Dies after 20 minute idle, won't restart

[zithy]

Just got my Comanche (1988, 4.0L inline 6 cylinder, 2wd) a couple months ago, and have been working through the various quirks.  It drives has been driving well, but two days ago I had to get towed home.  After driving for about 20 minutes, it died at a stop light.  Turning the key would crank the engine, but no fire.  I tapped on the fuel filter, poked about in the engine, and tried to start it for a while, but didn't want to run the battery down.  When my tow got there and pulled me into a parking lot, it started, but it died again after a few blocks and had to be towed the rest of the way home.  Looking around the forum here, I see it could be an O2 sensor, the ERG valve, or the IAC.  I pulled the IAC and cleaned that with some Carb cleaner.  I killed it by pulling on the ERG, but it started right back up again.  I let it idle until it died (about 20 minutes?) and it won't start now.  I will be checking the reading on the O2 sensor once I can get it running for a bit again.  I have only a little experience working on cars (thanks for the pinned Acronym list!), so any advice you can give me would be great.  Thanks in advance.

[Eagle]

My '88 4.0L does the same thing. I believe it's a bad CPS that gets heat-soaked -- the problem started after I replaced the CPS. Unfortunately, I've had too many medical issues and I can't crawl underneath to try a new CPS.

[DirtyComanche]

What Eagle says regarding the CPS seems to be fairly common.  The signal weakens as they heat up, until eventually it's not strong enough to do anything.  Check out Cruiser54's tips regarding the CPS and checking the output voltage from it while cranking.  Personally I would start with this and I'm fairly confident it will be the issue.

 

If it will start/run at part throttle, the IAC is out.

 

I don't think the EGR is your problem, it normally works as well as it's ever going to on the 4L.  But you can disable it by pulling the electrical connector off the solenoid that's on the fender by the airbox; you'll see it fairly obviously as there's two vacuum lines on it and one electrical connector.

 

You could also bypass the fuel pump ballast resistor, it's easy to do, as it's on the fender there also and you can just use some wire or whatever to short across the connector pins on it.  Just don't ground it out if you do that.

 

Otherwise it could be a bad coil, or ICM, or an overheating ECM, or many other things.  Try the CPS first and we'll go from there.

[zithy]

I checked the CPS according to Cruiser54's tips, and am only getting 0.035 VAC, so I think that might be it.  I have yet to do the ground reworking, as that is what I had planned for this weekend until this came up.  I also checked the resistance on the 02 sensor and was getting 800 ohms, so that may be bad as well.  

[zithy]

I picked up a CPS from the local Napa, and drilled out the top hole to 3/8", and installed it.  It fired once, and that was all.  Pulled out the CPS, and the end was broken off.  I ordered another as that was their last, so will try again tomorrow.  My question now is, do I need to get that 1/4" piece of plastic and metal out?  Is the metal piece on the end magnetic, and will it cause trouble sticking to the fly wheel?

[cruiser54]

I checked the CPS according to Cruiser54's tips, and am only getting 0.035 VAC, so I think that might be it.  I have yet to do the ground reworking, as that is what I had planned for this weekend until this came up.  I also checked the resistance on the 02 sensor and was getting 800 ohms, so that may be bad as well.  

800 ohms between the orange and black wire on the O2 sensor is good.

 

An O2 sensor won't cause it to die anyway. 

 

Go through Tips 1 through 5 before doing anything else.

[SVPete]

I had a similar problem on my 1988. Would run.....stumble and die (unless I caught it by always keeping my foot over the accelerator)....injectors would fire a few more times flooding the engine...either crank forever to start or wait about 15 minutes. Replaced the coil, spark plug wires, and EGR at the same time.

 

The EGR transducer was inop (comes with a new EGR.....the internal diaphragm spring had rusted to powder), but while waiting for that to come in, I had also ordered wires and coil (coil was the original, this was 2015)....unfortunately, I broke a plug wire while waiting for the parts, that's why I ended up replacing all items at the same time, not because I believed they, collectively, were my problem.

[cruiser54]

I had a similar problem on my 1988. Would run.....stumble and die (unless I caught it by always keeping my foot over the accelerator)....injectors would fire a few more times flooding the engine...either crank forever to start or wait about 15 minutes. Replaced the coil, spark plug wires, and EGR at the same time.

 

The EGR transducer was inop (comes with a new EGR.....the internal diaphragm spring had rusted to powder), but while waiting for that to come in, I had also ordered wires and coil (coil was the original, this was 2015)....unfortunately, I broke a plug wire while waiting for the parts, that's why I ended up replacing all items at the same time, not because I believed they, collectively, were my problem.

