Misfire in #1 cylinder


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Old 10-24-2012, 12:34 PM   #1
PrunedaleMike
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Default Misfire in #1 cylinder

Hey Guys and Gals,

My 97 XJ 4.0 has a misfire in cylinder #1 only and only when it warms up. The engine has headers, K&N free flow air filter kit, and did have a chip (shhh, California) installed. All wires have been checked, plugs replaced, sensors tested and passed. The check engine light comes on once it warms up and the misfiring in #1 starts. Driving me bonkers Please help!!
Thanks,
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Old 10-24-2012, 02:25 PM   #2
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Could be a partially clogged injector??

Have you tested the fuel system?

Physically checked for spark as it's "failing"?
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Old 10-24-2012, 07:54 PM   #3
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All the injectors have check out with isolation test and the different working temps. Haven't check for the spark at the time of failure. What would cause a misfire other than electrical or fuel problems, valve springs?
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Old 10-24-2012, 08:36 PM   #4
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Causes of misfires off the top of my head.....

Broken, cracked, faulty, fouled, incorrectly gaped spark plug
Bad wire
Bad/cracked/moiusture in or at dist cap
Loose/damaged rotor
Excessive play in distributor shaft
Incorrect firing order
Faulty injector
Bad ground
Bad harness
Valve timing
Compression issue
Low fuel pressure
ECM issues
Faulty sensors

That should be enough to get you started.
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Old 10-25-2012, 08:49 PM   #5
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Oka doka , Spark plugs new and rechecked, new wires, new distributor cap and rotor, firing order correct, injectors function tested, compression good and even, and sensors replaced.That leaves bad ground, bad harness, valve timing, fuel pressure, ECM issues, kwel thanks.
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Old 10-26-2012, 12:34 AM   #6
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This is a bit of a stumper, if #1 injector is firing via the ECU and you are getting fuel out of it then it can’t be ECU, pressure, harness, or injector. Only #1 is doing it so it can’t be valve timing, all of the above would result in other cylinders miss-firing. You have compression so it can’t be a burned valve or crack between the valves. If the springs were bad you would see it in the compression test.

Only thing I can think is spark plug, when you pull it and crank over and look at the spark, there is no pressure, so the path of least resistance is an arc to the side electrode, but when it is in the head there is pressure so if the insulator has a small crack it can arc to ground, had something similar to this and that was it, many many hours to find that one.

But just because it is new does not result in trust, pull the plug wire and measure it with an ohm meter, you should have less then 1K ohm per foot, when testing it bend the wire back and forth. Could also be a crack at #1 terminal on the cap or high resistance.

Only other thing I could think is to wiggle the #1 injector harnesses when it is running to see if you can replicate it.
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Old 10-26-2012, 06:31 AM   #7
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I would triple check the gap on the #1 plug as well. Also make sure there are no cracks in the porcelain. If you're not sure, you could switch 2 plugs and see if the cylinder misfire changes. You can also do it with the wires to try to narrow it down. Takes a small amount of time but atleast it doesn't cost any money to attempt. Let us know how you made out.
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Old 10-26-2012, 08:28 AM   #8
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Testing mobile bugs. Please ignore posts will automatically deleted within 24 hours.
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Old 10-27-2012, 01:43 PM   #9
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Quote:
Originally Posted by Rush Power Systems View Post
This is a bit of a stumper, if #1 injector is firing via the ECU and you are getting fuel out of it then it canít be ECU, pressure, harness, or injector. Only #1 is doing it so it canít be valve timing, all of the above would result in other cylinders miss-firing. You have compression so it canít be a burned valve or crack between the valves. If the springs were bad you would see it in the compression test.

Only thing I can think is spark plug, when you pull it and crank over and look at the spark, there is no pressure, so the path of least resistance is an arc to the side electrode, but when it is in the head there is pressure so if the insulator has a small crack it can arc to ground, had something similar to this and that was it, many many hours to find that one.

But just because it is new does not result in trust, pull the plug wire and measure it with an ohm meter, you should have less then 1K ohm per foot, when testing it bend the wire back and forth. Could also be a crack at #1 terminal on the cap or high resistance.

Only other thing I could think is to wiggle the #1 injector harnesses when it is running to see if you can replicate it.
Could a weak spring cause the miss after it warms up. It runs great when first started but after warming up it starts missing. Heat can change alot of different scenarios. Sure is a head scratcher.
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Old 10-27-2012, 02:15 PM   #10
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if the compression test was done on a hot engine then the results give an indication of a spring problem. i would opt for a leak down test when hot. but if the valve is opening it would be a lean fire not a misfire.
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Old 10-30-2012, 10:47 PM   #11
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Found the problem! Followed Rush Power Systems suggestion about the leak down test and found air being blown back into the crankcase. At idle the rings are cold so it runs rough and as the rpm increases I guess the pressure builds allowing cylinder to "help " a bit.
I am not sure what my most economical option is, rebuild or find a good used block. Any thoughts?

At lest I know what is the problem. Thanks to all of you folks who helped.

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Old 10-31-2012, 12:45 PM   #12
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If it were me, I'd grab my Haynes manual and try to replace the rings. I'd be lookin' at dropping the oil pan and crank, pull the pistons down and slap some new rings on 'em if possible. Sounds cheaper to me and you'll have a chance to check everything out in there. My $0.02
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Old 10-31-2012, 08:27 PM   #13
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Looks like a full set of piston rings are relatively cheap. I'd look into what else may need to be fixed on your engine, such as any leaks any ticks, knocks etc. If you have none of those then by all means replace the piston rings. No sense in throwing away a good engine. You may even be able to over haul all the piston components for less than a used engine.
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Old 11-01-2012, 07:15 PM   #14
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Wow that sounds great. I'm kidda new at "deep" work on my jeep, any good "how to books" out there you guys can suggest?
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Old 11-02-2012, 12:23 PM   #15
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Hit up the auto parts store for a Hayne's or Chilton's manual. They're pretty detailed and usually have pics to show you what's up along the way. Just be sure to read all the notes and warnings they throw in there... I ripped a head bolt out of a Yota one day cuz of that.


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