Misfire and Backfiring??? HELP (Kind of Long)

[dbranger94]

First of all I'm working on a SBF. TFS heads, EZ-EFI, MSD Ignition w/Digital 6 box and about 9:1 compression.

Ok, I replaced my spark plugs last weekend with another set of NGK plugs. The old ones had been fouled a couple of times while installing/tuning the EZ-EFI fuel injection system. But otherwise the truck ran great. Then I goofed up bad...

I left the D.S. plug wires laying on the intake manifold (on top of the coil and distributor wires for the MSD), then started the truck. It ran for about 5 sec. before shutting off. I reinstalled the plug wires and the truck wouldn't run at all. Replaced the coil with a good spare, still nothing. So, I borrowed a 6AL box and installed it. Engine fired right up, but misfired to beat hell. It's backfiring through the intake and exhaust and smells rich. This is where it gets wierd... I picked up the coil with the engine running and it starts arcing from the case to the block. I then replaced the coil with an E-core I had laying around and it arced from the + terminal to the coil wire. As far as I can tell all the grounds are in good shape. This is a recent build with only 750 miles on the truck. I haven't changed the timing in any way, and the truck ran perfect before this happened. You can hear it run in the link in my sig.

WTF... Any Ideas?

BTW, I tried the plug gap at .054 and .035, no difference. Also the engine has 15 deg initial and 34 deg total timing.

[Jim Nilsen]

Do you have the 6A box set for the right firing order? There are dip switchs inside of some of them to program them for the right igniton setup.Best to check just to eliminate the possibility and you can smell for the magic smoke that sometimes lingers.

It's gonna be interesting to see what fixes it.

[BlackPearl]

I had something like this when I had a SBC and my plug wire was arching through the boot against my header. It was a tight fit on my car then and someone, I won't mention here trimmed the boot slightly to clear leaving too thin so it arched out.

Just a long shot but it did happen and I thought I would throw it out there. I also had a bad 6AL box and it was brand new out of the box but when I exchanged it all was good. Good luck!

[dbranger94]

The spare box I have is an older (Pill Style) 6AL box, but it had never been used until the other day. It was still in the plastic, but, like BlackPearl said, that doesn't mean much with MSD stuff. That's why NASCAR teams have two of them in every car, because they are so reliable. I think the only setting on it was a couple of wires that you have to cut for 4 and 6 cylinder applications.

I am currently making up a remote mount HEI setup to eliminate the MSD boxes alltogether. I also ordered a new magnetic pickup, cap, rotor, wires and coil. I'll throw the old plugs back it it, then start the process of elimination. Hopefully by the weekend, I'll know more.

[anthonys 69]

The spark want to travel on the path of least resistance. we had a car in the shop the other day and a customer changed his own plugs. When he pulled the plug wires off he pulled on the wire and not the boot the plug wire slid up the plug boot so when he put them back on there was a gap between the plug and the end of the wire it looked right because the boot was over the plug. This built to much resistance in the wire so the spark found an easer way to go and ruined up his new cap. We had to replace the cap and rotor and plugs and wires. your making spark you just need to make it go were you want to go