the cam sensor suspect.
I think the fact that you had crap under the cap is strong argument for considering the cam sensor suspect.
CF Veteran
Joined: Dec 2015
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From: Syracuse, NY
Year: 1996
Model: Cherokee (XJ)
Engine: 4.0L
I would think that a failure in the ignition switch for the "On" would also cause the standard startup functions to fail to happen as well - in short, fuel pump priming and gauge light check. If/since the fuel pump prime occurs on each turn of the key, it's a good sign that the root cause is not the ignition switch.
I think the fact that you had crap under the cap is strong argument for considering the cam sensor suspect.
I think the fact that you had crap under the cap is strong argument for considering the cam sensor suspect.
Thread Starter
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Joined: Dec 2013
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Model: Cherokee
First off, thanks for all the help, I was pretty stuck on this one an learned a hard lesson: just because I’m not getting power to the ignition coil, doesn’t mean the problem can’t be in the distributor. It turns out the pickup coil was bad. I always figured you can track down a no spark problem by starting at the spark plugs and working your way back. I never knew the pickup coil can shut down the whole system if it’s not working properly. I always thought I’d still have power at the ignition coil, but then not at the distributor. What should’ve cost me 50 bucks and 2 minutes of work cost me close to 350 and probably 15-20 man hours. I did what I tell everyone not to do and set the parts cannon to full auto hahaha. Thanks again! Off to see if I can get my money back for a TPS and a CPS.
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Year: 1989
Model: Cherokee (XJ)
Engine: 4.0 L
BTW - Just a big THANK YOU for telling us what did/didn't work for you.
I'm also new to this vehicle (but learning) and reading what you tried, what didn't work, and your final solution (and how you got there) is VERY helpful and appreciated. (I haven't worked with points/distributors/coils in decades, it's all fuzzy to me but returning...)
Too many of us just post what didn't work, and then don't close the loop after finding what worked, especially if we realized we missed something basic. (Some don't admit they made a mistake, but we all make them... Just life dealing with older vehicles...)
Again: Your experience is helpful, thanks for sharing both the wins and winding path you took to get there...
I hope to do the same.
I'm also new to this vehicle (but learning) and reading what you tried, what didn't work, and your final solution (and how you got there) is VERY helpful and appreciated. (I haven't worked with points/distributors/coils in decades, it's all fuzzy to me but returning...)
Too many of us just post what didn't work, and then don't close the loop after finding what worked, especially if we realized we missed something basic. (Some don't admit they made a mistake, but we all make them... Just life dealing with older vehicles...)
Again: Your experience is helpful, thanks for sharing both the wins and winding path you took to get there...
I hope to do the same.
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