Hi Guys,

Now that I am logging a bit faster than before I am noticing that during WOT the RPM sometimes jumps backwards.

Is this because of the design of the CAS (ie the missing teeth)?

I am not getting any knock when this occurs...

Cheers
D.

 

Cause the clutch is going out, slipping then grabbing.

 

could be, but its very subtle.. normally clutch slip it revs up for a few hundred rpm then grabs and jumps down...

this is every now and again the RPM's reverse 20rpm, then resume..

i should have posted a graph - sorry.

let me get a graph and i will post it up in a bit..

 

My car has been doing that forever. There isn't a jump in RPM in my logs either. Just the drop. I've just been ignoring it.

 

I see that too on my RA. I blamed it on the pain in my *** SST. However now you 5 speeders are bringing it up.

I never ever ever ever ever ever see it on my Evo 8, ever.

Maybe it's a CAN thing?

 

No guys it the motor changing directions it skips a beat and rotates backwards lol

 

Maybe its an issue with high speed electrical interference? You could try and better shield the cam and crank sensor and see if it gets better.

Just a thought.

Mitch

 

definitely not the clutch and sounds like a timing issue possibly caused from cam sensor

 

Its not CAN, because the sensor is still connected to the ECU directly...

The evo 8 may not have done it because they used a different crank angle mesh thingy... Or because we were logging slower?

 

David can you post a screenshot of the RPM log plotted?

 

This first image is using RPM on the X-Axis, so you can see the AFR loop backwards:


And the log for that section of the graph:


Ignore the start of the graph, although that could be a similar problem... I would say its just how the ECU calculates RPM

 

Can you also plot the RPM curve?

Btw, is that your new logging visualizer?

 

it sure it...

I stole the graphing module that VD uses.. it's hell sweet

excel chart of just rpm


You can see the small dip at 5k

 

RPM ~= 1 / TCAS

TCAS = Time between CAS Interupts.

So if the ecu had a higher priority interrupt before it could get to the CAS, you would get a larger TCAS, and a smaller RPM.

Might not be noticeable on older ecus because you now have faster logging and higher resolution RPM.


Just a wild guess....



Looks like there might be a little dip in Load also?

 

Yeh I need to look into it again.

The TCAS difference should work, but if the ECU doesn't average the signal out then there will be trouble.

Since the crank wheel has 3 missing teeth, to allow the ECU to identify the actual crank angle...