Yes, another no-start thread
11-28-2012, 04:47 PM
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Year: 99
Model: Cherokee
Engine: 4L/6
Yes, another no-start thread
99 sport, OEM
After reviewing all the other no start threads, I cringed to start another no start thread but I am lost.
Jeep died on my son. I go and discover no spark. I tried the unplug CPS trick but still no spark. I tried to start it neutral too, no joy. I towed it home. CPS tested good, bought a new one for giggles and installed it. New CPS tested same, still no spark. New coil installed, nope, no spark. New ignition switch installed and #12 fuse checked good to ignition switch. All relays (ASD and fuel) check good. All fuses in power block checked good. All wiring inspected (to/from O2s, MAP, throttle position sensor, coil, etc),nothing unusual found. All sensors are getting the 5v ref from PCM. I even replaced the temp sensor and O2 sensors since I had them already.
Oh, I tried a new PCM too for a Hail Mary. TCM next? I'll vomit if the next $200 Hail Mary doesn't work.
I'll go do a resistance check on the CPS feed/return line now. It checked out fine.
Just verified voltage from CPS to PCM while the engine is cranking. Two different types of tests now verify good CPS.
The coil DG/Org line connectivity to PCM checked good too.
Oh, and no codes.
I have 12v in slot 30 in the Power Distribution Box for the ASD relay; ASD relay checked good.
After reviewing all the other no start threads, I cringed to start another no start thread but I am lost.
Jeep died on my son. I go and discover no spark. I tried the unplug CPS trick but still no spark. I tried to start it neutral too, no joy. I towed it home. CPS tested good, bought a new one for giggles and installed it. New CPS tested same, still no spark. New coil installed, nope, no spark. New ignition switch installed and #12 fuse checked good to ignition switch. All relays (ASD and fuel) check good. All fuses in power block checked good. All wiring inspected (to/from O2s, MAP, throttle position sensor, coil, etc),nothing unusual found. All sensors are getting the 5v ref from PCM. I even replaced the temp sensor and O2 sensors since I had them already.
Oh, I tried a new PCM too for a Hail Mary. TCM next? I'll vomit if the next $200 Hail Mary doesn't work.
I'll go do a resistance check on the CPS feed/return line now. It checked out fine.
Just verified voltage from CPS to PCM while the engine is cranking. Two different types of tests now verify good CPS.
The coil DG/Org line connectivity to PCM checked good too.
Oh, and no codes.
I have 12v in slot 30 in the Power Distribution Box for the ASD relay; ASD relay checked good.
Last edited by 99KeeSport; 11-29-2012 at 12:13 PM.
11-29-2012, 01:34 PM
#3
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Year: 1999
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Engine: 4.0 I6
try checking the wires going from the computer to the distributor. I had a similar problem, and one of the wires in that wiring harness was about broken. Thats all I can think of. Good luck man
11-30-2012, 09:41 PM
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After throwing a new CPS at it, resistence checking all the wires (12V at slot 30 for the ASD, PCM to COIL, PCM to CPS, etc, etc; it turned out to be issues under/in the Power Distribution Box.
When I was unclipping the PDB to have a look-see, the 20A fuse popped. Yeah, okay, I should have had the battery unhooked. Sure enough, a bastard mouse had set up shop under the fuse rack in the PDB. What I found was the crap this bastard had pulled into the PDB must have been just enough not to short the circuit from the ASD relay, but enough to degrade power away from the circuit to fire the coil. That is my theory anyway.
I cleaned out the PWD, checked for any chewing the bastard mouse may have done, reinstalled the PWD, replaced the 20A fuse, and VA-VOOM! I put a few 20A fuses in the glove box just in case.
When I was unclipping the PDB to have a look-see, the 20A fuse popped. Yeah, okay, I should have had the battery unhooked. Sure enough, a bastard mouse had set up shop under the fuse rack in the PDB. What I found was the crap this bastard had pulled into the PDB must have been just enough not to short the circuit from the ASD relay, but enough to degrade power away from the circuit to fire the coil. That is my theory anyway.
I cleaned out the PWD, checked for any chewing the bastard mouse may have done, reinstalled the PWD, replaced the 20A fuse, and VA-VOOM! I put a few 20A fuses in the glove box just in case.
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