Knock when Shifting

[DSM90AWD]

The below datalog shows a familiar knock pattern I experience only during racing (i.e. high RPMs + non-gental shifting) in which I see a spike in Knock which will then trail off towards the end of the gear only to duplicate but in larger scale in the next upshift.

I've tried to tune it out via JeffO e-prom + S-AFC.. but still present.

I do have some play in the driveline (causes a clunk during shifts) which I've narrowed down to either the rear itself or axles / bearings (the Driveshaft/Xfer case hase no play.. I checked).

Before I pin this knock issue on the drivetrain "clunking".. I'd like to understand why a single split-second "clunk" would show up thru the whole gear as Knock Sum.

Wouldn't my KS datalog mean the ECU saw more than a single knock incidence

BTW.. I do not see any "Phantom Knock" (i.e. random knock ~20+ under low loads) so think the above is explainable as it is consistant and predictable.

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[DSM90AWD]

I got a few offline responses to clairify how the ECU reads/reacts to what it percieves is "Knock".

What I surmise is that the ECU is picking up the "clunk" from my drivetrain as knock which when am shifting at high RPMs would last several revolutions so would sound to the ECU like a large knock incident. The higher gears 3-4 have a larger ratio so would likely make more noise in the shift than say 2-3 (hence the increase in knock with subsequent shifts).

Once the ECU reads the knock (though in my case is drivetrain noise) it will impact timing based on the amount read. Thereafter.. if no other Knock is read.. the ECU will slowly diminish the KS value which in turn will allow Timing to increase again.

Bottom line is I gotta get that noise fixed !

 

[TSIsean]

I had the same problem. But it went away eventually...

 

[iamtall77]

that sounds hard to believe that the drivetrain would cause knock. the knock sensor picks up only a certain frequency to detect knock (1600mHz or something) it's possible that the injectors are still firing during your shifts. an expample would be if you kept a part throttle on shift, but that doesn't seem to be the case according to your log. fix your clunck and get back to us. this seems to be interesting to me and i'd like to know what it is.

 

[DSM90AWD]

The KS (especially on the 1Gs) is not very discriminant. Noisy lifters and even bad engine mounts can trick the ECU into thinking there is knock.

I've not totally ruled out fuel (thinking a leaky Injector could cause rich knock).. but figure the drivetrain is a good place to start as it is a known issue.

 

[Syndicate13]

I am experiencing this as well with my 2G. All of my engine mounts are good and I have no audible clunk when shifting or driving. I think it may be caused by my boost spike, the small 16g holds boost so well during shifts if I shift too fast I sometimes get a 25+ psi spike. If I shift a little slower and get back in it it won't knock at all.

 

[4twenty]

I am also having the same problem with my 2g. I am running a evo3 16g at 20psi and dsmlink. I went to the track the past 2 weekends and my logs look identical.

Syndicate: you might be on to something since I am using the no-lift to shift feature of dsmlink. I will probably head out to the streets to do some more tuning and try lifting to shift before next track session. I also have a spike to 25 psi after shifts which is what I was blaming it on too.
J

 

[Syndicate13]

I am also having the same problem with my 2g. I am running a evo3 16g at 20psi and dsmlink. I went to the track the past 2 weekends and my logs look identical.

Syndicate: you might be on to something since I am using the no-lift to shift feature of dsmlink. I will probably head out to the streets to do some more tuning and try lifting to shift before next track session. I also have a spike to 25 psi after shifts which is what I was blaming it on too.
J

You may have been running into this more that I was. It just started since it finally cooled down here. It's pretty cold where you are all the time. I can't wait til my DSMlink gets here, 5750 stutter dropping 15 degrees of timing. Any guesses to how far the flame goes?

 

[4twenty]

I had my launch set to 5500 and now 4750 and all I get is tire spin on all four corners. My ic piping with maft blow thru and evo316g make for deadly spool
J

 

[Syndicate13]

I had my launch set to 5500 and now 4750 and all I get is tire spin on all four corners. My ic piping with maft blow thru and evo316g make for deadly spool
J

I no longer have a stock DSM 1st gear. My stutter now is set at 5k and I bog unless I slip the clutch a lot. A tad higher should yield better results for me.

 

[DSM90AWD]

I've not totally ruled out fuel (thinking a leaky Injector could cause rich knock).. but figure the drivetrain is a good place to start as it is a known issue.

Just an update.. I recieved a response from someone with the same issue who pinned it down to worn rear mounting bushings (rear itself had up/down play). Hoping to get around to chek mine today.

I assume there are no polyurathane replacements just OEM?