Rough idle after head and cam replacement
Thread Starter
Member
Joined: Jul 2010
Posts: 126
Likes: 4
From: Knoxville TN
Year: 1998
Model: Cherokee (XJ)
Engine: 4.0
From what you have said , before you, for whatever reason, put a cam and an aluminum head on an engine with 340k on it it ran fine with no codes. Only problem was the lifter noise.
Now:as I understand it:
1) it idles bad and sometimes backfires out the exhaust
2 it's setting an injector code on cylinder 4, but swapping injectors around doesn't move the code. The noid light doesn't show a problem
3) it has NOT set a misfire code, which is interesting.
I have no idea what's wrong with the thing but pretty clearly it occurred after all parts were replaced. Compression is ok, fuel pressure is ok, I really wonder if timing ( ignition or injector) is off on cylinder 4. Put the old distributor AND the old pickup back in and see what happens. There have been a lot of horror stories about replacement distributors having the gear 180 off, who knows what else could be wrong with it.
(Also,btw. You did all this work because of "horrible lifter knock" how did you confirm the noise was actually lifter knock and which cylinder was it?)
Now:as I understand it:
1) it idles bad and sometimes backfires out the exhaust
2 it's setting an injector code on cylinder 4, but swapping injectors around doesn't move the code. The noid light doesn't show a problem
3) it has NOT set a misfire code, which is interesting.
I have no idea what's wrong with the thing but pretty clearly it occurred after all parts were replaced. Compression is ok, fuel pressure is ok, I really wonder if timing ( ignition or injector) is off on cylinder 4. Put the old distributor AND the old pickup back in and see what happens. There have been a lot of horror stories about replacement distributors having the gear 180 off, who knows what else could be wrong with it.
(Also,btw. You did all this work because of "horrible lifter knock" how did you confirm the noise was actually lifter knock and which cylinder was it?)
Thread Starter
Member
Joined: Jul 2010
Posts: 126
Likes: 4
From: Knoxville TN
Year: 1998
Model: Cherokee (XJ)
Engine: 4.0
Thread Starter
Member
Joined: Jul 2010
Posts: 126
Likes: 4
From: Knoxville TN
Year: 1998
Model: Cherokee (XJ)
Engine: 4.0
CF Veteran
Joined: Jan 2017
Posts: 3,413
Likes: 399
From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
Also, valves are adjustable (sorta). Is the preload correct?
https://www.cherokeeforum.com/f2/new...stment-213117/
https://www.cherokeeforum.com/f2/new...stment-213117/
Thread Starter
Member
Joined: Jul 2010
Posts: 126
Likes: 4
From: Knoxville TN
Year: 1998
Model: Cherokee (XJ)
Engine: 4.0
Okay, I put the old dizzy back in it runs but seems the same, but now I have a P0500 code after driving it around the block.
Last edited by J/D/S; Jan 24, 2024 at 09:25 AM.
Thread Starter
Member
Joined: Jul 2010
Posts: 126
Likes: 4
From: Knoxville TN
Year: 1998
Model: Cherokee (XJ)
Engine: 4.0
Thread Starter
Member
Joined: Jul 2010
Posts: 126
Likes: 4
From: Knoxville TN
Year: 1998
Model: Cherokee (XJ)
Engine: 4.0
Also, valves are adjustable (sorta). Is the preload correct?
https://www.cherokeeforum.com/f2/new...stment-213117/
https://www.cherokeeforum.com/f2/new...stment-213117/
CF Veteran
Joined: Jan 2017
Posts: 3,413
Likes: 399
From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
If all the "maybe" reasons for P0204 have been ruled out, even though you inspected wiring IIWM I'd take the cause of P0204
and vet that out.
You can do that one of 3 ways:
1. Get a DRBIII tool and analyze (probably can't find one);
2. Get a SnapOn MT2500 or equivalent (very expensive).
3. Get an entry-level oscilloscope (about 150 bucks).
The above screen shows what the normal almost normal waveforms of a Cherokee 4.0 injector look like (one of mine AAMOF). Explanation T/F (if necessasry) but all you really need to do is compare the 6 injector waveforms. If (when) it shows that circuit is bad you can focus on the wiring or the driver (new PCM).
The injector current falls below a calibrated threshold
You can do that one of 3 ways:
1. Get a DRBIII tool and analyze (probably can't find one);
2. Get a SnapOn MT2500 or equivalent (very expensive).
3. Get an entry-level oscilloscope (about 150 bucks).
The above screen shows what the normal almost normal waveforms of a Cherokee 4.0 injector look like (one of mine AAMOF). Explanation T/F (if necessasry) but all you really need to do is compare the 6 injector waveforms. If (when) it shows that circuit is bad you can focus on the wiring or the driver (new PCM).
Last edited by Dave51; Jan 24, 2024 at 11:09 AM.
CF Veteran
Joined: Jan 2017
Posts: 3,413
Likes: 399
From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
From a ScannerDanner presentation. His injector open hump is more defined. My screenshot might have been my old injectors. Forgot.
Last edited by Dave51; Jan 24, 2024 at 11:18 AM.
Thread Starter
Member
Joined: Jul 2010
Posts: 126
Likes: 4
From: Knoxville TN
Year: 1998
Model: Cherokee (XJ)
Engine: 4.0
what am I using the gauge on, the factory vacuum lines? I wouldn't think a vacuum leak would be an issue since i have all the vacuum port in the intake capped off.
I'll give the intake a look, but other then taking it off is there an easier way to check it?
I'll give the intake a look, but other then taking it off is there an easier way to check it?
CF Veteran
Joined: Jan 2017
Posts: 3,413
Likes: 399
From: Connecticut
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0