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Unread 03-18-2014, 08:02 PM   #1
sparkieCHB
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Join Date: Mar 2014
Location: phoenix, az
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Forgive me father, I have sinned

I bought a zj, and its a pile of s#&t!!

This is my first post but I have lurked on here for years, I decided to join because I need some help getting this turd grand up and running.

A little info on the jeep first. 93 4.0, AW4, 249. 210,XXX, bone stock, sat for 2 years before I got it. I bought it for 400$ from a guy I know thinking if anything its worth it in parts (jeep runs, drives, stops, and STALLS!! More on that later). So I bought it, threw an old battery in it and drove it home. It had a rough idle issue when I first got it running but chalked it up to needing a tune up and sitting for years. Fuel pump went out shortly after I got it so in went a new Delphi pump and new filter. Threw plugs, wires, and fluid changes at it, decarbed it and ran some injector cleaner through the tank and it ran pretty good.

Started driving it around town and on short trips, ran great when you first fired it up but once warm it would start running rough in drive with the brakes depressed or with a load on the engine like running the air conditioning or turning the tires while stopped. I got it to actually die on me a few times and it had trouble starting after, never got a CEL and could only get it to throw a code 12 and 55, nothing out of place there. CEL would do it readiness check when key was turned forward, so I started testing sensors with my meter.

CPS, TPS, IAC, MAP, FPR, MAT, all either tested good or were temporarily replaced with known working units from another running driving jeep. No change

Checked all relays against each other and replaced any blown or questionable fuses. No change

Started poking around the PCM harness with the meter, #3 had full battery voltage, grounds were good.

About that time I started to get frustrated and after a night of drinking took it out in the desert and flogged the piss out of it. Died 2 times on me, piece of s#%t.

I started to double check everything I could and came up with nada. Crossed my fingers and shotgunned a PCM at it.

No change. Damnit, damnit, damnit!!! 190$ pissed in the wind

Now I'm about ready to part this thing out. This one has me licked worse than any problem I have ever had with a jeep, even my renix xj with +300,000 miles. The weirdest thing about it is it runs titties when i have my foot on the gas going down the road and has never once stalled or bucked while cruzing, only at a stop or close to it. It runs so damn good at 65 mph it blows me away its the same jeep sometimes.

Ready to set the Heep on fire, I'll take any help I can get.

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Unread 03-18-2014, 08:06 PM   #2
ZeeJay1997
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1997 ZJ 
 
Join Date: Dec 2008
Location: Sweet Home, Alabama
Posts: 6,902
Clean grounds on engine block.

see link in sig for more ideas
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Unread 03-18-2014, 08:18 PM   #3
porrsher
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1994 ZJ 
 
Join Date: Mar 2005
Location: Jefferson,GA, Georgia
Posts: 639
You're having a vacuum issue. This would explain the ok operation under WOT and the bad operation with the brakes depressed (brake booster).
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Unread 03-18-2014, 08:36 PM   #4
sparkieCHB
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@Zee - Thanks man that is a great write up, I have the better part of half already covered. I'll run through the few I haven't done already, I had actually run across that thread earlier in my search here, for some reason I didnt bookmark it for future reference, I definitely will now.

@Porrsher - Great suggestion but I'm certain it is not a vaccum issue, while idling in park for instance, if I depress the brakes the condition does not appear or worsen. It also does not have excessive idle or a default of air/heat to defrost, most of the factory emissions tubing has been replaced with new soft vaccum tubing, I think it is safe to say its not vaccum related

Also I forgot to include in my original post that it also stumbles slightly out of idle and then smooths out very nicely. If I put a full load on the heep, (in drive, brakes depressed, air on) it really idles rough and surges, almost to the point it feels like its overcoming the brakes. When idling in park with the air on if I abruptly slam on the gas it falls flat on its face or slowly struggles through the first 2000 rmp ( takes roughly 3 seconds).

Also I do have a fairly loud exhaust leak, I need to fix it but I assumed that the obd1 computer wouldn't be throwing too big of a fit with only 1 upstream o2, have I assumed wrong?
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Unread 03-18-2014, 08:39 PM   #5
stevethefolkie1
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1997 ZJ 
 
Join Date: Mar 2014
Location: Abbottstown, Pennsylvania
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Quote:
Originally Posted by porrsher View Post
You're having a vacuum issue. This would explain the ok operation under WOT and the bad operation with the brakes depressed (brake booster).
X2 - check the booster itself - really easy - engine running, friend in the drivers seat - put a bit of vacuum hose in your ear, other end on the booster, friend puts foot on brake - you hear "Woooosh" in your ear - booster membrane is knackered - typical for a vehicle that sat in a very arid atmosphere - if it's NOT the booster check the vacuum lines (really easy, can of starter fluid - spray it on the vacuum lines, if the idle goes up congrats - you just found the bad, leaking line!)

