94 4.0 with misfire / Dead Cylinder
02-12-2017, 07:04 PM
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Model: Cherokee
94 4.0 with misfire / Dead Cylinder
I read thru as many threads as I could to see if I could find a duplicate problem before I posted this, but I could not locate one.
My sons 94 XJ has a dead #2 cyl. I first checked the plug wire for spark, it was firing, but no change in the idle when the wire was removed. Changed out the plug with another brand (Autolite), same problem (Champion plugs to begin with). Plugs are less than a year old. I then removed the #2 injector plug and checked it with a noid light, appears to be firing the same as #1 which is operating properly.
I pulled the fuel rail and removed the injector on #2, checked it with a jig I made with an injector harness plug, it looks to be firing properly. Swapped #2 and #3 injectors, put it back together, same thing, #2 dead, #3 fine. Not the injector.
Then I checked compression on #2, 140lbs. Examined the plugs in #2 and #3, look the same, nice gray color, no oil, no raw fuel on either. Pulled the valve cover off and watched the valve train turn over a few times with the coil wire removed, seemed to be operating ok.
Then I removed the rocker arms off #2, put 125lbs of air to it with the compression tester and my air compressor, could hear no obvious leak in exhaust or intake. Talked with mechanic friend, said take the other two plugs out around it and pressurize it again to see if anything is going cylinder to cylinder. Did that, no problems, #1,#2 and #3 are all 130lbs.
When I went to put the rocker arms back on, I noticed the intake rocker on #2 looked like it was off a little. Looked closer and discovered the rocker bridge was bent. I pulled one off another 4.0 I have and put it on, appeared ok. Put the valve cover back on, #2 still not functioning.
I then changed out the distributor cap, rotor and plug wires, still no change.
I got to thinking about the rocker bridge, pulled the valve cover back off and checked the movement of the valves, rockers and springs on #2, seems to be fine, they travel like they should. I can't imagine a valve is broken, there would be no compression. The springs look fine. the valves are traveling the same as the others.
This one has me stumped. Any suggestions would be appreciated.
My sons 94 XJ has a dead #2 cyl. I first checked the plug wire for spark, it was firing, but no change in the idle when the wire was removed. Changed out the plug with another brand (Autolite), same problem (Champion plugs to begin with). Plugs are less than a year old. I then removed the #2 injector plug and checked it with a noid light, appears to be firing the same as #1 which is operating properly.
I pulled the fuel rail and removed the injector on #2, checked it with a jig I made with an injector harness plug, it looks to be firing properly. Swapped #2 and #3 injectors, put it back together, same thing, #2 dead, #3 fine. Not the injector.
Then I checked compression on #2, 140lbs. Examined the plugs in #2 and #3, look the same, nice gray color, no oil, no raw fuel on either. Pulled the valve cover off and watched the valve train turn over a few times with the coil wire removed, seemed to be operating ok.
Then I removed the rocker arms off #2, put 125lbs of air to it with the compression tester and my air compressor, could hear no obvious leak in exhaust or intake. Talked with mechanic friend, said take the other two plugs out around it and pressurize it again to see if anything is going cylinder to cylinder. Did that, no problems, #1,#2 and #3 are all 130lbs.
When I went to put the rocker arms back on, I noticed the intake rocker on #2 looked like it was off a little. Looked closer and discovered the rocker bridge was bent. I pulled one off another 4.0 I have and put it on, appeared ok. Put the valve cover back on, #2 still not functioning.
I then changed out the distributor cap, rotor and plug wires, still no change.
I got to thinking about the rocker bridge, pulled the valve cover back off and checked the movement of the valves, rockers and springs on #2, seems to be fine, they travel like they should. I can't imagine a valve is broken, there would be no compression. The springs look fine. the valves are traveling the same as the others.
This one has me stumped. Any suggestions would be appreciated.
Last edited by specauto; 02-12-2017 at 08:31 PM.
