Spark Plug Failures?

MKnight702 · Post by **MKnight702** » Mon Jul 11, 2011 1:02 pm

Hi, I'm running Megajolt on a tuned 1275 A Series fairly succesfully, however, I keep developing a misfire on no 4 cylinder. Pop in new plugs and it's fine for a while but then starts to run rough. I will check what part number plugs but I believe they are the resistor ones. Anyone got any ideas or hints on what (and potentially how) to check?

Thanks.

FULMNTE · Post by **FULMNTE** » Mon Jul 11, 2011 1:25 pm

When you get the misfire and disconnect the MJ, does it run ok on limp home mode?

Post by **brentp** » Mon Jul 11, 2011 3:42 pm

What do the spark plugs look like after it starts running rough?

MKnight702 · Post by **MKnight702** » Tue Jul 12, 2011 1:34 pm

FULMNTE wrote:When you get the misfire and disconnect the MJ, does it run ok on limp home mode?

Will try then report back.

brentp wrote:What do the spark plugs look like after it starts running rough?

A little sooty plus wet since there is no spark. I may be running rich but I have a session on a rolling road booked to have a look.

spandit · Post by **spandit** » Tue Jul 12, 2011 5:25 pm

Try swapping plug/lead to a different cylinder (make sure you get the coil pack terminals right, though!) - if this cylinder then starts misfiring, you know the plug/lead is the problem.

Have you done a compression test on your engine?

MKnight702 · Post by **MKnight702** » Fri Jul 15, 2011 11:55 am

Yep, tried swapping leads, new leads, new plugs, new coil pack. The misfire always comes back.

Compression is fine, having rebuilt the engine (twice, don't ask) in the last 4,500 miles.