P1391 and Jeep runs fine

I have a 97 Cherokee Sport, 4.0, manual that runs good. I had the engine overhauled in April while we were in the Phoenix area. When I got it back, it did not have nearly the same power as it did before it was rebuilt. I took it by the shop on short notice one day and they had a quick look and said for me to put some miles on it.

At the end of May I drove the Jeep to Colorado. I had to downshift a lot on hills and spent a fair amount of time in the slow lane with the 18 wheelers. I was convinced something was wrong with the engine.

Once in Colorado, I had the engine "smoked" to look for any vacuum leaks and none were found. After that we pulled the cap off the distributor and decided to move it back one tooth because the rotor was halfway between #1 and #5 post. While we were at it, we replaced the distributor because of shaft wear and oil in the bottom of it. In the new position the engine would crank but would not start. We eventually moved it back to where it was. (I've since seen a picture on this forum showing where it should be and that is where it was and is now.) While we were trying to figure out why it wasn't starting with the distributor move, we got a code about the CKP so we installed a new one. At the end of the day, the Jeep was back running just like it was at the beginning of the day with a new (reman) distributor and a CKP.

One thing I did notice that day was low manifold vacuum. Depending on whose gauge you used it was either 8" or 10" HG at idle. When I called the shop in Phoenix, they said that low vacuum was not right and asked if I could let them look at it. I drove it back to Phoenix and in less that 4 hours they had discovered the cam timing was off and had it fixed.

The engine felt strong. After my first fuel stop on the way back to Colorado, the CEL comes on. My scanner told me it was P1391 so I wiggled the wires around the distributor and erased the code. I drove the next 200 miles with no CEL. Shortly after I started from the next fuel stop, I got the CEL again.

So here I am now with the Jeep running good, with a reman distributor, a new CKP sensor and a P1391 code. I can erase the code and it will come back after the second start. I have checked the connections with a ohmmeter back to the PCM and don't find a wiring problem. I have erased the PCM memory and it didn't help.

Since there were no codes before the cam was re-timed, I'm thinking the cam position sensor may have to be moved.

Anyone have an idea of what I should try next? I'm about ready to take it to a Jeep dealer to see if they can do something,

Did you buy genuine Jeep sensors, or cheap crappy Chinese "Lifetime Warranty" parts ?


P1391 JEEP - CMP or CKP Signal Intermittent Condition.
Possible causes:

- Faulty Camshaft Position (CMP) Sensor
- Faulty Crankshaft Position (CKP) Sensor
- Camshaft Position (CMP) Sensor harness is open or shorted
- Camshaft Position (CMP) Sensor circuit poor electrical connection.
- Timing belt or chain stretched or jumped

P1391 JEEP Description: The ECM detected the actual Camshaft Position Sensor (CMP) position disagreed with the expected CMP level.

The distributor is a Cardone reman and the CKP is a BWD Automotive. Neither were cheap and both were ok for the 900 mile trip to Phoenix.
Thanks for the reply.

Tim_MN said:

Did you buy genuine Jeep sensors, or cheap crappy Chinese "Lifetime Warranty" parts ?

Click to expand...

This.

The last BWD boxed part I purchased was made in CHINA. Now, while we all would expect that BWD would have an on-sight engineer ensuring quality control in the Chinese factory, in our heart-of-hearts we know that isn't how it is done.

Sorry, but just having an "old time" part name on the box is NO GUARANTY of quality.

Is the OP still around? I've got a similar problem. During an engine rebuild I replaced the distributor with an A1 cardone unit, and reused the original CPS (207K, worked fine prior). I've got the P1391 CEL but everything runs just fine. The CEL comes on after I park it, then start it the second time around. If I reset the CEL, it comes back on second time, every time.

Yes, I'm still here. The Jeep still runs good but the CEL is on all the time. I occasionally will reset it just to make sure there are no codes other than the P1391.

I'm convinced that the cam timing is slightly different than what the PCM expects. The engine rebuilder used the "split overlap" method to time the cam the second time. This is different from the Jeep service manual.

It says to line up the timing marks on the cam and crank sprockets. Then to verify, count the number of chain link pins between the marks when the cam sprocket mark is at 3 o'clock. There should be 15 pins. (7-1/2 links).

I'm thinking one of these days I'll pull the cover off and count the pins.

Thanks for the reply but that's not what I wanted to hear. :-/

I haven't gotten a chance to play with my CEL yet for all the typical P1391 issues (replace CPS with new Mopar sensor, try the toothpick trick, try installing the old distributor, try rotating the distributor slightly within the crow's foot/bolt hole, etc.).

Have you tried replacing the CPS with a Mopar sensor?

Did you use a stock cam? Or Upgrade? I have no idea what method my engine rebuilder used for timing the cam. Mine has good power consistent with the cam profile, no misfiring issues or power loss.

I sent you a PM.

Were either of you able to finally fix it? I've had the P1391 code for almost 2 years now, replaced Cam and Crank sensor, new coil pack, checked all grounds, checked vacuum lines at manifold, and sacrificed a goat to try to clear the code. Same thing happens every time, code is clear until I stop and restart the Jeep.

It started when I was left stranded with a no-start. Local garage changed the sensor under the dist. and got it running again, but then the CEL light came on and I've been chasing it ever since.

Got any updates?

Thanks.

@Jdunning - No updates here. I still have the check engine light and everything still runs great. I'm glad you chimed in though, because I replaced the OE distributor with an A1Cardone rebuilt. My first step trouble-shooting will be to replace with A1Cardone distributor in the Jeep now back with the OE I had in it before.

My money is on that.

Sidenote... I did fix my exhaust leak which should cut down on the heat the CPS is seeing.

Mine is still the same. Runs fine with the check engine light on. It started when the cam timing was changed.

Grits4jim said:

.......I can erase the code and it will come back after the second start. I have checked the connections with a ohmmeter back to the PCM and don't find a wiring problem. I have erased the PCM memory and it didn't help.

Since there were no codes before the cam was re-timed, I'm thinking the cam position sensor may have to be moved.

Anyone have an idea of what I should try next? .....

Click to expand...

OBD II will only set a code when the PCM sees the
second consecutive fault, that's why the CEL stays off
for the first restart after clearing the code.

As for moving the cam sensor, that's what I'd try.
Maybe trim off the plastic index tabs and move it
about 1/4 inch each way and see what that does...?

Well, this is an update on a real old thread. I don't drive the Jeep very much these days, it still runs well with the CEL on all the time. This past weekend I decided to fix this.

My plan was to modify the cam sensor somehow to make it think the cam was retarded some. Remember, the CEL was not on with the cam retarded and the new distributor.

When I pulled the distributor cap off, I saw that it was not like the one shown in my service manual. After looking at the internet, I realized that the new distributor that I had bought was for a Renix system. The Renix engine control system was used in XJs from 1987-1991. My Jeep is a 1997. At the time both the counter man and the service technician said it was the right one and I didn't know any different.

I bought a new distributor yesterday. I opened it at the parts store to make sure it was right and installed it. The CEL is OFF! I've started it 3 times and the light has not come on.

Hopefully, this is the end of this thread.

Thanks for the update!