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Unread 09-02-2013, 06:27 PM   #1
Akumakis
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1991 YJ Wrangler 
 
Join Date: Sep 2012
Location: Kelowna, BC
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On the table; a tricky one for the YJ experts:

2 years or so back, my 1991 YJ 4.0L started this habit of quitting after it runs for a while. Engine temp is nice and cool, and it'll happen in summer or winter, after about an hour of continuously driving. It happens faster after lots of uphill grinding, though it will quit on the highway if it's hot out. When it quits, it seems to just lose spark. Sometimes it would backfire (stopped this after the new air cleaner, below), and often I hear a "pressure release" sound, which I assume is back pressure in the exhaust. After it quits I wait a minute, then it starts and runs fine, but dies again a minute later. Once it starts this, it will run about twice as long as I let it rest. Up in the bush, if I kill the engine on downhills or stop every 20-30 minutes or so for a beer, it'll never quit, since it gets enough rest breaks.

I couldn't find an obvious solution, so I took it in to a general mechanic who had worked on the jeep. Not surprisingly, he couldn't get it to quit, and found nothing wrong. I drove until it quit, then limped up just as it died - he still couldn't figure out anything wrong.

I was in the process of doing some upgrades, so I expanded the process, did some research, and replaced lots of old stuff that could be the culprit. I though I had it beat last fall, but this summer it cropped up again.

- New stuff (since it first died). All high performance gear:
Coil
Spark plug leads
Plugs
Distributor
Air Cleaner
Fuel filter
Sensors: oxygen, intake temp, TPS (twice), crank position, water temp, oil press
Injectors
Battery
Header/Exhaust (never had CC within the issue timeframe)
Radiator/Thermostat

- Current Engine Codes:
12 - battery disconnected last 50 starts: yeah, I did.
33 - air con clutch relay: I don't have air conditioning.
15 - distance sensor or circuit - I understand this is due to an electric speedo. Doesn't fit the symptoms from what I see.
*24 - sometimes it shows, sometimes not. I've replaced it twice, once right after the jeep died. Died again 15 minutes later.

Whoever figures it out wins the Jeep Genius award.

Awaiting brilliant input.

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Unread 09-02-2013, 08:23 PM   #2
laybackman
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1995 YJ Wrangler 
 
Join Date: Dec 2002
Location: Massachusetts
Posts: 6,040
Quote:
Originally Posted by Akumakis View Post
On the table; a tricky one for the YJ experts:

2 years or so back, my 1991 YJ 4.0L started this habit of quitting after it runs for a while. Engine temp is nice and cool, and it'll happen in summer or winter, after about an hour of continuously driving. It happens faster after lots of uphill grinding, though it will quit on the highway if it's hot out. When it quits, it seems to just lose spark. Sometimes it would backfire (stopped this after the new air cleaner, below), and often I hear a "pressure release" sound, which I assume is back pressure in the exhaust. After it quits I wait a minute, then it starts and runs fine, but dies again a minute later. Once it starts this, it will run about twice as long as I let it rest. Up in the bush, if I kill the engine on downhills or stop every 20-30 minutes or so for a beer, it'll never quit, since it gets enough rest breaks.

I couldn't find an obvious solution, so I took it in to a general mechanic who had worked on the jeep. Not surprisingly, he couldn't get it to quit, and found nothing wrong. I drove until it quit, then limped up just as it died - he still couldn't figure out anything wrong.

I was in the process of doing some upgrades, so I expanded the process, did some research, and replaced lots of old stuff that could be the culprit. I though I had it beat last fall, but this summer it cropped up again.

- New stuff (since it first died). All high performance gear:
Coil
Spark plug leads
Plugs
Distributor
Air Cleaner
Fuel filter
Sensors: oxygen, intake temp, TPS (twice), crank position, water temp, oil press
Injectors
Battery
Header/Exhaust (never had CC within the issue timeframe)
Radiator/Thermostat

- Current Engine Codes:
12 - battery disconnected last 50 starts: yeah, I did.
33 - air con clutch relay: I don't have air conditioning.
15 - distance sensor or circuit - I understand this is due to an electric speedo. Doesn't fit the symptoms from what I see.
*24 - sometimes it shows, sometimes not. I've replaced it twice, once right after the jeep died. Died again 15 minutes later.

Whoever figures it out wins the Jeep Genius award.

Awaiting brilliant input.
Unplug the VSS sensor plug from the VSS in the TC. You'll lose your speedometer. See what it does then.

Make sure the MAP sensor has good vacuum.
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Unread 09-02-2013, 11:51 PM   #3
Akumakis
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1991 YJ Wrangler 
 
Join Date: Sep 2012
Location: Kelowna, BC
Posts: 9
I'll try the VSS trick. My understanding, however, is that this component regulates idle at stop - it shouldn't affect hot running performance at throttle.

