Dead Cylinder in COP, Fine Using Wasted COP

[slow94formula]

Got a BBC with a 58x crank reluctor, 1x cam position sensor (vortec distributor). When set in COP mode Cylinder #7 is dead cold. When switched to wasted COP everything runs as it should. I am wondering if it has to do with the cam position sensors "position". Does it need to be moved so that the tooth gap occurs at a different time in relation to the crank trigger's missing teeth?

Here is a screenshot from the composite log.

BBC Composite.png (79.31 KiB) Viewed 437 times

[billr]

Nobody else biting on this one? The position of the CMP pulse looks fine to me. I think you have some coils miss-wired.

[slow94formula]

Forgot to mention all coils and injectors were tested via test mode prior to initial start. They are for sure correct.

[billr]

Can you see that dead cylinder (#7) sparking using a timing light? Have you verified it is at the correct crank position? Have you tried firing the engine on every cylinder as a "single cylinder" engine? That will make it absolutely clear which ones are firing and which are not.

I can only suggest having somebody else check your wiring and how you are using test mode. I find that once I make a mistake, I "see" things the way I know they are supposed to be, not the way they really are. Only a second pair of eyes, or stepping away form the situation for a while, can break me out of this loop.

PS: When you say "#7 is dead cold", do you mean low temp at the exhaust port, as indicated by feel or a temp sensor?

[slow94formula]

I was going to dig out a timing light and check it that way, but haven't gotten around to it yet. Need to get it out anyway to confirm timing is synced. As far as the 1 cylinder engine goes, 4 and 7 are at TDC together as they should be and 4 gets up to temp with the others. The valves were confirmed to be functioning correctly. I'll have to round up a timing light tomorrow and try sequential again.

[billr]

Have you tried swapping coils around, see if the problem follows the coil or stays with #7?

[slow94formula]

I have not. Is there a reason a coil could be to blame if it works in wasted spark? Thanks for the input btw

[billr]

Nothing I can think of, but it is easy to try. Post an MSQ, and MSLs while running in both modes (COP/wasted-COP).

[slow94formula]

I'll see what I can do tomorrow

[slow94formula]

Put the timing light on it. In wasted spark the timing light is consistent with it's pattern (and flashes twice as fast obviously), with ignition in sequential mode the timing light is inconsistent. I tried to capture it on video so you can see. It doesn't seem to have a dead miss like it did the other day... The only difference from then to now is swapping the plug wires between 5 and 7. Going to let the headers cool off and see if when I start it again in sequential if that cylinder stays cold like it did before.

https://www.youtube.com/watch?v=8mjSwSXHONU

[slow94formula]

Headers have cooled off. Started engine, timing light flashing. No heat in the cylinder. Almost like it's skipping the injector on #7.

Also just grabbed #4 myself instead of letting others tell me it was hot... there's no heat there either. So it's something wrong with 4 and 7 which are opposing in the firing order. Why do they both get warm while in wasted though still baffles me.

[billr]

So, both 4 and 7 are not getting hot in COP, but do in wasted-COP? That makes it seem even more certain they are mis-wired. Why not try swapping the inputs to them? It is easy enough to do and won't hurt anything to try.

[slow94formula]

ok so....

BBC standard firing order is 18436572
that makes
1=a
8=b
4=c
3=d
6=e
5=f
7=g
2=h

Just tested them in the output mode and 4 and 7 are definitely correct in terms of that firing order

I have a new theory now

the cam has been ground on a 4/7 swap

which would make the firing order 18736542

that would explain why it works in wasted but not in seqential and in turn would be wired wrong for that firing order

need to pull valve covers to check my theory now

[slow94formula]

Theory was correct. 4/7 swap on the cam. Switched 4 wires and all better. Wish I had known that when initially wiring... Oh well

[billr]

Does that 4-7 swap mean you have a bad cam, or is that a known BBC aftermarket option? If it is a real option, what is the purpose? Is this a "flat crank" cam, do you have a flat-crank?

[slow94formula]

Supposed to idle smoother, more balanced bank to bank fuel distribution (in a carb setup), supposedly cooler cylinder head temps, possibly less harmonics at high rpm. Those are all theories I've seen. Not sure how true they are. I had no idea that's what was in it until this morning when I thought to ask for the cam card. Found the box and in the top right corner it's written "4/7."

[taank]

d*** swap cams