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Unread 12-29-2013, 04:53 AM   #31
86cj74.2L
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Go buy a scan tool that also reads live data its money well spent.

After buying it I'd look at the LTFT's for bank 1&2.

However looking at those require correctly operating O2 sensors. If they have over 150,000 miles its worth thinking about.

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Unread 12-29-2013, 04:54 AM   #32
WJDaddyTrick
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Check the fueling. Get the fuel meters checked on an obd2 scanner.
Sounds exactly like the symptoms I had when the mixture was wrong. If the fuel meters are off it'll run too rich ( or lean ) and give those symptoms.

May point to the fault. Likely need the O2 censor cleaning or replacing now.
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Unread 12-29-2013, 05:09 AM   #33
86cj74.2L
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You already verified you have the correct fuel pressure at the fuel rail, correct?
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Unread 12-29-2013, 12:09 PM   #34
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Any recommendations on a scan tool that reads live data? Is there anything out there that works with a PC or smartphone to reduce cost (without compromising functionality)?

I assume that when you say "check the fueling", it is something that would be done using this scan tool? Is that correct?

I did check the fuel pressure - duct-taping the gauge to the windshield and driving. It was in the 50PSI range. The needle did start jumping around (flickering) when the car started jerking. I assumed that the flickering was from something the computer was doing - from the injectors "open-time" varying rapidly. Is this a bad assumption? I had replaced both the filter/regulator and the in-tank pump before doing this measure. Is there a way to probe the 12V feeding the pump to make sure it is staying there steady?
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Unread 12-29-2013, 12:53 PM   #35
86cj74.2L
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What is meant by flickering. 5psi? 20psi

It could've a failing fuel pump
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Unread 12-29-2013, 07:20 PM   #36
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The pump (and regulator/filter) had just been replaced when I finally did the pressure test. The flickering was a sort of fast twitching of the gauge needle, like a blur. Seemed to stay centered at the 50PSI, but flickering maybe +/-10PSI. It was as if the gauge was seeing fast pressure pulsations.

When the Jeep was not jerking, the needle reading was very stable.
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Unread 12-29-2013, 08:17 PM   #37
86cj74.2L
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You need a scan tool that reads live data or a friend that has one and knows what he's looking at.

What's your volt gauge do when this is happening?

How are the braided ground straps that go from the firewall to each injector rail/ ignition coil area.

There was a thread a few months ago about those ground straps. I deleted the pictures from my phone.
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Unread 12-29-2013, 10:53 PM   #38
runningonempty
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Keep posting. I too have a 2004 GC and I have the same problem which I mitigated a bit by replacing the throttle body due to a vacuum leak. Yes you may have a vacuum leak in some of the hoses.
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Unread 01-03-2014, 02:13 PM   #39
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The Jeep is fixed. Believe it or not, it was the Park/Neutral switch.

I have to confess that I caved (again) and took it to a shop. A different one this time, and apparently an honest one. I'll be doing business with them in the future. I told them the whole story and what I had done to it so far. They checked/rechecked a bunch of things, kept a computer connected while test driving and had a fuel pressure gauge taped to the windshield just like I had done previously. After four hours of diagnosing they were still stumped. 6 hours and several test drives into it, the tech replaced the P/N switch, just to eliminate that code, and surprisingly the problem was gone.

That P1899 code has been thrown on this Jeep for years with no symptoms. I'd clear it, and in a few weeks it would come back. The internet said that this sensor told the computer that the car was in Park or Neutral so that cranking would be allowed. It always cranked fine, so I ignored it. Apparently the failure progressed recently, and this lagging/jerking problem emerged. The technician could see that the old sensor was consistently reading that it was in Park/Neutral while driving. Maybe it was previously just glitching occasionally, but recently became more constant.

So why would this cause the lag/jerk problem I've been having? The folks at the shop were not sure, and were surprised that it did, but theorized that the computer was doing some kind of partial rev-limiting/fuel cutoff action. Based on my symptoms, the computer must have ignored this input for the first few minutes, then started paying attention to it. I can't explain why the engine responded so inconsistently the way it did.

Thanks for all your help and guidance through this diagnosis. This was my first Jeep Forum thread, and a great experience.
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Unread 01-15-2014, 06:10 PM   #40
cr8zynelly
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Any updates on the Jeep? Still running good after the P/N switch replacement?
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Unread 01-19-2014, 07:07 PM   #41
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The P/N Switch still seems to have been the problem. I'm hyper-observant now, and have noticed a bit of roughness in the idle, and a shift now and then that is not a smooth as it should be. I still need to give the throttle body a better clean out. That might help with the idle.

But the big problem I was having is gone. It was not subtle - it was a major jerking / bucking hard when I tried to accelerate hard. I'm still surprised that it was the P/N switch causing that behavior. And yes, I feel stupid because that was the one code set through the process.

My Jeep was failing by reporting Park/Neutral when in Drive, so it always cranked fine. But when the computer sensed that it was in Park/Neutral when at highway speeds, I suppose it assumed it was Neutral, and apparently activated some kind of aggressive fuel limit to prevent over-revving. Hope this helps someone else if they ever have the same problem.
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Unread 01-21-2014, 06:24 PM   #42
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I was about to tell you check compression. I had the same thing happen and turned out to be a blown head gasket and fixed it. Seems same scenarios just different fixes with everyones jgc can be very frustrating.
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Unread 01-21-2014, 09:56 PM   #43
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I've been having the same problem which I fixed a bit with the vacuum leak. But it still bucked just not as bad. So because of your thread I had the P/N switch replaced (it was only a $75 repair at the dealer). Seems to run better, I don't get the bucks but I haven't takin it out for the cruise control/interstate test yet. I'll get back to you guys when I do.
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Unread 01-25-2014, 09:52 PM   #44
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Quote:
Originally Posted by runningonempty View Post
I've been having the same problem which I fixed a bit with the vacuum leak. But it still bucked just not as bad. So because of your thread I had the P/N switch replaced (it was only a $75 repair at the dealer). Seems to run better, I don't get the bucks but I haven't takin it out for the cruise control/interstate test yet. I'll get back to you guys when I do.
Well shoot! She passed the interstate/cruise control test! Yup it musta been the park/neutral switch. After I had the vacuum leaks repaired she ran better in town but I still had the bucks driving it on the interstate especially going up hill with the cruise on. Well I took her out and waddaya know, no bucks!
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Unread 01-29-2014, 10:05 AM   #45
shaggyz1
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Have same problem, but it just started happening after I replaced the tps. It is actually stalling while at Highway speeds. First looses power when accelerating, then accelerator stops working and she stalls. Get to side of road, start her up, and she runs fine for about 10 mins. All this is preceded by transmission shifting all over the place. TPS replaced last weekend as it was stalling when cold, after it warmed up all was good. Trans working fine for years before that. MAP sensor?? anything else I can check. Really seems like a sensor thing. Ideas??
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