High Fuel Pressure, Misfires and Low Idle
#31
CF Veteran
When you get a chance to look at it. If it won't start...then turn the key to the on position. Note the position of the voltmeter and the fuel level gauge. If they are "dead"...Then this list of symptoms is a hallmark for a failing crankshaft position sensor. Particularly on your year of XJ. (No computer comms, dead voltmeter and fuel gauge, ignition problems after warming up, and misfires). The fact that it is not starting now, might just mean it has finally completely failed.
I wonder if the mechanic scoped the cam and crank sensor signals while the problem was present.
Any crankshaft or camshaft sensor replacements in the recent past?
I wonder if the mechanic scoped the cam and crank sensor signals while the problem was present.
Any crankshaft or camshaft sensor replacements in the recent past?
#32
Member
Thread Starter
Join Date: Sep 2014
Posts: 122
Likes: 0
Received 3 Likes
on
2 Posts
Year: 2001
Model: Cherokee
Engine: 4.0
When you get a chance to look at it. If it won't start...then turn the key to the on position. Note the position of the voltmeter and the fuel level gauge. If they are "dead"...Then this list of symptoms is a hallmark for a failing crankshaft position sensor. Particularly on your year of XJ. (No computer comms, dead voltmeter and fuel gauge, ignition problems after warming up, and misfires). The fact that it is not starting now, might just mean it has finally completely failed.
I wonder if the mechanic scoped the cam and crank sensor signals while the problem was present.
Any crankshaft or camshaft sensor replacements in the recent past?
I wonder if the mechanic scoped the cam and crank sensor signals while the problem was present.
Any crankshaft or camshaft sensor replacements in the recent past?
#33
Junior Member
Join Date: Feb 2018
Posts: 68
Likes: 0
Received 0 Likes
on
0 Posts
Model: Cherokee(XJ)
Engine: 4.0L I6
Sorry for your headache and frustration and what was a seemingly bad pressure gauge and subsequent misdiagnosis. Jordan gives solid advice and knows his crap. His recent post on troubleshooting a bad ignition coil is particularly helpful. Sorry again.
#34
CF Veteran
When you went through all that trouble to replace the pump, but it also had the high pressure, that fact is pretty strange. Did you ever get a chance to confirm that pressure with another gauge? or the mechanic?
If they were both truly high, that would be well worth troubleshooting first.
If they were both truly high, that would be well worth troubleshooting first.
#35
Member
Thread Starter
Join Date: Sep 2014
Posts: 122
Likes: 0
Received 3 Likes
on
2 Posts
Year: 2001
Model: Cherokee
Engine: 4.0
FINAL UPDATE (I hope). Went to the mechanic today and started running electrical tests. After a stressful amount of research I learned that no PCM connection usually means a short somewhere in the 5v circuit. The previous owner had replaced the PCM along with a multitude of parts trying to chase down this issue that everyone in the Cherokee forum seems to have. When I purchased it, I noticed the oil pressure sensor was broken which was not a concern since I went through 3 of them on my other XJ. This doesn't effect the performance of the vehicle.......usually. Turns out there is a 5v line going to the oil pressure sensor and guess what? That's where my short was. Removed the connecting harness and the Jeep fired right up. I'm guessing the mechanic must have hit the sensor when installing the new coil rail. So, I'm still not sure if the rail was actually faulty, but I'm just so relieved to have fixed the issue, I do not care. The mechanic was nice enough, despite what happened and let me use some of his tools and helped me relocate a ground.
No more misfire, no more rough idle, purrs like a kitten. RPM is still a bit low (in my opinion) but the engine does not sound like it's struggling whatsoever.
My advice to anyone with the famous XJ misfire problem. CHECK YOUR ELECTRICAL!!!! IT"S PROBABLY A SHORT SOMEWHERE!!!!!!!! I've probably read every single XJ misfire forum out there. Nobody ever solves it because they keep throwing parts at the problem. Nobody ever tests their electrical which is stupid because it's free to do. I should have done that from the beginning but do not be like me. DO NOT THROW PARTS AT THE PROBLEM!!!!!
No more misfire, no more rough idle, purrs like a kitten. RPM is still a bit low (in my opinion) but the engine does not sound like it's struggling whatsoever.
My advice to anyone with the famous XJ misfire problem. CHECK YOUR ELECTRICAL!!!! IT"S PROBABLY A SHORT SOMEWHERE!!!!!!!! I've probably read every single XJ misfire forum out there. Nobody ever solves it because they keep throwing parts at the problem. Nobody ever tests their electrical which is stupid because it's free to do. I should have done that from the beginning but do not be like me. DO NOT THROW PARTS AT THE PROBLEM!!!!!
#36
CF Veteran
My advice to anyone with the famous XJ misfire problem. CHECK YOUR ELECTRICAL!!!! IT"S PROBABLY A SHORT SOMEWHERE!!!!!!!! I've probably read every single XJ misfire forum out there. Nobody ever solves it because they keep throwing parts at the problem. Nobody ever tests their electrical which is stupid because it's free to do. I should have done that from the beginning but do not be like me. DO NOT THROW PARTS AT THE PROBLEM!!!!!
As a follow up, do you think the high fuel pressure thing was just a bad pressure gauge? Now that the comms are back online, you could use a scanner to check your fuel trims and double check that it isn't doing anything strange.
#38
Junior Member
Join Date: Feb 2018
Posts: 68
Likes: 0
Received 0 Likes
on
0 Posts
Model: Cherokee(XJ)
Engine: 4.0L I6
Agreed. Many people get very intimidated by electrical.
As a follow up, do you think the high fuel pressure thing was just a bad pressure gauge? Now that the comms are back online, you could use a scanner to check your fuel trims and double check that it isn't doing anything strange.
As a follow up, do you think the high fuel pressure thing was just a bad pressure gauge? Now that the comms are back online, you could use a scanner to check your fuel trims and double check that it isn't doing anything strange.
#40
CF Veteran
If we are talking about a 5v line, then definitely not. Voltage to the pump can easily be measured at the fuel pump relay, just as the amperage can.
#41
Member
Thread Starter
Join Date: Sep 2014
Posts: 122
Likes: 0
Received 3 Likes
on
2 Posts
Year: 2001
Model: Cherokee
Engine: 4.0
Agreed. Many people get very intimidated by electrical.
As a follow up, do you think the high fuel pressure thing was just a bad pressure gauge? Now that the comms are back online, you could use a scanner to check your fuel trims and double check that it isn't doing anything strange.
As a follow up, do you think the high fuel pressure thing was just a bad pressure gauge? Now that the comms are back online, you could use a scanner to check your fuel trims and double check that it isn't doing anything strange.
#42
Member
Thread Starter
Join Date: Sep 2014
Posts: 122
Likes: 0
Received 3 Likes
on
2 Posts
Year: 2001
Model: Cherokee
Engine: 4.0
TPS
MAP Sensor
crankshaft position sensor
Camshaft position sensor
Oil Pressure Sensor
Vehicle Speed Sensor
I think these were two unrelated issues or perhaps the short was messing with my PCM and throwing everything off. I haven't gotten the chance to check the fuel pressure again.
Thread
Thread Starter
Forum
Replies
Last Post
Max Conrad
Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go here
19
12-13-2018 09:33 AM
Lars_XJ99
Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go here
1
08-06-2018 04:03 PM
darren509
Stock Grand Cherokee Tech. All ZJ/WJ/WK Non-modified/stock questions go here!
53
07-11-2016 07:20 PM
Chad'sCheep
Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go here
21
01-04-2016 09:39 PM
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)