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Old 08-03-2013, 09:31 AM
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2001 Jeep WJ 4.7 Engine Stumble power loss

Hello Everyone,

I am new to your forum although I have read through many of your posts looking for possible solutions to my problem. Sorry for the long post.

My Jeep is a 2001 WJ 4.7 that we purchased new. It has been a great car and we have had few issues with it until this problem started almost a year ago.

My Jeep does what I call stumble it also quits on occasion but only when stopped or moving slowly such as backing out of a parking spot. When driving around town the Jeep will stumble, losing power, pressing the accelerator has no effect, the engine speed drops and then the Jeep lurches as the power is regained and will continue on normally until it repeats the stumble / loss of power issue. The duration of the stumble varies sometimes it is momentary and sometimes lasts 2 - 3 seconds. No engine light comes on and it has never stalled in this situation while at speed driving down the road.

No engine light or codes have been identified while the Jeep has been exhibiting these symptoms.

Took it to a local dealer after being frustrated with the problem. Supposedly they found a P201 code and replaced injector #1 and said all was fine. This did not resolve or change the issue so I scheduled another appointment and left the car for 2 days. When I called back they said it was the PCM, I explained I had already replaced the PCM a couple times but they insisted that was the problem so under warranty from the PCM manufacturer I exchanged the PCM again. No change in stumble issue.

Gave up on dealer and back to working on the issue myself.

I have continuity tested, ground tested, and tested for short to voltage all injectors, coils, cam and crank position sensor, IAC, and TPS wiring harnesses while pulling, wiggling, harnesses and connectors no issues found. Checked and cleaned as many grounds and connectors as I can find related to the engine, PCM, etc. all connectors looked good no corrosion or moisture in any connectors.

Tested fuel pressure and volume both are normal, but is it possible there is an intermittent issue and a brief loss of fuel pressure could cause this symptom? Some times when the stumble occurs for a longer period of time it does somewhat feel like it is starving for fuel although when the issue is not occurring the Jeep runs very well good power accelerates normally etc. so I have not focused on the fuel pump and supply system.

Thanks in advance for any help or direction in troubleshooting this intermittent issue. I really don't want to get rid of the Jeep but am getting close to that point.


Parts replaced in the last 12 months:

PCM - Two different modules from one reman company and two from different company. - A couple of the PCM's introduced new issues but none have resolved the primary issue.
Fuel pressure regulator - Advance Auto
Crank position sensor - Chrysler
Cam position sensor - Chrysler
Transmission input sensor - Chrysler
Transmission output sensor - Chrysler
Throttle position sensor - Chrysler - improved idle & surging at stop
Idle control motor - Autozone - further improved idle
Fuel Injectors
Spark plugs
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Old 08-03-2013, 09:59 PM
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Re: 2001 Jeep WJ 4.7 Engine Stumble power loss

Welcome to the garage.
This kind of problem can be hard to solve due to its intermittent caracter.
Does the problem occur in any kind of circumstance, ie on cold engine or only on hot engine etc. The more details, the better we can close in on the culprit.
Did you check yourself for any fault code set after the problem showed up? If you don't have a scanner, do the key dance: ignition switch off/on three times and leave in on at the third time. The odometer will show DONE when all ok, or a fault code(s).
You changed already most of the sensors who could kill the engine and tested the wiring, so that should be ok. A bad fuel pump would slowly let it loose power and finally kill the engine, so won't expect this to be the problem.
Did you already try swapping the auto shut down relay in the power distribution center under the hood. When i remember well its the same as the transmission control relay. Ofcourse when the relay is bad, it would introduce an other problem in the transmission control, but you would see a difference in the engine operation.
Cam sensor, crank sensor and TPS all share the same 5 V sensor supply, but also the MAP sensor does. A short in one of these sensors will bring the 5 V supply down and the engine stops. But this is just a wild guess.
Just to be sure, key symbol from the SKIS system on the instrument panel doesn't light up when the problem arrises, does it?
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Old 08-03-2013, 11:06 PM
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Re: 2001 Jeep WJ 4.7 Engine Stumble power loss

Thanks for your response Frank.

The problem seems to occur more when the engine is at normal operating temp. and possibly when the car is loaded such as 3 or 4 passengers. I have not been able to determine any other consistencies.

Yes I continued to check for codes regularly since this issue started and have never found any other than those I intentionally generated by disconnecting injectors, iac, coils, etc.

Yes I have swapped the auto shutdown relay with no change in symptom.

No the SKIS indicator does not come on.

I was reading through the shop manual today and noticed the MAP sensor was also on the 5 volt supply circuit. I was considering swapping it out so since you mention it also I will give it a try tomorrow.

I also noticed today when test driving that when graphing the upstream O2 sensors they don't seem to switch consistently and will stay at a voltage level for a period of time. I think I will swap both upstream O2 sensors tomorrow as well.

Test driving today and monitoring fuel pressure I did not see any significant change in fuel pressure when the issue occurred although I did notice at various times generally when the engine was at lower RPM or decelerating the fuel pressure gauge would jump erratically between about 45 psi and 60 psi.

