Another crank but not start problem - Page 2

dllama · 06-30-2009, 06:35 PM

Quote:

Originally Posted by jlindseyjr

The crank and cam sensors can both cause you problems without throwing a code.

Yes, but would it make the check light NOT come on nor the "on/off/on/off/on" code retrieval not work?

In my mind there is a big difference between not throwing a code and the light and code retrieval not working..

I'm all but resolved to installing a new PCM tomorrow.

jlindseyjr · 06-30-2009, 06:38 PM

The "on/off/on/off/on" has never worked on my '97. You don't even get the MIL for a few seconds when you turn the key to on?

dllama · 06-30-2009, 07:19 PM

Quote:

Originally Posted by jlindseyjr

The "on/off/on/off/on" has never worked on my '97. You don't even get the MIL for a few seconds when you turn the key to on?

That's right no MIL at all. Same behavior with the PCM unplugged.

rooster51 · 06-30-2009, 07:55 PM

go with a cps first. you should by Mopar first, I learned this the hard way. the cps controls the obdII on my 97 so it probably controls your codes too. If this doesnt work, I bought my re-man pcm from advancedauto for $285 w/ a $60(?) core return. good luck.
Also my bad pcm was giving me false codes, so dont trust any codes completely if you suspect a bad pcm.

ZeeJay1997 · 06-30-2009, 08:36 PM

Unplug the CPS and see if your PCM comes back online. Someone just posted this problem on another forum and the CPS was the culprit.

If you're not getting a MIL for 3-4 seconds when key comes on, it's the PCM, power/ground to the PCM, or a rouge sensor shorting the PCM out.

On a side note, the CPS does not control the OBDII or the codes.

dllama · 06-30-2009, 09:30 PM

Quote:

Originally Posted by ZeeJay1997

Unplug the CPS and see if your PCM comes back online. Someone just posted this problem on another forum and the CPS was the culprit.

If you're not getting a MIL for 3-4 seconds when key comes on, it's the PCM, power/ground to the PCM, or a rouge sensor shorting the PCM out.

I'm not getting a MIL at all, ever. This mean I can't retrieve codes as the MIL doesn't come on. I read up on the PCM delay due to bad caps, even replaced the caps, still same.

Quote:

Originally Posted by ZeeJay1997

On a side note, the CPS does not control the OBDII or the codes.

Understood. My only remaining doubt is that the PCM does some kind to pre-test when the key is put to "on" (not start). Some strange logic like:

If bad/no signal from CPS then don't energize the fuel pump or ASD.

This would explain why I can't get fuel in just the "on" position. But then it wouldn't make sense for the PCM to keep this a secret and disable the MIL instead of throwing a code.. Unless the PCM designer is just pure evil

Everything keeps coming back to the PCM.

ZeeJay1997 · 06-30-2009, 09:37 PM

Quote:

Originally Posted by dllama

Some strange logic like:
If bad/no signal from CPS then don't energize the fuel pump or ASD.

It can fail and cause your problem.

I would disco CPS and 02 sensors before i called PCM dead.

it may bring your PCM out of its funk. worth a shot and only takes 5 minutes.

dllama · 06-30-2009, 09:51 PM

Quote:

Originally Posted by ZeeJay1997

It can fail and cause your problem.

I would disco CPS and 02 sensors before i called PCM dead.

it may bring your PCM out of its funk. worth a shot and only takes 5 minutes.

True, I will try disconnecting the sensors in the morning. If I get the same result I'll swap the PCM.

StellaTheZJ · 07-01-2009, 01:07 AM

Note that you SHOULD get a MIL glowing briefly during the "bulb test" when you first turn the key to on. In fact, this is when all your warning lights should illuminate. The reason they should all come on when you first turn the key is to check for burned out warning bulbs!! Maybe you have no MIL, and have never seen one, because the bulb is dead.

Confirm the bulb is good, make sure it glows when the key is first turned to "On," and only then can you check for codes with the MIL.

ZeeJay1997 · 07-01-2009, 05:18 AM

Quote:

Originally Posted by StellaTheZJ

The reason they should all come on when you first turn the key is to check for burned out warning bulbs!! Maybe you have no MIL, and have never seen one, because the bulb is dead. Confirm the bulb is good, make sure it glows when the key is first turned to "On," and only then can you check for codes with the MIL.

The PCM goes through a self test routine at key on and lights the MIL while doing so. Its more than a simple bulb check. If the PCM is bad, it will not come on. The bulb could be bad, but not likely unless someone took it out.

dllama · 07-01-2009, 08:04 AM

Quote:

Originally Posted by ZeeJay1997

The bulb could be bad, but not likely unless someone took it out.

That did cross my mind. I bought the Jeep about 2 years ago from a trustworthy source so I doubt that is the case unless some unscrupulous mechanic fooled him in the past.

There is a test to verify the MIL function but it requires a jumper from the instrument cluster connector (C5 I think) back to the PCM..

dllama · 07-01-2009, 01:24 PM

It was the PCM.

For anyone with a similar problem I will try summarize the problems and solutions I went through getting to the PCM.

Crank, won't start.
1) Stop cranking, turn the key to "on" and look for the MIL/Check Engine light.
If it's not there you likely need a PCM.
If it's not there try waiting with the key on, it might be the capacitors in the PCM and they might eventually work and give you the check engine and a start. If this is the case follow the great advice earlier in this thread about replacing them.

If the check engine comes on but still won't start there is likely something else wrong.

Pull the codes! Use the "on/off/on/off/on" trick and see what the PCM says is wrong.. it just might be right. Now if you need a PCM you will not have the check engine and therefore can't pull the codes.

Again without trying to start, just in the "on" position check for pressure in the fuel rail. It should be there. Release it, turn the key off, then back to "on" and try again.
pressure = good ASD, Fuel Relay, and pump. Likely cause now is spark; CPS and Coil.
no pressure = bad Fuel Relay, ASD (powers the Fuel Relay), or fuel pump. Swap the A/C Relay for the ASD, try again, Then swap the Fuel Relay, try again. If these don't work you can try to force the fuel pump to work by jumping terminl 30 and 87 with a hairpin. If that works it's a relay problem, if not it's fuel pump problem.

Do the continuity test on the CPS and test for spark at the coil and plug. Since I didn't go down this road you are on your own, but if the continuity test failed you should replace the CPS as it can disable the spark but not the other way around.

Hope this saves someone the time and expense of chasing the wrong part.. Anyone want to buy a used but working fuel pump?

rooster51 · 07-01-2009, 10:48 PM

Quote:

Originally Posted by ZeeJay1997

On a side note, the CPS does not control the OBDII or the codes.

Maybe, but when my cps died I was unable to get a code, my scanner read "ERROR", and I lost all instrument cluster, replaced cps and the cluster worked again and the scanner retrieved my code again.

ZeeJay1997 · 07-02-2009, 05:31 AM

Quote:

Originally Posted by rooster51

Maybe, but when my cps died I was unable to get a code, my scanner read "ERROR", and I lost all instrument cluster, replaced cps and the cluster worked again and the scanner retrieved my code again.

I think "control" is a bit strong. "Can Affect" would be more like it.

StellaTheZJ · 07-02-2009, 05:44 PM

My friend just had his (recently purchased) '97 Land Rover fail emissions. He was surprised, because it hasn't turned on the MIL. Guess what, his bulb HAD been pulled!! Lovely. After replacing the bulb, he found a bunch of stored codes, including O2 sensor failures on one side. You never know about the previous owners... or a dealer (as in his case).