08 4.6 Misfires

[Zoso]

A check engine code has started to show up on a 2008 Shelby GT. The cars has Ford hot rod cams and Kook's long tube headers and cats. There is also has a tune.

Last year, the car threw a code for cylinder misfire. Finally trace to a bad plug ( ??? car only has 18k ) So, the plug solved the problem for a while - now I'm getting new misfire codes.

I plan to replace all the plugs shortly - question is why are plugs good for 100k failing at 18k.

I've been told it could be a car computer problem and the coil packs.

Any insight would be appreciated.

 

[Juice]

You cannot expect plugs to last for 100K on a modified engine. (that is never driven hard? lol)
Cams + long tubes and who tuned it?
You may not actually have a misfire, but the pcm thinks there is a misfire due to the cams. Just a guess here.

Basics first: Compression test.
Post pics of ALL the spark plugs, that may help point you in the right direction.

 

[Aussie-Parnelli]

Hi
I just found the cause to my misfires on my highly modified '06
I replaced the plugs and coils only for the miss to return
It ended up being the COP wire connectors
Seems to be fine now and was an easy fix

 

[Zoso]

I driven the car recently - no misfires - no codes - so far....

The car was tuned by Mo's Speed Shop outside Atlanta.

I hear you about the modified engine's SP's not lasting - could be a factor - pics of the old plugs is a good suggestion. The car has had the cams for a long time (years) no issue - Headers and tune are newer mods - 1 year.

I will remember that cop connection as possible issue.

One other thing someone mentioned was - that the car cpu is over-driving - sending a high voltage - to the cop's causing a misfire. $600 for a used cpu.

Thanks

 

[Speedracer67]

Sorry to ask but what is a COP?

 

[LikeabossTM]

Sorry to ask but what is a COP?

Coil on plug, directly, versus remote coil with spark plugs wires.