Q7Q7Q7

I had my car in for a coolant leak (the check engine light came on when this problem occurred) but when the truck was hooked up to the scope, they found a multiple cylinder misfire. I did not notice anything odd about the car before that (although after they fixed the problem with new ignition wires, I am beginning to think that my car accelerates better/smoother...but then again, I think that too after I wash my truck!). Not being a "techie", what should I have noticed, and what causes this problem. The vehicle is 13 months old with 26,000 kms.

matthewsjl

If a coilpack goes bad, you know about it with a rough running engine. I suspect that you had codes flagged that indicated a misfire had occured and they changed coil leads on the basis of that.

I think you're probably getting the placebo affect of new parts!

John.

Jusforfun

If its multiple cylinder then its probably irregular, making the car feel slightly like its clearing its throat the odd time. It would be more noticable under acceleration and yes it would slow it somewhat.
There can be several causes like;
damp on the leads (highly unlikely).
scratches or marks on the surface of the leads.
deterioration caused by overheating or heat exposure.
proximity to metal objects causing periodic shorting (unlikely).
kinks or twists at any stage in the manufacture or handling of leads.
deterioration of inners due to strong current (my bet).
Minute Imperfections during manufacture.

On top of all that it may be the point of attachment at either end where the leads were cut and some sort of conductor or spike inserted. Take this in combination with some of the above and you could easily create the conditions for irregular missfires.
Remember these things are passing extremely high voltage about 25 times a second at 3000 rpm so no wonder the odd miss is difficult to detect.
SOLUTION...BUY A DIESEL

AutoUnionQ7

Probably when the ignition wires were changed, the plugs were cleaned, so they went bad