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Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go hereXJ (84-01)
All OEM related XJ specific tech. Examples, no start, general maintenance or anything that's stock.
So from what I can gather, the P1391 has occurred on 2 entirely different engines (except for the flexplate)? You put new sensors on the old engine, but reused them on the new engine? What year is the replacement engine?
Flex plate is off the 99.
New engine is 92 block,95 head, all 99 hardware and sensors.
Flex plate is off the 99.
New engine is 92 block,95 head, all 99 hardware and sensors.
There's at least a minor difference between OBDI and OBDII flexplates (diameter). Did you fully explore their interchangeability? The forum discussions are not clear on this point (some weird stuff about 60° clocked difference and you have to shift the distributor a tooth).
The P1391 on the 2 engines could be for 2 different reasons.
I imagine pulling the flexplate out would be the last thing on the troubleshooting list...
There's at least a minor difference between OBDI and OBDII flexplates (diameter). Did you fully explore their interchangeability? The forum discussions are not clear on this point (some weird stuff about 60° clocked difference and you have to shift the distributor a tooth).
The P1391 on the 2 engines could be for 2 different reasons.
I imagine pulling the flexplate out would be the last thing on the troubleshooting list...
My research said use the same Flex plate that matches the sensors.
Any strange noises coming from around the flexplate?
Yes, it has a knock sound. With a wrench on the pan you hear it Better, but when you put it on the starter you really here it clearer, but it's tight tight on the torque converter, and I can't see any cracks.
I wouldnt accept his money back, but thank him for his time so far...
7 degrees, did you say earlier that was right on the max ?...is that 7* of slack ? I can't find the source I read this from, I can't find it in the fsm for my 99.
I dont have much experience with chains wearing & stretching, but it does happen on engines with high mileage, set a code on models with electronics
there should be be other people that know all about Jeep timing chains, the XJ has a pretty robust looking arrangement..the GM Alloytec not so much
Originally Posted by Dave51
"If the timing chain deflects more than 12.7 mm (1/2 inch) replace it."
where is that measurement taken from?
Originally Posted by awg
I am suggesting making piggyback wires with safety pins to probe the connectors. So the original & piggyback will be in place..(unless a short is suspected)
Yes to one at a time. Clearly you need to be sure on which wire is which!...you seem to have that info.
If the sensor has an earth wire to the PCM, that has to be duplicated..each wire to the suspect sensor/s
start, check CEL, try again should the CEL go away right away if this works?
I have personally used this method to find some weird electrical faults
If your truck starts and runs perfectly, I do not see how it can be the crank or cam sensor
(all subject to you checking the chain slack, I think you can remove the dizzy & rotate the engine to check)
if I havent done something wrong here, I back probed harness side to pcm on all signal,supply, ground wires for cmps,ckps,pins pushed in until the sopped. I made sure nothing felt loose. Each time I disconnected the battery which always ditches the CEL, so I had to start to start up twice each time to make sure the code was firing or not. I did all six wires, CEL never went away. vehicle was at operating temp, i shut it down and moved wires as soon as CEL showed up.
Last edited by 4x4jeepmanthing; 06-22-2019 at 07:38 PM.
afaic, a code clearing device is needed to clear CEL, unless the PCM capacitors are drained by a process of short battery terminals, headlights on for 30secs etc etc..otherwise the code will be retained by the PCM ?
now that is cleared up, are you saying you had a code P1391, changed your entire engine, and have it still, on a another engine! (albeit with original flexplate) ??
If the above are both true, and you have eliminated the common possible causes of harness & PCM
what else is common apart from flexplate ?..dizzy ? sensors ?
as a matter of logic, you would think it has to be a common component
possibly may have read a post about the issue of later/earlier sensors & flexplates causing issues when swapped,
I would be curious the correct gap between crank sensor and flexplate
afaic, a code clearing device is needed to clear CEL, unless the PCM capacitors are drained by a process of short battery terminals, headlights on for 30secs etc etc..otherwise the code will be retained by the PCM ? I can repeat this today and put positive terminal to the negative and then the headlights, i always wondered if this made a difference because the CEL dissapears if you disconnect a battery terminal. either way ill try this method and make sure we have all stones unturned to drain the capacitors.