A faulty MAP should send codes (never did), and a classic symptom should be rough running, which my jeep doesn't suffer from - it runs perfect until it dies, then perfect again after a rest.

All that said, I'll try these out and let you know...thanks.
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Unread 09-03-2013, 12:46 AM   #4
Fattynutzkin
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Sounds like a camshaft position sensor.

Is your fuel pressure within operating limits.
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Unread 09-03-2013, 07:09 AM   #5
WDNewman
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Location: Central Mississippi, Mississippi
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Originally Posted by Fattynutzkin View Post
Sounds like a camshaft position sensor.
Sure does. If they are faulty, heat really works on them. Worth a check.
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Unread 09-03-2013, 07:12 AM   #6
laybackman
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Quote:
Originally Posted by Akumakis View Post
I'll try the VSS trick. My understanding, however, is that this component regulates idle at stop - it shouldn't affect hot running performance at throttle.

A faulty MAP should send codes (never did), and a classic symptom should be rough running, which my jeep doesn't suffer from - it runs perfect until it dies, then perfect again after a rest.

All that said, I'll try these out and let you know...thanks.
#24 is the TPS DTC. But if the MAP sensor signal does not correlate with the TPS sensor that code can pop on.
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Unread 09-03-2013, 08:00 AM   #7
Que89YJ
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1989 YJ Wrangler 
 
Join Date: Apr 2008
Location: Detroit, Michigan
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Akumakis, you posted your Jeep info in your thread, please put the info into your profile. It helps when you dont have to go digging to help someone figure out what is going on.
You need to see what is being lost when it stalls and will not start. You need to do some leg work first.

The speedo sensor will effect the calibration for decel. It can cause a no start without a fault code if the connector shorts. Repair the connector or replace the sensor.

You replace the TPS. It will set a code if it disagrees with the input from the Map sensor. The Map is usually not an intermittant sensor so it is a curious fault to be setting.

Clear the stored fault codes by disconnecting the the battery for a long 10 count. Check your codes to make sure you only have the 12,33, and 55. Get a pressure guage. Run the standard pressure test; 31 psi engine running, disconnect the vacuum line to the pressure regulator 39 psi, and bleed down it should hold more then 20 psi for 20 minutes. Take it for a drive and get it to stall out. Check your codes and see if the tps or any othe codes set. Check for spark at the plugs and see if you have spark at the plugs. Hook up your pressure guage to the fuel rail and run the pressure test. You will not be able to test the running pressure but ignition on it should be comparable to what you measure before. Post back the results.

We can get it figured out if you will do the leg work.
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Unread 09-04-2013, 06:33 PM   #8
Akumakis
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1991 YJ Wrangler 
 
Join Date: Sep 2012
Location: Kelowna, BC
Posts: 9
Que89YJ, that stuff didn't show up in the tablet version. Filled it in now, thanks.


And thanks to all for the ideas. I didn't even know about the camshaft position sensor...I'll dig into these as soon as I have Jeep time, and report back!

1991 Jeep YJ Renegade 4.0L
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Unread 09-04-2013, 06:49 PM   #9
Que89YJ
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Yeah. I posted to the forum admin. on the info. Same problem on my android app. Post back what you find.
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Unread 10-03-2013, 05:56 PM   #10
The_Goob
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Id sure love to see if you figured this out, since its exactly whats happening to my 91
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Unread 10-03-2013, 07:09 PM   #11
Que89YJ
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Amukakis any update?
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Unread 10-03-2013, 09:05 PM   #12
DirtKar
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This is an interesting one... I sent him a pm requesting results, Que.
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Unread 10-03-2013, 10:51 PM   #13
Akumakis
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The Continuing Saga of the Jeep Gone Wild

Tried a few things, but not the CSPS yet.

Testing for resolution is tough. It takes a while to heat up to the point of quitting, and we tend to stop for beers when out 4beer4ing. Even enough downhill seems to give it sufficient time to rest.

As I have time to try things and test properly, I'll keep posting on it.

Thanks, all.
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Unread 10-04-2013, 12:37 PM   #14
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4beer4ing sounds fun, but I have a CDL so none of that for me
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Unread 10-04-2013, 09:30 PM   #15
linusb
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I suggest VSS as well. I grenaded my TC once and as it was dying, the engine would stall and not restart from the VSS having gotten too hot.

VSS it does funny things to CPU and it will absolutely cause a no start condition.

You'll get a bad idle with it unplugged as well as a CEL code.

If that don't work, check your wiring. I recently had a hot stall issue that I seem to have elongating by routing large wire loom on pass side away from engine. I think I might have a bad wire and it was shorting against block occasionally.
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