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Old 08-15-2014, 06:36 PM   #1
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Cylinder 1 Misfire. P0301.

Hey Wrangler Forum,
I'm here to ask for help figuring out my Cylinder one misfire (P0301) code that intermittently comes on in my 1999 Sahara. I bought the jeep about a year and a half ago and it would come on, then disappear every now and again, nothing too serious, but not its's showing up every time I start my engine after sitting for more than 6 hours.

I have:
Replaced, checked and double checked my spark plugs. they look fine to me.
Replaced checked and tested the OHM's from the plug wires.
Replaced distributor cap and rotor. **see picture of wear on inside, I think I was sold one a bit too small, but don't think this is the issue.**
Checked ignition coil. (it's still there and no cracks or visible wear.)

The engine doesn't have a rough idle, or loud knocking, or pinging, gas doesn't smell funky.

The thing that stumps me is that it only shows up within 1 minute after starting, and if I reset the CEL after its warmed up, the CEL won't show up until it sits and gets cold again.

I'm stumped. I've thought I've fixed it only for it to show up the next day. It's been a roller coaster and a wild goose chase.
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Old 08-15-2014, 07:23 PM   #2
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Hi.

From the picture of the distributor cap, I see you have a 4.0l.

Since you mentioned that you replaced and rechecked the spark plug, I'll assume you checked the gap setting during that process and it is correct.

I'd suggest you take the ignition coil from cylinder 2 and swap it with the coil on cylinder 1. If the code follows the coil from ignition one, you will get a P0302 code. If the misfire does NOT follow the coil (again assuming your checks were accurate and correct) I would check the compression on cylinder 1.

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Old 08-15-2014, 07:27 PM   #3
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He only has one coil on the '99.
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Old 08-15-2014, 07:33 PM   #4
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He said he has a 99 Sahara so it has to be a 4.0 and 97-99 have a distributor as shown and thus ONE coil whose spark is distributed to proper cylinder via the plug wires

For a single cylinder miss think ignition fuel or mixture
Plug and plug wire
Injector and injector harness
Vacuum leak near that runner
Although valve for that cylinder possible less likely but could also do compression test



Swapping plug say 1 and 3
Swapping plug wire say 1 and 2
And swapping injector say 1 and 4
If miss moves with swap you know which is bad if it stays you know three things that are not bad
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Old 08-15-2014, 07:59 PM   #5
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Quote:
Originally Posted by jkp View Post
He only has one coil on the '99.
Youre right...I completely missed the year
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Old 08-15-2014, 08:32 PM   #6
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Quote:
Originally Posted by Digger84 View Post
He said he has a 99 Sahara so it has to be a 4.0 and 97-99 have a distributor as shown and thus ONE coil whose spark is distributed to proper cylinder via the plug wires

For a single cylinder miss think ignition fuel or mixture
Plug and plug wire
Injector and injector harness
Vacuum leak near that runner
Although valve for that cylinder possible less likely but could also do compression test



Swapping plug say 1 and 3
Swapping plug wire say 1 and 2
And swapping injector say 1 and 4
If miss moves with swap you know which is bad if it stays you know three things that are not bad
Very nice with swapping to check for DTC moving to other cyls.

Another thing to consider would be a slightly leaking head gasket. Let it sit and get cold, then check for accumulation of water/coolant that can cause that plug to misfire.
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Old 08-16-2014, 10:29 AM   #7
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Quote:
Another thing to consider would be a slightly leaking head gasket. Let it sit and get cold, then check for accumulation of water/coolant that can cause that plug to misfire.
How do I check for this? pull the plug and look in? The plus isn't wet, even when I pull it and the picture shown doesn't show signs of being wet... I will look at this though. Thank-You!
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Old 08-16-2014, 10:33 AM   #8
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Quote:
Originally Posted by Digger84 View Post
He said he has a 99 Sahara so it has to be a 4.0 and 97-99 have a distributor as shown and thus ONE coil whose spark is distributed to proper cylinder via the plug wires

For a single cylinder miss think ignition fuel or mixture
Plug and plug wire
Injector and injector harness
Vacuum leak near that runner
Although valve for that cylinder possible less likely but could also do compression test



Swapping plug say 1 and 3
Swapping plug wire say 1 and 2
And swapping injector say 1 and 4
If miss moves with swap you know which is bad if it stays you know three things that are not bad

Makes sense, I'll have to give this a try.


How likely is it that an overdue Oil Change is causing something to stick and cause this?

Next step is to replace the fuel injectors. after testing. I have a feeling it could be one of the sensors on the intake manifold... or even the Camshart position sensor in the Dizzy...
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Old 08-17-2014, 09:58 AM   #9
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Well, I swapped cables with cyl 1 and 4, cleaned my IAC, which if you haven't done this to your own vehicle, I highly suggest doing it. There was so much carbon build up it was crazy. my idle is way smoother. I also changed my oil and put 10w-40 with 1 qt of Lucas oil in it.

Any way, I drove it after I let it sit to get cold and the cal 1 misfire happened again. A part of me wants to believe it was and still might be buildup on a sensor.

Next weekend project is replacing the fuel injector. I'm not going to test it, if I'm taking the time to pull them and check, I might as well replace it with a new one right?

I'll keep you all posted..
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Old 08-17-2014, 09:59 AM   #10
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You can just swap it with the injector from another cyl and see if the prob follows.
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Old 08-30-2014, 04:16 PM   #11
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So, long story short(ish)-
swapped cables 1 with 2, swapped spark plug 1 with 3. pulled and cleaned fuel injector. (didn't swap, idk why). and the CEL still came back on. The fuel injector on CYL 1 looked brand new, newer than the rest infact, but I cleaned the whole thing with q-tips and towels. I saw a post somewhere talking about it being the camshaft sensor. So, last weekend I pulled the cap off, and cleaned the hell out of my camshaft sensor. It's under the dizzy cap, and was slightly dirty. checked out the wiring and flattened out some kinks. Everything since this has been OK. then a couple days ago the car starts BUCKING on the highway with my cruise control on, and a p0121 pops up on the CEL. So I just took my throttle body off and cleaned every sensor on it excluding the MAP, that there is not something i want to mess with. cleared the codes and so far so good. I will try and keep this updated incase anyone has a similar problem, I want to document if I fixed it or not.

Also, side note I had some really ghetto wiring done on my Coolant temp Sensor. Just got around to putting a new sensor and electrical connector on it as the previous own did some sketchy soldering on the old one. so, that could've been my issue but idk. again just updating everything.

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