Just broke down. Ideas?

[coolwind57]

 Today is final day and I left work to drive to my technical school. I came off the interstate, about a 20 minute drive onto a highway with lots of stoplights. After waiting on the first light, I accelerated and was building up to speed and then the engine just died.   Does not appear to have overheated, oil looks good. If I let it sit for a few minutes it will start, although grudgingly. And then it dies after a few seconds. If it starts and I feather the gas, the pedal does not seem to increase RPM. It just  ignores my attempts to increase the RPM and just struggles to stay running at a low RPM. 

 

 Air filter clean. It’s hotter than hell out here so I had the air conditioner set at Max the whole way. No  idiot lights. Fuel pump or regulator, perhaps? Anything I can do to check?   Anything else come to mind?    Found some shade and awaiting your response if anybody’s available. I suppose I’ll have to call a tow truck soon. 

[eaglescout526]

How’s the CPS? That is prone to heat soaking. 

[trinity5007]

how hot is the engine? ive had 92s do that when they over heat. with idiot lights i guess its hard to tell. maybe pop hood and let cool down? 

[yxmj]

Like said above CPS is overheated

 

I would not advise this but....I once limped an xj home by pulling my rubber windshield washer line off and pointing it at the cps fastened it with a zip tie.....every time it warmed up and stalled i pushed the wiper button.....gave it a moment to cool down and the fired it up and kept going.......

 

Do you have a spray can of parts clearer or brake cleaner nearby.....spry some on as it evaporates it will cool it off enough to limp a bit farther.....???

[Eagle]

52 minutes ago, eaglescout526 said:

How’s the CPS? That is prone to heat soaking. 

 

^^^ This. It sounds exactly like a classic case of a heat soaked CPS.

[Smokeyyank]

16 minutes ago, yxmj said:

.I once limped an xj home by pulling my rubber windshield washer line off and pointing it at the cps fastened it with a zip tie.....every time it warmed up and stalled i pushed the wiper button

 

HAHAHHA Jeep people never cease to amaze me......especially those unibody folk. We get $h*t done. 

 

Back to the issue. You can check fuel pressure on the Schrader valve to easily check a fuel issue. Obviously have a towel handy so you're not spraying gas everywhere. On my wifes KJ it had similar symptoms before it crapped out. Otherwise heat soak could be the culprit. 

[omega_rugal]

1 hour ago, coolwind57 said:

If it starts and I feather the gas, the pedal does not seem to increase RPM. It just  ignores my attempts to increase the RPM and just struggles to stay running at a low RPM

 

this kinda dischards the CPS being hot and points to the fuel system... clogged filter?

[Minuit]

My first check would be fuel pressure. If fuel pressure is correct, my next move would be to heat the CPS with a heat gun to attempt to reproduce the failure...if you can fit a heat gun in there. If not, I'd try to make it happen again and check CPS output with a meter once the problem resurfaces. If you have to drive it, consider using something to cool the CPS back down. Canned air, bottle of water, whatever. Common trick I use to diagnose thermally-dependent failures in electronics. If hitting it with some freeze spray fixed it, that tells you exactly what part to replace.

 

Or just take the easy route and wing a CPS at it if the fuel pressure is good. That works too, but I don't like to spend money I don't need to.

 

[gogmorgo]

Kinda late now, hopefully you made it to school. 

 

I would also say it sounds fuel related. Spark problems are usually an all or nothing sort of deal, either it runs or it doesn't.

First thing I would do at the side of the road is bypass the fuel pump ballast resistor. If that fixes it, Bob's your auntie, either replace it or leave it bypassed, up to you. 

Failing that I'd look at fuel pressure, like Minuit says. Depressing the schraeder valve only tells you there's some pressure, it doesn't tell you it's enough pressure. For that you need a gauge. 

[coolwind57]

I sure appreciate the input fellas.  Here's what went down after I posted:

 

I attempted to start every 8-10 minutes with the same results.  At each fresh attempt, It would initially run for only a second or two and sound really bogged down.  Twice it backfired before dying.  Loud backfire too.  Each time I added a second attempt, it would simply turn over, not coming close to starting again. 

 

I called a tow truck and they gave me an hour ETA, so I was accepted my fate that I was going to have to tow my truck back home across the State line.  This would had been about a 30-mile tow.    $45 hook up fee and $3 per mile if I remember the quote correctly.  

 

I had let her set for about a half-hour undisturbed before got a wild hair and decided to crank her over again.  Damn thing came back to life as if nothing ever happened.  I called and cancelled the tow company and made my way to school in the right lane (in case she died again) of multi-lane Dixie Highway in Louisville.  It was a 100-degree heat index day, by the way and my rear was puckered the whole trip.  I was convinced that she'd die again at one of Dixie Highway's many LOOOONG stop lights but she drove without a hiccup.  

 

Got a 97% on my final and nervously drove home at 11pm, again without a hiccup.  

