97 4.0 has a misfire on cylinder 6 (could it be fuel injector resistance?)

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barrios35

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New to me Jeep, started to get a misfire cylinder 6. I changed plugs ( Champion Copper), wires, rotor, cap and ignition coil. Have the diagnostic hooked up and getting the preliminary misfire without triggering the engine light. Took a reading on the injectors all where 12.4 except #6 at 12.0. Service manual was at around 12.

Is that enough of variance do consider it a bad injector?

1997 161,700 miles, 4.0L
 
barrios35 said:
New to me Jeep, started to get a misfire cylinder 6. I changed plugs ( Champion Copper), wires, rotor, cap and ignition coil. Have the diagnostic hooked up and getting the preliminary misfire without triggering the engine light. Took a reading on the injectors all where 12.4 except #6 at 12.0. Service manual was at around 12.

Is that enough of variance do consider it a bad injector?

1997 161,700 miles, 4.0L
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I wouldn’t consider it out of spec.
You could move #6 to another cylinder and see if the misfire moves with it.
But since it’s new to you. Is this a fresh tank of fuel?
 
never monday said:
I wouldn’t consider it out of spec.
You could move #6 to another cylinder and see if the misfire moves with it.
But since it’s new to you. Is this a fresh tank of fuel?
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I have owned it for about a month. Fresh fuel from yesterday.

I did not think so either. I wonder if it might be dirty/partially clogged.

I need to clean the throttle body. Should I throw in fuel injector cleaner in the tank.

Old plugs looked like the had carbon build up. Might be have been running rich.
 
barrios35 said:
I will try that this weekend. Thanks
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I should expound on my thought.
A missfire can happen from losing any one of the 3 legs of the fire triangle. You’ve ruled out ignition with the new plugs. Rule out fuel by moving the injector. If the misfire persists on #6 then you have an “air” problem. Makes it time for a compression test on that cylinder.
 
never monday said:
I should expound on my thought.
A missfire can happen from losing any one of the 3 legs of the fire triangle. You’ve ruled out ignition with the new plugs. Rule out fuel by moving the injector. If the misfire persists on #6 then you have an “air” problem. Makes it time for a compression test on that cylinder.
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Absolutely, I went the least expensive and easiest for me. Never pulled an injector but will try to move it this weekend.

I have read the post on the valves. Hopefully not an air problem. 😩
 
So I took the injectors out and swapped out cycl 6 and cycl 1. I did clean them out as they were really gunked up. Attached a 9 volt to them and sprayed them with carb cleaner. So far day two with no pending misfires. Maybe it was just a dirty injector.

I don't think they have ever been pulled out so it was a pain.

Wanted to thank everyone for their input. Hopefully it stays running good.
 
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barrios35 said:
So I took the injectors out and swapped out cycl 6 and cycl 1. I did clean them out as they were really gunked up. Attached a 9 volt to them and sprayed them with carb cleaner. So far day two with no pending misfires. Maybe it was just a dirty injector.

I don't think they have ever been pulled out so it was a pain.

Wanted to thank everyone for their input. Hopefully it stays running good.
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And I spoke too soon. I got the pending misfire cycl 6 on the monitor. So I did fuel, and spark. Anything else to try?
 
Weasellee said:
Update?
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Well I have not really driven the Jeep. I had to drop the fuel tank as I had a strong fuel smell. Had to cut off some of the bolts that hold up the tank. Remove as much as I could rust and repaint. Turns out the pump was completely off. Crazy! Replaced the fuel filter while it was out and tank seal. Parts took forever. As far as the misfire, I did find the intake manifold and exhaust manifold loose, especially near cylinder 6, hopefully that was my random misfire issue. I won't know until the tank is back up. I will report back hopefully soon.
 
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Just wanted to give another update. Fuel tank is back in. Been through a tank of gas and it is running so smooth. I am thinking the loose bolts on the intake and exhaust where the reason. Just another point to check for the misfire.

If anything changes I will chime back in. Thanks to everyone for their help.
 
barrios35 said:
Just wanted to give another update. Fuel tank is back in. Been through a tank of gas and it is running so smooth. I am thinking the loose bolts on the intake and exhaust where the reason. Just another point to check for the misfire.

If anything changes I will chime back in. Thanks to everyone for their help.
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The intake and exhaust leaks could create a lean condition which could trigger a misfire....
Another problem that can cause a specific cylinder misfire would be carbon accumulation in the combustion chamber,
 
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