Cylinder 2 Misfire

Jonathan Technical Support Specialist New Hampshire Posted   Latest  
Unsolved
Driveability
2004 Jeep Wrangler Sahara 4.0L (S) 5-spd (NV3550)
P0302 — Cylinder 2 Misfire Detected
Misfire

2004 Jeep Wrangler 4.0L 93k miles M/T

Tested Spark from coil OK. New Spark plugs just installed by another tech

Injector Pulse OK, Rear O2 sensor also shows rich running misfire condition as well

Static and Dynamic Compression tests compared to another cylinder same results 125psi static 70psi dynamic. Throttle snap running same results.

I do not have access to a in cylinder transducer

I have read on identifix cam lobes can wear on these engines and wear out lifter. Next test I am going to perform is remove valve cover and measure lift of rocker arm compared to another cylinder.

Any other thoughts/constructive criticism on my diagnostic process???

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Antonio Owner/Technician
Oregon
Antonio
 

Stuck open injector or Leaking?

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Jürgen Owner
Mexico
Jürgen
 

Under which condition does the misfire occur? Always, idle, load…? A worn cam lobe will show up on a running compression (snap) test, won't it? Although the injector pulse may be good the injector still may be leaking or otherwise be damaged. Can you check the secondary ignition on a good cylinder and compare it to #2?

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Jonathan Technical Support Specialist
New Hampshire
Jonathan
 

operating temp. Mostly at idle. Higher rpm and under load not as bad.

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Verne Technician
Michigan
Verne
 

Vaccum leak on intake?? Whats fuel trims doing at idle??

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Ray Diagnostician
Ontario
Ray
 

I would first connect a pressure transducer in the intake and another transducer in the tailpipe, disable the fuel system and crank the engine to compare each cylinder's intake stroke vacuum pulls and each cylinder's exhaust stroke pressure pulses. You could put a transducer on the dipstick tube to check for excessive cylinder blow-by compression pressures in the crankcase with the engine…

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Helpful
Glenn Owner/Technician
Texas
Glenn
 

Hi Jonathan, An 04' with only 93K on the clock? I would suspect twice that amount here in TX. Seeing how your static and dynamic compressions are all the same, I would take a mechanical issue off the diagnostic table for the moment. You mentioned the rear O2 sensor, what is the front O2 sensor reading? What is the MAF/MAP reading? Do you have a good old fashion basic vacuum gauge? If so hook…

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Shaun Technician
Nevada
Shaun
 

Check Cam Crank Correlation/Distributor sync with a capable scan tool.

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Richard Technician
New York
Richard
 

Can you do a relative compression test with a scope. If no scope available, I would hook up a vacuum gauge to see if the needle is rock steady. At this point you are going to want to rule out mechanical issues first.

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Agree
Timothy Owner/Technician
Wisconsin
Timothy
 

Since you state that the rear O2 sensor is always rich, what are the fuel trims on the truck? If they're negative, I'm leaning towards a fuel injector issue. Regardless of pulse. Keep in mind, that a rear O2, after cat light-off, is always around 600-700mV.

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Glenn Owner/Technician
Texas
Glenn
 

Hi Jonathan, Any updates on progress?

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Jonathan Technical Support Specialist
New Hampshire
Jonathan
 

swapped injector no change. Has to be worn cam lobe and mushroomed lifter. I don’t think I’m catching on a running compression tester with my analog gauge. It only starts to misfire at idle when warmed up to operating temp. No misfire cold. Customer declined tear down at this time. trying to get into buying pressure transducers to confirm incidents like this with a scope. Do you know of any…

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Glenn Owner/Technician
Texas
Glenn
 

Hi Jonathan, There are hundreds of hours of You Tube and instructor classes online. Go to ATS and watch some of the testing Bernie does, he is real sharp. Scanner Danner is another one I highly suggest. Stay away from the DIY ‘weekend warrior’ videos. Of course, avoid the ones that are only trying to sell you something. As for a good transducer setup, PICO is one of the best, but expensive…

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Jonathan Technical Support Specialist
New Hampshire
Jonathan
 

awesome thanks I have watched a bunch of Bernies videos, very intelligent man. I need to get these tools so I can practice with them.

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Jürgen Owner
Mexico
Jürgen
   

Jonathan, until you get your pressure sensors you can use the MAP sensor on vehicles equipped with such to see the intake pulses. AC-coupling will enhance the signal resolution if your scope allows for it. You also can use a MAP sensor on MAF engines, just power the sensor up with a suitable voltage and ground, connect it to the intake manifold and your scope to the signal wire. On you tube…

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Glenn Owner/Technician
Texas
Glenn
 

That is a great idea. I have never tried doing that with a MAP sensor. For the record it will take a 5V power source. Good video also.

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