So, my Pop's is giving me his old '90 Jeep Cherokee with the 4.0 I6. Damn thing has over 400K miles on it. It has a reman. engine and transmission that was replaced ~150K ago. He said it runs great and everything works on it.
The only issue it has is he, for example, runs up to the store really quick, shuts it off to go inside, and comes back out to leave it won't start. He says it only happens if the engine is shut off for a brief period of time (~5 minutes). It never happens if the engine is allowed to cool a little or if it's shut off for ~30 minutes or longer. He says once it happens he has to let it sit a while (again, ~30 minutes) and it will start up fine.
I know some of you have an idea on what could be causing this issue.

3/16/2009 9:14:31 AM

when it wont start, will it still spin over?

3/16/2009 9:33:51 AM

yeah, he says it will just turn over but never fire. i'm actually going to pick it up tomorrow. i have not witnessed it do this yet so i can't tell you if it's getting spark or a possible fuel problem. i was just wanting to throw this out there in case one of y'all has heard of this being a jeep problem and knew what the culprit was.

3/16/2009 9:42:00 AM

i would start with an ignition tune up and maybe a coil

those things are notorious for puking oil all over the plug wires and coil and shorting out, the coolant temp sensor would also be a good thing to check, fairly easy, just check resistance hot and cold

3/16/2009 11:33:44 AM

I'm wondering if he's got a leaky injector or two and it's bleeding down fuel pressure. Given the heat level, once you bleed off enough fuel, the rest in the line will vaporize. Almost like vapor lock on a carbed engine. I'd be willing to bet it's a combination of heat soak on the rail and just enough leak for this to happen.

3/16/2009 12:09:54 PM

i would think a coil, but dans, sounds cooler

3/16/2009 12:15:23 PM

what about that check valve in the fuel system that is notorious for bleed-down?

3/16/2009 12:17:05 PM

What these are notorious for is crank sensor failures, I have seen it several times- check spark, pulsewidth and fuel pressure when your no start condition comes up and that will help diagnosis.

3/16/2009 12:20:54 PM

^winnAr

3/16/2009 12:39:36 PM

^^will do.

3/16/2009 1:36:40 PM

Yeah, Joel is right. I did not think about that...but you really do need to check spark and/or injector pulse (using a noid light) and fuel pressure. If significant heat soak occurs, then the crank angle sensor may be experiencing thermal failure or dropout. This, by the way, occurs on a lot of different sensors that function in a similar manner (everything from ignition modules to crank angle sensors including Nissan's infamous optical pickup thermal failures).

So not a bad idea. You really need either a dwell meter and the knowledge to use it or an oscilloscope to properly diagnose waveform/pulsewidth on the sensor. Or...most OBD-II full-function scanners should be able to show realtime data acquisition to that effect.

3/16/2009 1:38:02 PM

By pulsewidth I meant injector pulse

3/16/2009 1:46:20 PM

Quote :

"If significant heat soak occurs, then the crank angle sensor may be experiencing thermal failure or dropout."

dingdingding.

3/16/2009 1:51:24 PM

Quote :

"I'm wondering if he's got a leaky injector or two and it's bleeding down fuel pressure."

That's what happened to mine. two leaky injectors.

3/16/2009 6:26:28 PM

ask jeepman, he goes through crank sensors like toilet paper

3/16/2009 7:09:53 PM

He doesn't use toilet paper.

3/16/2009 7:12:39 PM

wiping your ass is about all they are good for

3/16/2009 7:13:10 PM

my doo doo smells like roses.

and i was going to suggest the cps buuttttt it had already been suggested. I've seen em intermittently go out and sometimes just die for the hell of it.

2 x on my jeep
1 x on my brother
1 x on my neighbors
various others that I have forgotten

