cjimmy

Recently purchased this 08 E350. Changed the oil and it started missing and throwing code P0302. It had the wrong spark plugs in it, changed the plugs and tested the compression. Still throwing the cylinder 2 missfire code.

1 - 115psi
2 - 110psi
3 - 115psi
4 - 120psi
5 - 120psi
6 - 120psi

Those seem on the low side to me, but nice and consistent. Is 110 enough to fire in this car? I have had other cars with less that ran, but am not that familiar with this motor. Swapping coil packs with another cylinder did not move the problem. How do I test the injectors?

Thanks

gogydm

Why not try moving the injectors around also?

cjimmy

Thanks for the suggestion. I will try that today.

n33kolas

Did this move the misfire?

cjimmy

No, it did not move it it multiplied it. I moved the injector from cylinder 2 to cylinder 1 and got a misfire in both 1 and 2. My theory at this point is the the misfire in 2 caused some carbon buildup on the valves reducing compression and causing cylinder 2 to misfire even with a good injector. I got frustrated and walked away... I took the car to a mechanic I trust yesterday. We will see what he says.

tjts1

Why would you move the injector? Move the ignition coil.

gogydm

He has already tried the coil and spark plug as said in the first post, that is why I suggested the injector. My guess now would be carbon buildup. Just as a FYI I have a friend that experienced similar issues with a misfire. When it threw the code the ECU would shut down the injector. Everything started and after an oil additive was added. After many tests it turned out that the hydraulic lifter would not close the valve all the way because the additive got to the lifter and prevented it from fully closing. A couple of oil changes with the right oil with 250-500 miles on each got rid of the issue.

tjts1

Ah I see that now. I still wouldn't be swapping injectors quite yet.

cjimmy

Following up on this. After much frustration and basically giving up I took it to an indy and he essentially used Sea Foam to clean up the carbon build up in the cylinders. Essentially it had been running poorly long enough that the carbon build up was keeping the valves from sealing properly causing more misfires and low compression. After a few rounds of Sea Foam the compression is at 160 across all 6 cylinders and it is running great.

Thanks for the help and advice.