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knever3

Flex Plate, No Start

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Specs first,

 

1987 Jeep Comanche had 4.0L 2wd ba-10/5

 

Installed aw-4 trans, 242 case and all under hood wiring and fuse box from 1990 XJ. Ran fine until I noticed the flex plate knock. Thought it was a rod bearing so I decided to install my stroker motor. '96 block and head, kept all the renix stuff including the flywheel from the last motor, which was from the '90 donor.

 

After noticing the noise was on the new motor I removed the flex plate and ordered a new one for an '87 Comanche. I noticed that the windows in the outer ring were in different locations than the old one I pulled. Sure enough, installed it and the timing is so far off it won't start. Ordered one for the '90 XJ and it turned out to be the same part.

 

So the question is which flex plate do I need? I have the renix system but the clue is that the donor XJ had a Chrysler sticker under the hood instead of an AMC one. I am assuming trying a '91? The part has no markings on it so I can't cross reference. The parts aren't a stock item so I would have to order them and match them up.

 

Thoughts?

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Thanks for posting the numbers, but how do I figure out what flex plate to buy if the one it "should" be isn't the correct one? All I can think of is to call the dealer with the vin from the '90 donor and cross reference that to an aftermarket part. Except it's the weekend as uaual. :soap box: I wish dealers had an 800 number you can call for help and a linked computer to the network to see if my closest one had the part. This whole year it seems it's been the weekends when I need something from the dealer. Go figure.

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Posted the p/n's so hopefully you could troll the net and find pics of each and perhaps determine the correct notch layout you'll need for your application. I'm assuming as you are the 53006324 might be golden with your setup.

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Is your ECU located under the dashboard, over the driver's right foot, or under the hood between the air box and the fender? For an '87 MJ (or any Renix) the 33002675 should be the correct part number.

 

Another question: The '87 4.0L and the '90 4.0L were both Renix models. Why did you install the underhood wiring from the donor? All you should have had to install was the TCU and the associated harness for that.

 

Are you certain the '90 donor wasn't a '91? Do you still have it, or a record of the VIN number?

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I still have the '90 donor. The reason is because my '87 was a manual, the '90 was an auto with A/C, both which I wanted. The computer is up under the dash. My '87 had the c101 connector, the '90 did not.

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Computer under the dash is Renix. Maybe the flex plate you ordered for an 87 Comanche is not for an 87 Comanche? And the one you ordered for the 90XJ also isn't?

 

Would not be uncommon for people (and computers) to think that all parts interchange from 84 right through 92, meaning they gave you one (two) for 91-92 model year with the Chrysler OBD I setup.

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Who did you order the new flex plates from, what brand are they (if the box shows a brand), and what's the part number?

 

AutoZone shows me a flex plate number FRA-333 for an '88 Cherokee 4.0L. They show the same one for a 1990 MJ. Price is $54.99.

 

For a '92 MJ, they show me part number FRA-480, and the price is $96.99.

 

If all else fails, Crown uses the same part numbers as Jeep, and their stuff is good quality. My dealer supplies Crown where the factory parts are no longer available (which I'm sure is the case for a Renix flex plate). I think my dealer will ship -- call Todd or Rich at 860-274-8834, ext 3. Tell them Harwood suggested them as the miracle workers and see if they can get you hooked up.

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Try sticking a timing light on it while cranking to see if it syncs with the timing marks on the damper and timing cover. That will tell you a lot.

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Try sticking a timing light on it while cranking to see if it syncs with the timing marks on the damper and timing cover. That will tell you a lot.

 

Considering that the Mopar CPS operates on a completely different theory than the Renix CPS, I'd be surprised if there's any signal at all to trigger a timing light.

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I called AutoZone today and they put me on hold to help customers in the store, for more than 7 minutes to which I hung up. I tried again at 6pm. The same guy answered and they have one in stock for a '91 for $93.00. Way more expensive than the '87-90 one I had ordered from Advance Auto. I don't remember the part number for those two. So fingers crossed tomorrow I will take my old one to AutoZone to see if it matches up. Hopefully I can talk them down on price too!!

