Unusual amounts of knock at unusually low timing

[Danspeed1]

Hello,

So I am running into little problem with knock on the 1990 Corvette I am working on. The motor is a fresh rebuild with the factory cam advanced 2 degrees, ported heads, tpis miniram, and all the bolt ons. I have been working with Tunerpro RT to try and get it dialed in and so far I have been very successful. I was initially getting knock when tuning WOT, but the problem was apparent by the fact that my injectors were maxed out and I couldn't get any better of an afr than mid 13's at WOT. I just dialed in a set of ZO6 28lb injectors and the car runs great at part throttle but I am getting heavy knock at WOT. I have my afr set to around 11.3 to start and I am getting knock at just 18 degrees? I am running a normal compression ratio, stock plugs, plenty of fuel on tap... you can hear heavy knocking. I'm really lost, let me know what you think

Dan

[steveo]

a few points, just to make you think:

- if you can hear knocking, and your timing isn't too far advanced, and it isn't lean.... logically something in your engine is broken. if something sounds like mechanical clatter, it usually is.

- you have to go REALLY lean or REALLY advanced to actually hear 'heavy knocking'

- if you were actually getting audiable pre-detonation, your spark plugs would be melting, so what do they look like...?

- lots of types of engine noise will set off a knock sensor, too

a few questions,

I have my afr set to around 11.3 to start

and is this on a wideband or just commanded AFR? if wideband, are you sure of accuracy?

I am getting knock at just 18 degrees?

actual timing or commanded? is your base timing set correctly? just 'cause your aldl data says 18 degrees, or your timing table, doesn't mean your physical timing is 18 degrees.

[Danspeed1]

Hey Steveo thanks for the reply. Definitely looking forward to getting to the bottom of this as I am so close to having this car perfect!

- I hear rattling (knock) at WOT. This is confirmed by my ever increasing knock count on Tunerpro. The engine has about 30 miles on it, its brand new. I have Z06 Injectors now so plenty of injector and pump. Logically I agree, plenty of fuel, timing "seems" low, car should drive well, yet it rattles even jumping into it at 1500 RPMS. I don't feel like anything is "broken" at this point, car drives well locally and under light and part throttle.

- My wideband is showing an AFR when I go WOT of about 11.3

- Attached is a photo of my spark plugs. I decided to include a copy of my tune as well in case anyone whats to critique it (be nice please)

- I agree again that I may need a less sensitive knock sensor but I can also audibly hear the rattling, this makes me nervous.

1. The wideband is reading 11.3 at WOT, in accordance where I decided to set it to start it.

2. I'm not sure how to answer your second question. My aldl data says 18*, I thought I could take it at its word??? I will attach a log as well, but its not a very good log. I didn't do much driving before laying into it although it was up to operating temperature

12708-MMS-1491441103000-attachment1-20170405_205747.jpg12708-MMS-1491441103000-attachment1-20170405_205747.jpg
knockonlightpull.xdl
90VetteLS6InjectorsPEonminus4degrees4.5.17.bin

[steveo]

those plugs don't look like they've experienced detonation. i think you have mechanical noise and false knock. exhaust leak, perhaps.

I'm not sure how to answer your second question. My aldl data says 18*, I thought I could take it at its word???

depends on what you're using for timing reference, distributor base? cam sensor? what ecm?

[Danspeed1]

Yea, the plugs looking pretty good. I find it odd that I am even having this happen but I can't imagine what else it could be that makes such a similar noise at wot.

Its got a stock 1990 ECU, I'm using and $8D Bin. I can't remember off hand but I believe its a 7727? There is no cam sensor on these.

Dan

[Danspeed1]

Can you elaborate on how I can verify my true timing? I want to make sure i'm on the right track here...

[Danspeed1]

I'm sorry, I made a mistake, reviewing my log, I was actually receiving 26* of advance just prior to the knock beginning. In regard to my previous 2 posts; below is a screenshot of the knock occurring.

Please correct me if I am on the wrong track. Spark advance relative to TDC: This is the actual spark advance occurring within the engine (26*), Knock Retard: after the knock occurs 7* of timing is pulled from 26* bring my total down to 19*

Not sure how spark relative to reference pulse plays into this

Also, Please review the two charts I have up as well. You may noticed I removed about 7 degrees of timing from the stock map of SPARK ADVANCE vs RPM vs MAP, and then removed another 7 degrees from the Idle Spark Base Advance as well. I'm not 100% i'm sure how this works but I am assuming that my distributor is set to 6* btdc, plus what the ecm sees on the "Spark advance vs RPM vs MAP" table, plus the "initial base advance" table.

KnockScreen1.jpg