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Cylinder#1 Misfire!


 
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FloridaJeep11
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Joined: 05 Apr 2007

PostPosted: Sun Aug 17, 2008 2:16 pm    Post subject: Cylinder#1 Misfire! Reply with quote

Can anyone tell me what can cause a cylinder to misfire?
things i have checked, Spark plugs, loose spark plug cables, distributor, spark plug gap.
any other advise would be greatly appriciated. Shocked

Thanks.
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Polar01
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Joined: 20 May 2008
Location: Motor City

PostPosted: Mon Aug 18, 2008 7:06 pm    Post subject: Reply with quote

What is the nature of the misfire? Occasional, stuttering or constant?

Witout more detail, it's tough to monday-morning quarterback it from here. I don't want to insult your automotive knowledge, and I don't know your skill level, so i'm just going to throw some ideas to you.

What engine and how many miles on it? I'm not super-familiar with the TJ straight sixes, but I've had 2 CJ's, both with the 258-6, and rebuilt both of them, along with a slew of V8's, some VWs, a few Audis, and a Land Rover (Series IIA - not the soccer mom Disco).

1. Timing. You said you checked the distributor, but didn't go into detail as to what you checked with the distributor. There is initial timing, mechanical advance, and vacuum advance. Is the hold-down bolt working itself loose? If the engine is high mileage, the timing chain and sprockets may be very worn. A certified Jeep mechanic friend of mine said the 4-cyl's are notorious for extreme timing chain stretch after only 65K miles.

2. Valvetrain (pray to whoever it's not your valves/seats/pushrods/lifters) Both my CJ's bent pushrods.

3. Camshaft. This is a bit of a long shot, but camshaft lobes sometimes wear down (called rounding-off) causing a very wierd misfire and running condition. 305 Chevys were known for this, and i've seen it on a few poorly maintained others. Misadjusted valvetrain usually causes this.

4. Electronic Fuel injection. I'm more of a carb guy, which i'm guessing you don't have. As far as EFI goes, my experience is somewhat limited, I've never had to mess with mine on my Jeep, so i'm not sure if the injectors are rebuildable, some can be disassembled and cleaned. If they can, you might need a couple of special tools. If not, try running a couple bottles of Injector Cleaner thru her, "Lucas" and "Chevron with Techron" are pretty good in my experience. Also Oxygen sensors and Mass-AirFlow sensors can cause false readings sent to the computer which can result in a piss-poor running vehicle. If you run an oiled air filter element (K&N) the oil in the filter can coat the wires on the MAF sensor, dirt and crud will cling to them, and send false readings to the computer. They make MAF sensor cleaner, for like $6. If you have an exhaust leak ahead of the O2 sensor, again, it will send bad readings to the computer. The computer runs in either MAF or Speed-Density mode, some use both. (not sure what Jeep computers use)

I could speculate all night, but it boils down to Fuel/Spark/Mechanicals. For you, if it's [/b]only the number one jug, I would look at mechanicals.[/i]
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'01 TJ- Rubi springs, BDS shocks, 33x10.5-15 BFG KM's, soft top, Bestop full soft doors, PIAA's, WP corners, interior by Herculiner, etc...
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Polar01
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Joined: 20 May 2008
Location: Motor City

PostPosted: Mon Aug 18, 2008 7:10 pm    Post subject: Reply with quote

And apparently I can't operate the bold/italics features when posting replies. hahaha.
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'01 TJ- Rubi springs, BDS shocks, 33x10.5-15 BFG KM's, soft top, Bestop full soft doors, PIAA's, WP corners, interior by Herculiner, etc...
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FloridaJeep11
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Joined: 05 Apr 2007

PostPosted: Tue Aug 19, 2008 8:55 am    Post subject: Misfire cylinder. Reply with quote

1998 TJ, 135K miles, 6cylinders, 4.0L Fuel injected, not running rough at all, RPMs at idle run at about 760.
What happened was I purchased a OBD computer because my "check engine light" came on...then it went off. But it came back on.
The OBD was was giving me a trouble code P0301 I believe...and it stated Cylinder#1 misfire.
I'm not much of a mechanic..very basic knowledge....try to do my own routine maintenance among other things.
thanks.
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Polar01
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Joined: 20 May 2008
Location: Motor City

PostPosted: Tue Aug 19, 2008 5:40 pm    Post subject: Reply with quote

Man, thank god it's nothing serious.

Usually, when the Check Engine light comes on, it's an emissions issue. I had the same problem with my '01, and it was an exhaust manifold gasket leak. The exhaust manifold will suck in a bit of air at the leak during scavenging, giving your oxygen sensor false readings, which the computer will try and correct, in my case, with alot more fuel.

I don't know what exact code came up with mine, I did the ignition on/off trick and called my Jeep connection. It was a couple years ago and I can't remember exactly how to do it, maybe someone reading this will know, but from what I remember, you switch the ignition on and off 3 (i think) times (without starting the vehicle - the last switch position before she cranks) and the Check Engine light should flash a certain number of times, count them, and then look up the number in a trouble code list. Mine came up as oxygen sensor something-or-other. Like I said, it was a while ago. I installed a new gasket, disconnected my battery for a little while to completely reset the computer, and it ran fine.

I dont know if the six cylinders have an O2 sensor before and after the Catalytic converter (one for rough engine tune before the cat, and one for fine tune after the cat - but I don't think Jeeps are that fancy), mine has one before the cat. But with as many miles as you have, I would look at replacing the O2 sensor(s) and checking the emissions systems for possible causes.

If you do get a new O2 sensor(s), make sure to get the right one if you go aftermarket. There are narrow-band, and wide-band versions. I don't know which the factory one is for the six. A new Cat would'nt be a bad idea either with that many miles.

Hope that helps a little.
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