My 99 DII keeps giving me a SES code stating a misfire at bank 5. Have installed the 8mm magnecors as well as new plugs( Bosch +4s). The connections have been doublechecked, and the coil tested okay according to my mechanic. Any ideas? Spring has also brought the leaky sunroof.

 

did you have the mis fire before the new wires?

 

So, you are saying after plugs and wires, #5 still has a 305 code? How many miles on your engine, if high miler, have you done a compression test, what octane gas are you running?

 

The truck has 91k on it.The 305 code was the first, and only code that popped up just two days after I purchased the vehicle. This led to the mechanic discovering the head gasket. Both gaskets were replaced. as well as many hoses, and the water pump. I know the heads were pressure tested, however, I'm not sure cylinder compression was tested. The wires and plugs were replaced after the head work was done, and still the code appears after being cleared. I've alwaays used 93 octane gas.

-DN

 

I don't like where this could be headed... I'm guessing you are suggesting low compression could cause the misfire code, meaning the rings are shot and the engine needs to be rebuilt??

 

yeah, it could be... or they could have missed a bent valve on the head re-do. Happened to a buddy of mine...

 

what must be done for me to safely perform the compression test? Also, what is the accepatable psi range?
thanks

 

One of 2 tests, maybe both may be needed, a compression test and a leak down test.

 

Go to AutoZone and rent a compression tester.
Remove #1 spark plug.
Install compression tester.
Crank engine over for 5 seconds or so.
Write down reading.
Repeat on all 8 cylinders.
Compare readings, should not be more than + or -10 psi difference between cylinders.
I do not know what the correct PSI should be. (125 ?)
I do not know how to do a leak down test.

Now you do not want the engine to start so remove the fuse to the fuel pump before you start the compression test.
The compression tester screws in like a spark plug.

 

Compression should be in the 150 range, based on wear. The main thing to look for is a noticable difference between one cylinder and the rest.