99 PCM replace/update
Thread Starter
CF Veteran
Joined: Jun 2016
Posts: 1,011
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From: CO
Year: 99
Model: Cherokee (XJ)
Engine: 4.0
how did you go checking the female harness pins for loose ? other than visual nothing, but I'll fiddle closer tomorrow
did you clear all codes with a reader ?
I have before, but I'll see if I can't get my hands on it tomorrow.
If your truck is running fine, the chances of a bad wires are low imo
I am of the belief you will have symptoms if PCM earths are affected, not just codes.
did read a thread where a guy ran earth wire to PCM, due to a failure, his truck would not run.
This would suggest PCM earth is same as -ve, so an ohmeter between PCM earth and body should show a very low resistance (if this is correct)
ohm the pcm body to the vehicle? Otherwise i believe the pcm takes a few grounds, but A4 is our cam/crank ground.
You said you "thought" you may have a miss...either you do, or dont..how does it manifest itself? there's a constant shutter that rpm tacky shows. It's light but present while idling. If it's not misfire, Idk what it is.
access to a scope is probably needed to further diagnose the situation imo
awaiting this mechanic to return from vacation, I hope I can get pictures instead of putting money on a tool I can almost guarantee will never be used again.
as the flywheel is one of the few common parts, I once again suggest checking its runout
did you clear all codes with a reader ?
I have before, but I'll see if I can't get my hands on it tomorrow.
If your truck is running fine, the chances of a bad wires are low imo
I am of the belief you will have symptoms if PCM earths are affected, not just codes.
did read a thread where a guy ran earth wire to PCM, due to a failure, his truck would not run.
This would suggest PCM earth is same as -ve, so an ohmeter between PCM earth and body should show a very low resistance (if this is correct)
ohm the pcm body to the vehicle? Otherwise i believe the pcm takes a few grounds, but A4 is our cam/crank ground.
You said you "thought" you may have a miss...either you do, or dont..how does it manifest itself? there's a constant shutter that rpm tacky shows. It's light but present while idling. If it's not misfire, Idk what it is.
access to a scope is probably needed to further diagnose the situation imo
awaiting this mechanic to return from vacation, I hope I can get pictures instead of putting money on a tool I can almost guarantee will never be used again.
as the flywheel is one of the few common parts, I once again suggest checking its runout
do we assume no run out to be present us normal, or just extremely little? How much run out is worth raising an eyebrow to?
CF Veteran
Joined: Jan 2017
Posts: 3,438
Likes: 417
From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
Is the new distributor correctly installed and indexed? Is it a Mopar part?
Check the 0.020" gap.
http://cruiser54.com/?p=68
https://www.cherokeeforum.com/f2/cru...ip-why-203927/
https://www.autoinc.org/hard-start-mystery/
Check the 0.020" gap.
http://cruiser54.com/?p=68
https://www.cherokeeforum.com/f2/cru...ip-why-203927/
https://www.autoinc.org/hard-start-mystery/
CF Veteran
Joined: Jan 2017
Posts: 3,438
Likes: 417
From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
Thread Starter
CF Veteran
Joined: Jun 2016
Posts: 1,011
Likes: 20
From: CO
Year: 99
Model: Cherokee (XJ)
Engine: 4.0
Is the new distributor correctly installed and indexed? mopar distributor was indexed 4 times to be sure. replacement I indexed twice to be sure. The first time re-index was done because it wouldn't start, I had it 180 out on the exhaust stroke, easy fix. it a Mopar part? Mopar no longer makes dustributors, not to happy here, I would've likely gotten one.
no change on either distributor, each index other than the first whoops, was followed to the FSM.
Check the 0.020" gap. looking up what this is.
http://cruiser54.com/?p=68
https://www.cherokeeforum.com/f2/cru...ip-why-203927/
https://www.youtube.com/watch?v=xRHW0i3V6qM
https://www.autoinc.org/hard-start-mystery/
no change on either distributor, each index other than the first whoops, was followed to the FSM.
Check the 0.020" gap. looking up what this is.
http://cruiser54.com/?p=68
https://www.cherokeeforum.com/f2/cru...ip-why-203927/
https://www.youtube.com/watch?v=xRHW0i3V6qM
https://www.autoinc.org/hard-start-mystery/
Thread Starter
CF Veteran
Joined: Jun 2016
Posts: 1,011
Likes: 20
From: CO
Year: 99
Model: Cherokee (XJ)
Engine: 4.0
1.5yrs into this code on my one and only vehicle, this has been quite difficult.
CF Veteran
Joined: Jan 2017
Posts: 3,438
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From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
This would also necessitate having 2 different causes for the 1391, and not being so far out that it shuts down the fuel system. But looking is cheap (maybe the price of an old distributor cap if you don't use the scribe technique).
CF Veteran
Joined: Jan 2017
Posts: 3,438
Likes: 417
From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
Thread Starter
CF Veteran
Joined: Jun 2016
Posts: 1,011
Likes: 20
From: CO
Year: 99
Model: Cherokee (XJ)
Engine: 4.0
Too true sir, learned to little to late there. I had a few caps around, I think I tossed them. Cruisers post is odd, I'm not a renix motor, but I do believe the stock pin hole does not like being smoothly installed to TDC settings. His reference to dropping it in a 4 o clock is baffling, whatttttt! The locator is about 1-2 before you drop it in to get it to line up. The littlest but off, likely a tooth or it wouldn't seat, and the retaining hole wouldn't line up at all.
CF Veteran
Joined: Mar 2016
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Year: 96
Model: Cherokee (XJ)
Engine: 4.0
if your tacho shows a RPM flutter, something is amiss there, and needs to be investigated.
a PCM controlled engine should have rock steady idle
BAFX code reader is about $20, hooks up to Anrdroid phone via Bluetooth,,has an electronic tacho, live data, clears codes in seconds, to your door in a couple of days, leave it connected to OBD port ?
have you been able to find, or do any research on other instances of P1391 code setting ?
for the flexplate, nothing fancy, just to rule it in/out...if a dial gauge shows truth to within say 0.02" that might be ok, but twice that might not,
doubtful, I expect it would make some noise if it was bad
a PCM controlled engine should have rock steady idle
BAFX code reader is about $20, hooks up to Anrdroid phone via Bluetooth,,has an electronic tacho, live data, clears codes in seconds, to your door in a couple of days, leave it connected to OBD port ?
have you been able to find, or do any research on other instances of P1391 code setting ?
for the flexplate, nothing fancy, just to rule it in/out...if a dial gauge shows truth to within say 0.02" that might be ok, but twice that might not,
doubtful, I expect it would make some noise if it was bad
Thread Starter
CF Veteran
Joined: Jun 2016
Posts: 1,011
Likes: 20
From: CO
Year: 99
Model: Cherokee (XJ)
Engine: 4.0
Oh yeah, she was hydro locked alright. Poor thing ran like a champ even before pulling the engine.
Thread Starter
CF Veteran
Joined: Jun 2016
Posts: 1,011
Likes: 20
From: CO
Year: 99
Model: Cherokee (XJ)
Engine: 4.0
Looking back it seems in may 18 I had p0340 and replaced cam sensor which resolved that issue, then august 18 p01391. Hydrolock was a full year before this.
Last edited by 4x4jeepmanthing; Jun 29, 2019 at 01:02 AM.
CF Veteran
Joined: Jan 2017
Posts: 3,438
Likes: 417
From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
Try disconnecting the TCM and see if the 1391 disappears. It seems as though there is a relationship between the CPS and the speed sensors.
CF Veteran
Joined: Jan 2017
Posts: 3,438
Likes: 417
From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0