Ok, Stalls while driving like you had turned the switch off... read my history

[mimsand]

I have a problem with this 1994 Grand Cherokee Laredo starting for the longest. Turn the key on and the fuel pump wouldnt run sometimes resulting in no start. I replaced the fuel filter which was totally blocked (after 225K miles). Seemed to fix that issue.

At this point, I can be driving the vehicle after 10 minutes or 30 minutes it will cut off like you turned off the switch. After about 10-20 minutes it will start up like nothing ever happened. Puzzling....

While troubleshooting the fuel problem last year, I replaced the CPS with an after market one. Getting code 11 and 12. 11 is no signal to the coil from dist. 12 is battery disconnected from ECM.

I have been working on this for a while. Had it towed twice but man this is a great car! Just need to get this issue identified. Any help would be awesome!

 

[SteelHeadz]

The first question that comes into my mind is what's shutting down. From the DTC's you have, i would look into the code 12 a little bit more closer since the symptoms you described seems more relevant to the condition when the shutdown event happens. Be ready with a test lamp and a volt meter when you duplicate the event and start testing the voltage and ground circuits without disturbing it's condition so you could isolate the cause. Start your diagnostics from the battery, PDC all the way to the ignition switch then down to the PCM. If when the shutdown occurs and the dash lamps are still illuminated and the gauges are still functioning, i would check the supply and ground from the PCM, check connections to the PCM for loose or corroded terminals. The theory behind this is as follows; The battery supplies voltage to the PDC and distributes it to various components including the ignition run position then to the PCM. So with this IF the dash is functional even when the engine is shutdown, you know the ignition circuit from the battery to the switch is good and the possibility of a voltage fault would be between the ignition and the PCM. IF the dash and everything else has also shutdown with the engine when the fault occurs, i would start the diagnostics from the battery. Is this a 318 or a 4.0 engine?

 

[mimsand]

Thanks. This is a 4.0 6 cyl. The dash and idiot lights still function yes.

The first question that comes into my mind is what's shutting down. From the DTC's you have, i would look into the code 12 a little bit more closer since the symptoms you described seems more relevant to the condition when the shutdown event happens. Be ready with a test lamp and a volt meter when you duplicate the event and start testing the voltage and ground circuits without disturbing it's condition so you could isolate the cause. Start your diagnostics from the battery, PDC all the way to the ignition switch then down to the PCM. If when the shutdown occurs and the dash lamps are still illuminated and the gauges are still functioning, i would check the supply and ground from the PCM, check connections to the PCM for loose or corroded terminals. The theory behind this is as follows; The battery supplies voltage to the PDC and distributes it to various components including the ignition run position then to the PCM. So with this IF the dash is functional even when the engine is shutdown, you know the ignition circuit from the battery to the switch is good and the possibility of a voltage fault would be between the ignition and the PCM. IF the dash and everything else has also shutdown with the engine when the fault occurs, i would start the diagnostics from the battery. Is this a 318 or a 4.0 engine?

 

[mimsand]

Also, after it starts up, 10 15 minutes later, it will die again. Cycle will repeat over and over.

 

[SteelHeadz]

I suggest testing the circuits after the ignition towards the PCM and isolate the power and grounds.

 

[mimsand]

PCM? Is that referring to the Engine control module under the hood against the driver side fender?

M

 

[SteelHeadz]

Yes, ECM.

 

[mimsand]

I spent yesterday going over all the grounds in the engine compartment. Found light corrosion on them but nothing you wouldn't expect. None the less, I removed them and the bolts. Sanded, wire brushed and sprayed with WD-40 upon reassembly. I found ground wires on the coil bracket, alternator and on the inner fender by the battery. I also removed the PCM connection bolt and the connector. I saw nothing out of the ordinary there so I sprayed it too and reassembled it. Can you guys tell me where I may find other ground points to check?

It is running fine for now but ya never know when it might die again.
I installed my bike rack on the back and put my bike on it. This way if it leaves me stranded, I can go get a Diet Coke while waiting....

 

[mimsand]

Just died on my way to lunch. Dash stuff died too. Turn the switch off then back on, Dash stuff works but wont start again. Gave the ig switch a couple whacks and it started. I will let you know more later.

 

[mimsand]

AGHH! Ok, Stalls while driving like you had turned the switch off... read my history

Scratch that. about 5 minutes it died again. I am gonna replace the fuel filter again just in case. Has 228k miles on it.
Another thing I tried is the fuel supply.
There is little or no fuel pressure at the valve stem on the rail but if I unplug the supply hose from the rail, fuel flows. Could the fuel pump be pumping but unable to maintain pressure? Could a clogged or partially clogged filter cause this?

Michael

 

[SteelHeadz]

If whacking the ignition switch gets it to start up, i would think the issue is somewhere there.

 

[mimsand]

If whacking the ignition switch gets it to start up, i would think the issue is somewhere there.

Well that was a fluke. Only happened once.

 

[carnuck]

Could be ignition slider or the ground wire on the block is corroded and loose (common)

 

[mimsand]

Next Chapter:
I started the process by making sure it would crank while in the driveway.

I dismounted the relay/fuse block under the hood, removed the dash around the steering column and dismounted the ignition switch.

I started the engine and began to move, jiggle and manipulate the harnesses, fuses, relays etc. Also manipulated and jiggled the ignition switch. Wiggled, pushed and pulled on the harnesses in the kick panels and elsewhere.... All this trying to get the engine to stall. No Luck.

Followed the manual and tested the distributor and CPS and found them to be good.

I jacked up the jeep and crawled under it to remove the CPS for a visual inspection and re-mount. I found the bolt to be loose. I removed it, inspected it and re-installed it. When I re-stalled it, I first left it loose with the bolt in place. Started the engine and tried to wiggle the CPS while running. It still didn't stall.

So now, I have cranked it several times, driven it short distances and had no issue. This not uncommon and it might die at any moment unless!!!.....

Perhaps the CPS being loose and in combination with heat and driving it lost function somehow. I can only hope!

One note that is peculiar, while the engine was running, I disconnected the distributor connection and the engine never skipped a beat... kept running... with the distributor connector unplugged!!! So if the engine is running, the CPS must provide enough information to fire plugs and fuel injectors? And the distributor is for additional or back up?

Michael

 

[DeadHammer]

I would think a loose CPS would cause it to stall while driving down the road.