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Unread 03-11-2013, 07:35 AM   #1
harkinsc
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2004 WJ 
 
Join Date: Apr 2010
Location: Atlanta
Posts: 62
Missing, Hesitation, Starvation, HELP!

1997 4.0L 176,000 miles

I am experiencing some hesitation / starvation in my 4.0L. I am slowly running out of remedies. I haven't been able to pinpoint a specific scenario that causes the issue. It happens at start up (cold or hot), after driving for 30+ minutes. It has happened while idling around my neighborhood, shifting between R-N-D, pretty much whenever it feels like acting up. It is most frequent at low RPMs (500 - 2,000) combined with very little throttle input. Idle is very stable around 600 RPM. No check engine light illuminated.

What I have checked:
Throttle body has been thoroughly cleaned.
TPS cleaned
PCM connections checked

Things I have replaced:
Plugs
Wires
Cap
Rotor
Coil
CrankPS
Fuel Pump (&filter)
Fresh oil change

Things left to check:
Injectors
MAP sensor
bad PCM?

Any help or suggestions would be appreciated!
-Chris

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Unread 03-11-2013, 08:17 AM   #2
ZeeJay1997
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1997 ZJ 
 
Join Date: Dec 2008
Location: Sweet Home, Alabama
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Hi Chris, very familiar scenario there. I see you have checked the PCM connections, how did you accomplish this? There are a couple of common failure modes there with one being bad or dirty contacts and there other being bad solder joints inside the PCM.

Click the green link in my signature for some ideas on how to ferret out the gremlin without spending more money.

Good luck.
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Unread 03-11-2013, 12:06 PM   #3
harkinsc
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Quote:
Originally Posted by ZeeJay1997 View Post
#12. Restricted exhaust: – Tough one… it got me… If your vehicle has been running rich or backfiring, the catalytic convertor is probably shot. It can fail in one of two ways. The back end can blow into the muffler, or the front end can melt and stop up the chamber. So either way there will most likely be varying amounts of loose stuff floating around in your exhaust system. About all you can do without doing exploratory surgery is to listen for a rattle, most prominent when the engine is shutting down or just banging on the exhaust pipe with a 2x4. Don't be fooled by a loose heat shield. if you hear the cat rattling, get under there and check the welds to be sure the shield is not loose. You can drill some relief holes in the pipe forward of the cat and see if it runs better and have them welded up later. This type failure may cause it to stall under load at higher RPMs, accompanied by a rise in engine temperature. The rise in temperature on mine was about 10 degrees.
About an hour ago I was driving home for lunch on the interstate. Then came the stalling/bucking/misfiring. Managed to get it home and now the catalytic converter is rattling like marbles in a can. It's 8+ years old and the muffler is 11+. Looks like I will be welding up a new exhaust system this week.

-Chris
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Unread 03-11-2013, 12:32 PM   #4
ZeeJay1997
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One of two things has happened: Either the cat is simply worn out or some other problem is causing it to backfire and the rattling cat is the result. Is this the first time you've noticed it and how long has the stalling problem persisted?
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Unread 03-11-2013, 12:35 PM   #5
harkinsc
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Today, after the incident on the interstate, was the first time I noticed the rattle. It is very pronounced and unmistakable.
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Unread 03-11-2013, 12:41 PM   #6
ZeeJay1997
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If it were mine i wouldn't pull the trigger on a new cat until the stalling problem is worked out. Is it running rich too?
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Unread 03-11-2013, 12:52 PM   #7
harkinsc
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Now that I think more about it. I have been getting an intermittent downstream O2 CEL after driving for 15+ minutes. However, that CEL has been intermittent for well over 2 years now. Should have mentioned this earlier, but its become so commonplace I quit thinking about it. This stalling problem is 1 week old. The engine temp seem fine... ~185. I don't think its running rich, but how can I tell?

-Chris
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Unread 03-11-2013, 01:17 PM   #8
ZeeJay1997
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Strong exhaust fumes while idling when engine is hot is an indication of rich fuel mixture.

The downstream O2 doesn't have an input into the fuel mixture formula. it is there to monitor the performance of the cat. However, my cat was clogged down to a 1/2 orifice and the cat efficiency code never popped.

One way to tell if the cat may be clogged is to find a long hill on an open highway and climb it at a brisk pace. Watch the temperature gauge and note the power (or lack thereof). If it starts dogging out and temp rises, that's a dead giveaway.
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Unread 03-11-2013, 02:01 PM   #9
dylantheheeler
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When you do go for a new cat, check out eBay. 40 dollars beats 130. They work just as good.
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Unread 06-07-2013, 07:09 AM   #10
harkinsc
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Well, the old ZJ is back at it. Trying to kill me in rush hour traffic. I got the new cat, muffler, and O2 on it. This cured the CEL and seemingly fixed the stalling issues. Everything was fine for a month or so. But the stalling and hesitation has returned! When I'm stopped or coming to a stop (in gear or neutral) it likes to sputter and die. While driving at speed it tends to hesitate and misfire. It typically happens in the mornings when the motor is cold and hasn't been run in 12 hours. Sometimes it can go for a day or two without a problem. I've cleaned and checked the ground near the coil. Any ideas or thoughts out there? PCM (its zip-tied and passed the wiggle test), injectors, MAP sensor, cam sensor (distributor).
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Unread 06-07-2013, 07:15 AM   #11
Rich93ZJ
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Quote:
Originally Posted by harkinsc View Post
Well, the old ZJ is back at it. Trying to kill me in rush hour traffic. I got the new cat, muffler, and O2 on it. This cured the CEL and seemingly fixed the stalling issues. Everything was fine for a month or so. But the stalling and hesitation has returned! When I'm stopped or coming to a stop (in gear or neutral) it likes to sputter and die. While driving at speed it tends to hesitate and misfire. It typically happens in the mornings when the motor is cold and hasn't been run in 12 hours. Sometimes it can go for a day or two without a problem. I've cleaned and checked the ground near the coil. Any ideas or thoughts out there? PCM (its zip-tied and passed the wiggle test), injectors, MAP sensor, cam sensor (distributor).
Crank sensor or bad ground somewhere.
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Unread 06-07-2013, 08:27 AM   #12
dellis
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Quote:
Originally Posted by harkinsc View Post
It typically happens in the mornings when the motor is cold and hasn't been run in 12 hours.
A broken or poor solder joint is more likely to evidence intermittent problems when cold. As the device heats up, the metal of the joint expands and makes a more solid contact.



BTW, the expansion/contraction of a solder joint can cause intermittent problems when hot but not cold ... the point is, if temperature is affecting operation then one cause is a failed solder joint. Of course, lots of stuff fails when it gets hot, but if it is only failing when cold then there's a good chance you have a solder joint problem.
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Unread 06-07-2013, 11:24 AM   #13
harkinsc
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Quote:
Originally Posted by dellis View Post
A broken or poor solder joint is more likely to evidence intermittent problems when cold. As the device heats up, the metal of the joint expands and makes a more solid contact.



BTW, the expansion/contraction of a solder joint can cause intermittent problems when hot but not cold ... the point is, if temperature is affecting operation then one cause is a failed solder joint. Of course, lots of stuff fails when it gets hot, but if it is only failing when cold then there's a good chance you have a solder joint problem.
Thanks for the suggestion! The ZJ has been put in the 'time-out' corner of the garage until further notice. Pulled my garage queen WJ out in the interim. I will dig into the PCM this weekend and assess.
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Unread 06-18-2013, 08:26 AM   #14
harkinsc
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I replaced the PCM over a week ago and I'm happy to report I have not experienced any stalling or misfiring since! Fingers crossed!
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