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Unread 06-10-2008, 11:06 AM   #1
zpedrick
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1999 TJ Wrangler 
 
Join Date: Sep 2007
Location: Pedricktown, NJ
Posts: 38
misfire when I hit a bump

Hey everyone, I have this problem that's really starting to piss me off... Every time I hit a bump in the road my engine sputters/miss fires. Sometimes the rpm gauge shows the rpm's going up really high or down and sometimes it doesn't change at all. I've gotten an error code before, 1391 (way to be descriptive Jeep). Also the up shift light would come on in 5th gear, but I think if you need one of those lights, you should drive an automatic, so I removed the bulb, don't know if it's still doing that. I've replaced the cam shaft position sensor, but it hasn't fixed the problem. So the only other things I can think of are, cam shaft position sensor, or the computer (ECU) or something else??? It's a 99 6-cyl 5-speed. So just a couple questions, hopefully someone knows...

1.) What controls the rpm gauge (i know it's not simple but is it the cam or crank position sensor (or both))?

2.) If I do a tune up on the ignition system http://www.quadratec.com/products/17610_60X_PG.htm will it also replace the crank position sensor? (My guess is yes since it requires an adapter plug, just want to make sure.)

3.) If I were to replace the computer, A.) Can I do it myself=(read B) B.) Do I have to also replace the gauge cluster (I remember reading something somewhere that the cluster and computer will no work if only one of them is replaced). Does it have to be programmed at a dealership?

4.) Could it be the knock sensor?

Sorry for the long post, but I've asked a lot of people and everyone shrugs, someone's got to have at least an idea. If I can't fix this thing I'm going to gut the entire Jeep and "upgrade" to an LS2. But I don't want to do that, I'm broke! THANKS


Last edited by zpedrick; 06-10-2008 at 11:21 AM..
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Unread 06-10-2008, 11:28 AM   #2
mdm
Farm Wheeler
2000 TJ Wrangler 
 
Join Date: Apr 2005
Location: Elkmont, AL
Posts: 9,723
There's no knock sensor on your Jeep.

If you have a miss when you hit a bump it sounds like you have an electrical problem. A loose plug, a broken wire, ... Something is opening when you hit a bump. Simulate the bumps by shaking the wiring, moving plugs, move the coil rail, etc.
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Unread 06-10-2008, 11:28 AM   #3
klimb2xs
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2005 LJ Wrangler 
 
Join Date: Apr 2007
Location: Iowa
Posts: 497
Here are a few things I would check.
Plug wires and rotor wire. One of these could be bad, shorting out or opening, causing a drop in RPM.
TPS - Could be dirty
Wiggle all of the electrical conectots while the engine is running. Inspect the wiring harnes for and bare wires that could be shorting to ground.
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Unread 06-10-2008, 12:07 PM   #4
Jerky bump
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2003 TJ Wrangler 
 
Join Date: Jan 2007
Location: Ontario
Posts: 1,179
..engine ground.. battery clamps..corroded terminals
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Unread 06-10-2008, 01:57 PM   #5
zpedrick
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1999 TJ Wrangler 
 
Join Date: Sep 2007
Location: Pedricktown, NJ
Posts: 38
PROOF that jeeps have a personality

I have living (dead) proof that jeeps have a personality... SHE JUST DIED hahaha. It wasn't 30 minutes after I posted this, pulled into the florist parking lot (a dozen roses for the lady). The lady in the store said don't leave these in your car in this heat (101.F) or they'll wilt, I said yeah, I know. Went out to start the Jeep, and she sputtered and then quit, it turns over but wont start. The Jeep must have gotten jealous, or mad that I was talking about it. Oh well, I'll let the mechanic figure it out, it's too hot to mess with it today. Thanks people, I'll post when I find out what it was.
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Unread 06-10-2008, 09:50 PM   #6
BigDaddyChoice
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2000 TJ Wrangler 
 
Join Date: Jun 2007
Location: Toronto, ON
Posts: 136
Quote:
Originally Posted by zpedrick View Post
Every time I hit a bump in the road my engine sputters/miss fires. Sometimes the rpm gauge shows the rpm's going up really high or down and sometimes it doesn't change at all.
Is the backfire from the exhaust or the intake manifold?

If the backfire is from your tailpipe (imbalance in air to fuel ratio where fuel is too rich), then I had the exact same problem this past winter.
My mechanic and I spent weeks diagnosing and trying to recreate the problem, but when the Jeep was stationary, nothing ever happened. There was never a code recorded when hooked up for diagnostics.
There were times when the Jeep ran great for days and then other times, the RPM would shoot up and down and the engine threatened to stall.
I ended up replacing the throttle position sensor, and the idle air control sensor -- but to no avail.

Finally, my Jeep stalled on me in February and I could not restart it. I had it towed to my mechanic's shop where finally, he found the culprit...

It was a broken wire from the ignition coil that, from time to time whenever I hit a bump in the road, a bare wire would make contact with the engine block and short out. Keep in mind that this is the same cluster of wires that he considered as a possible cause previously.

He had to strip the protective plastic loom to uncover a single wire (from the dozens) that had a tiny tear in the plastic covering that would intermittently cause me grief.

Once properly spliced, soldered, heat shrinked and tied back in under the loom, the problem never came back.
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Unread 06-11-2008, 07:26 AM   #7
zpedrick
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1999 TJ Wrangler 
 
Join Date: Sep 2007
Location: Pedricktown, NJ
Posts: 38
Quote:
Originally Posted by BigDaddyChoice View Post
Is the backfire from the exhaust or the intake manifold?

If the backfire is from your tailpipe (imbalance in air to fuel ratio where fuel is too rich), then I had the exact same problem this past winter.
My mechanic and I spent weeks diagnosing and trying to recreate the problem, but when the Jeep was stationary, nothing ever happened. There was never a code recorded when hooked up for diagnostics.
There were times when the Jeep ran great for days and then other times, the RPM would shoot up and down and the engine threatened to stall.
I ended up replacing the throttle position sensor, and the idle air control sensor -- but to no avail.

Finally, my Jeep stalled on me in February and I could not restart it. I had it towed to my mechanic's shop where finally, he found the culprit...

It was a broken wire from the ignition coil that, from time to time whenever I hit a bump in the road, a bare wire would make contact with the engine block and short out. Keep in mind that this is the same cluster of wires that he considered as a possible cause previously.

He had to strip the protective plastic loom to uncover a single wire (from the dozens) that had a tiny tear in the plastic covering that would intermittently cause me grief.

Once properly spliced, soldered, heat shrinked and tied back in under the loom, the problem never came back.
Ok, sounds exactly like my problem, i'll look at it asap. THANKS!
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