if it was mine I would swap the plug and wire and see if that pattern follows the swap. the air gap is clearly letting the plug fire, odd things can happen at high voltages. maybe a short circuit having to do with the boot. If the miss stays after swapping the wire and the plug, try a new dist cap.

I've tried a few different plugs. I think the plug is fouling because the miss does follow the plug, but after a few minutes of running the miss reverts to cylinder 5. I've tried new plugs and old plugs, same behavior. I've tried different plug wires too (I put all new ones on, I tried several of the old ones and switching the new ones around), same result. Also tried putting the old dizzy cap back on, same thing.

My fear is that if it isn't fuel, and isn't ignition, it must be valves or rings - which would make me cry.

My last compression test had all cylinders around 150, give or take a couple of lbs.

 

On 3/19/2018 at 9:03 PM, dakinez said:

I dunno man, looks like you drink too much coke to me

So over a period of time, injector #1 shot nearly double injector #3?

No, injector #1 shot only half, at most, of what it was supposed to.  Assuming that #3 was close to spec.  The injectors rarely shoot more, since clogging is the problem, not flow path enlargement.  If #3 was under spec, then #1 was even leaner.  And lean seems to be your problem.

And, at idle, since all injectors squirt at the same time, most of them on to closed valves,  and the throttle blade is closed so there is very low air flow, there is backflow of fuel vapor in to the main plenum of the manifold.  That could be why you don't see an effect from pulling an injector wire.  There's fuel from the other cylinders available.

sure seems like an air leak somewhere, lean running mix will create low vacuum readings, misfires, all at idle, things work better above idle. make sure EGR is sealing well. Maybe its a problem that effect higher RPM, getting lost in the problem. If plugs are fouling, could be oil or gas. Did you ever post up some pics of how the plugs look?

This would be a good place to use one of those clear spark plugs.  I seem to recall from back in the stone age when riding dirt bikes that a fouled plug could be overcome by pulling the spark boot up just a bit to create an air gap from the term to the boot. Not sure why but something that could get you out of the woods in a pinch.

Edited March 23, 20187 yr by Dave WM