Getting knock at low vaccum @ 2500-3000rpms???

[Phoenyx]

Ok, I'm baffled by this one.

In normal driving, I have noticed that in the 2500-3000rpm range, I get knock when I'm about 17% throttle (about -8 vaccum on the boost gauge). I suspect it is something fishy going on with the fuel or some electronics or something. No matter what I do to the SAFC (richen or lean) at that rpm range, the knock is prevelant. It's intermittant and doesn't happen every shift, and the ECU doesn't pull timing by much unless the car is cold, in which case, the knock goes up to 43 counts and the car bogs. If I give it anymore throttle than 17-19%, the knock is zero. I'll just take off at a light, go into 2nd (it doesn't happen in 1st), and just barely press on the gas and watch the rpms climb to 2500rpm and the datalogger shows the knock starting to rise and then fall once I'm past 3000rpms.

Here is what I suspect is wrong:

1) Fuel Filter never changed. I've never changed this since I bought the car and I doubt if anyone did either..this is a maybe.

2) For some reason I think the fuel pressue is dropping across the rail at that rpm range and that throttle setting.

3) Fuel pump not giving enough voltage at that rpm? Fuel pump is a brand new 190.

4) Spark wires?

Other than that, I'm out of ideas..

Anyone?

-M

 

[Phoenyx]

Bump

 

[Razor_DSM]

i get this same thing goning on, its allways in low rpms and very little throttle position. second, third, and fourth at wot have no knock at all. if im going rather slow in first or second(2.5k) and give it minor gas knock count goes to 43 where if i floor it no knock whatsoever. you con feel some vibration comming fron the bay when the knock is presant at low rpm.


im running 18psi on 94 octane, i have basically new upper engine w/ported head and arp studs, pump rewire, perfect charging system (14.2v) and she dont knock at all after a bit of heavy drivin. you con feel some vibration comming fron the bay when the knock is presant at low rpm.

im thinking either the fuel filter, or phantom knock from a motor mount or somthing. the filter may be patrialy clogged causing the low rpm responce to suck and not provide the correct fuel pressure.
im running rather ritch too, 22.4ms @WOT 70000rpm, no knock in higer gears. i can email the tmo log to anyone who has tmo and would like to see whats goin on

 

[Phoenyx]

All:

Ok, I mentioned this to a fello DSM mechanic and here's what he had to say.

There is a knock inherent to all DSM motors and the Starion motors which happens at this rpm range at low throttle (17%-20%). The DSM motor was designed to counteract this imbalance with balance shafts. They supposedly sit near the knock sensor, so that when the engine is at an imbalance these shafts are working their most.

Evidently, the only way to fix it is to have the motor rebalanced!

Oh well, I guess I'll deal with it for now...btw, I changed the fuel filter yesterday and there was no change to it. So it's not the fuel pressure at the rail.

You must be logged in to view this image or video.

-M