RPM jumping about

[Guest |164|]

When I do a data log run in the higher gears, my rpm seems to jump around back and forth by about 150rpm. This is shown on the tracer and on the log data. Car runs fine and was fine when holding steady state on dyno. Car is a R33 gts-t with PnP and the clutch is good/ not slipping. Only running 280bhp @ 0.6bar.

Thanks Jim

[rayhall]

The RPM the ECU shows comes from the Trigger 1 signal. If the the edges of the signal move around then so will the RPM value shown. The edges moving can be due to the drive for the CAS having movement. This is why on very high rpm engines a crank trigger is the best.

Ray.

[Guest |164|]

The RPM the ECU shows comes from the Trigger 1 signal. If the the edges of the signal move around then so will the RPM value shown. The edges moving can be due to the drive for the CAS having movement. This is why on very high rpm engines a crank trigger is the best.

Ray.

So is this likely to cause any damage to my engine with regards to DET.If you say the rpm is moving about, does that mean the ignition timing/TDC ref will be moving about too????

jim

[rayhall]

It will not damage the engine. The timing will move a little. Have a look at the CAS and see if you can find a cause for the movement.

Ray.

[Guest |164|]

Thanks for the help Ray, i will check the CAS out later on in the week and report back

regards

jim

[Guest |208|]

After many years of tuning the RB25, RB20 and RB26 I found the original CAS is really showing its age. I am finding most are worn to the point of giving unreliable RPM signals which can cause all sorts of tuning issues. Sometimes timing belt whip can also cause RPM flucuations. When everything is in good mechanical order you should be able to put a timing light on and see very steady ignition timing. It is best to lock the timing to see this. Usually when the CAS is worn or has a problem it will jump around. I suggest you replace the CAS in this case.