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  #1  
Old December 3rd, 2018, 20:54
Roch Road Roch Road is offline
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Cylinder 1 Misfire Mystery!

I have a 97" XJ with a 4.0. I currently have the code telling me I have a cylinder 1 misfire. The CEL is on. I have tried 27 different things to fix it and a friend of mine who is a Jeep Mechanic and Engine builder has helped me too. I have 15 hours in the car trying to fix it with no avail. Here is a list of what we have done to try to fix the partial misfire.
New Distributer Cap, New rotor, New plugs, new spark plug wires, re-phased the distributer, Compression test (120-150), Leakdown test (at TDC & BDC), New fuel injector, Noid light test, checked for intake leaks, Put seafoam in the gas tank, changed the injector harness connector, New ECU, cleaned ECU terminals and put dialectric grease on harness plugs, fuel pressure is 49.3, checked the timing, OBD 2 scanned with Chrysler scanner, rocker arm and spring check, checked the squarewaves on the CPS, changed the CPS, changed the Camshaft position sensor, inspected with a camera down through the spark plug hole for cylinder wall damage, inspected the intake manifold with a camera for obstructions, new throttle body and sensors, check the voltage on the fuel injectors. Doesn't look like the cam is flat. Any thoughts? Your help would be GREATLY appreciated.
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Old December 4th, 2018, 03:22
RCP Phx RCP Phx is offline
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Re: Cylinder 1 Misfire Mystery!

It could be the signs of harness damage.
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Old December 4th, 2018, 04:18
RCP Phx RCP Phx is offline
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Re: Cylinder 1 Misfire Mystery!

BTW, you didn't mention checking the cam for "flat-spotting".
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Old December 4th, 2018, 08:05
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Tim_MN Tim_MN is offline
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Re: Cylinder 1 Misfire Mystery!

Weak valve springs ? Burned valves or valve seats ? Excess carbon deposits on valves ?

Chrysler has a TSB for Multiple Cylinder Misfire due to carbon deposits on exhaust valves.
It does not strictly apply to 1997's, but there is no reason to not read the TSB and do the suggested fixes.

Chrysler TSB 0900303
1999-2004 with 4.0 L engine
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Old December 4th, 2018, 10:16
92xjRJ 92xjRJ is offline
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Re: Cylinder 1 Misfire Mystery!

Quote:
Originally Posted by RCP Phx View Post
BTW, you didn't mention checking the cam for "flat-spotting".
I was going to suggest this. I have personally seen it on a 4.0 that wasn't driven very hard at all and the cam being flat spotted was the issue.
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Old December 4th, 2018, 21:03
Roch Road Roch Road is offline
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Re: Cylinder 1 Misfire Mystery!

Thanks for the help. I did look at the rocker arm geometry and the valve springs as I cranked the motor over a number of times. I did not put a dial indicator on the valve springs because they looked like they had just as much lift as the other cylinders. I think this would have eliminated the possibility of a flat cam lobe. The oil also does not show any signs of metallic material. The valves did not look like they working sticking in the guides either. No funny sounds. The Noid light test I did reveals the same pulse on the #1 injector compared to the other 5. Maybe I need to to try to decarbon with the molar stuff. I tried seafoam but noticed no improvement.
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Old December 4th, 2018, 21:17
Roch Road Roch Road is offline
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Re: Cylinder 1 Misfire Mystery!

Sorry for the typos. I am going to try the mopar combustion chamber cleaner tomorrow. I just read the tbs that u guys suggested in respect to valves that may have carbon deposits are are not rotating properly. Only confusion is that the Leakdown test was perfect that we did.
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Old December 5th, 2018, 07:09
RCP Phx RCP Phx is offline
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Re: Cylinder 1 Misfire Mystery!

Quote:
Originally Posted by Roch Road View Post
Thanks for the help. I did look at the rocker arm geometry and the valve springs as I cranked the motor over a number of times. I did not put a dial indicator on the valve springs because they looked like they had just as much lift as the other cylinders. I think this would have eliminated the possibility of a flat cam lobe. The oil also does not show any signs of metallic material. The valves did not look like they working sticking in the guides either. No funny sounds. The Noid light test I did reveals the same pulse on the #1 injector compared to the other 5. Maybe I need to to try to decarbon with the molar stuff. I tried seafoam but noticed no improvement.
You must have "Superman" eyes if you can "see" the difference in .300" and .250", I have to use a dial indicator!
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Old December 5th, 2018, 21:54
Roch Road Roch Road is offline
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Re: Cylinder 1 Misfire Mystery!

Point taken.
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Old December 5th, 2018, 21:58
Roch Road Roch Road is offline
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Re: Cylinder 1 Misfire Mystery!

I tried the mopar combustion chamber cleaner stuff today and followed the directions from the tsb. No results were produced. I am going to pull the motor tomorrow and take a look at things a little more deeply. Hopefully we see something. I’ll keep u guys posted.
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  #11  
Old December 6th, 2018, 13:22
92xjRJ 92xjRJ is offline
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Re: Cylinder 1 Misfire Mystery!

Quote:
Originally Posted by RCP Phx View Post
You must have "Superman" eyes if you can "see" the difference in .300" and .250", I have to use a dial indicator!

My thoughts as well, I still say you pull that cam out before you pull the motor. but that's just my two cents.
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Old December 6th, 2018, 13:23
92xjRJ 92xjRJ is offline
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Re: Cylinder 1 Misfire Mystery!

If its the cam you should be able to see the wear on the lobes, or just use a dial and don't take it apart
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Old December 6th, 2018, 16:15
RCP Phx RCP Phx is offline
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Re: Cylinder 1 Misfire Mystery!

I wouldn't take anything apart until I knew what was going on, There's alot you haven't done yet that could prove what's up.
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  #14  
Old December 10th, 2018, 17:35
Roch Road Roch Road is offline
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Re: Cylinder 1 Misfire Mystery!

We pulled the head off of it and noticed the #1 exhaust seat was beat up. With a flashlight you could see light passing through the valve and seat. Also, the exhaust valves were pretty pitted and a few of them were not spinning anymore. Hopefully rebuilding the head fixes the problem. If not we will check the cam. Thanks for the help.
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  #15  
Old December 11th, 2018, 06:56
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Re: Cylinder 1 Misfire Mystery!

I know you did SeaFoam, but from 50 years experience, run a can of BG44K through the fuel. I do it every 10K miles on every vehicle.

Now another thing to try. Swap a couple of injectors and make sure the misfire does not follow the injector.

Make sure the injector plugs are on the matching injectors. Getting them swapped can cause interesting issues on vehicles using sequential injector firing instead of batch mode.

Might be a weak valve spring or "lazy" lifter / bent valve push rod. If you have good compression, and the valve seat is not looking right, it might be a spring or lifter.

Can you feel the miss? If so, is it only under load?
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