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  #1  
Old October 11th, 2010, 23:19
zluster's Avatar
zluster zluster is offline
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P1391:

Back Story:

Installed 44k mile 01 engine in a 96 XJ(new rotor, cap, plugs and wires), ran it for awhile today and I have a pretty regular misfire/stumble and a CEL.

Code shows P1391, cleared and then started up, comes back after a few seconds. Seems to me that the CPS usually just goes, and doesn't cause a problem like this.

Reading around shows something about CKPS/CPS synchronization, but everything I read indicates this is on 2000+ with the Distributorless ignition. I've also seen other distributored owners talking about doing the synchronization.

I've read the couple of articles posted
http://autorepair.about.com/library/faqs/bl850d.htm
http://motorage.search-autoparts.com...30/article.pdf

I can find TDC easy enough, but, where the heck are we talking about putting in the toothpick?

Am I even barking up the right tree looking for my misfire here?
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  #2  
Old October 11th, 2010, 23:42
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yossarian19 yossarian19 is offline
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Re: P1391:

Quote:
Originally Posted by zluster View Post
Back Story:

Installed 44k mile 01 engine in a 96 XJ(new rotor, cap, plugs and wires), ran it for awhile today and I have a pretty regular misfire/stumble and a CEL.

Code shows P1391, cleared and then started up, comes back after a few seconds. Seems to me that the CPS usually just goes, and doesn't cause a problem like this.

Reading around shows something about CKPS/CPS synchronization, but everything I read indicates this is on 2000+ with the Distributorless ignition. I've also seen other distributored owners talking about doing the synchronization.

I've read the couple of articles posted
http://autorepair.about.com/library/faqs/bl850d.htm
http://motorage.search-autoparts.com...30/article.pdf

I can find TDC easy enough, but, where the heck are we talking about putting in the toothpick?

Am I even barking up the right tree looking for my misfire here?
No direct experience, though I do hear rumors and fables of CPSes failing intermittently and frequently due to thermal failure. You can test the CPS like so

CPS TESTING PROCEDURE 1991 – 2001 4.0L H.O. engines

1. Near the rear of intake manifold, disconnect sensor pigtail harness
connector from main wiring harness.
2. Place an ohmmeter across terminals B and C (A-B-C) looking into
connector left to right with the part with the notch in the middle on
the right) Ohmmeter should be set to 1K-to-1OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace
sensor if a low resistance is indicated.
4. Rattle the CPS with a screwdriver & zap it with a heat gun while the car is running. Any changes? If so... replace the CPS.
CPS TESTING PROCECURE for 1987 – 1990 4.0 L engines

Test # 1

Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the CPS
and measure across the CPS connector's A & B leads. Your meter should
show a CPS resistance of between 125 - 275 ohms. If the CPS is out of
that range by much, replace it.

Last edited by yossarian19; October 11th, 2010 at 23:46.
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  #3  
Old October 12th, 2010, 13:42
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zluster zluster is offline
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Re: P1391:

Ok so I tested it via that procedure, I see nothing wrong there, appears to be an open circuit via my multimeter.

I ran it some more, when it idles it will hunt for idle and surge some(which I could attribute to other things), but during the process it will run rough and miss, and then run smooth, and then run rough and miss, etc.

Which brings me back to the synchronization thing....... anyone have any input for me there?
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Old October 12th, 2010, 13:50
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zluster zluster is offline
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Re: P1391:

Oh, I should also mention, I ran it at idle for a few minutes and the code did not reappear, it was not untill I revved up the engine that it came back.
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  #5  
Old October 12th, 2010, 16:32
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zluster zluster is offline
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Re: P1391:

Ok so I did more research and reading, the resyncronization stuff I was reading had to deal with the tone ring inside the distributor having gotten out of place, the toothpick in the hole was meant to realign the ring so that it fired at the correct time.

I then read another thread that talked about the little bit of play when the bolt is loose, you can turn the distributor a whole whopping degree or two with the bolt in place. Someone said to try the other end of the spectrum and see if it was any different in reference to a renix XJ. Well I tried that, turns out at the one end of the just few degrees difference I had it would just stall and not start or run.

So I took the bolt out, rotated it past where the bolt hole aligned and used a screwdriver to hold it in place. Started it up, ran smooth and idled nice, no more missing and hunting idle.

So that means I was off a tooth on the distributor (just one) and had lucked out(or not lucked out because it caused me more problems) with the one or two degree's that it can be adjusted and would barely run, had I tightened the distributor down just slightly different it would not have run at all, and I would probably have tried to adjust it by one tooth at the beginning of the day.

So I looked at it, saw which way made the improvement to the timing, and then saw that meant I needed to "retard" the timing by one tooth.

Now because the oil pump is driven off the bottom of the distributor shaft that means you cannot simply pull the dizzy up, turn it, and put it back down. IF you do this you get the tooth alignment right, but the end of the shaft will not re-engage the oil pump(unless you then have a helper to just tap the key and turn the engine over a little untill it engages and the dizzy goes down all the way, or you have a helper to turn the engine over by hand with a socket and breaker bar on the engine crank pulley bolt.)

So that means you have to pull it up, stick a straight screwdriver in, and turn the oil pump by hand untill the shaft direction seems to closely match where it needs to point on the dizzy.

Took me a few tries, but I got it, Jeep runs smooth and sounds good! Glad I didn't blow $50 on a new CPS - which also tested fine BTW.

Lesson learned, even one tooth off it would still run, but just one more degree and it would not.
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  #6  
Old December 9th, 2010, 06:32
RAHS93 RAHS93 is offline
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Re: P1391:

I just wanted to say thank you. I have been working on my brothers 98 limited for 3mons. This thing has been missing and unable to rev passed 1500rpm. I have pulled open the harness,changed sensors,and computer. I was so sure it was an electrical problem I got tunnel vision. As soon as I read what you did with tthe distributor I said I'm an idiot. 15 mins. later a was smoking the tires in the parking lot at work.
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