I just got a new set of plug wires for my car. But something was messed up and half are 7mm and 8mm. I needed to use the car today so I ran it with the different size wires. The car ran good for about 30 seconds, then it started shaking real bad. Like taking off then stopping then taking off again almost stalling. Is this from the wires? Or did I F something else up?

 

Mix all you want - 6, 7, 8, 8.5mm - it doesn't matter as long as the insulation on all of them is good.

I'm betting that something else is the main problem, unless some of those "new" wires were not any good. If the set is mixed,it may have been returned, and some less-than-scrupulous individual may have swapped a couple of old, dead wires into the set.

 

Well I'm gonna go exchange them tomorrow for a correct set. So I'll see if thats the problem.

 

I've had to mix brands before (some Accel with some Napa or something). The car ran terrible. It stumbled and shook and jerked and I was convinced I had some other problem. Since I knew I had to do something about the wires, anyway, I bought a set of MSDs, cut them to length, and crimped them. That fixed the problem completely. So, my opinion is that if the car ran ok before mixing the wires and ran bad once you mixed the wires, it will run ok again once you put on a set of matched wires.

Now, there could actually be bad wires in there like too. I hate to come on here with an opinion different from Vader since I know he has helped me before.

 

Hey, Mike!

Somebody has to keep me honest. There are a lot of possibilities, and you may very well be right. I was only pointing out that in theory, a set of good wires shouldn't make an engine run roughly. It's more likely that there is another problem, or one of the "new" wires isn't a good one (or possibly fell off or shorted to the block). Even a new set of MSDs (and MSD is good wire) will have different resistances and inductances as a result of their varying lengths. I do know that some of the newer DIS ignition systems with shared coil packs can be sensitive to plug wire length/inductance differences, but I'm guessing that this isn't his type system.

 

Most likely you have a boot that is not all the way on at one of the plugs. Wire length is inconsequential with most ignition systems assuming all the wires are connected.

 

It's not the length of the wires that was different, it was the width, some where the stock 7mm and others were 8mm, but one of them came dissconnected from a plug. I haven't tried the car since i put it back on since I'm getting a new set today anyway.

 

Yeah, most V8s don't run too well on 7 cylinders

 

I meant width, just goes to show what that first cup of coffee or lack of it does to my thought process. Either way it does not matter at all, something else is going on and you'll most likely correct it by going over it again.