Yep. Maintenance stuff.

 

They're due for plugs, wires, cap and rotor every 30,000 miles. 

[HOrnbrod]

I picked up a CPS from the local Napa, and drilled out the top hole to 3/8", and installed it.  It fired once, and that was all.  Pulled out the CPS, and the end was broken off.  I ordered another as that was their last, so will try again tomorrow.  My question now is, do I need to get that 1/4" piece of plastic and metal out?  Is the metal piece on the end magnetic, and will it cause trouble sticking to the fly wheel?

 

Pull the flywheel inspection plate off the bottom of the bell housing and see if it's laying in there. If not, try rotating the flywheel in neutral 360* and see if it can be found.

 

Then install your new CPS w/o drilling out the mounting hole - you don't need that now. It'll probably fire up and run fine.

[cruiser54]

 

I picked up a CPS from the local Napa, and drilled out the top hole to 3/8", and installed it.  It fired once, and that was all.  Pulled out the CPS, and the end was broken off.  I ordered another as that was their last, so will try again tomorrow.  My question now is, do I need to get that 1/4" piece of plastic and metal out?  Is the metal piece on the end magnetic, and will it cause trouble sticking to the fly wheel?

 

Pull the flywheel inspection plate off the bottom of the bell housing and see if it's laying in there. If not, try rotating the flywheel in neutral 360* and see if it can be found.

 

Then install your new CPS w/o drilling out the mounting hole - you don't need that now. It'll probably fire up and run fine.

 

There's something wrong as far as the CPS contacting the flywheel. There's a ton of clearance.

 

Incorrect mounting bolts? 

[Eagle]

 

 

I picked up a CPS from the local Napa, and drilled out the top hole to 3/8", and installed it.  It fired once, and that was all.  Pulled out the CPS, and the end was broken off.  I ordered another as that was their last, so will try again tomorrow.  My question now is, do I need to get that 1/4" piece of plastic and metal out?  Is the metal piece on the end magnetic, and will it cause trouble sticking to the fly wheel?

 

...

 

There's something wrong as far as the CPS contacting the flywheel. There's a ton of clearance.

 

Incorrect mounting bolts?

 

 

Notice where he said he drilled out the top hole. I'm going to guess that he read some "expert" on the Internet advising to do this to get a stronger signal.

 

God save us from the Internet experts ...

[cruiser54]

 

 

 

I picked up a CPS from the local Napa, and drilled out the top hole to 3/8", and installed it.  It fired once, and that was all.  Pulled out the CPS, and the end was broken off.  I ordered another as that was their last, so will try again tomorrow.  My question now is, do I need to get that 1/4" piece of plastic and metal out?  Is the metal piece on the end magnetic, and will it cause trouble sticking to the fly wheel?

 

...

 

There's something wrong as far as the CPS contacting the flywheel. There's a ton of clearance.

 

Incorrect mounting bolts?

 

 

Notice where he said he drilled out the top hole. I'm going to guess that he read some "expert" on the Internet advising to do this to get a stronger signal.

 

God save us from the Internet experts ...

 

That would be me. This is the first time I've EVER heard of one colliding with the flywheel.........And yes, it does strengthen the signal. 

[Eagle]

And if the result is to get the tip of the CPS closer to the teeth on the flywheel, it will generate a stronger signal. The problem is when it results in an interference fit -- as it seems to have done here.

[cruiser54]

And if the result is to get the tip of the CPS closer to the teeth on the flywheel, it will generate a stronger signal. The problem is when it results in an interference fit -- as it seems to have done here.

First time I've ever seen this in decades of doing it. 

 

The high altitude CPS and IIRC, the ones in the patch harness kit, already had the larger upper hole.

 

And no matter how large you drill the upper hole, the CPS can only slide down until it hits the bell housing. 

 

 

Guys on other forums have drilled BOTH holes without this result. 

[HOrnbrod]

Probably didn't use the correct shoulder bolts.........

[DirtyComanche]

Or they came loose...

 

Hey, as they say, $#!& happens.  Hopefully he's put the new new CPS on and it's running fine. :cheers:

[blondejon]

I chased down a randomly dying on my MJ for a long time. Over time, I replaced pretty much everything. 

 

Replaced EGR, coil, ignition control module, injectors(swapped in ford 19b) , 2x Mopar TPS, 2x mopar CPS, deleted the C101, fixed a bunch of bad wiring, plugs, cap, rotor, plug wires , 02, fuel pump, fuel filter air filter, relays, battery, alternator, ignition switch, IAC, MAP sensor, and the intake temp sensor, known to be in great working order ECU and TCU,  welded up exhaust leaks, verified the CAT was good,   thing was still randomly dying, and it actually started getting worse. 