3/16/2009 7:45:00 PM

picked the damn pos up today. fucking thing has a leak somewhere. stinks to high hell like mildew. headliner is sagging like hell and the carpet is still soaked. great, something to look forward to.
anyway, he said he's already replaced the cps. not saying it couldn't still be the issue since the thing has 400K miles on it and there's no telling when he replaced it. i am wanting to believe it's a fuel related issue somewhere along the lines of what dan suggested. reason i say this is he showed me how it has to be started. turn key to "on" position, wait until you hear the fuel system primes (it's weird because you can actually hear an odd gurgling sound in addition to the normal f.p. whine.), turn key back to off, repeat process until you can no longer hear the fuel system being primed. fuckin'-a, on the 4th time "priming", it only "burped" one quick time when i turned the key on and the noise quit. on the 5th time, no noise was heard and it started right up. it will not start if this process isn't performed.
obviously i haven't tinkered with anything yet but i did look under the hood and everything was surprisingly clean except for a slight leak from the valve cover gasket. everything underneath is leaking, though. interior is actually pretty decent other than the headliner and wet carpet. replace the headliner, take carpet out and clean it after leak is fixed the interior would be pretty close to perfect. also found out the transmission is original with only one fluid change at 225K. engine was replaced when transmission fluid was changed.
not bad for free i don't guess. just something else to work on in my spare time that i don't have.

[Edited on March 17, 2009 at 8:52 PM. Reason : -]

3/17/2009 8:49:27 PM

^yup free is free, beggars can't be choosers

3/17/2009 8:52:46 PM

^^yeah, that's definitely sounding like a classic case of pressure bleeding down for some reason or another.

not too surprising on the transmission actually if it's an auto. that's an aw4, pretty damn tough unit.

i'll take it if you don't want it.

3/17/2009 10:10:22 PM

talked to my dad a little more about it today. he said it's not a bleed down issue or a check valve or anything of the sort. i actually didn't have any issues with it at all today. i'd try to crank it's like a normal car and it fired right up. he said when it does have the issue the ecu is not sending spark or injecting fuel. he actually tried to diagnose the problem but never finished. he said the ecu thinks one of the sensors are bad and that's why it's not letting the engine start. he's checked 4 out of the 7 and they're fine. if only i remembered what sensors he said were fine. he again said that once it happens to let it sit for about 10 minutes and it'll fire right up.
i washed the thing today, pulled out the headliner and backing board, removed the radio and found out it has a bad ground, removed the roof rack to silicone everything underneath and reinstalled it, and removed the windshield molding to check for leaks there.
do junkyards have windshields? if not, where can i buy one? i've always had somebody replace them for me but i have installed them on other vehicles just never had to buy one. this one does have a crack so i figured i'd go ahead and replace the damn thing since i need to stop it from leaking.

[/blog]

3/18/2009 7:47:20 PM

Quote :

"he said the ecu thinks one of the sensors are bad and that's why it's not letting the engine start."

yeah, it can trigger the ASD relay if there is a problem with a sensor or the wiring. check the o2 sensor and harness first. the most common issue i've seen when this happens is the wiring getting burned on the exhaust and causing a short.

3/18/2009 9:02:17 PM

^he did say he has not checked the o2 sensor yet. shit gets confusing because i'm jumping into the middle of a problem. it would probably be easier if i just started from scratch.

3/18/2009 9:33:34 PM

update on Gus:
the jeep still runs strong. i ended up just pulling the headliner and trashing it. i painted the top inside to match the dash. yanked and trashed the carpet. scuffed the floorboard and applied the roll-on bedliner i found on clearance at walmart for $15/gal. tinted the windows using the pre-cut tint found on ebay for $15. look decent.
now to the no-start issue. it took a while for the problem to finally occur. luckily i was at home when it did. there was no voltage from the ecu to the ignition module. a few months of no problems starting when it happened again. same deal, no voltage. finally the problem started to occur more frequently about a month ago. took joel and dan's advice about replacing the crank position sensor and bam, not a problem since. thanks! it has developed an issue where it takes about 5 seconds or so of cranking but it'll hit everytime and run.
currently looking for a cummins 4BT to swap in. that should take care of the electrical gremlins that have plagued these jeeps.

1/2/2011 5:37:26 PM

Best thing to do is buy a bread truck for the drivetrain, then I will buy the body from you for $100 and make it into a storage shed.

1/2/2011 11:46:25 PM

i can actually get a bread truck(turned racecar hauler) for a good price.

1/2/2011 11:59:18 PM

^^i bet you would give me $100 for the body. i, however, will not pay $3800 for the drivetrain!

http://raleigh.craigslist.org/cto/2100947121.html

1/3/2011 10:12:54 AM

Poor unibody

1/3/2011 3:12:15 PM

^yeah, i know. that's another issue. i need to figure out how much reinforcement would be needed to support the extra 500 lbs. the swap definitely has a cool factor along with the added mpg's but it may not be worth it.

1/3/2011 9:57:58 PM