Hey all,

Lately I've noticed the Tephra KnockCEL flashing on the first part-throttle pull I do. I can be driving for 15 minutes not going much about 3000 rpm's, but once I do a harder pull (e.g. 50% throttle), I'll usually get 2-3 counts of knock. Subsequent pulls do not have enough knock to trigger the knockCEL. Is this normal? I think so, but could someone explain why this happens? This seems to have started recently with the colder weather (40-50F). Thanks!

BTW, I also will get knock on the first WOT pull in the same manner. The engine is definitely fully warmed up (I make sure to drive at least 5 miles before doing a part or full throttle pull).

 

What kind of timing are you logging on tip-in throttle-partial throttle?

What kind of Air/Fuel, boost, etc?

It's most likely just spool up knock or false knock, get me the information I asked and I will probably rule it out false knock...

 

Driving 5 miles does not necessarily mean warmed up... neither does the coolant bar on the dash being at warm. Your engine is *ok* at that point, but the wastegate actuator might still be cold causing you to overboost (this is even worse with an MBC). If it is really cold out you usually need to "warm the car up" with a few low boost actions to get everything warm, and if it is really cold that still may not be enough.

With colder weather and electronic boost control you can overboost easily because the turbo can suck in more air per unit of work. This is because the air is more dense. Ideally, take a log to make sure you are not overboosting, and also to make sure you are not hitting higher load at a lower RPM than you did in the summer.

 

Thanks all, I haven't had a chance to log it. I'd be surprised if I were overboosting though, since it doesn't knock on the second pull (just the first). When I did overboost last winter, I got a P1235 and had to adjust my airflow tables.

I'll try to get a log soon, but with xmas just around the corner, I dunno

 

When the turbo and motor are cool you will get knock almost certain.

You need at least 2 runs before your boost and fuel will stabilize. As well as monitor for overboost with cold weather, you generally need to run less WGDC.