1996 ZJ 5.2 warm stalling - JeepForum.com
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Unread 01-30-2014, 08:14 AM   #1
MSSchmenk
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1996 ZJ 
 
Join Date: Oct 2007
Location: Ohio
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1996 ZJ 5.2 warm stalling

Runs well cold except for some hesitation shifting 2nd to 3rd. (always had that issue since Iíve owned it) Once she warms up it will stall if I am forced to stop. RPMs just dive. If I ease into a stop all is OK.

Did the usual digging and thinking TPS but figured I would post to give more info.

Some background: 150k miles, burns oil > needs plenum gasket, long time warm stall issue but only 1-2x per year. For the longest time I got away with periodically cleaning IAC and problem went away and ran great. Thanks to you guys! Some time ago threw a CEL and via OíReillyís it was a generic code and guys thought maybe an O2 sensor but a reset would be good for now and come back if it comes on type of thing and have not seen a CEL for months. Ran into the issue recently and decided to replace IAC it as I felt the plunger was working loose. Ran good for awhile but had some crazy cold weather and had starting problems and ran rough. Removed power to reset and ran fine until today when wifey used it to run oldest to school since the roads are horrible.

I had replaced the TPS years ago to fix the same issue and it worked so I suspect it is time. Also if you can believe it a few times I got away with replacing or cleaning the PCV valve! Gonna get a new one and try it since its cheap. Regularly dealing with this type of issue always made sense to me with the plenum gasket/oil issue.

I am starting to wonder if the O2 sensor could play a role here due to the CEL. Far as I know they are the original. I believe she has always run rather rich but 12.5MPG per console so seemed daoble to me. Have I just masking the underlying issue with an O2 sensor by replacing the other sensors? Not sure what changing them entails or cost. Probably a little out of my league and no good mechanics local but have a BIL that takes of what I can't do but he is not much of a JEEP/Mopar tech.

When weather warms I will need to look at that 12 step thing and check grounding since I saw that pop up on a few threads I looked atÖ

Any thoughts appreciated. Many thanks in advance!

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Unread 01-30-2014, 08:58 AM   #2
PolkaPower
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1998 ZJ 
 
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Location: The Abyss, MD
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You are on the right track. TPS, IAC, 02 are all things that will cause that. Failing fuel pump is another. I noticed that more around turns when the fuel sloshed around though. If those 02 sensors are original they are way past due for replacement. Your MPG is terrible. I would get that plenum done. All that oil getting burned off through the intake is bad for a lot of things like the cat and 02 sensors.
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Unread 01-30-2014, 10:46 AM   #3
MSSchmenk
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1996 ZJ 
 
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Thanks Polka!

Good point on the fuel pump. All seems good there BUT I bet the filter is original too. Something else to consider... Just checked on MPG and it is indeed low. I could swear the last time I looked it was in range. That's definitely O2 sensor related right?

Replaced cat a year ago... Quotes I am getting for plenum gasket are a grand and the few guys I asked told me to replace a bunch of other stuff while I am at it like $2k. Trying the get my BIL to do it with the write up here but he is a little freaked out. Too big a job for me. Can't justify it for that since she her body is just about ready to get ugly.
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Unread 01-30-2014, 01:21 PM   #4
PolkaPower
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Quote:
Originally Posted by MSSchmenk View Post
Thanks Polka!

Good point on the fuel pump. All seems good there BUT I bet the filter is original too. Something else to consider... Just checked on MPG and it is indeed low. I could swear the last time I looked it was in range. That's definitely O2 sensor related right?

Replaced cat a year ago... Quotes I am getting for plenum gasket are a grand and the few guys I asked told me to replace a bunch of other stuff while I am at it like $2k. Trying the get my BIL to do it with the write up here but he is a little freaked out. Too big a job for me. Can't justify it for that since she her body is just about ready to get ugly.
It only costs about 120 bucks for the hughes plenum kit and a day to do. Most of the time will be spent cleaning. That is if you want it spotless like me. I never had done anything like that before and it wasn't hard at all. Just took time. I started Saturday afternoon and let the intake soak in degreaser over night. Sunday morning I bolted it back on and fired it up. I did replace the cam sensor and some of the hoses were brittle so those got replaced too.
I used muffin trays and a marker to keep things organized.
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Unread 01-30-2014, 02:28 PM   #5
MSSchmenk
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It wouldn't be the biggest job I've ever done but I always have too much "life" in the way. I can probably get the BIL to agree to it with my help and a printed writeup handy if I push the issue... He owned a shop and is a great old school tech.