I appreciate any ideas you have that may help resolve this issue.

Thanks

Tim
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Old 08-04-2013, 01:31 AM
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Re: 2001 Jeep WJ 4.7 Engine Stumble power loss

Hi Tim, do you use a scanner which can show live data?
It would be interresting to see what the fuel trims are. A faulty O2 sensor could cause a negative fuel trim and a too lean mixture, eventhough the PCM could (or should) set a fault code for a too lean mixture and that it probably would start misfiring and set a code for that as well. At least it would be good to see if the trim for both banks are more or less equal.
But indeed the O2 sensors should change the voltage rapidly and if they stay for a longer period at the same voltage level, then the sensor could be faulty.
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Old 08-04-2013, 09:46 AM
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Re: 2001 Jeep WJ 4.7 Engine Stumble power loss

Hey Frank, I use a OBDII bluetooth adapter and my android phone and tablet which I run an application called "Torque". Yes this application gives some ability to display live data. You have to be careful to only capture a few live parameters or the display update will slow down.

I will see if I can capture the fuel trims. I know I can display them but not sure about logging and saving them.

I will post the results later today.

Thanks

Tim
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Old 08-04-2013, 10:02 AM
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Re: 2001 Jeep WJ 4.7 Engine Stumble power loss

Best would be to see how the trims are when running ok and at the moment the problem is there.
I did use the torque app before (the free one, cheapass me) , but I prefer my normal scanner.
I still would try the keydance once in a while to see if that comes up with any fault that is not shown on torque, just to be sure.
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Old 08-04-2013, 10:27 PM
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Re: 2001 Jeep WJ 4.7 Engine Stumble power loss

Well I replaced the upstream O2 sensors and the MAP sensor this morning and then went for a test ride. Initially it was running well and then after a few miles it started running rough when stopped and idling also black smoke out the tail pipe. Checked fuel trims with Torque app and discovered both short and long term fuel trim for bank 1 was 32.8% so i checked the O2 output and the bank 1 upstream O2 sensor was staying at .1 volt.

Let it cool down removed 1 - 1 0 O2 sensor and took it back for an exchange. Installed replacement O2 sensor and went for a test drive. Both upstream O2 sensors look normal when graphed with the Torque app now. Only drove for a short 20 or so mile test drive but during that drive car felt good and I did not have any of the stumbling issue.

I have used a different scanner through this trouble shooting process as well as the key dance and have only seen codes when I intentionally caused them. In each case the Torque app also showed the code. Today I received a bank 1 lean code when the bad O2 sensor was installed.

Keeping fingers crossed hoping either the O2 sensors or the MAP sensor resolved the problem. I will drive it for a few days and if it doesn't show the stumble issue I will re-install the old MAP sensor to try to determine what the real fix was.

I will reply tomorrow with an update.

Thanks

Tim
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Old 08-07-2013, 08:53 PM
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Re: 2001 Jeep WJ 4.7 Engine Stumble power loss

Tim,

Did you ever find out if it was the O2 sensor or the MAP sensor? I am having the symptoms that you have experienced.
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Old 08-08-2013, 05:22 AM
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Re: 2001 Jeep WJ 4.7 Engine Stumble power loss

I have not had the chance to swap in the old MAP sensor yet due to a lot of rain this week. I plan to swap in the old sensor this Friday and will post the results.

Thanks

Tim
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Old 08-11-2013, 12:13 PM
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Re: 2001 Jeep WJ 4.7 Engine Stumble power loss

After spending the last 2 months testing and trying to diagnose what was causing the same issues you were experiencing, I wanted to let you know what fixed my jeep (2000 Jeep GC with 4.7). I have been doing a lot of searching in the web and reading different forums trying to find other folks who were having the same trouble as myself. I did try changing the PCM after all the sensors tested ok and that did not help (sent it back). I bought 1 coil pack and tried swapping out all 8 of them, one at a time, once a day so I could drive and let them heat up to see if this would solve the problem, but that did not work either. I do have a scan tool, so I checked my O2 sensors and they seemed to be functioning correctly. I came across this thread, with was the most informative and helpful out of all the ones that I have found. I also noticed that a lot of folks do not respond and let people know what actually fixed the problem.

So I want to let you know that the MAP sensor ended up being the culprit.

Good luck with yours.

Steve
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Old 08-11-2013, 08:18 PM
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Re: 2001 Jeep WJ 4.7 Engine Stumble power loss

I swapped back in my old MAP sensor today to verify that the MAP sensor was the caused my issue. With the old MAP sensor installed the car went back to its old habit of stumbling etc. randomly. I reinstalled the new MAP sensor and it is back to running normally.

I also picked up almost 2 MPG after the replacement of the O2 and MAP sensors. Nothing to get too excited about but up from about 12.5 MPG to about 14.5 MPG. This showed up according to the overhead console computer as well as getting about 30 more miles out of the last tank of gas.

Steve,

I'm glad this thread helped you resolve your issue. I ran into the same thing you did when researching this issue on the web. Many threads that nobody ever posted the solution which is one reason I wanted to post my final results.

Frank,

Thanks for your help and insight on this issue!

Tim
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