 

I think I'm going with an overheated CPS on this one.  Although I do believe my fuel pump probably needs replacement because of an unrelated issue--I have been plagued with slow-to-start conditions for a year now (I've posted on this previously).  It is about the only thing I hadn't replaced regarding this sometimes hard-cranking issue.

 

I have never had experienced such a curious, sudden dying of the engine before.  First thing that went through my mind was that the engine just blew.

 

11 hours ago, Minuit said:

If hitting it with some freeze spray fixed it, that tells you exactly what part to replace.

I like this idea.  I'll steal some keyboard compressed-gas duster and tuck it in my official rag/spare oil cubby next to my breather box.  That stuff comes out cool when sprayed and just may be a temporary solution if this happens again.    I don't recall ever running the AC at MAX for this long before....I rarely run it at all.  I wonder if things just got unbearably hot for the CPS.  It is an aftermarket CPS and not the original.  I also advanced it a bit when I installed it, as recommended by Cruiser54.  

 

8 hours ago, gogmorgo said:

First thing I would do at the side of the road is bypass the fuel pump ballast resistor.

I didn't think of this at the time.  Good idea.  What I did do is check connectors, wires, fuel lines and all general connections throughout the engine bay.  I checked the air filter.  I inspected engine oil (for evidence of blown head gasket).  I squeezed coolant hose and checked overflow bottle for signs of overheating (there was no noise, stains or anything...at the time, the engine was too hot to pull cap and check for adequate coolant).  

 

This morning i drove to work.  She performed absolutely normally.    

[Minuit]

As a side note, I want to take this time to address something I've seen repeated quite a lot on this forum - that using "MAX A/C" is bad or runs the A/C harder than normal. In truth, it's actually putting less load on the system on MAX than it is on NORM. On a Comanche, two things happen when you switch from NORM to MAX:

 

- The fresh air door closes and the recirculation door opens, meaning the system is pulling air from the cab and running it through the evaporator, rather than pulling in outside air. The cabin air is probably cooler than the outside air (unless you've been parked outside all day and just started the truck) so the A/C has less heat to get rid of. The longer you run MAX A/C, the cooler this air gets, so even less load on the A/C system!

- At least on HO models, it increases the blower fan voltage by roughly 1.5V.

 

That's all. The only component being stressed MORE is the blower motor. That's a valid concern to have, but it won't cause an overheating problem. In the long term, it may melt the fan speed switch if your blower fan is old, shaggy, and drawing too much current and you run the fan on full blast all the time. Even on extremely hot days, I don't need to run my fan on full blast to keep the truck cool (2nd fan speed usually does it, 3rd fan speed if it's REALLY hot), so if you do, you may have an A/C performance problem on your hands.

 

So why does MAX A/C cause less load? Our MJs have an A/C system based on a high pressure cutoff switch and an evaporator probe. Some models have a low pressure switch too, but neither of mine do so we'll ignore it. Those are generally the two things that control whether the compressor is on or off. The high pressure cutoff switch prevents the compressor from turning on if there is no refrigerant in the system or if there is a dangerously high pressure in the system. The evaporator probe controls compressor duty cycle (how often it's on) based on the temperature of the A/C evaporator. Once it reaches a certain temperature (somewhere around 35 degrees, I think) it turns the compressor off. Remember, the evaporator is the part that gets the hot incoming air blown over it, turning it into cold air. The hotter the incoming air is, the more heat gets transferred from the incoming air to the evaporator. The more heat transferred to the evaporator, the more the compressor needs to run to keep the evaporator cold. MAX A/C generally pulls cooler air across the evaporator than NORM does, so the compressor doesn't need to run as much to keep the evaporator cold!

 

I didn't REALLY mean to write a college heat transfer textbook here, but sometimes things happen. Have no fear about using MAX A/C. It's less likely to make your truck run warm than NORM. I pretty much always have mine on MAX.

 

Using the A/C, no matter what setting, will add a significant heat load to the cooling system, so if your cooling system isn't up to the task, turning the A/C on might push it over the edge. If BOTH fans are working properly and your cooling system is in otherwise good condition, this should be no problem. It was 93 degrees this afternoon, and my temperature gauge stayed right where it should with a Mopar temp sender - right on top of the "2" in 210 even when at a stop.

[AZJeff]

22 hours ago, Minuit said:

As a side note, I want to take this time to address something I've seen repeated quite a lot on this forum - that using "MAX A/C" is bad or runs the A/C harder than normal. 

————

I didn't REALLY mean to write a college heat transfer textbook here, but sometimes things happen. Have no fear about using MAX A/C. It's less likely to make your truck run warm than NORM. I pretty much always have mine on MAX.

 

 

Nice work on writing up the facts that most Jeep owners don’t understand about their HVAC system👍

[Minuit]

44 minutes ago, AZJeff said:

Nice work on writing up the facts that most Jeep owners don’t understand about their HVAC system👍

 

Hopefully more to come soon.