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Unread 10-16-2013, 07:07 PM   #1
Hani96zj
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1996 ZJ 
 
Join Date: Aug 2013
Location: Pearland, Texas
Posts: 21
1996 ZJ 4.0 problems...again

Hello guys. I am totally stumped as to what is wrong with my jeep. I have been having an intermittent power loss once the jeeps is at full operating temperature. It almost seems like it running out of gas. So far i have changed the following:
Plugs
Wires
Tps
Iat
Fuel filter
Cap and rotor
Magnaflow cat
NTK O2 sensors, both

I checked fuel pressure at the rail and it was solid at 49-50 psi.
I really do not know what else to do! Any suggestions? When cold runs strong then five miles later its lost 75% power.
No codes either.

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Unread 10-16-2013, 07:38 PM   #2
ZeeJay1997
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1997 ZJ 
 
Join Date: Dec 2008
Location: Sweet Home, Alabama
Posts: 6,740
heat related problems are usually associated with a weak connection or flaky sensor or coil.

give us a better description of intermittent power loss. what do gauges do? idiot lights? headlights? if cruise is on, does it cut off?

the crank sensor is suspect also but i don't recommend changing it until you check it. see this post

also click the link in my sig and try 1, 2, 3, 4, 7 (check coil), 8 and 9
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Unread 10-16-2013, 07:57 PM   #3
Hani96zj
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1996 ZJ 
 
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Location: Pearland, Texas
Posts: 21
Thanks for the reply. By power loss I mean if I put any kind of load on the engine it will buck and cut out. The jeep has never shut off it just will not accelerate. If i try and go WOT it may run up to 2500-3000 rpm and buck and cut out. I have not noticed any gauge issues. What connections are usually suspect?
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Unread 10-16-2013, 08:04 PM   #4
ZeeJay1997
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1997 ZJ 
 
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add number 12 to the list.
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Unread 10-16-2013, 08:44 PM   #5
Hani96zj
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1996 ZJ 
 
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Location: Pearland, Texas
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Thanks i will begin hunting again tomorrow!
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Unread 10-25-2013, 01:13 PM   #6
Hani96zj
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1996 ZJ 
 
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Location: Pearland, Texas
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Ok guys, so its looks like i may have finally found my bogging and hesitation issue when warm. After throwing more parts at it i decided to seafoam it. With the seafoam i discovered i have cracked exhaust manifold. Would i cracked manifold cause the issues i am having?
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Unread 10-25-2013, 04:39 PM   #7
BoostinBubba
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1993 ZJ 
 
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Cracked manifold wouldn't cause that problem.
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Unread 10-25-2013, 05:20 PM   #8
Hani96zj
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Ok, that sucks. I am at a loss here. The thing runs fine cold and then gradually develops a bucking hesitation under load. It has never stalled and starts perfectly. Vacuum and fuel pressure good.
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Unread 10-25-2013, 05:55 PM   #9
Uniblurb
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1996 ZJ 
 
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Location: Central, Ohio
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So did you test the crank sensor as mentioned by ZJ and how'd it read? If not the link is in my signature.

The last CKP I had go bad was all heat related and once the engine warmed up is when I started having problems. As already mentioned a cracked manifold will not cause the problems you've been having.
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96 4.0 ZJ Laredo, 2004 4.7L WJ Limited, 93 4.0 XJ (spare), 96 4.0 XJ (son's)

-Stalling ZJ? 12 things to check before replacing a sensor; the Dirty Dozen
-Crankshaft position sensor multimeter test. & video of testing.
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Unread 10-25-2013, 05:57 PM   #10
Hani96zj
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I am going to pick up a meter tonight and test in the morning. Thanks for the help
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Unread 10-26-2013, 12:52 AM   #11
Uniblurb
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Location: Central, Ohio
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No problem and make sure you place your probes correctly on the pins in the connector to the crank sensor itself. Black probes goes on the middle B pin (ground cavity), red probe goes on the C pin (power, right pin w/locking tab up), and any resistance at all with meter set to the lowest ohm setting you have a bad sensor.

I have a 96 4.0 just like you and have found the crank sensor to be one of the most finicky electronic devices on a ZJ. And having clean grounds as mentioned in ZJ's dirty dozen thread, especially on the engine block, are super important.

I had a bad PCM ground on one of the coil studs which took out the PCM. The PCM grounds all the sensors so it most likely took out the crank sensor too. Didn't know any better back then and had the dealer replace the PCM but they didn't clean this ground wire off on the block. So it then took out another PCM and possibly another crank sensor. Not until all my grounds were clean, especially the coil stud which was corroded/covered in oil, did my problems cease. Of course it only took 3 PCM's, 4-5 bad crank sensors (shouldn't even count the 2 new/faulty aftermarket ones), and ZeeJay to figure this out!

If your crank sensor tests bad only go with a Mopar replacement and let us know how the test goes. Good luck!
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96 4.0 ZJ Laredo, 2004 4.7L WJ Limited, 93 4.0 XJ (spare), 96 4.0 XJ (son's)

-Stalling ZJ? 12 things to check before replacing a sensor; the Dirty Dozen
-Crankshaft position sensor multimeter test. & video of testing.
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Unread 10-26-2013, 03:10 PM   #12
Oldfrog
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1997 ZJ 
 
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Quote:
Originally Posted by Hani96zj View Post
Ok, that sucks. I am at a loss here. The thing runs fine cold and then gradually develops a bucking hesitation under load. It has never stalled and starts perfectly. Vacuum and fuel pressure good.

I had a bad TPS do that once. Weird.

Stay with the advice you've gotten so far, but keep a clogged cat in the back of your in mind...even though it's been replaced.

That cracked exhaust manifold can screw up your fuel trim after it's warmed up and it could even burn an exhaust valve if the crack is high enough on the manifold. I'd go ahead and replace it when I could, if it were mine. Get the one with the flex joints. While you're in there, you might as well swap the 5 large freeze plugs and the motor mounts too. Much easier doing it all at once.
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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 10-27-2013, 06:57 PM   #13
Hani96zj
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1996 ZJ 
 
Join Date: Aug 2013
Location: Pearland, Texas
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Well I checked the crank sensor and the meter showed no change at all. Looks like its good. I guess next i will clean the grounds. One thing i noticed is that it now does not wait to get warm to run weak.
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Unread 10-28-2013, 08:11 AM   #14
Hani96zj
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1996 ZJ 
 
Join Date: Aug 2013
Location: Pearland, Texas
Posts: 21
Ok I have another update. While driving in to work this morning, the jeep did the same thing. 15 mins into the drive the jeep would not take anything over 1/4 throttle. If I put in neutral and just hold to the floor is will rev to about 2500-3000 and just cut out and act like its out of gas. Now heres the weird thing, I get to work turn the jeep off and then restart it. Now with the restart it revs just fine?? I also noticed that when I cycled the fuel pump it only buzzed for a maybe second. Normally, when cycle the fuel pump is give a good 2 sec buzz.
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Unread 10-28-2013, 06:42 PM   #15
ZeeJay1997
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1997 ZJ 
 
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Location: Sweet Home, Alabama
Posts: 6,740
check the fuel pressure while it's acting up. The pump may be getting hot and quitting.
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