vadergator

first off, i know i 'm on the wrong thread. but, desperation makes you reach out for new opinions. i have a 97 Jeep Grand Cherokee 4.0L inline 6 motor 2wd. this thing runs and sounds like it just rolled off the showroom floor of any dealership. i cannot find any fault in this vehicle except for one thing. this one thing is why i'm on here now. 3 different garages and probably about 15 mechanics have lost sleep due to this one thing that they cannot figure out. after driving for any length of time without any problems, if the Jeep sits for more than an hour, it will not start again. it will turn over just fine, but won't crank. after 3 or 4 tries, it will fire up and run beautiful again for about 5 seconds before instantly dying. wait till the next day, and we will start the whole scenario all over again. get in and take off with a smile; an hour later you fall into Jeep - induced road rage.. electrical system checks out fine. fuel system and delivery checks out fine. computer works fine. sensors work fine. this Jeep likes to store a hard code of PO351 ( primary coil / secondary bank ) that doesn't trigger any MIL or check engine light. on 2 occasions that resulted in the Jeep being towed home, i 100% lost all spark and fuel pressure. next morning, it was like nothing had ever happened. i have changed out the following : O2 sensors ( up & downstreams ) , catalytic converter & muffler , crankshaft position sensor ( twice to be sure ) , camshaft position sensor , idle air control valve , throttle position sensor , coolant temperature sensor , intake air temperature sensor, asd relay , cap & rotor , plugs , plug wires , and the battery ( it needed to be changed 7 years old ). changed valve cover and throttle body gaskets, cleaned throttle body thoroughly with a toothbrush and throttle body cleaner, and sprayed contact cleaner on any and everything i could find. inspected wiring harnesses with no loose solder joints. grounds are good. i feel like it could be ignition related. like the ignition control module or the exterior switch box. also, i saw where the speed sensor on the tranny helps regulate the flow of gas and the ignition timing. does any of these things sound like a potential culprit? this one requires a expert who has been through the mill in troubleshooting Jeeps. i'm putting this on as many forums as possible in an attempt to find even just one person who can say, i know exactly what it is. or, i can narrow it down to 3 specific things. the mechanics working on it now could use a helping hand. help me obi-wan, you're my only hope.

Radi

It's throwing a coil error and the mechanic changed everything except the coil? (I assume you still have the single coil being a '97, not the newer multi-coil setup)
It's a common failure- the coil intermittently fails, particularly when hot, then works fine after it cools off again. That's where I'd look next. Don't test with a meter, test by substitution.

The Rooster

i also agree the coil can fail sometimes and not all the time when hot.... the coil is not totally toasted yet.... I would start with the coil... also the ignition control module will fail when hot and be fine after it cools off again... i had that problem in my datsun 280zx.... and no worries about posting in this section we are here to help you out

vadergator

i forgot that the coil has been changed twice. there's been about 6 tried out just in case.

Firestorm500

Quote: "...it will turn over just fine, but won't crank."

Not trying to be nitpicky here, but turning over is cranking. Sounds like it's not firing when it does that, however.

Ignition control module been changed yet? I don't remember seeing it had been changed.

hbracing13

I would go with the pip same as ignition control. That would allow it to crank all day with no start until it cools down. The only way really is to replace it. I had the same problem with a Ford, would test out fine every time but checking the ohms showed one bad signal and the others a few values off.
Any shop should have thought of that problem being the first thing by checking fuel and spark when it died and to continue to check it after it would start and die again. Someone jerking you around I think.

CobraMarty

Probably needs a new ECU. Just a guess.

Cherockee

X2

It sounds like you can replicate the problem, so why hasn't a mechanic been able to tell you what's happening when this occurs? Meaning, when the trouble starts does the Jeep still have fuel and pressure? Does it have spark? Do the fuel injectors get a trigger pulse? Will it start when gas is poured into the TB? Is the spark stong and blue?

Since you've replaced and checked nearly everything that makes the motor run and still haven't figured it out I am going to vote for trying a new ECU.

tjwalker

There would be no ignition control module on a 97. 1990 was the last year for those..

Try a salvage yard computer.

Firestorm500

Well I guess that's why no one has changed the ICM module yet.

97AT4x4XJ

On some Mitsubishi distributor cap gasket was missing and engine stalled sometimes. It happened when air had a lot of moisture.
Learn how to check fuel pressure and spark. You have to diagnose, when engine doesn't start/stalls.
Ok, here you go:
disconnect fuel injectors
remove spark plugs and connect them by wire (wire goes around tread). Attach wire to engine bolt.
Connect spark plug wires to spark plugs, let somebody "start" engine, watch for sparks.

crimsondragon

Did you change the MAP sensor? I see you changed everything else so might as well change that. Is the CEL coming on and then turns off after a few seconds when you first turn on the car? That indicates a healthy ECU.

weebur

Interesting problem, please post back if you find out what the problem was.

letsgomuddin

My vote for the ecu

CCKen

"100% lost all spark and fuel pressure"

[XJ Body based comments]

If you lost both ignition AND fuel pressure (pump shut off), I would suspect that the PCM is not receiving signals from the crankshaft position sensor circuit that the engine is running, or this function of the PCM is defective.

The fuel pump circuit is independent from the ASD circuit; the only thing in common is the PCM. When the PCM is signaled that the engine is rotating by the crankshaft position sensor it will pull in the ASD relay control coil, which closes the ASD power contacts to power the ignition coil, fuel injectors, and O2S heaters. At the same time the PCM will pull in the fuel pump relay control coil, which closes the fuel pump relay power contacts, powering the fuel pump. You should hear the fuel pump run for 1-2 seconds when the key is placed to RUN, before starting the engine, then stop. This indicates the PCM is activating the fuel pump relay to prime the fuel rail. The fuel pump will be activated by the PCM after the engine starts, as described above.

The fuel pump shutting down (?) may be a by-product of the PCM ignition coil driver failure, shutting down the engine.

The PCM will not store a diagnostic trouble code for fuel pressure.

Here are a few of the possible causes of P0351:

OPEN/HIGH RESISTANCE IN THE ASD RELAY OUTPUT CIRCUIT [Not necessarily the ASD Relay]
IGNITION COIL DRIVER CIRCUIT OPEN
COIL
IGNITION COIL DRIVER CIRCUIT SHORTED TO GROUND
WIRING HARNESS INTERMITTENT
POWERTRAIN CONTROL MODULE (IGNITION COIL DRIVER)

Here's a test of the PCM ignition coil driver at the ignition coil:

Turn the ignition off.
Disconnect the coil primary harness connector.
Connect one end of a 12 volt test light to a good 12 volt source (B+) [battery]
Warning: Keep clear of the engine’s moving/rotating parts.
Check the ignition coil driver circuit at the primary harness connector (2 pins to choose from, one power, the other the PCM driver circuit), with the other end of the test light, while cranking the engine.
Does the test light blink/flicker? If so, the PCM driver and related wiring is working. If not, the PCM driver circuit is not working or there is an open or short between the PCM and the coil.

Here's a diagram of the 97 XJ ignition coil circuit.