Primary Coil Circuit Troubles....
07-22-2013, 01:57 PM
#1
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Year: 1998
Model: Cherokee
Engine: 4.0L
Primary Coil Circuit Troubles....
Coming off of ozzdog's post a few days ago... I'm having similar problems so posting a new thread rather than hijack his...
Summary:
98 XJ - 4.0L - 5spd - 293,000miles
Engine died on freeway, similar to as if the CPS failed. Restarted for another mile, sputtered, HUGE backfire, then stalled.
Have crank with no spark and no signal to injectors. Fuel rail at 49psi.
ASD - test good.
CamPS - volt/ohm check tests good.
CkPS - volt/ohm test good.
Coil - bench tests good.
AllData Dx tree suggest replacing the pcm.
Still no start.
Bought a code reader - both pcms are throwing P0351 (primary coil circuit code). Troubleshooting that circuit shows no shorts and good voltage.
Old pcm was throwing the CamPS and CkPS codes. After erasing these codes, they aren't back again. Just the P0351 coil circuit code.
Could I have jumped teeth on the timing chain during that backfire?
This then causing either the CamPS or CkPS to halt the engine?
Thanks,
JW
Summary:
98 XJ - 4.0L - 5spd - 293,000miles
Engine died on freeway, similar to as if the CPS failed. Restarted for another mile, sputtered, HUGE backfire, then stalled.
Have crank with no spark and no signal to injectors. Fuel rail at 49psi.
ASD - test good.
CamPS - volt/ohm check tests good.
CkPS - volt/ohm test good.
Coil - bench tests good.
AllData Dx tree suggest replacing the pcm.
Still no start.
Bought a code reader - both pcms are throwing P0351 (primary coil circuit code). Troubleshooting that circuit shows no shorts and good voltage.
Old pcm was throwing the CamPS and CkPS codes. After erasing these codes, they aren't back again. Just the P0351 coil circuit code.
Could I have jumped teeth on the timing chain during that backfire?
This then causing either the CamPS or CkPS to halt the engine?
Thanks,
JW
07-22-2013, 09:29 PM
#2
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Year: 1998
Model: Cherokee
Engine: 4.0L
This guy had trouble posting, so filling in...
Originally Posted by 99XJSprt
You should be measuring a short (or less than 10 ohms) on the plug. The HiV output to either plug position should be several 30,000 or so. If you are reading (no shorts) sounds as if the coil is open.
Once you replace the coil, and the car starts; immediately check the voltage across the battery. My coil went bad, everyone said it was a normal failure, however the alternator was generating 17 volts at the battery. The PCM is bad, if I had let if go, I could have burned it, or toasted the lights, instrument cluster, radio etc.
I'm not permitted to post, don't know why
Once you replace the coil, and the car starts; immediately check the voltage across the battery. My coil went bad, everyone said it was a normal failure, however the alternator was generating 17 volts at the battery. The PCM is bad, if I had let if go, I could have burned it, or toasted the lights, instrument cluster, radio etc.
I'm not permitted to post, don't know why
Ohmed it out again. .9 across the terminal and almost 11K from either terminal to HiV terminal. That sound about right... yes?
JW
07-22-2013, 11:08 PM
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If you put a test light between the coil (+) terminal and ground, does the light turn on when you crank? (it should).
If not there's no power to the coil.
Between the coil (-) and ground- does it flash (more like a pattern of dim/bright/dim) when you crank? (it should).
If it stays off, there's no coil power (see first test), or the coil primary is open. If the light stays ON and does not dim, there's no control signal from the PCM.
If there is no control signal from the PCM, first suspect is bad CPS- especially if your injectors are not firing.
DVM testing of the HO CPS's does not tell you much, the best test is substitution.
You might also want to check continuity between the PCM CPS connector (A8) and the CPS itself, and between the PCM igntion coil driver (A7) and the coil (-) terminal.
PCM pinouts below:
If not there's no power to the coil.
Between the coil (-) and ground- does it flash (more like a pattern of dim/bright/dim) when you crank? (it should).
If it stays off, there's no coil power (see first test), or the coil primary is open. If the light stays ON and does not dim, there's no control signal from the PCM.
If there is no control signal from the PCM, first suspect is bad CPS- especially if your injectors are not firing.
DVM testing of the HO CPS's does not tell you much, the best test is substitution.
You might also want to check continuity between the PCM CPS connector (A8) and the CPS itself, and between the PCM igntion coil driver (A7) and the coil (-) terminal.
PCM pinouts below:
Last edited by Radi; 07-22-2013 at 11:12 PM.
