Cylinder 1 Misfire. NOT plug,coil,or injector. Help

[1955moose]

Do a compression test of that cylinder, actually I would do all banks to be sure their all balanced within each other and pull valve cover and inspect it visually. I know the new technology can show basic engine balance, and compression through scanners, but nothing like doing a full eight cylinders compression test with a quality screw in gauge like Snap on, or Matco. A cylinder balance test with a pressurized gauge is standard procedure with any compression issue. Tells you if you've got bad valve, valve guide seals or rings. A weak valve spring is a little tougher to diagnose. Unless it's visable, like laying in the valve cover, a weak valve spring would usually require pulling that cylinder head, dismantling that suspect spring, and tensile test it. Not a common issue, but anythings possible.

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[stamp11127]

Looking back at your first post, what criteria did the dealer use to determine it is cylinder #1#if there were no codes?

 

[BrinkExpo]

Looking back at your first post, what criteria did the dealer use to determine it is cylinder #1#if there were no codes?

He had his computer plugged in and when I drove the truck and got it to misfire, I could see cylinder 1 spike on his graph when all the others remained consistent. It did this several times.

Not sure what this was reading but that’s the best I can explain.

 

[BrinkExpo]

Do a compression test of that cylinder, actually I would do all banks to be sure their all balanced within each other and pull valve cover and inspect it visually. I know the new technology can show basic engine balance, and compression through scanners, but nothing like doing a full eight cylinders compression test with a quality screw in gauge like Snap on, or Matco. A cylinder balance test with a pressurized gauge is standard procedure with any compression issue. Tells you if you've got bad valve, valve guide seals or rings. A weak valve spring is a little tougher to diagnose. Unless it's visable, like laying in the valve cover, a weak valve spring would usually require pulling that cylinder head, dismantling that suspect spring, and tensile test it. Not a common issue, but anythings possible.

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Are most shops able to do a compression test with a quality screw in gauge to learn more of what’s going on or is the dealer the best place?

 

[1955moose]

Of course they can. It's difficult to get at the back cylinders, that's an understatement. But any decent repair facility should be able to do it. What bugs me is you now stated his scanner had a kv spike. Guys correct me if I'm wrong, but that's generally a secondary ignition malfunction!

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[BrinkExpo]

I brought it to the dealer again to have them really dive into this and they said the next step was to take passenger valve cover off and check for broken rocker arm or valve spring. We did that and everything looks great. Put it back together and it is misfiring on multiple cylinders on passenger side(it is hard to read the misfires above 2500 RPMS I was told). They replaced 1&2&3 plugs and moved coils around and it still misfires. They also said that the misfires happens between 3000 and 4500 RPMS and then it clears up. Fuel injectors are spraying fine. Fuel injector harness looks good. Relative compression is good.

The dealer is at a loss now and doesn't even know what to try. Possibly a clogged catalytic converter but they said normally a whole bank of cylinders misfires if that is the case.

I do not want to throw anymore money at this issue but it is bugging me and I don't want it to leave my wife on the side of the road with our 4 kids. Any other thoughts? Or just drive the darn thing?

 

[1955moose]

Maybe I'm missing something here. One item that wasn't mentioned is the fuel pump control module. Usually a spark related issue gets worse as rpm climbs. That's why they usually show up at highway speeds. You state that it clears up above 4500, which is close to redline. Have the shop or someone check to see if the fuel pressure is fluctuating. A failing fpcm may be causing a starving sensation under load. The only other thing comes to mind would be a small pinhole in combustion chamber of #7 head, causing misfire of coolant and fuel trying to fire.

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[BrinkExpo]

I replace the fuel pump control module last year.

 

[BrinkExpo]

That is in the back on the drivers side frame right?

 

[stamp11127]

What was being monitored that showed the spike?

I don't see where a kv spike was mentioned.

Did they compare the signals between the crank and cam position sensors while it was misfiring?