Engine missing, actually it's still there...

[Wolfie]

I have an odd problem, I think...
Vehicle:
2007 Chevy Express Van 6.0 litre LQ4.
Stock except the cats somehow misteriously leaked out.
I had a new engine installed (long story) about 2 months
and 30,000 miles ago.
I was getting a ses light about once every couple days,
was the random misfire code. I did the case relearn a few times.
The other day, it started missing badly, dropped one cylinder.
Turned out #4 spark plug wire fell off. OK, I put it back on.
It ran fine for a couple days, or so I thought.
The ses light came back on with the random misfire code again.
I started monitoring the cylinder misfires, and #1 and #6 seem
to be misfiring quite a bit, but all cylinders except #4 do misfire.
Could this be due to incorrect plug gap from the factory?
The wires and plugs were installed new with the new engine.
I am thinking about installing Granetelli coils & wires, but would
like to find the actual cause first. I am asking before I do a teardown,
as I loose too much money when the van os not on the road...
Thanks
Wolfie...

[hquick]

No idea....but love the work you old bastards do on the bikes!

[ssvolvo]

Throw the factory tune back into it and drive it for a day or two. Post up a log for all 2 see. I'll guess you have a large air leak around the intake somewhere. Fresh fuel filter? Fuel pressure ok?

Sometimes the rearmost fuel injectors get full of crap from the tank. Believe it or not the stuff has been known to go right thru the fuel filter.

John