now that is cleared up, are you saying you had a code P1391, changed your entire engine, and have it still, on a another engine! (albeit with original flexplate) ?? this is correct, new engine same code,original 99 flex plate
If the above are both true, and you have eliminated the common possible causes of harness & PCM i believe i have gone through the procedure according to your description, i will redo this today with the headlight trick. We know my matching replacement pcm did not work upon disconnecting old, plugging in new- second start CEL still shows up.
what else is common apart from flexplate ?..dizzy ? sensors ? 99 flex plate retained from old motor, supposedly all 90-99 flex plates are the same, the 4.0 block is a 4.0 block so no change to how it bolts up. Dizzy is new by 2 months-no change to code, sensors almost 2years old,but diagnostic + multimeter showing these are synced/ transmitting to PCM. 92 block, 95 7120 head, all 99 everything else.
As far as the CKPS, this has no adjustability by design, this is a 99 ckps reading a 4.0 99 flex plate. the question here- is there any logical reason to replace a sensor that is shown to be reading by scope diagnostic and multimeters? all sensors are mopar. AW4 is the 99 as well, though the code is unrelated.
P1391 code checklist:
Alternator- 1month napa new, no change in code Ignition coil- 3 months new napa echlin, no change in code Dizzy/cap rotor- 3 month new, changed out original 222,000 mopar unit in case gear was worn, no change in code Flex plate- stock 99, all TC bolts tight Tone wheel- dizzy is new, old tone wheel well intact also Harness- back probed harness to PCM continuity, signal, 5v supply, gr-ound confirmed on digital multimeter twice, analog multimeter twice, Shop Scope diagnostic once- signals to PCM in sync and verified ckps- mopar less than 2 year old, replaced from car dying while driving before p1391 was ever seen. visual and plug connection confirmed, ohm test completed. cmps- mopar less than 2 year old, replaced on old engine for p1391 in attempt to fix code, new engine still shows code. anaolg meter voltage verified,visual and plug connection confirmed magnet solid and in place. Old mopar cmps tried for the heck of it- results in hesitation starting. timing chain- timing chain and slack pictured in above posts, 7 degree from 0 on counter clockwise rotation until dizzy rotor turns, new donor rebuilt engine 4 months installed with estimated 30,000 miles on it. others-? pcm, JY pcm matching year and number tried based on shop diagnostic recommendation, no change after disconnecting battery,plugging in donor pcm, start shutdown, restart- CEL returns
as a matter of logic, you would think it has to be a common component
possibly may have read a post about the issue of later/earlier sensors & flexplates causing issues when swapped, so far i read 90-99 use the same flex plate, mopar part number is revised, but this is what youll get as a replacement.
I would be curious the correct gap between crank sensor and flexplate
Now this is a new thought,but how is this achieved with an engine installed?
ill try whatever we can think of, this is really kicking my butt, open to suggestions guys
Last edited by 4x4jeepmanthing; 06-23-2019 at 05:26 AM.
Well here's an interesting tidbit-- P1391 is triggered when there are 20 failures in two consecutive trips. That would seem to explain the pattern.
There are differences in flexplates as previously noted, so IIWY I wouldn't completely discount that as the source of the issue. And since you've fired the parts cannon at literally everything EXCEPT that, as big of a PITA as it is, IMO you're getting pretty close to that.
That said, the sequence of events tends to preclude that as a possibility.
THAT said, there have been so many things done (and surprises along the way)(like "Oh BTW did I tell you this is a different engine?") I am in total bafflement.
So to regroup, what were the SPECIFIC conditions of the first appearance of the 1391?
Now this (the correct gap between crank sensor and flexplate) is a new thought,but how is this achieved with an engine installed?
Yeah, ya can't do that. Besides I don't think it's an air gap problem.
ill try whatever we can think of, this is really kicking my butt, open to suggestions guys
OK here's a thought. Instead of changing the air gap, change the position of the CPS over the reluctor windows. Put some shims under the CPS to move it out a little more.
Anyway, if my CPS was becoming thermally sensitive I'd want to know that sooner rather than later.
Let's remember this code will fire second start. Meaning I can turn on the engine cold, immediately shut it down and upon restart it'll be a CEL.
Again, FSM states the ckps bolts to be made so there's no play in its position, why would we want to shim this if we rule out heat? As Dave also says he's not thinking this is an air gap issue. Malfunctioning sensor then?
Whatcha thinking?
Last edited by 4x4jeepmanthing; 06-23-2019 at 04:03 PM.
06-20-2019 | 11:43 AM
