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Old 09-14-2013, 07:02 PM   #1
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Cylinder 2 misfire with lots of diagnosis. Now Lost, need help!

1998 2.5L auto

Received code P0302 indicating cylinder 2 misfire relating to primary circuit.

... Replaced spark plug
... Has plenty of spark from wires
... Unplugged injector connector and no change, unplugging any of the others cause stalling
... Replaced injector and same problem, no change when unplugging connector
... Switched injectors around and still only cylinder 2 no change
... Ohm'd out the injector plugs and cylinders 1,3,4 and they are around 3.5, cylinder 2 is around 3.9
... Cylinder 2 voltage is at 13.5 volts, it goes to 13.5 volts through both wires when connected
... Cut the injector plug for cylinder 2 and directly connected the wires to the injector, still no change.

Now at a loss. Is it a wiring harness problem, computer problem?

Haven't checked compression on the cylinder itself, don't have the gauges currently

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Old 09-14-2013, 07:52 PM   #2
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Do a compression test on the cylinder.

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Old 09-14-2013, 08:05 PM   #3
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Your tests thus far are saying its not a fuel problem.
Without proper compression the fuel looses its ability to be easily ignite by spark, along with the fuel/air mixture is being leaked out of the combustion chamber ergo bad rings, or valves.
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Old 09-14-2013, 08:29 PM   #4
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Quote:
Originally Posted by DmnSlyr View Post
1998 2.5L auto

Received code P0302 indicating cylinder 2 misfire relating to primary circuit.

... Replaced spark plug
... Has plenty of spark from wires
... Unplugged injector connector and no change, unplugging any of the others cause stalling
... Replaced injector and same problem, no change when unplugging connector
... Switched injectors around and still only cylinder 2 no change
... Ohm'd out the injector plugs and cylinders 1,3,4 and they are around 3.5, cylinder 2 is around 3.9
... Cylinder 2 voltage is at 13.5 volts, it goes to 13.5 volts through both wires when connected
... Cut the injector plug for cylinder 2 and directly connected the wires to the injector, still no change.

Now at a loss. Is it a wiring harness problem, computer problem?

Haven't checked compression on the cylinder itself, don't have the gauges currently
Same shit happened to my old car it was compression
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Old 09-14-2013, 11:12 PM   #5
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How many miles? For what it is worth you can swap around plug wires (or just OHM them out to see if you have a bad one). Otherwise -yes may have low compression on hole # 2-no poping noise? in intake like from bent pushrod, or clicking noise? like rocker arm backed off. May have a hole in the piston-but usually when that happens-there is a lot of blow-by out the oil cap/PVC valve.If you do find low compression-fist step is to pull off valve cover-check rockers at # 2. maybe rounded cam lobe if rockers don't open/close right. turn engine over with plugs out, batt disconnected, use socket/breaker bar on crank to turn/watch rockers.
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Old 09-15-2013, 12:00 PM   #6
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It only has 105k miles on it. When measuring ohms cylinder 2 read 3.9 and everything else was around 3.5. None of those listed noises are present
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Old 09-15-2013, 02:04 PM   #7
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Originally Posted by DmnSlyr View Post
It only has 105k miles on it. When measuring ohms cylinder 2 read 3.9 and everything else was around 3.5. None of those listed noises are present
If your concerned it's a bad injector it's pretty quick and easy to swap it for another, if number 2 comes back and the cylinder you swapped the injector to drops out you've verified your issue.

If not, go back to basics and run a compression test.
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Old 09-15-2013, 02:10 PM   #8
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Some '97-98 TJ engines had a bad/weak set of valve springs installed into them that eventually start causing random misfires that can't be fixed by replacing the usual items like plugs, wiring, distributor cap/rotor, fuel injectors, etc.

The only fix is new valve springs and depending on how long it has been going on, a complete valve job may actually be required.