 

 

Every time I put my snap on MT 2500 with the renix adapter on it, it would just happen to run great- everything read normal every time, I was pulling my hair out, but I could never catch it when it died.... finally one time that it died, I actually caught it, right after it died.

 

The culprit:

 

The damn coolant temp sensor under the manifold

 

It would intermittently read way off, like switching between -16* and the actual temp of 195*, then 150*, then -22*, then back to 195*, etc etc. . After spending all that money and time(mostly time, I had a lot of these parts on hand , I hoard renix stuff) , I swapped in a 20$ CTS and it has not died once since, and that was weeks go, and the CTS reads normal all the time,  whereas before It would die after constantly , you couldn't go around the block. 

 

 

I suppose when it was reading -22*, -10*, 5*, etc instead of operating temp , between 180-210* wherever it actually was ,  that it would instantly either dump a ton of fuel and flood it badly and kill or maybe lean it out horribly bad... and letting it sit for 30 mins always fixed it....well, almost always...

[cruiser54]

I chased down a randomly dying on my MJ for a long time. Over time, I replaced pretty much everything. 

 

Replaced EGR, coil, ignition control module, injectors(swapped in ford 19b) , 2x Mopar TPS, 2x mopar CPS, deleted the C101, fixed a bunch of bad wiring, plugs, cap, rotor, plug wires , 02, fuel pump, fuel filter air filter, relays, battery, alternator, ignition switch, IAC, MAP sensor, and the intake temp sensor, known to be in great working order ECU and TCU,  welded up exhaust leaks, verified the CAT was good,   thing was still randomly dying, and it actually started getting worse. 

 

 

Every time I put my snap on MT 2500 with the renix adapter on it, it would just happen to run great- everything read normal every time, I was pulling my hair out, but I could never catch it when it died.... finally one time that it died, I actually caught it, right after it died.

 

The culprit:

 

The damn coolant temp sensor under the manifold

 

It would intermittently read way off, like switching between -16* and the actual temp of 195*, then 150*, then -22*, then back to 195*, etc etc. . After spending all that money and time(mostly time, I had a lot of these parts on hand , I hoard renix stuff) , I swapped in a 20$ CTS and it has not died once since, and that was weeks go, and the CTS reads normal all the time,  whereas before It would die after constantly , you couldn't go around the block. 

 

 

I suppose when it was reading -22*, -10*, 5*, etc instead of operating temp , between 180-210* wherever it actually was ,  that it would instantly either dump a ton of fuel and flood it badly and kill or maybe lean it out horribly bad... and letting it sit for 30 mins always fixed it....well, almost always...

I have a DRB, not an MT2500. Can you monitor sensors in real time with the MT? I can. 

[HOrnbrod]

Very impressive. I have an Actron OBD scanner with a Chrysler OBD1 cable adapter. Can read both OBD1 and 2 sensors in real time, plus a whole lot more. Costs maybe $60 total.

[cruiser54]

I've often wondered how the DRB for Renix and the MT2500 compared. 

 

I generally just read the sensors in real time vs using the other options. 

[DirtyComanche]

Very impressive. I have an Actron OBD scanner with a Chrysler OBD1 cable adapter. Can read both OBD1 and 2 sensors in real time, plus a whole lot more. Costs maybe $60 total.

 

Oh jeeze.  Just because we're in the stone age doesn't mean you have to come in here and flaunt the magic of your fire.

[HOrnbrod]

 

Very impressive. I have an Actron OBD scanner with a Chrysler OBD1 cable adapter. Can read both OBD1 and 2 sensors in real time, plus a whole lot more. Costs maybe $60 total.

 

Oh jeeze.  Just because we're in the stone age doesn't mean you have to come in here and flaunt the magic of your fire.

 

 

Stone age - good one Dirt-man.   :clapping: :clapping: 

[cruiser54]

We might be in the stone age but we've kept the fire burning......

 

[zithy]

Update: Made it to another weekend, and got the second CPS installed.  It runs like a champ now.  Thank you all for your help.  I never did find the piece that broke off, but needless to say I didn't drill out the second CPS.  Now I just need to weld up the holes in the flooring, replace the swiss cheese exhaust, find out what is squealing, get the stereo to stop buzzing on low tones, get working door locks, etc.  I can see why this can become an obsession.  Obsessive Comanche Disorder?

[cruiser54]

Here's a photo I took today. The tip of the CPS is a good 1/4" from the flexplate ring.