 

To be continued...

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Ok dead end again. The part i had was for a 90. The dealer part numbers crossed to the dorman or atp one i ordered. So i can't find out why the timing is off when i installed it the first time. I am about over this stupid problem, every time ineed to order the part. The 91 was way different, i also checked with the dealer and the part is no longer available through them.

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Has been a long time since I had a flywheel off, and never took a flywheel or flex plate off a Jeep 4.0, so a question: is there a key or something that indexes it to the crankshaft? Or is there more than one orientation to bolt it on.

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Pull the trans, install your old flywheel, see if it starts to rule out the flexplate. I'm starting to think you may have damaged the cps.

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Pull the trans, install your old flywheel, see if it starts to rule out the flexplate. I'm starting to think you may have damaged the cps.

 

I was thinking the same thing.

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Considering that the Mopar CPS operates on a completely different theory than the Renix CPS, I'd be surprised if there's any signal at all to trigger a timing light.

 

Doesn't matter - HV to the plug #1 is the same result. The timing light will trigger if the timed HV signal is there thru the mag pickup. It will also tell you if the timing is completely AFU resulting in a no-start condition. I'd rather do this first than pull the tranny and change flexplates. That's nuts.

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The CPS is new since I put together the truck. I ran it for about 1000 miles I figure. I don't know why the CPS would not read one flywheel and then another. Tomorrow Advance will get in another '90 flexplate. I might take some pics and upload them to give you guys a look. I will also check the CPS for damage when I'm under there.

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So here's the update today. I went to Advance to get yet another flexplate for a '90 XJ/MJ. It was sealed and when I opened it up to compare it was exactly the same as the first three I saw. I took some comparison pictures for you all to noodle on.

 

Old one with the crack, reason for the whole debacle.

 

DSC_0355.jpg

 

Old one vs. new one.

 

DSC_0388.jpg

 

New one sitting on top of the old one indexed with the crank bolt pattern.

 

DSC_0389.jpg

 

DSC_0390.jpg

 

DSC_0391.jpg

 

DSC_0392.jpg

 

DSC_0393.jpg

 

DSC_0394-1.jpg

 

As you can see what I was talking about the timing windows are "off" between the two.

 

Here's some pics of the CPS.

 

DSC_0396-1.jpg

 

DSC_0401-1.jpg

 

DSC_0402-1.jpg

 

I haven't found the number on the cps usefull for a cross reference. The number doesn't turn up anywhere. I haven't tried to test the sensor yet and I don't have a timing light since I don't have any carburated cars.

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Considering the mismatch on the flex plate signal windows, I don't see any point at all in trying a timing light or testing the CPS. That new flex plate ain't a-gonna work, and you can take that to the bank.

 

Call Todd or Richie at Bradshaw Jeep and ask them to order a Crown flex plate for you. I put one into an '88 XJ a couple of years ago (same problem, original was cracked) and it worked fine.

 

860-274-8834, Ext 3

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Thanks for the contact Eagle. I bought a flexplate from Crown, I even checked the box to make sure. The same result. The windows are in the wrong spot. I guess I should put it back in and just adjust the dist untill the timing is correct. That is really crazy since the dist is supposed to be set to TDC 0 degrees and the computer is supposed to adjust the timing according to the knock sensor and such.

 

Picture of all three, my original on the bottom, Advance Auto's ATP/Dorman, and the Crown is on the top. The flexplates do have different holes drilled in them in some locations most likely for balancing.

 

DSC_0405-1.jpg

 

Back to square one...

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Adjusting the dizzy isn't gonna work. The ECU tells the coil when to throw the spark, not the internals of the dizzy. All turning the dizzy does is move the tip of the rotor further or closer to the cap terminal.

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Adjusting the dizzy isn't gonna work. The ECU tells the coil when to throw the spark, not the internals of the dizzy. All turning the dizzy does is move the tip of the rotor further or closer to the cap terminal.

 

Plus the CPS & ECU also tell the injectors when to squirt.

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