Intermittent no start: lost big time

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acrenz113

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Apr 25, 2021
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All- my yj 4.0 has an intermittent no start problem. Im pretty sure the guy who sold it to me in november did so because of this issue. It randomly doesnt wanna start even with starting fluid. If it does start on one of those "no start days," it'll run horribl

what i have done: new fuel pump, crank position sensor, spark plugs, plug wires, cam position sensor, MAP sensor, etc. I've done everything sensorwise i can think of.

any help? Im now at a total loss.
 
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Gremlins....Had a similar issue with mine, but it was never a "no start", it was just cutting out on every bump in the road.
And it would absolutely stall in a hard left turn. No codes.
Turned out to be a stressed/broken power wire on the 2 pin plug into the coil.
Is it throwing any codes?
 
jeepjoe43 said:
Gremlins....Had a similar issue with mine, but it was never a "no start", it was just cutting out on every bump in the road.
And it would absolutely stall in a hard left turn. No codes.
Turned out to be a stressed/broken power wire on the 2 pin plug into the coil.
Is it throwing any codes?
Click to expand...
It had thrown one for a bad map sensor, but ive already replaced that. I have no idea what could be the cause at this point
 
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acrenz113 said:
It had thrown one for a bad map sensor, but ive already replaced that. I have no idea what could be the cause at this point
Click to expand...
Sounds like something in the ignition wiring, start inspecting all the engine harness plugs.
I went down this rabbit hole too, replaced every sensor I could find except the CAM sensor.
Then I found the broken wire while changing out the coil, still going to change CAM sensor, but I'm just going to get the whole distributor.
Mine didn't start throwing codes until I put in the wrong t-stat, then she threw codes out the wazzoo.
Welcome to the "Bug" hunt...
I still don't trust mine, after owning her for 3 years, I've only got about 150 miles in the saddle. It's a work in progress.
 
jeepjoe43 said:
Sounds like something in the ignition wiring, start inspecting all the engine harness plugs.
I went down this rabbit hole too, replaced every sensor I could find except the CAM sensor.
Then I found the broken wire while changing out the coil, still going to change CAM sensor, but I'm just going to get the whole distributor.
Mine didn't start throwing codes until I put in the wrong t-stat, then she threw codes out the wazzoo.
Welcome to the "Bug" hunt...
I still don't trust mine, after owning her for 3 years, I've only got about 150 miles in the saddle. It's a work in progress.
Click to expand...
Somehow it aint gettin enough spark, but at this point it has to be wiring like you said
 
acrenz113 said:
Somehow it aint gettin enough spark, but at this point it has to be wiring like you said
Click to expand...
That's what it sounds like, especially not firing with starting fluid.
The PO on mine said he'd just put in a new ECM, should have been a red flag, later found a new Crank sensor.
Ya, mine we're hunting, too.
 
Ive already replaced and checked cam, crank, and MAP sensor and their plugs and wires looked fine, same with the ignition
 
Spark needs the crank sensor, PCM, coil, plug wires, distributor cap, rotor.

Be sure the coil 2 wire connector is good, mine was shot and it would just cut off driving down the rd.
 
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If you have a carb motor 4.2 there is no crank position Sensor, as I have learned. Do a nutter bypass. Check YouTube on how to do it. Coil might be on its last legs if you hadn’t changed it. I’ve fought this battle for a while. I changed the ECM and it just made the same problem different. If I figure it out I’ll post
 
When you flip the key to acc or run (before starting it), does the check engine light light up? It should, and then it should go off. Sometimes the capacitors in the PCM go bad and then that process doesn't happen. If you flip the key and then a few minutes later the CEL lights up, you would also hear the fuel pump prime and then it would start right up.

However, the fact that yours runs poorly after starting makes me think it's something else. Bad PCM capacitors usually cause a long start, but once it's started, runs fine.

You very well may have a wiring issue, since it's not starting with starting fluid and also not working any better after replacing all those electrical components.
 
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