car cranks but wont start

[tobs]

Hey guys,

first of all I know that thing with the "engine cranks but wont start" is a common issue with those jeeps, I read a lot about it but it seems like I cant work that out myself...

if got a jeep Cherokee xj 1996 4ltr auto.

a few days ago I serviced my transmission. after doing that my car didn't want to start. the car cranked over but i had had no spark and fuel pump didn't want to gauge either. I got it started after i did the ignition dance (50 times on off to reset the computer).

my check engine light came on and stayed on. i checked for codes without a scanner but nothing serious came up, just code 12.
I drove around for a week with no issues at all, till i decided to get rid of that check engine light by detaching the negative battery cable what didn't work. so I did the ignition dance again cause i thought that would do it's job, but it didn't. i started the car normally, went home turned the car off, five min later tried starting the car, same problem again.. it cranks but no spark & fuel pump doesn't gauge.
after checking different sensors, fuses, plugs etc and not able to find one helpful faulty bit, i decided to swap my computer. the car started straight away just that the engine turned back off after 2-3 seconds.

so now I'm totally stuck, any helpful advice would be greatly appreciated guys!!

 

[greg92jeepxj]

Hey Toby , sorry to see you got jeep trouble so close to the holidays . But trouble never takes the day off . If I read your post right , this all began after the trans service ? No trouble at all before ? Strange , I know . I'd have to say this is an electrical problem . You swapped the PCM and the engine stalled seconds after. Sounds like your going to have to start with the basics , no matter how boring that will be . But it seems that something will be overlooked if we don't look for everything and starting right from the battery . You definately want to check every ground from the battery negative cable and engine ground to chassis or firewall as it is possible the PCM is not getting a good ground . Also , we need to be sure that the positive cable is feeding cleanly the PDC and that the ignition switch is receiving battery voltage . I've said this so many times , on and off this forum , but you've got to diagnose any computer circuit with a computer safe test light and computer safe DMM when looking for voltage and continuity . Always disconnect the PCM harness when performing a continuity check of any circuit that will lead to or from the PCM. You can read voltage and check for ground with PCM circuitry but never send voltage to a PCM with an ohm meter. When wiring is declared good continuity wise , then you may reconnect PCM and look for voltage readings and grounds . Before trying to crank this engine in an attempt to start it again , you will need to do the checking first . It is harmful as you know to the starter and the engine cranking excessive . Overheats starter and engine cylinder walls don't get lubed due to low to no oil pressure. That would go for all engine parts .
You said your not getting any trouble codes with either PCM installed ? This sounds like power is lost intermittently . But I keep focusing on one thought , transmission service . The down stream O2 sensor would set a code but your not even getting that . That's near by in your trans service , but not saying is related . Just an item to check and not over look .
Just to let you know , fuse F15 in the PDC is tied in with the trans controller , fuel pump relay and auto shutdown relay . Look for voltage there when cranking . Don't know if your getting spark , but it sounds like your not getting fuel and you posted the fuel pump is not going on when cranking ? In general , you want to be sure that fuses and relays pertains to ignition and fuel pump relay are fed and voltage is moving passed to coil and fuel pump . Not saying the trans controller is the problem but this circuit is tied in at fuse F 15 . Primarily , look for spark and look for reading at the injector harness . Fuel pump relay must register while cranking on all terminals . If spark is found while cranking , then fuel pump circuit must be concentrated on and injector harness reading checked while cranking if injectors are firing . Remember , use a computer safe test light . Do not use a regular 12V test light on computer circuits . Measure voltage with a 10 mega ohm impedance DMM as well . Most good meters today are rated computer safe but be certain as you don't want to jeopardize the PCM and just make more problems .
Hope this helps . I have a wiring diagram for '92 jeeps if needed . Greg

 

[Utah_jeepster]

A quick question, when you swapped your PCM, did you get it set to your VIN number? Your keys have a chip in them, your PCM needs to be flashed for the vin# which is set to the keys transponder #. The start up...run a few seconds is exactly what happens when you run an uncoded key without a transponder chip.

 

[tobs]

A quick question, when you swapped your PCM, did you get it set to your VIN number? Your keys have a chip in them, your PCM needs to be flashed for the vin# which is set to the keys transponder #. The start up...run a few seconds is exactly what happens when you run an uncoded key without a transponder chip.

No I did not get it reset and I don't think i got a chip in my key either I haven't even got a immobilizer

 

[Utah_jeepster]

No I did not get it reset and I don't think i got a chip in my key either I haven't even got a immobilizer

A quick call to your local jeep dealer will tell you.

 

[Ftballguy21]

Similar problem where my Jeep will crank.. sounds like it keeps cranking as if I kept the key turned. But it wont start. happened months ago then went away. Now its happening regularly. Yesterday I got an "transmission overheat" message while trying to start it. Never seen that before. I let the car sit a few mins with the hood open. Then tried it again... started on the third crank. This morning started right up on a cold start. Wondering if it could be transmission sensor or maybe Starter wire?
2007 Grand Cherokee.

 

[superj]

i cannot help with a 2007 grand cherokee. what motor is in that, the v6?

 

[Gennybro]

ignition relay switch is bad

 

[JPNinPA]

Or the crank position sensor. They go flaky then bad. When they do it results in no start condition.

Also search the error message. IIRC there is a direct cause. I'll post back here if I could find it.