Cheers

Steve
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Unread 03-18-2014, 08:47 PM   #6
sparkieCHB
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@Steve - Thanks for the suggestions, I know by the way I'm explaining it, it sounds like the issue is what you are describing but I have sprayed ether all over the vaccum lines, tb, and manifold. No leaks I can find and the diaphragm in the booster seems good I can hear no loss of air when the brakes are depressed, pedal feels good, not too firm.
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Unread 03-18-2014, 09:57 PM   #7
somebody5788
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Location: Warsaw, Indiana
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Quote:
Originally Posted by sparkieCHB View Post
@Steve - Thanks for the suggestions, I know by the way I'm explaining it, it sounds like the issue is what you are describing but I have sprayed ether all over the vaccum lines, tb, and manifold. No leaks I can find and the diaphragm in the booster seems good I can hear no loss of air when the brakes are depressed, pedal feels good, not too firm.
Sorry but that's not the way you test this. I would put my money on a bad booster, you need to see if it holds vacuum.

My 5.2 Dakota has the same symptoms from a bad booster.
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Unread 03-18-2014, 10:07 PM   #8
sparkieCHB
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Quote:
Originally Posted by somebody5788 View Post
Sorry but that's not the way you test this. I would put my money on a bad booster, you need to see if it holds vacuum.

My 5.2 Dakota has the same symptoms from a bad booster.
I suppose it could be the booster then, how would I go about testing it?

I'm still fairly confident that its not a brake booster, there are too many variables to explain away with a bad booster. Like the condition worsening when the heep is warmed up or when the air is turned on.

You may be giving me gold though so I'll try it
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Unread 03-19-2014, 01:51 AM   #9
Oldfrog
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1997 ZJ 
 
Join Date: Feb 2008
Location: Louisiana/Texas
Posts: 4,245
The PCM you bought.....did you get it from any place in Florida? If so, it's still a suspect. Those 2 places in Florida suck. Get an A1 Cardone PCM if you cant find anything else wrong with the Jeep. I would also replace the o2 sensor with an NGK sensor.

Go through Zeejay's list...( we've all been there) slowly and methodically. Even something as simple as slightly low tranny fluid can cause the stalling issue. Also, wiggle the wires to the IAC and TPS while it's idling....see if the idle changes. If your CPS isn't Mopar...replace it too.

You can find the culprit....it just takes time. Good luck !
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Words of wisdom, Posted by Zeejay:
"..it's not air, it is the opposite of air... suckage so to speak."

Stalling? Work through Zeejay's list
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Unread 03-19-2014, 02:20 AM   #10
bobinAZ
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1993 ZJ 
 
Join Date: Feb 2014
Location: bullhead city, AZ
Posts: 194
dont know if the 4.0 has the coolant sensor, (not the one that goes to the gauge in the cab) i'm guessing it does. on my 5.2 its right of the Tstat housing. mine was bad and was reading wrong to the PCM, it had a little hiccup in the idle but never came close to dying..
was $19. at autozone.
good luck brother
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Unread 03-19-2014, 08:23 AM   #11
sparkieCHB
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Thanks guys, I did have the foresight to get a borg warner PCM with a good warranty from the local O'Reilly auto, I had read on here before to stay away from those outfits in Florida.
I'm going to monkey with it today after work. See if I can get it to throw me a code and start running through the odds and ends of the dirty dozen I haven't done yet.

Any chance the cracked manifold and exhaust leak are pissing off the o2? Its an obd 1 with only 1 upstream so I figured it wouldn't be too picky about it, could the o2 be a major culprit?
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Unread 03-19-2014, 10:27 AM   #12
bobinAZ
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If it's sucking clean air in before the O2 sensor that would mess it up
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Unread 03-19-2014, 10:43 AM   #13
Oldfrog
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1997 ZJ 
 
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Location: Louisiana/Texas
Posts: 4,245
I've also seen upstream o2 sensor wires chaffed and shorted. Check them out.
__________________
Cajun Recipes and Fishing tips

Words of wisdom, Posted by Zeejay:
"..it's not air, it is the opposite of air... suckage so to speak."

Stalling? Work through Zeejay's list
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Unread 03-19-2014, 11:17 AM   #14
jnowak
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1993 ZJ 
 
Join Date: Nov 2011
Location: dahlonega, ga
Posts: 474
Two thoughts, one if the leak is bad enough the 02 will be pissy, disconnect it and see if it changes the operation of the jeep. 2nd your comment about it over coming the brakes sounds like a torque converter stuck in lockup. It would cause the rough idle, stalling at stop, and over coming the brakes. Also would explain why it runs good on highway.
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Unread 03-19-2014, 03:39 PM   #15
sparkieCHB
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Location: phoenix, az
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Quote:
Originally Posted by jnowak View Post
Two thoughts, one if the leak is bad enough the 02 will be pissy, disconnect it and see if it changes the operation of the jeep. 2nd your comment about it over coming the brakes sounds like a torque converter stuck in lockup. It would cause the rough idle, stalling at stop, and over coming the brakes. Also would explain why it runs good on highway.
Didn't even think about the torque converter, where is the signal wire to lock up the converter clutch? I would think it would be a part of the abs loom since the converter clutch disengages when the brakes are depressed, or is it a part of the TCM harness? Anybody have a clue where to look? It stumbles in park as well with a load from the air conditioning, do you think the converter would cause a running condition in park?

Thanks for the suggestions everyone, going to look into the o2 a little more.
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4.0 , hesitation , misfire , stalling , zj

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