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4.0L Won't run, no spark
11-03-2013, 09:08 PM
Post: #1
4.0L Won't run, no spark
OK, this is one that I have my own theory on but I want to hear what someone else has to say.

1998 Jeep Cherokee Classic, 4.0L, Automatic. I haven’t seen it & only have what information was relayed to me. They pulled a blown engine out and put a used one in. They claim that they have spark to the coil wire but not to the plug wires. They claim to have changed the cap, rotor, & even the whole distributor.

Given that little bit of information where would you start and what would you suspect?

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Garner

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11-03-2013, 09:41 PM (This post was last modified: 11-03-2013 09:46 PM by Rupe.)
Post: #2
RE: 4.0L Won't run, no spark
I'd want to know if they used new parts for the ignition or unknown used parts. Does the dist turn and is it in time? Have they checked more than one plug wire for spark? Is the spark they have "good" spark or something on the weak side that may not get there?

You know the rest of the drill: weak battery, slow cranking, and all the usual stuff that happend in a DIY engine swap, right?

Did they mention if it even coughs, like maybe they used a replacement ECM and the security system is blocking something? That's common on GM for this era and I don't recall who makes their ECMs.

Edited to add: one thing this board does not allow is the use of 2 arrows with a G in the middle for the old fashion grin. Big GrinBig GrinBig Grin
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11-04-2013, 11:58 PM
Post: #3
RE: 4.0L Won't run, no spark
I don’t have any other information than what I posted. Another one of those friend relaying what a friend told him, deals. However, what you mentioned seems in line with what I thought that they should be checking.

They keep changing the flex plate/flywheel. They are saying that it is the Crank Sensor that is stopping the spark because it has the wrong flywheel. I thought that if it had spark to the coil that would pretty much eliminate the crank sensor as a suspect??? Right? Wrong? I don’t remember anymore and I can’t find a wiring diagram.

If they don’t get it going they are going to have me look at it. I just want to have a good idea of the correct things to be looking at. I doubt that I will be able to pick anything up with the scanner since it hasn’t run. I’m thinking a mechanical issue like a broken dist. shaft or another issue like if it has a “trigger wheel” under the rotor? I’m just looking for extra information now to help narrow things down if I have to work on it.

Thanks for your input.

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Garner

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11-05-2013, 03:03 AM
Post: #4
RE: 4.0L Won't run, no spark
Sounds like to me that they changed everything needed... but the one thing I didn't see mentioned was whether or not that they cuanged the spark plug wires. There might be a broken wire somewhere on the old set
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11-05-2013, 10:32 AM
Post: #5
RE: 4.0L Won't run, no spark
Obviously some of the info you have from them is incorrect as a crank sensor can't stop the spark half way to the plugs.

With that in mind, they say they have spark but in working the key we both know there can be a "stray signal" when things power up and power down so maybe this spark is just a momentary blip and there really isn't any spark while cranking?

Not all that familiar with this car so not sure where the crank sensor is mounted but do know it's going to read flywheel teeth or something else on the flywheel, depends on where it's mounted. If it's the teeth then just the fact that the starter works should confirm it's also reading the teeth because they need to be in the same location. If it's something else on the flywheel then you'd need to compare old versus new to see what's up. Perhaps it got broken during the install?

When you to see this in person you will probably have the diagnosis narrowed down within a few minutes. It's going to be no spark, no fuel, not enough cranking speed, or something basic. Finding the cause and fixing it will be another ordeal in itself.
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01-03-2014, 03:35 AM
Post: #6
RE: 4.0L Won't run, no spark
I had a similar problem a while back and it turned out to be the computer. Lots of research and learned about the problem. Ground solder points inside where the harness plugs into the computer come lose. I resoldered them now everything is fine. An easy way to check if it is the computer, have someone move the harness on the computer while cranking to see if it sputters or starts, if it does there is the culprid.

PS. Sorry i have not been on here, my computer ate it and i could not remember the site. I sure missed all the info.
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01-03-2014, 12:07 PM
Post: #7
RE: 4.0L Won't run, no spark
Well, they finally got this one running. They changed the flywheel not once, but twice and it still didn’t run. In fact, they said that nothing had changed. I kept telling them that it wasn’t the flywheel so someone finally started looking elsewhere and found that the distributor was 180 out. They turned it around and it fired right up and ran great. My friend got in, headed home, and another truck backed into him doing another $2,500.00 damage. This poor guy just can’t win!

Thanks for all of the help and information. Welcome back PTBLL.

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Garner

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01-03-2014, 03:29 PM
Post: #8
RE: 4.0L Won't run, no spark
This goes back to my first post on the subject. Now I have to wonder why they had the dist out in the first place as typically you swap a WHOLE AND COMPLETE engine when you get used parts. IOW, it ran before the swap so what changed? Sometimes I just shake my head.
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01-03-2014, 09:53 PM
Post: #9
RE: 4.0L Won't run, no spark
Same thing that I was talking about when they were saying that it didn't have spark??? If all you did was turn the distributor it must have already had spark, just not at the correct time. I get in on a lot of these projects where you have to sift through crap to get to the truth. It would be so much easier to just hear the truth or at least have them listen to what you are trying to tell them. Oh well.

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Garner

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01-03-2014, 11:30 PM
Post: #10
RE: 4.0L Won't run, no spark
good to see they got it running sorry about the rear end getting hit, thanks garner. I have problems of my own with an 88 cherokee 4.0. I will post up in a new thread.
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