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Unread 07-10-2010, 04:14 PM   #1
Douglas S.
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Junkyard MPFI Problem

Just finished my junkyard MPFI swap from a '92 cherokee into my '87 YJ. I have fuel and spark, but when I crank it it seems like it is trying to fire, but can't get going. Every few times the engine turns over it will seem like it's trying to start, but almost immediately dies. I tried reading the codes, but that doesn't seem to be working.


Any help is appreciated.

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Unread 07-10-2010, 04:20 PM   #2
idaholtby
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Did you swap the flywheels over as well?
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Unread 07-10-2010, 04:21 PM   #3
Douglas S.
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I used a Hesco CPS relocation kit on the front dampener.
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Unread 07-10-2010, 04:31 PM   #4
idaholtby
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Your '87 dash does not have a provision for the CEL lamp, so it would be difficult to check codes. You could hook up a noid light to power and -32 of the ecm connector and see if you can retreive any codes that may be useful.
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Unread 07-10-2010, 04:38 PM   #5
Douglas S.
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I tried putting a test light on the CEL output from the PCM and didn't get anything. I'm going to recheck that the distributor is properly indexed, but I'll try to retrieve the codes first.
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Unread 07-10-2010, 05:41 PM   #6
ajs96
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make sure you have the distributor indexed correctly, do a search on here...there are at least 4 threads with gross details to ensure it's correct, it's really easy to have it off by a tooth
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Unread 07-10-2010, 08:59 PM   #7
Douglas S.
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Just went out and checked my codes.

12
34
33
41
54
55

The only problem here, that I can see, is 54. Not exactly sure what to do about it though.
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Unread 07-11-2010, 06:11 AM   #8
idaholtby
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54 is your distributer synch pick-up sensor. I assume you swapped over the distributers as well?
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Unread 07-11-2010, 10:12 AM   #9
Douglas S.
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I did, but I'm going to go to the junkyard and grab another dist to see if it solves the problem. I'm also going to install a fuel pressure gauge on the rail to ensure my fuel delivery system is up to par.
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Unread 07-11-2010, 11:48 AM   #10
idaholtby
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If the new distributer does not work for you, then ohm out the following wires.... For the '92 Cherokee harness from the distributer pick-up sensor connector... The Blk/Lt.Blu wire to ecm connector pin -4, The Org wire to ecm -7, the tan/yel wire to ecm -44. Good luck!
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Unread 07-11-2010, 12:14 PM   #11
Douglas S.
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Distributor didn't work, I'll give your suggestion a try.

What kind of resistance should I be expecting? 0 ohms for all?
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Unread 07-11-2010, 12:17 PM   #12
idaholtby
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Should be zero or reallllly close to it for each wire tested. Of course do this with the ignition off and battery disconnected.
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Unread 07-11-2010, 12:31 PM   #13
Douglas S.
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Yep, 0 on all three. This is starting to get annoying. Bad ECM? I know it usually isn't, but I'm beginning to wonder.
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Unread 07-11-2010, 12:37 PM   #14
idaholtby
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Also test each of these wires to a chassis ground as well. If one of these wires is shorted to ground anywhere, you will still read good continuity between both ends, but could also be shorted to ground. Beyond that, several other sensor tie into the same wiring and could be causing an issue. I would suggest in the very least for you to pick up a Chilton's that covers the '92 Cherokee to aid in your troubleshooting. It would be difficult to troubleshoot all the possibilities over the internet. This way you can continue troubleshooting on your own, and when questions arise, report back to the forum for help.
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Unread 07-11-2010, 01:28 PM   #15
Douglas S.
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Ok, here's where it gets weird.

I disconnected the battery to check for the resistance in those wires and following reconnection attempted to start it again, and there were some glimmers of hope (seemed like it was catching, but wasn't quite there) as well, code 54 was gone.

I made a small adjustment to the timing just by turning the distributor body. After cranking for a few seconds it caught, ran rough for a few seconds and then immediately shot to about a billion rpm's and I shut it down. I can keep trying to start it, but it still shoots to WOT.
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