I think I will test/clean PCV valve and reset computer/disconnect battery to start things out tonight. Then throw a TPS in if that doesn't help. Hoping that will allow me to keep her from stalling for now. Sound feasible?

Then check into O2 sensors to improve mileage. From memory we stuck the old sensor back in the aftermarket cat but not sure... My mileage actually improved slightly with the new cat...

Thanks again.
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Unread 01-30-2014, 04:34 PM   #6
JasonStebbins
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1997 ZJ 
 
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Try unplugging the upstream oxygen sensor and see if the symptoms go away. My money is on that especially since it happens after it starts stalling after being warmed up.
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Unread 01-31-2014, 06:37 AM   #7
MSSchmenk
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UPDATE: the pcv valve is working well so I disco'd the battery for 10 minutes and all is working well. Drove and tested it and is a definite improvement. RPMs didn't dive when accelerator was released once it warmed up. They returned to about 700 as they normally do. RPMs do eventually drop to 300 and that is usually once it is totally warmed up. I think that is a bit low from reading here... Passed the drive to school this am so I am least functional.

Will read up on the upflow 02 sensor. I think that is on the manifold and down flow on cat. Upflow is the critical one and downflow checks to see if uplow is working right? I think the O2 sensor could be intermittent and is part of the issue. Would love to see a bump in mpg. Any other classic zj mpg things to consider?

I have some other items to attend to now. Air intake hose is shot bottom looks like it melted and full of cracks/holes. Tranny fluid leak. Tail gate support struts. Tail gate bumpers.

Oh yeah, I have the 12 points printed now...

THANKS. The is forum is invaluable!
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Unread 01-31-2014, 06:58 AM   #8
JasonStebbins
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Good to hear you got it running. If the o2 sensor is original it's long overdue for replacement. You are right about the sensor descriptions. A full ignition tune-up with new oxygen sensors and a high flow exhaust are about the only things you can do for the MPGs in these beasts. Good tire pressure makes a big difference as well.

Get the intake hose from a junkyard. The struts and bumpers can be had on RockAuto for pretty cheap.
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Unread 01-31-2014, 07:24 AM   #9
PolkaPower
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300 is way low for idle. Should be around 700-750.
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Unread 01-31-2014, 08:47 AM   #10
MSSchmenk
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Full ignition tune up done maybe 10k ago. Did the exhaust and cat around that time as well.

WOW! The prices of the O2 sensors at Rockauto are half that of Oreilly's and lift supports even better. THANKS! I saw the name dropped before but never looked at the site.

I should replace both O2? Think that might help with idle? I am the type of guy not to fool with things unless they're broken (thanks Dad) so I am worried that replacing them will just cause new problems. Is changing the upstream DIY? Hit with penetrant a few times and go fer it? Thought I saw some post that it is not easily accessible.

Been a few years since I did the boneyard... But you guys got me fired up. I would be totally stoked if I scored a intake hose.

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Unread 01-31-2014, 09:00 AM   #11
JasonStebbins
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Half my Jeep is built with RockAuto parts.

You might as well replace both if you have the extra $30.00 or so and be done with it. They are a maintenance item. As long as you get Mopar/NGK you won't have any problems, aftermarket sensors are what usually don't work. I would highly recommend using heat rather then PB Blaster. That thing is really in there and you risk tearing the metal if it doesn't budge. I just hit it with a propane torch for a couple minutes and it spun right out.
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Unread 01-31-2014, 09:05 AM   #12
MSSchmenk
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Thanks for the tip for the heat. Happen to have a map gas setup... Is it easy to get to/without lift?

If you guys keep it up I am gonna end up tearing apart the dash to fix my heater blender door... Stuck on defrost/feet THANK GOD.
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Unread 01-31-2014, 10:16 AM   #13
JasonStebbins
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Yep, crawl under from the front and it's right on the down pipe. No lifting required.

Stuck on defrost is most commonly a vacuum leak, but could be a blend door/actuator issue.
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Unread 02-03-2014, 06:40 PM   #14
MSSchmenk
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Well, pretty sure the defrost only IS a vacuum line leak. Started nosing around and found this... The line is just crumbling and what little was there snapped off right at firewall. Wonder if I can get access to it with removing the dash cover. I could swear I also read a post about removing the the glove box would work but can't find the post...

Man, I wish it was the cruise control line, I never use it...
leak.jpg  
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