Jeep Enthusiast Forums banner

no start

3K views 49 replies 8 participants last post by  ratmonkey 
#1 ·
ok there is a long story that goes along with this but for time savings i have a 96 4.0 GC, i have no spark, i have tested for power at the coil and when i turn the key on i do have power, what i do not have is the pcm controlled ground, now everything i have read says crank position sensor, so like a dump ars i went to advanced and got one, well still no spark, so i broke down and purchased a mopar one. installed it and still have no spark, so whats the chances i got a bad ckp from mopar, i tested the one from advance and it has resistance from terminal B to C, which means it bad, but i didnt test the new one from stealership before installing it, now i just went outside after looking at the test again i though heck why not, so i tested it and it has 1 m oh resistance, everyone says it should be a open circuit which i assume on my meter should read OFL. Now i took the advance ckp and hooked it up the the connector and when i wave it past a metal object i can hear the ads relay and evap can clicking and i assume injector pulse also. Can someone maybe shed some light on wth is going on here am i overlooking something super simple or does my zj hate me
 
#32 ·
715raccing said:
Please overlook my interrupting your conversation.
I had a similar condition and went through all of the agony you're experiencing only to find that the used computer I installed was the problem.The original quit and the replacement was defective too.
No interruption at all, I am really starting to believe its the PCM. I just want to cover all the bases before I throw a couple
Hundred dollar part at it and it be something stupid like a shorter wire or something.

Zee ok that was something I was unsure of was if PCM used both ckp and cps to fire the coil or not. I'm going to head out and do some quick checks before I have to go to work
 
#34 ·
And may I ask why you think it's not the PCM?? I understand you can get a bad sensor sometimes but to get a bad crank and cam sensor at same time?? I have 5v supply today I will check 5v output, I didn't have anyone to turn the vehicle over for me yesterday, but have my grandfather today when I wake up for work so will check it then
 
#36 ·
Ok so I check sensor ground which is good, and ckp pulse, got nothing now weird thing is when I went to check cam it went right to 5v so I thought ok it's just in that window, so I cranked it and it staye at 5 volts. I'm sorta of Monday and Tuesday so I am going to pull the inspection cover for trans just to make sure everything is ok before I go and buy another crank position sensor.
 
#37 ·
I had the same problem it just died on me one day and wouldn't start back up my pcm would not respond when i turn the key over no check engine light at all the over head gauges didn't work the fuel pump would stay on it wouldn't prime and stop like it should have are you having any of these problems?
 
#45 ·
Sorry no update yet, mandatory overtime. Racer if you read the post I replaced the crank position sensor twice. I am supposed to be off this weekend so hopefully I get some time to work on the jeep. Oh one update, I did take the new cam sensor out and replace it with old and I still have constant 5 volt return to PCM, what I need to do is disconnect it and see if without the sensor I have it at connector so I know if its back feeding from PCM or is it sensor itself
 
#48 ·
Sorry work has been crazy, I got home this morning and disconnected cam sensor and checked harness side of connector, and I is e 5v constant on both outside wires of cam sensor, tomorrow before work I am going to disconnect at PCM and check and see if voltage is present at pin out there, if it is how do I tell where is coming from, I would assume a shorted wire put if it is coming direct from PCM where would I start looking
 
#49 ·
Looking back at the diagram, pin 1 is the sensor 5v from the PCM, pin 2 is ground, and 3 is the signal output from sensor.

I think you already have this figured out, but is appears the PCM is producing the 5v you are reading with the connector unplugged. So you are headed the right direction to pull the connector off the PCM and see if the voltage disappears on pin 3.

I dont know if you ever determined what is on pin 2. It should be ground with switch on. best way to check is use pin 1 for red lead and pin 2 for black. Should get 5V. The will give you an indication idea if something else is causing the PCM to output the voltage on the cam sensor input. If this is not the case, most likely the PCM is shot.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top