Return of a Tuning Tale. Chasing classic knock

[XfireZ51]

It may be hard to believe, but I actually think I have arrived at a final tune. Really running well. Very few changes needed for VE tables and of the changes needed we're looking at BLMs off by +- 1 from target for the most part.
Any KC came from me either lugging the motor in 3rd gear from a light, or jabbing the throttle to 100% TPS several times. Otherwise nada.
As always, there will be something that pops up to conquer. Maybe I can take a break. Yeah sure!!!!

[XfireZ51]

I continued to do additional logging and VE/SA table tweaking. But I have finally solved the Knock Retard puzzle. The engine would exhibit “knock” in a pretty specific range of rpm and MAP. Had lunch w Marc and he said it he could only think it would be something mechanical and not knock at all. The spark plugs did not exhibit any sign of pre-ignition.
Well, it was a loose rear muffler hanger on the driver’s side. Made one and now no knock. Time to put timing back into the tables.

[jss06c6]

There ya go! Glad you found it...

Sent from my SM-G950U using ZR-1 Net Registry mobile app

[XfireZ51]

An update on this. I had a newly rebuilt short block installed by Dr. Greekenstein.
Turns out the old block had front and rear crank bearings worn in opposite sides plus the crank thrust bearing. The assessment is that detonation had caused the wear and even after removing the original cause of the detonation, ie faulty injectors, the damage had been done to bearings enough for a false knock to be present at very specific load and rpm.
Bloc and crank are fine with no damage altho the pistons and cylinder barrels are suspect which is why I am selling them as “momentos”. 😁

[Neat]

I know it's late, but cutting off the threaded portion of the spark plug would help you read them. You can chuck the porcelain in a drill, turn the drill on, and lay a hacksaw at the base of the threads.

Trying to read the plugs after some drive / idle time is pretty tough; but a new plug, pulled as quickly as possible after the knock event, will give you the best chance of seeing what's really going on.

On my LS powered Mustang, I have a switch on the dash that shuts off the coil and the fuel injector on the #7 cylinder. That way I can install a new spark plug in #7, make a pass at the drag strip, flip the switch, drive the car back to the pits on 7 cylinders, and have the best chance of getting a good read on the #7 spark plug. I don't know how involved a single cylinder kill switch would be on an LT5, but something like that might help give you the best chance at the most accurate plug reading possible. You'd do a new plug in whichever cylinder, drive the car to the knock event, flip the switch and shut down that cylinder, and then drive it home to read the plug.

The second photo shows some slight detonation / preignition in my opinion, but with the post knock run time on the plug I can't be certain. Mayne someone with some more plug reading experience could make that call with certainty, I'm not sure. Regardless, a new plug with as little run time as possible after the knock event, is the easiest to get an accurate reading from.

Glad you found the false knock issue, good luck with everything!

[XfireZ51]

Neat,

Thx for the advice. However, I have an epilogue to this story. I began tuning the ?new? motor and everything appeared fine, but then I started recording knock again. Sort of ready to tear whatever hair I have left. Put new plugs in and #2 appeared to NOT be firing or running extremely lean. The datalogs showed a lean condition just a 1-2 frames before Knock Retard was activated by the ECM. Sometimes, quite a lot of it. So I started w the more easily replaced items.
1. I did fuel pumps which apparently were originally in the car when I bought it 10 years ago. No change.

2. Replaced right side O2, which was showing very lean readings, sometimes for quite a few frames while the left side appeared normally swinging. No change.

3. Poured in a can of injector cleaner. No real change altho it can?t hurt.

4. Finally, I decided to do the plenum pull which I was trying to avoid, to check on
the #2 injectors.

In the course of doing the plenum pull, I decided to check primary and secondary coil windings on the bench, especially since I had gotten a higher ohm reading for the #2/3 coil when testing from plug end to plug end. However, it was still within spec <20k ohms. The other coils tested at ~14k, while 2/3 tested @~ 17k.

Close inspection of the coils revealed cracks in the casings of 3 of the 4 coils, including #2/3. Carbon tracks were visible on the body of the coil.

New coils are in and ready to pop plenum on today. 🤞

Just a side note to the Registry. It really doesn?t make sense that altho I am not a registry member, I can?t even expand the pics to the content that I myself provide. Just sayin!

[WARP TEN]

Originally Posted by XfireZ51

....Just a side note to the Registry. It really doesn?t make sense that altho I am not a registry member, I can?t even expand the pics to the content that I myself provide. Just sayin?.

Hey Dom--you should be a member and support the Registry, then no problems. Just sayin...--Bob

[XfireZ51]

Originally Posted by WARP TEN

Hey Dom--you should be a member and support the Registry, then no problems. Just sayin...--Bob

Bob,

I consider the content I provide as support. Apparently, you?ve read it.

[Neat]

Originally Posted by WARP TEN

Hey Dom--you should be a member and support the Registry, then no problems. Just sayin...--Bob

I'll cover him for a year, who do I PayPal?

[Jagdpanzer]

Dom,
MSD 8224 DIS coils?
How old?