I had the same issue on my '97 TJ & new valve springs took care of 90% of my random intermittent misfires. It would have taken a valve job to get rid of them all.
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Old 09-23-2013, 10:50 AM   #9
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Update: We did a compression test and cylinder 2 would not hold pressure. It would bump up to 30 psi but drop immediately to 0. We took the valve cover off and all the springs looked fine. We even started it and everything looked like it was working well. There is almost no blowback if any coming from the oil cap and the valve cover wasnt oily at all.

Anyone else have any diagnosis help?????
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Old 09-23-2013, 03:34 PM   #10
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Update: We did a compression test and cylinder 2 would not hold pressure. It would bump up to 30 psi but drop immediately to 0. We took the valve cover off and all the springs looked fine. We even started it and everything looked like it was working well. There is almost no blowback if any coming from the oil cap and the valve cover wasnt oily at all.

Anyone else have any diagnosis help?????
if its not holding pressure wouldnt it be rings/piston/cylinder issues?
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Old 09-23-2013, 05:43 PM   #11
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Originally Posted by DmnSlyr View Post
Update: We did a compression test and cylinder 2 would not hold pressure. It would bump up to 30 psi but drop immediately to 0. We took the valve cover off and all the springs looked fine. We even started it and everything looked like it was working well. There is almost no blowback if any coming from the oil cap and the valve cover wasnt oily at all.

Anyone else have any diagnosis help?????
Next step would be to run a "Wet" compression test simply add several drops of engine oil into the sparkplug hole and retest your compression. If the compression increases it means you have a worn ring/cylinder condition if it does not increase you have a burnt valve or blown head gasket concern.
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Old 10-10-2013, 08:13 AM   #12
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We ended up taking the head off and sending it to a motor machinist to check it out. The piston heads looked fine to the naked eye. All the valve rods were fine too.
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Old 10-18-2013, 06:44 AM   #13
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Update: The machinist said that our valves were actually bad. He is replacing them and milling the entire head for cheap.
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Old 10-18-2013, 06:53 AM   #14
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Quote:
Originally Posted by flflash View Post
Next step would be to run a "Wet" compression test simply add several drops of engine oil into the sparkplug hole and retest your compression. If the compression increases it means you have a worn ring/cylinder condition if it does not increase you have a burnt valve or blown head gasket concern.
What would happen if one were to perform this test with a perfectly good engine? You say if the pressure goes up there is a problem, if it does not go up there is a problem.

I generally try to apply logic to what I read, and either I'm reading it wrong, flash misspoke, or there is no logic to be had with this test.
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Old 10-27-2013, 09:47 AM   #15
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Alright guys here is another update. We got the completely redone head installed with new gaskets, new bolts, new valves, and new springs. We have everything put back together and to no avail it still has a misfire. The engine mechanic said if the pistons were bad we would see large gouges or scrapes in the cylinders and there were none. We know we have spark in the misfiring cylinder (cylinder 2). The only diagnosis we have is when we unplug the censor on fuel injector 2. When we unplug it/plug it back in there is no change but if we unplug any other sensor from their injector the engine about dies. All of The fuel injectors sensors are getting 14V. Any help would be greatly appreciated. I should be able to answer any questions you have
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Old 11-07-2013, 10:06 AM   #16
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Wondering if you solved the problem yet as I am in the process of fixing similar issue in my 95 YJ. Head is off, going to check valves and go from there. Good luck with yours and thanks to everyone for making owning and working on a jeep so much fun.
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Old 11-08-2013, 11:27 AM   #17
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Wondering if you solved the problem yet as I am in the process of fixing similar issue in my 95 YJ. Head is off, going to check valves and go from there. Good luck with yours and thanks to everyone for making owning and working on a jeep so much fun.
Actually we had a friend come by with his computer tester and my computer wouldn't even talk to his. So we ended up ordering a refurbished computer with lifetime warranty. I should know this weekend if that solved it
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Old 11-08-2013, 09:50 PM   #18
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Did you recheck the compression since the head was back on?
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Old 11-11-2013, 05:57 AM   #19
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No but with the new computer it is running beautifully. After we put the head on we found that the connector on fuel injector 2 was not telling it to fire. We tested the injector and the injector was fine so we determined it had to be electrical or computer related.

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