dragula
NAXJA Forum User
- Location
- Nashville TN
1999 Jeep Cherokee (4x4)
135,000 Miles
4.0 I6
---------------------------------------------------------------------------------------
Initial Symptoms-
Occasionally while slightly pressing the gas pedal (such as pulling out of a parking space) there would be a slight delay in throttle response. It would not be a typical miss… it would just bog down ever so slightly and then take off as normal and function as normal for the remainder of the trip. The problem was very intermittent and so I never tried to diagnose the issue.
---------------------------------------------------------------------------------------
The Downfall-
On a trip we were driving with cruise control on at 75mph when there was a sudden quick buck of the vehicle as if it had a quick miss. It continued on down the road without stalling then bucked twice as if it were having further running issues. We took the next exit and had trouble with it missing, bucking and sputtering as we tried to get into the nearest gas station.
No check engine light came on during this time.
We then had it towed to the closest Jeep dealer to have it diagnosed. I had a Jeep that had a fuel pump going out that had similar symptoms and asked them to check if that was the problem. They recommended that I needed a tune up with Ignition Coil, Distributor Cap, Rotor, Spark Plugs and Wires. I then asked them if they had checked the fuel pressure at the rail and they assured me that it was in fact the coil causing the issue. Since the repairs were fairly simple I did them myself and replaced the-
-Ignition Coil
-Distributor Cap
-Rotor
-Spark Plugs
-Plug Wires
Unfortunately the Jeep ran exactly as it had before with the stumbling and missing issues. I then thought that it might be possible that a sensor was causing the issues and proceeded to replace the-
-Idler Air Control Motor
-MAP Sensor
-Air Temp Sensor
-Coolant Temp Sensor
After these parts the Jeep still had the same problem, running rough especially when between 1000-2000 RPM and at this point it was only occurring under load for the most part (in drive). I pulled one of the plugs and it already appeared to be covered in black which should indicate a rich running condition.
I then decided to see if a dead spot in the Throttle Position Sensor was causing the issues and replaced the-
-Throttle Position Sensor
At that point it wouldn’t run very well at all. We decided it was time to take it to a professional. They went through their diagnosis and replaced-
-Crank Position Sensor
-Coil (again)
-Cam Position Sensor
-Wiring to the coil (this seemed to be the real issue)
After their work it ran well for about a week and started having intermittent misfires again. At that point I decided to source another wiring harness to replace the one on the vehicle in case other wires were in bad shape as well.
After replacing the wiring harness it still had missfire issues and for the first time threw a code p1391 for intermittent loss of Crank or Cam Sensor, which had already been replaced.
I read that the upstream O2 sensor can sometimes cause intermittent issues and replaced that as well, but it did not seem to help it either.
I called the second shop and they think that the bad wiring might have damaged the computer. At that point I sourced a used computer to replace mine. I installed it and it will only run for 2 seconds and then shut off. I think this is some sort of a immobilization anti theft device on the new computer that is causing it. Can the dealership reset this computer for my application?
Any ideas on what it might be other than the computer? It used to buck and miss on the highway the worst and now it just does it on start up (during the first five minutes) After that it is usually fine.
Lucky for me this is my smog testing month and I have to get it fixed (can't show a check engine code)… but I am so tired of paying both professionals and doing work myself without any results.
Any new ideas are appreciated-
Main Issue
-Intermittent Missing and Bucking - Code P1391
Parts Replaced
-Ignition Coil (x2)
-Distributor Cap
-Rotor
-Spark Plugs
-Plug Wires
-Idler Air Control Motor
-MAP Sensor
-Air Temp Sensor
-Coolant Temp Sensor
-Throttle Position Sensor
-Crank Sensor (x2)
-Cam Sensor
-Upstream O2 sensor (Downstream was done about a year ago)
-Wiring Harness
Soon to be replaced – the computer if I can get it programmed correctly?