07-23-2013, 08:04 AM
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Year: 1998
Model: Cherokee
Engine: 4.0L
If you put a test light between the coil (+) terminal and ground, does the light turn on when you crank? (it should).
If not there's no power to the coil.
Between the coil (-) and ground- does it flash (more like a pattern of dim/bright/dim) when you crank? (it should).
If it stays off, there's no coil power (see first test), or the coil primary is open. If the light stays ON and does not dim, there's no control signal from the PCM.
If there is no control signal from the PCM, first suspect is bad CPS- especially if your injectors are not firing.
DVM testing of the HO CPS's does not tell you much, the best test is substitution.
You might also want to check continuity between the PCM CPS connector (A8) and the CPS itself, and between the PCM igntion coil driver (A7) and the coil (-) terminal.
PCM pinouts below:
If not there's no power to the coil.
Between the coil (-) and ground- does it flash (more like a pattern of dim/bright/dim) when you crank? (it should).
If it stays off, there's no coil power (see first test), or the coil primary is open. If the light stays ON and does not dim, there's no control signal from the PCM.
If there is no control signal from the PCM, first suspect is bad CPS- especially if your injectors are not firing.
DVM testing of the HO CPS's does not tell you much, the best test is substitution.
You might also want to check continuity between the PCM CPS connector (A8) and the CPS itself, and between the PCM igntion coil driver (A7) and the coil (-) terminal.
PCM pinouts below:
Thanks much.
JW
07-27-2013, 12:47 PM
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Year: 1998
Model: Cherokee
Engine: 4.0L
It was all THREE....
So it turns out that the coil, the CPS, and the CamPS all went at once.
So my thinking is the CPS went, causing the shutdown on the interstate. The coil must have gone then as well, b/c the first thing I did to repair was to replace the CPS. Then I had crank - no start - no spark - and no voltage to the injectors.
Switching relays with ASD caused no change.
Coil bench tested fine, so assumed it was OK.
Tested CamPS voltage during crank, it was OK.
So must be the PCM. New PCM = no change.
Bought a scanner for $50 at AZ.
New computer was throwing a Primary coil circuit code and a failure to read TCM code (I have a manual...so couldn't figure that out)
Old computer was throwing CPS code, CamPS code, and Primary coil circuit code - still in the PCM from engine failure.
Erased codes from old computer, cranked the engine for a while and reread. Threw CamPS code and Primary Coil Circuit code again.
New CamPS took care of the former. Still tried to troubleshoot the coil circuit -other than the coil- as the original bench tested fine.
The next steps in the ALLdata testing process involved building some crazy three pronged capacitor jumper and shorting things out. I figured for that effort I might as well buy a new coil before spending that much time and money. Sure enough...it started after installing the new coil - which by the way - bench tests exactly the same as the old coil. Tried starting with the old CamPS, and it started, but threw same CamPS code with the old one installed.
So new CPS, Coil and CamPS.
Anyone ever had all three go at once?
Returned new PCM, so I'm only out a few parts and some time. Got a scanner to boot.
Thanks for the suggestions...
JW
So my thinking is the CPS went, causing the shutdown on the interstate. The coil must have gone then as well, b/c the first thing I did to repair was to replace the CPS. Then I had crank - no start - no spark - and no voltage to the injectors.
Switching relays with ASD caused no change.
Coil bench tested fine, so assumed it was OK.
Tested CamPS voltage during crank, it was OK.
So must be the PCM. New PCM = no change.
Bought a scanner for $50 at AZ.
New computer was throwing a Primary coil circuit code and a failure to read TCM code (I have a manual...so couldn't figure that out)
Old computer was throwing CPS code, CamPS code, and Primary coil circuit code - still in the PCM from engine failure.
Erased codes from old computer, cranked the engine for a while and reread. Threw CamPS code and Primary Coil Circuit code again.
New CamPS took care of the former. Still tried to troubleshoot the coil circuit -other than the coil- as the original bench tested fine.
The next steps in the ALLdata testing process involved building some crazy three pronged capacitor jumper and shorting things out. I figured for that effort I might as well buy a new coil before spending that much time and money. Sure enough...it started after installing the new coil - which by the way - bench tests exactly the same as the old coil. Tried starting with the old CamPS, and it started, but threw same CamPS code with the old one installed.
So new CPS, Coil and CamPS.
Anyone ever had all three go at once?
Returned new PCM, so I'm only out a few parts and some time. Got a scanner to boot.
Thanks for the suggestions...
JW
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