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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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Old 09-26-2014, 07:15 PM   #12
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I wanted to follow up on this. The previous issue with the p0121, was my dumb ass not connecting my Cold air intake properly and falling off while driving. Dumb I know.

I still have a Cylider 1 misfire after two days of the dealership looking at it and doing a compression test on it and telling me its not the valve.
So far,
Ive tested and ruled out the following.
Spark plug and wire.
fuel injector
Crank Shaft Sensor (replaced with new one)
valve

What else should I test???
I'm thinking about buying a new distributor because its basically the same cost as a "cam shaft sensor" or distributor pickup coil, or whatever name it's called.

Please, all ideas are welcome. Im absolutely stumped. I don't think it's mentioned here but this is a manual transmission.
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Old 09-26-2014, 07:21 PM   #13
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Fuel injector harness to that injector

Vaccum leak as big vacuum port on number one intake runner
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Old 09-26-2014, 07:22 PM   #14
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Also dist cap
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Old 09-26-2014, 07:23 PM   #15
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The cam sensor is used to sync the injector timing.

The crank sensor fires the coil.

I'd replace both of them at this point.

And yes, you can change out the distributor for the same cost as the sensor. That's what I did on my '92.
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Old 09-26-2014, 07:28 PM   #16
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Quote:
Originally Posted by Digger84 View Post
Fuel injector harness to that injector

Vaccum leak as big vacuum port on number one intake runner
Digger can you please expand on this? Ive been trying to listen for any leaks, where would I find a big vacuum port on number one intake?
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Old 09-26-2014, 07:32 PM   #17
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Neither crank or cam sensor should affect a single cylinder so quit throwing new parts and make a plan

Like I said

Swap spark plug wires one and two at both ends
Swap plugs one and three
Swap injectors one and four
If miss stays at one it was not plug wire or injector
Moves to two was wire
Moves to three was plug
Moves to four was injector

That would leave if stays at one
A valve issue (compression check and leak down test)
Or
A vacuum leak near intake runner one ( look and see)
Or
A bad injector harness at one (use a test light)
Or a bad dist cap (inspect and if damaged or cracked replace)

Notice we spent almost money and only consider replacing a part if bad

When you throw parts at a problem you waste money and muddy the diagnostic waters and the dealers love it
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Old 09-26-2014, 07:40 PM   #18
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He has replaced the plugs, wires, distributor cap and rotor.

I don't think he ever replaced or swapped the injector with another one.
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Old 09-26-2014, 07:44 PM   #19
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This port I think it feeds evap system found on early tj pre horse shape 4.0 intake

If it lets in excess air one and or two will run lean

To test I would just pull the line and plug it at manifold with a rubber cap, it will probably add a code but who cares if it fixes cylinder one miss you know that somewhere it is letting in excess air if it doesn't reattach clear code and look elsewhere
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Old 09-26-2014, 08:00 PM   #20
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Should read pre horseshoe shape intake not horse shape
Those straight runner intakes were used in 97 98 and 99 TJ 4.0
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Old 09-26-2014, 10:18 PM   #21
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Quote:
Originally Posted by Digger84 View Post
Neither crank or cam sensor should affect a single cylinder so quit throwing new parts and make a plan

Like I said

Swap spark plug wires one and two at both ends
Swap plugs one and three
Swap injectors one and four
If miss stays at one it was not plug wire or injector
Moves to two was wire
Moves to three was plug
Moves to four was injector

That would leave if stays at one
A valve issue (compression check and leak down test)
Or
A vacuum leak near intake runner one ( look and see)
Or
A bad injector harness at one (use a test light)
Or a bad dist cap (inspect and if damaged or cracked replace)

Notice we spent almost money and only consider replacing a part if bad

When you throw parts at a problem you waste money and muddy the diagnostic waters and the dealers love it
I have done all these things and yet the issue still remains are CYL one. The only thing left is to look for an air leak, i've been combing the damn thing every day trying to find one. and i've also wiggled the injector 1 harness and receive no CEL/Misfire when messing around with it and the cel is off.

I appreciate your help, but i've practically gone though all these things. took it to the dealer they didn't fix the issue so they gave it back to me without any cost, not I'm back to tinkering with it. I agree, i doubt throwing money at it will fix any issues, but i feel its all i have left. I really don't want to.
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Old 09-27-2014, 06:49 AM   #22
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The first and last government motors vehicle I owned had a 350 v8 where the GM bean counters decided to save a couple bucks by pressing in the rocker stubs instead of threading the holes for them in the head.