After two months of working on this and trying to diagnosis it my love for the 4.0 is coming into question... I guess I can't complain when it's my 1991 450,000 mile jeep that still is getting us from Point A to Point B-
If you made it through all that reading, thanks-
135,000 Miles
4.0 I6
---------------------------------------------------------------------------------------
Initial Symptoms-
Occasionally while slightly pressing the gas pedal (such as pulling out of a parking space) there would be a slight delay in throttle response. It would not be a typical miss… it would just bog down ever so slightly and then take off as normal and function as normal for the remainder of the trip. The problem was very intermittent and so I never tried to diagnose the issue.
---------------------------------------------------------------------------------------
The Downfall-
On a trip we were driving with cruise control on at 75mph when there was a sudden quick buck of the vehicle as if it had a quick miss. It continued on down the road without stalling then bucked twice as if it were having further running issues. We took the next exit and had trouble with it missing, bucking and sputtering as we tried to get into the nearest gas station.
No check engine light came on during this time.
We then had it towed to the closest Jeep dealer to have it diagnosed. I had a Jeep that had a fuel pump going out that had similar symptoms and asked them to check if that was the problem. They recommended that I needed a tune up with Ignition Coil, Distributor Cap, Rotor, Spark Plugs and Wires. I then asked them if they had checked the fuel pressure at the rail and they assured me that it was in fact the coil causing the issue. Since the repairs were fairly simple I did them myself and replaced the-
-Ignition Coil
-Distributor Cap
-Rotor
-Spark Plugs
-Plug Wires
Unfortunately the Jeep ran exactly as it had before with the stumbling and missing issues. I then thought that it might be possible that a sensor was causing the issues and proceeded to replace the-
-Idler Air Control Motor
-MAP Sensor
-Air Temp Sensor
-Coolant Temp Sensor
After these parts the Jeep still had the same problem, running rough especially when between 1000-2000 RPM and at this point it was only occurring under load for the most part (in drive). I pulled one of the plugs and it already appeared to be covered in black which should indicate a rich running condition.
I then decided to see if a dead spot in the Throttle Position Sensor was causing the issues and replaced the-
-Throttle Position Sensor
At that point it wouldn’t run very well at all. We decided it was time to take it to a professional. They went through their diagnosis and replaced-
-Crank Position Sensor
-Coil (again)
-Cam Position Sensor
-Wiring to the coil (this seemed to be the real issue)
After their work it ran well for about a week and started having intermittent misfires again. At that point I decided to source another wiring harness to replace the one on the vehicle in case other wires were in bad shape as well.
After replacing the wiring harness it still had missfire issues and for the first time threw a code p1391 for intermittent loss of Crank or Cam Sensor, which had already been replaced.
I read that the upstream O2 sensor can sometimes cause intermittent issues and replaced that as well, but it did not seem to help it either.
I called the second shop and they think that the bad wiring might have damaged the computer. At that point I sourced a used computer to replace mine. I installed it and it will only run for 2 seconds and then shut off. I think this is some sort of a immobilization anti theft device on the new computer that is causing it. Can the dealership reset this computer for my application?
Any ideas on what it might be other than the computer? It used to buck and miss on the highway the worst and now it just does it on start up (during the first five minutes) After that it is usually fine.
Lucky for me this is my smog testing month and I have to get it fixed (can't show a check engine code)… but I am so tired of paying both professionals and doing work myself without any results.
Any new ideas are appreciated-
Main Issue
-Intermittent Missing and Bucking - Code P1391
Parts Replaced
-Ignition Coil (x2)
-Distributor Cap
-Rotor
-Spark Plugs
-Plug Wires
-Idler Air Control Motor
-MAP Sensor
-Air Temp Sensor
-Coolant Temp Sensor
-Throttle Position Sensor
-Crank Sensor (x2)
-Cam Sensor
-Upstream O2 sensor (Downstream was done about a year ago)
-Wiring Harness
Soon to be replaced – the computer if I can get it programmed correctly?
After two months of working on this and trying to diagnosis it my love for the 4.0 is coming into question... I guess I can't complain when it's my 1991 450,000 mile jeep that still is getting us from Point A to Point B-
If you made it through all that reading, thanks-
