01' WJ engine trouble - JeepForum.com
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post #1 of 30 Old 03-21-2019, 07:20 AM Thread Starter
Cjdemoines
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01' WJ engine trouble

My jeep is a quadradrive WJ, straight 6, 4.0. It idles smooth, and runs fantastic under load, but at higher speeds (35mph and above) it starts to run rough, only when the accelerator is released.
I have recently replaced the spark plugs, and the heads were rebuilt last year.
If anyone can point me towards the right diagnosis I would greatly appreciate it.

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post #2 of 30 Old 03-21-2019, 08:40 AM
jtec
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try a scan* - let us know .

A fuel pressure test, leak down, and vacuum gauge might help find issue.

Jeep is STOCK engine wise - no mods?

*SCAN not key on off.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 30 Old 03-21-2019, 09:05 AM Thread Starter
Cjdemoines
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Yes the engine is completely stock, I will scan the onboard today and see if it's throwing any codes.
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post #4 of 30 Old 03-21-2019, 12:47 PM
jtec
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you will need to use a SCANNER - not the key on off .

Scans are free at many auto parts stores.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #5 of 30 Old 03-21-2019, 03:25 PM
Mattyjm
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Quote:
Originally Posted by Cjdemoines View Post
My jeep is a quadradrive WJ, straight 6, 4.0. It idles smooth, and runs fantastic under load, but at higher speeds (35mph and above) it starts to run rough, only when the accelerator is released.
I have recently replaced the spark plugs, and the heads were rebuilt last year.
If anyone can point me towards the right diagnosis I would greatly appreciate it.
What spark plugs did you put in?

2000 Laredo. Now a donor vehicle to my
2002 Laredo. Baloo. Currently a work in progress.
2004 Rocky Mountain Edition. Froggy Bandit. Wife's Daily Driver. PRISTINE! Stock height and may stay that way.....
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post #6 of 30 Old 03-21-2019, 04:05 PM
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My guess is an air problem. Intake or exhaust.



Simple stuff like pcv and air filter good?
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post #7 of 30 Old 03-22-2019, 06:05 AM Thread Starter
Cjdemoines
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I used autolite platinums, I don't remember the exact part number offhand.
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post #8 of 30 Old 03-22-2019, 06:19 AM Thread Starter
Cjdemoines
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I also changed the air filter about 300 miles ago, but I will take a look at the pic fittings and make sure they are up to snuff.
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post #9 of 30 Old 03-22-2019, 06:43 AM
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Do these vehicles have an EGR valve?
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post #10 of 30 Old 03-22-2019, 06:58 AM Thread Starter
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It does in fact have the egr valve, I am planning to completely replace it shortly.
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post #11 of 30 Old 03-22-2019, 07:13 AM
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Quote:
Originally Posted by Cjdemoines View Post
It does in fact have the egr valve, I am planning to completely replace it shortly.
Another possible culprit. Good luck.
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post #12 of 30 Old 03-22-2019, 07:19 AM Thread Starter
Cjdemoines
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Now I've got a nice long list of possible repairs, I'm gonna run with this for a while and see if I can resolve the issue. Thanks to everyone for helping me out and I will post here any updates or changes.
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post #13 of 30 Old 03-22-2019, 07:54 AM
jtec
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I would suggest you SCAN for codes - as suggested above.

Put correct plugs on the shopping list,
Let us know if there is a schraider valve on fuel rail, we want to do some tests..
And not worry to much about the EGR or PIC fittings?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #14 of 30 Old 03-22-2019, 08:10 AM
JGCJeep
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Quote:
Originally Posted by jtec View Post
I would suggest you SCAN for codes - as suggested above.

Put correct plugs on the shopping list,
Let us know if there is a schraider valve on fuel rail, we want to do some tests..
And not worry to much about the EGR or PIC fittings?
What’s a PIC fitting?
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post #15 of 30 Old 03-22-2019, 08:11 AM
JGCJeep
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Was the problem happening before you replaced the spark plugs?
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