Slight random engine knock under hard acceleration?

[ck_taft325is]

Anyone else get that when in, say 4th gear at 3,000rpm accelerating to say 5,000rpm and having a slight engine knock on their S50? Just curious as it's not steady or constant just every now and again while passing someone on the freeway I'll get a slightly diminished power curve and some rattling from what sounds like the bottom end almost. Imagine lugging the engine slightly while going up hill in 1 gear too high for the grade. It's just like that but it is not consistent and generally if I just goose it a bit down the road at the exact same rpm's it's just fine?


Curiosity more than anything.

[E30SPDFRK]

Could be detonation. There isn't a single good knocking sound lol.

[ck_taft325is]

Hrm. School me on detonation? Bad tune? Failing spark plugs? Bad injector? I think that could have a million causes.

[Adrian_Visser]

Your knock sensors are supposed to prevent detonation. Are you getting a knock sensor code that would indicate that they aren't working?

[Farbin Kaiber]

Are you running 91? Add a full tank of premium and some octane booster and try to replicate the issue.

[ck_taft325is]

Only premium goes in currently. 91 Octane.


Both knock sensors are new on the top end refresh. Actually, I might be lying about that. I think I replaced both but maybe just one got done. Fffffuuu.

[gobuffs]

Rod knock? Spun bearing?

[Farbin Kaiber]

So the bottom end is as good as the top end was? All gone through, right? :rollseyes:

[ck_taft325is]

I wouldn't think so. I'll see if I can't dig up pictures of the bottom end via oil pan off and of the pistons themselves when I had the head done. It all looked fantastic. Something to note is the VANOS is rattling around 3,000 pretty much all the time currently.

[ck_taft325is]

It was the MAF sensor.

[Adrian_Visser]

Phew!

[ck_taft325is]

Phew!

Tell me about it. That MAF sensor turned down really threw me off. It's one of those things I just completely over looked in poking around. Car has no more down low rattle that's random, runs stronger and smoother. I also found that two wires in the boot (which has become quite worn) where bare wire and nearly contacting. So, I remedied that and changed out brake lines, rotors, calipers and pads. She's tip top again ;)

[giantkeeper]

That MAF sensor turned down really threw me off.

You referring to the position of the sensor?

[ck_taft325is]

Yup.

[giantkeeper]

Yup.

I assume it was down and you turned it up?