What I learned is a exhaust valve that does not open well is very hard to discover

Compression is fine, leak down is fine but the cylinder has no power and pre OBD there is no way to isolate the weak cylinder except pulling plug wires and listen and watch rpm

Your system actually isolates the miss for you
It is a long shot but if you are absolutely sure you have spark fuel and compression a worn cam lobe or bent rocker or collapsed lifter preventing exhaust valve opening is a possibility

Before I went there I would verify injector harness three ways
1) verify constant plus 12 at injector plug with key on and stays plus 12 when you move harness wires around
2) get a plug that can plug into harness in place of the injector (early saabs before gm redesigned them have an o2 sensor plug that will fit) and attach a test light start engine verify good flash even with wiggle of harness wires
3) if any doubt make a temp injector harness that gets its ground pulse from tapping into proper wire at PCM right near and plus 12 directly from battery and see if that makes it run right

If all that failed and you actually did the parts swap around the way I said I would pull valve covers and observe valve movement with all spark plugs pulled and cranking
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Old 09-27-2014, 09:22 AM   #23
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I think I can rent a test light from the auto store, I will have to try this. I'll go test the harness today.

Something That I've noticed it that my gears grind really bad when I shift into reverse, then have a hard time sticking into 1st/the rest. I have a locked out rear diff, would this cause my cyl 1 to misfire because the gearing if off somehow?
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Old 09-27-2014, 09:32 AM   #24
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Not sure what you mean by a locked out rear dif but that sounds like a clutch issue and should not cause a cylinder one miss

Light is best but a stick or mechanic stethoscope listing to injector click when running is a useful test. You listen to suspect injector harness Injector at idle and compare to sound of click of non suspect injector
Touch the stick or stethoscope probe directly to injector body when you listen
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Old 09-27-2014, 12:43 PM   #25
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So I think I've narrowed it down to a sticky lifter. Could this be causing the cal 1 misfire?
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Old 09-27-2014, 02:45 PM   #26
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A collapsed lifter could but it should also make a constant rpm dependent tapping sound

Also if on intake side it should make compression test low but if on exhaust side compression would be normal
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Old 09-27-2014, 04:32 PM   #27
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Dealership said the compression test was normal. I saw a video online talking about putting a paper against the tail pipe and if it sucks in, you most likely have a sticky lifter. I did this and there is a slight ticking noise from the engine.

I also looked at that rubber "L" vacuum line, everything checked out ok.

Drained my oil, placed some sea foam in it, and will run it for the next couple hundred miles keeping an eye on how gunked up the oil gets so I don't blow the oil filter. might dump some of the "engine flush" in it before I change the oil mid week see if it helps.
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Old 09-30-2014, 09:49 PM   #28
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welp. oil change complete and put 10w-30 into it with 1 qt lucas. started it up and immediately got cyl 1 misfire. The engine sounds like it runs better, but even after I cleared it and went for a drive, it came back on.

This leads me to believe its a stuck lifter or something along those lines. would thicker oil help with sticky lifter or would thin be best???
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Old 10-01-2014, 02:04 AM   #29
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I have done all these things and yet the issue still remains are CYL one. The only thing left is to look for an air leak, i've been combing the damn thing every day trying to find one. and i've also wiggled the injector 1 harness and receive no CEL/Misfire when messing around with it and the cel is off.

I appreciate your help, but i've practically gone though all these things. took it to the dealer they didn't fix the issue so they gave it back to me without any cost, not I'm back to tinkering with it. I agree, i doubt throwing money at it will fix any issues, but i feel its all i have left. I really don't want to.
Air leak past mass airflow sensor would throw a P0171 System Lean Code. System lean code happens because too much fuel gets thrown in the loop to make up for more air. gets past 20% trim and boom. Seriously doubt its an air leak.

How is your upstream o2 sensor? Get some voltage readings. If there's a cyl misfire, it's gonna be throwing unburnt gas at your upstream o2. The sensor bounces rapidly anywhere between .2 and .8 volts. If its .5 or .6 to .8 or .9 then that verifies issue.

What kind of gas are you using? Spark plugs gapped with feeler gauges?
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Old 10-05-2014, 09:25 PM   #30
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So I took it back to the dealership and got the worst news.
Told me I needed a valve job. cyl 1 exhaust valve wasn't seating right. I asked if they would just replace the spring, and turn the valve like the TSB on multiple cylinder misfire said to do and he said nope. We either valve job or you go somewhere else.

So I'm now $1400 more poor.

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