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Cylinder 1 Misfire Mystery!

Roch Road

NAXJA Forum User
Location
Anaheim
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.
 
It could be the signs of harness damage.
 
BTW, you didn't mention checking the cam for "flat-spotting".
 
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
 
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.
 
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.
 
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!
 
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.
 
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.
 
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.
 
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?
 
Thanks for the insight. You can definitely feel the misfire. It is always there. Under a load and at idle.I tried new injectors and swapped them. The misfire stays on cylinder 1. I need to check the valve springs as well. I also did not check the lifters. The injector harness’s are also on the correct injectors.
 
Jeep is running great now! After the head rebuild with new exhaust valves and seats, everything is back to normal! Thank u guys for all your insight and help.
 
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