4.0l stumbling above 1700rpms - Page 2 - JeepForum.com

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post #16 of 40 Old 07-17-2013, 08:59 PM Thread Starter
bigb229
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Well I put pressure on top of the sensor while it was tightened to make sure it was seated firmly. It is hard to crank as the ECM is advancing the timing nearly 30 degrees. Once it starts it idles great. Give it some fuel and around 1700 rpms it starts to stumble and bust up really bad.

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post #17 of 40 Old 07-17-2013, 09:02 PM Thread Starter
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I put in the four port Bosch injectors. They are rebuilt and warranties and working. We're getting like .4 ohms resistance through the grounds and 5 volts on the supply. No resistance to speak of in the signal wires .....this is testing from signal terminal to signal wire at sensor
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post #18 of 40 Old 07-17-2013, 11:17 PM
dellis
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Deleted.
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post #19 of 40 Old 07-17-2013, 11:33 PM Thread Starter
bigb229
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It's got to be something like that. We can reset the timing to 0degrees at tdc pointing slightly past one as the fsm says....it'll crank run for awhile. Switch it off and it's trying to adjust it 30 degrees advanced.....
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post #20 of 40 Old 07-17-2013, 11:35 PM Thread Starter
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My dad has been a diesel mechanic for over thirty years and thinks this is the craziest thing he's ever seen
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post #21 of 40 Old 07-17-2013, 11:41 PM
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Quote:
Originally Posted by bigb229 View Post
It's got to be something like that. We can reset the timing to 0degrees at tdc pointing slightly past one as the fsm says....it'll crank run for awhile. Switch it off and it's trying to adjust it 30 degrees advanced.....
By the way, I removed that post simply because I couldn't find any reference that would correlate that problem with your symptoms ... I am not one to send people down random holes looking for gold.
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post #22 of 40 Old 07-17-2013, 11:44 PM Thread Starter
bigb229
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Can't blame you. We just don't have the tools at home to run a full diagnostic on it like they do at the dealership. It's gonna set my wallet on fire but its worth a shot.
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post #23 of 40 Old 07-18-2013, 04:49 AM
ZeeJay1997
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Dellis, there's nothing wrong with grasping at straws. Sometimes its the only option and sometimes it works. This is is most likely something that was disturbed during the engine change so we have to cover all the bases.

OP, the 30* advance you are speaking of... it seems like when I was looking at mine on the scanner, it would advance up to 30 initially. Will check this AM when i go to work.

Sorry i was vague about the injectors, I meant to check across the coil of the injector. They should all be 11-13 ohms i believe... dont have time to look it up
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post #24 of 40 Old 07-18-2013, 08:01 AM
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Originally Posted by ZeeJay1997 View Post
Dellis, there's nothing wrong with grasping at straws.
OK ... I'll repeat it ...

The camshaft and crankshaft signals can be misaligned. Large misalignments are corrected by mechanically adjusting the timing chain, but once the chain is on the proper teeth then the signals also need to be fine tuned if they are out of alignment by more than 4 degrees. Proper alignment looks like the two oscilloscope traces below, where the rise and fall of the cam signal (the upper trace) occurs midway between the sets of four pulses coming from the crankshaft position sensor (the lower trace):



The reason I removed the earlier post is that I don't know how an engine behaves (or the PCM compensates) if it is, say 5 or 6 degrees out of alignment. When I measured these signals on my jeep with an oscilloscope, they were about 2 to 3 degrees out of alignment, and the PCM was handling that just fine - no apparent problems.

The fine-tuning of the alignment can only be done through a setting in the PCM, and one needs to have access to either the Chrysler or Snap-on interface.
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post #25 of 40 Old 07-18-2013, 05:45 PM
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Quote:
Originally Posted by dellis View Post
The fine-tuning of the alignment can only be done through a setting in the PCM, and one needs to have access to either the Chrysler or Snap-on interface.
Why couldn't you turn the distributor and use the pulses to sync it?

I checked my start up timing this AM with scanner. It initially advanced 11 degrees, then warmed up at 4.
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post #26 of 40 Old 07-18-2013, 08:17 PM
dellis
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Quote:
Originally Posted by ZeeJay1997 View Post
Why couldn't you turn the distributor and use the pulses to sync it?
I've never played with the timing, but all the experts say that timing cannot be manually adjusted on a ZJ.
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post #27 of 40 Old 07-18-2013, 08:41 PM
ZeeJay1997
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I dont think it's a setting in the PCM, I really don't know. All I know is the c cam signal needs to be fine tuned after you remove and replace distro. Seems like if you can see both signals and you know what the synchronization should be, you could do it by moving the distro.
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post #28 of 40 Old 07-18-2013, 09:38 PM Thread Starter
bigb229
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The distributor has an ear on it that bolts to the block it can't be turned to advance or retard the timing. We can manually hold it in and get it running fairly well at high or low rpm but not both
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post #29 of 40 Old 07-18-2013, 10:26 PM
dellis
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Quote:
Originally Posted by ZeeJay1997 View Post
I dont think it's a setting in the PCM, I really don't know. All I know is the c cam signal needs to be fine tuned after you remove and replace distro. Seems like if you can see both signals and you know what the synchronization should be, you could do it by moving the distro.
Again, I have not done this. But I was concerned earlier this year that my cam and crank were off synch by 2-3 degrees, and I wanted them perfectly aligned. All my research pointed to (a) it cannot be done manually and (b) you have to have a Chrysler DRB or a Snap-on Scanner or some other $10,000 interface to the PCM in order to fine-tune the synchronization ... at least with my '98.
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post #30 of 40 Old 07-19-2013, 07:08 AM
ZeeJay1997
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On the other hand, I've seen people on this board that have used the "TDC - 5 oclock" method and it ran like a top.

Op, I'm going to ask the obvious here because I've seen people in similar situations that overlooked the simple things...

Are the plug wires on the cap in the right order?
Is the cap cracked?
Is the rotor cracked?

Have you taken the MSD coil off and tried another one?

I'm also curious to know if you checked the sensor supply voltage.
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