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  #1  
Old December 13th, 2006, 19:21
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'91 XJ HO NO SPARK SOLVED

I've done a lot of searching and reading on this site, but I haven't posted any so let me give a little background. I have a '91 XJ with the HO and AW4 tranny, they were wore out when I got it so I found a '89 with a good engine/tranny and bought it for parts. I used the 89 short block and tranny, the 91 transfer case although I had to swap input shafts due to one being 21 spline and the other being 23 spline, I had the HO head rebuilt, swapped over all accessories and sensors and slapped it in. It purred like a kitten after ironing out a couple of little bugs after starting it, but when I took it out for the maiden voyage this past Sunday it didn't go so well. I drove it around for a couple of hours, which included trails, steep hills, and mud and then we stopped to build a fire. After sitting at the fire for about an hour it wouldn't start, no fire from the coil, so my buddy who is a mechanic by trade and I started troubleshooting as best we could in the middle of nowhere. We thought we narrowed it down to the coil (didn't really think that was it) or the crank position sensor so we set out to get the parts. Put them on and nothing still, turned out to be the distributor pick-up coil, or I guess what some call the cam position sensor which by the way does not exist on this model. Oh yeah, and this problem was somewhat intermittent because after we gave up and he started pulling me out of there to my truck and trailer, I kept trying to start it and on about the 8th try and after about 30 minutes of towing it fired right up. We drove around for about another hour and 15 minutes before it suddenly quit again and I never did get it started again until I fixed the problem.

Just wanted to post my findings on this problem since this is fairly common on these.
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Old December 17th, 2006, 20:06
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Angry Re: '91 XJ HO NO SPARK SOLVED

Now it freakin died again today, no spark again!!!! The codes I am getting are 11 and 76. I am researching these now, but thought I would go ahead and post and see if anyone has any ideas.

76= ballast bypass relay-open or short in fuel pump relay circuit

11= camshaft signal or ignition signal-no reference signal detected during engine cranking

I did check and I don't have voltage on either side of the ballast. I will do more troubleshooting tomorrow.

I would really like to go a week without problems out of this thing!
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Old December 17th, 2006, 20:19
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Re: '91 XJ HO NO SPARK SOLVED

this might sound dumb but dont the flexplates on the '91 and '89 have different tooth patterns for different CPSs? Are you sure you got the one for an 89 instead of a 91?
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Old December 17th, 2006, 20:21
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Re: '91 XJ HO NO SPARK SOLVED

Quote:
Originally Posted by MoparManiac
this might sound dumb but dont the flexplates on the '91 and '89 have different tooth patterns for different CPSs? Are you sure you got the one for an 89 instead of a 91?
wouldnt matter if he re-used the 91 flywheel, right? err flexplate i mean...havent had an auto trans in a while, heh
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Old December 17th, 2006, 20:27
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Re: '91 XJ HO NO SPARK SOLVED

Not dumb at all, been there done that. When I first tried to start it after the engine swap, I realized I didn't swap the flywheel and had to pull the tranny back out and swap them. Fired right up after that, I didn't have any ignition problems before the engine swap so I don't know if it's something I did or just a fluke. It has always been slow starting, last week after I replaced the pick-up coil it started pretty quick (2-3 seconds), but I noticed it taking progressively longer every time I started it. Then today it just quit on the trail with no warning at all.
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Old December 17th, 2006, 20:32
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Re: '91 XJ HO NO SPARK SOLVED

You wouldn't have an extra TCU that would work in my '89 2wd would ya?
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Old December 17th, 2006, 20:40
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Re: '91 XJ HO NO SPARK SOLVED

OK I have to plead stupid, what is the TCU? I probably do have it though since this thing was complete before I tore into it.
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Old December 17th, 2006, 20:41
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Re: '91 XJ HO NO SPARK SOLVED

directly under the dash on the passenger side. Box with wiring harness coming out of it and a fuse on the harness.
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Old December 17th, 2006, 20:45
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Re: '91 XJ HO NO SPARK SOLVED

I'll check tomorrow and reply back here. What does TCU stand for?
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Old December 17th, 2006, 21:07
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Re: '91 XJ HO NO SPARK SOLVED

transmission control unit
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  #11  
Old December 18th, 2006, 13:38
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Re: '91 XJ HO NO SPARK SOLVED

Haven't gotten home to troubleshoot yet, but I just remembered that the "maintenance required" light has been on since just before I did the engine swap. I have tried resetting it but it has yet to go off. I doubt that this has anything to do with the ignition problem, but it might.

Any ideas????

Also, should there be voltage at the "ballast" on the inner fender with the key in the ignition position or in the start position? It has no voltage on either side in the ignition position, I haven't tried the start position yet because I was by myself and I ain't rubberman!
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Old December 18th, 2006, 13:46
BIGSLVRXJ BIGSLVRXJ is offline
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Re: '91 XJ HO NO SPARK SOLVED

Quote:
Originally Posted by TXRIVERRAT
Haven't gotten home to troubleshoot yet, but I just remembered that the "maintenance required" light has been on since just before I did the engine swap. I have tried resetting it but it has yet to go off. I doubt that this has anything to do with the ignition problem, but it might.

Any ideas????

Also, should there be voltage at the "ballast" on the inner fender with the key in the ignition position or in the start position? It has no voltage on either side in the ignition position, I haven't tried the start position yet because I was by myself and I ain't rubberman!
Do you have the fuel pump ballast resistor bypassed? If not I would recommend that. It's given me fits before.
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  #13  
Old December 18th, 2006, 14:23
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Re: '91 XJ HO NO SPARK SOLVED

Bypassed?? No, I haven't heard of doing that. I was under the impression that it lowered voltage to your pick-up coil and would burn it up if bypassed. I'll look into it tonight!
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Old December 18th, 2006, 14:30
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Re: '91 XJ HO NO SPARK SOLVED

The ballast resistor lowers the pump voltage and makes it more quiet. Early years didn't have it.
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  #15  
Old December 18th, 2006, 14:32
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Re: '91 XJ HO NO SPARK SOLVED

This ballast resistor is for the fuel pump, ignition system no longer need a ballast resistor.
The one for the fuel pump just cuts the noise a little.
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