P1391 Code Help!!!!!
Thread Starter
Seasoned Member
Joined: Oct 2015
Posts: 407
Likes: 25
Model: Cherokee
P1391 Code Help!!!!!
99 Xj 4.0
146,000
A little back story:
Okay so about 2 months ago my car died while driving. I pulled it over to a safe spot. The car had no spark. Read the code and it showed for tps. So I went to jeep and bought a new tps and installed it and it had the same problem. So after some trouble shooting it turned out to be the coil. The car ran great.
About a month ago I decided to do a full tune-up.
Cap and rotor
Taylor spark plug wires
Champion gapped to .035
Air filter
Ntk o2 up and downstream
Again the truck ran great until about a week ago. The motor felt like it was stumbling at idle. Almost like a misfire. I then figured it was a sensor on the throttle body so I swapped the iac, tps, and map all with working sensors.
My next step was to get a mechanical fuel pressure gauge and check the rail but on the way home it threw a p1391 code.
Is there any way of this being related or am I just over thinking it being the crank positioning sensor or cam position sensor???
146,000
A little back story:
Okay so about 2 months ago my car died while driving. I pulled it over to a safe spot. The car had no spark. Read the code and it showed for tps. So I went to jeep and bought a new tps and installed it and it had the same problem. So after some trouble shooting it turned out to be the coil. The car ran great.
About a month ago I decided to do a full tune-up.
Cap and rotor
Taylor spark plug wires
Champion gapped to .035
Air filter
Ntk o2 up and downstream
Again the truck ran great until about a week ago. The motor felt like it was stumbling at idle. Almost like a misfire. I then figured it was a sensor on the throttle body so I swapped the iac, tps, and map all with working sensors.
My next step was to get a mechanical fuel pressure gauge and check the rail but on the way home it threw a p1391 code.
Is there any way of this being related or am I just over thinking it being the crank positioning sensor or cam position sensor???
Last edited by BlackXJay; Mar 8, 2017 at 05:53 PM.
CF Veteran
Joined: Nov 2010
Posts: 5,841
Likes: 117
From: In the middle of Minnesota!
Year: 1999
Model: Cherokee
Engine: 4.0
Trust the code. Yup, a P1391 can be either a cam sensor OR a crank sensor. Or the wiring for those sensors too, for that matter.
The crank sensor is arguably one of the most common engine management sensor failures on the 4.0. If you plan on keeping your XJ, replacing it, you really wouldn't be wasting your money, ESPECIALLY if this is the original crank sensor. Is it original?
You can test both sensors with a meter and a manual, but unless you test them when they are failing, they will likely test within spec. But I'd test em anyway to see if data yields any clues.
And if you've seen my posts, you know that I'm not a big fan of aftermarket for either of these sensors. Good luck and keep us updated!
The crank sensor is arguably one of the most common engine management sensor failures on the 4.0. If you plan on keeping your XJ, replacing it, you really wouldn't be wasting your money, ESPECIALLY if this is the original crank sensor. Is it original?
You can test both sensors with a meter and a manual, but unless you test them when they are failing, they will likely test within spec. But I'd test em anyway to see if data yields any clues.
And if you've seen my posts, you know that I'm not a big fan of aftermarket for either of these sensors. Good luck and keep us updated!
Last edited by tjwalker; Mar 8, 2017 at 07:06 PM.
Thread Starter
Seasoned Member
Joined: Oct 2015
Posts: 407
Likes: 25
Model: Cherokee
Yes they both are original from what I know. I bought the truck from my uncle so I will contact him but I'm almost positive they are original. If one was failing could it cause the rough idle?