Nosy rpm signal with CAS?

[tineira]

Hi,

for some reason when logging, the engine RPM trace gets rough above 5000 RPM. This is using the PC logging and Ecu logging. The engine is a CA18DET with the stock CAS. I get no sync or trigger errors. The engine seems to run smooth and it's not missfiring. What could cause this?

[tineira]

Maybe changing the chopper disk to something like this may help. What do you think?

http://www.aemelectronics.com/cas-disk-for-rb25det-vg-and-some-rb26-engines-50mm-od-1251

[Simon]

Make sure the drive to the CAS is in perfect condition and there is no play in the cam drive as any movement of this sensor can cause triggering problems.

Also check what the dwell is doing in a log, if this is unstable it defiantly points to the triggers and then if all the drive line to the CAS checks out one of the trigger disks showen above would be an option.

[tineira]

Thanks for the fast reply. I'm sure there is no play on the CAS drive.

What do you think of the dwell trace here?

[Dave Kriedeman]

Hi Tineira,

How old is your timing belt ?

Worn or loose timing belt can cause the issue you are seeing.

Nissan RB series engines are also prone to this.

This may not be the issue, but definately worth checking.

Also, remove the cover from the CAS and check for rust deposits in the housing, i have had the CAS shaft bearing fail due to no lube (old age).

Regards

Dave.

[tineira]

Dave,

the timing belt is relatively new, but it is the cheap version of OEM parts (Nissan "Key Value"). The car is in the shop right now, among other things, they are installing a Greddy timing belt. The bearing inside the CAS seems to be OK by the feel you get when turning the shaft. If the new timing belt doesn't help, I'll buy the chopper disk and change the bearing just to be safe.

Thanks.

[tineira]

I have not received the car back from the shop yet, so I have not tried the new chopper disk, but there is another thing I have not tried that may help. Would changing the filtering settings on the trigger have an effect on this problem? Both trig1 and trig2 are on the lowest filtering setting.

[Dave Kriedeman]

You can try changing the filter level and test it.

Just be aware that if you do change your trigger disc to the one you have shown, that your trigger mode setup will require changing, NISSAN OPTO 360 will no longer work, the decoding will be different.

Have you tried turning Low Resolution Mode on and checking the signal.

I would wait until you get the car back and recheck with the new timing belt, is he changing the tensioner bearing also.

Make sure the belt is tensioned correctly, too loose or too tight can cause belt deflection (harmonics).

I would also log Ignition Angle 1 and Injection angle and see if there is any effect on these parameters when the rpm signal is noisey.

Make sure that your CAS wiring is well clear of ignition coils etc.

Regards

Dave.