MoTeC Global Forum

Does anyone else have issue's with the RPM going hay-wire in GTR's with M800's? It seems intermittent, doesn't happen with every car and seems to start around 8000+ RPM. The RPM on a data log fluctuate's around 500-800 rpm from 6000-8000 then it jumps to like 11000 causing the engine to hit the RPM limiter and missfire. M8 ecu's dont do it,and on early M800's (when they 1st came out) i had to fit a resistor on the cam signal which seemed to work but then was told not to do this. Anyone had this problem? Is there a fix? It seems worse on R32 GTR's for some reason. Again NOT every car does it even though you do your best to simulate/copy what way you wired individual cars. I would like to avoid changing to a balancer mounted trigger of possible,but if there's no answers then it must be looked at... BTW i recently had an R33 on a chassis dyno that had issue's at anything over 7200 then on the road 8500 was fine!!!!

Thanks for any help please....

Hi,

I have seen this problem before, and the fix in that case was to fit a trigger on the crank, which is always the best approach for absolute timing accuracy anyway.

I believe the problem to be mechanical, with the difference from m8 to m800 being a faster updating RPM channel.
The tension on the timing belt, and specifically the tightness of the crank angle sensor fitting to the cam being the cause. Perhaps try fitting a thicker O-ring to the crank angle sensor drive?

For you, does this happen only under load, or free revving as well?

And do you see any ref or sync errors when this happens??

Personally I would be fitting a crank mounted trigger on an engine that is running anything like that sort of RPM purely for the fact that it will give better timing acuracy.

BUT here is a few things you could look at...

If you haven't done this already connect the black wire on the sensor to ground, use the same ground point used for the ECU ground and disconnect it from ECU 0V (if that is where you have it connected).

Connect a 4K7 pull up resistor between the Ref input and 5V.

Supply the sensor with 12V instead of the 8V normally used.

Thanks for both of you guy's replying. The pull up resistor method worked for way back in 2002 but i was advised later that this was no longer required (by Motec staff in 2003) and it didn't rear its ugly head until recently. No ref or sync error comes up, just the RPM varies about 500 rpm wen logged 20 times a second. Then when its having a bad day you get a massive jump, sometimes 14,000+!!! Will try the resistor and give you fead back.. Thanks again.

Hi,

Have this problem on a personal GTR and clients' GTRs too.
All cars are 500+ps. From what I've seen on the scope, ref
teeth being very tiny (360 of them on the wheel !)
blur with the engine speed and boost increase confusing the ECU,
so you get screwed RPM reading. Don't know why Nissan
placed ref sensor on the cam. Its certainly bad idea for high
revving, high power boosted engine like RB26. AEM does make a replacement
trigger wheel with 24 slots for ref and 1 for sync which is far more
reasonable for this engine. So you would need to disassemble the
sensor to replace the wheel and change to multi tooth setup.
Did set R34 with 2.9 motor and GT42 recently on M600 and though
rpm does jump around +/- 500 with boost over 1.5 bar but there is no
erroneous rpm reading.

I do agree that RB needs crank mounted ref sensor to run perfectly,
so will go this route on my car. If anyone knows a company that
makes such setup available for sale please let me know. Buddy
tried to use Moroso trigger wheel and sensor made specially for ATI
crank damper on his drag R32, but no luck at first attempt. For some
reason negative or positive part of the tooth signal was disappearing
so, switched back to OEM setup at the moment.

I have no idea how is the factory ECU is reading this sensor on
modified cars, but personally seen number of 700 ps cars running
reflashed stock ECUs and doing fine. Perhaps it may be switching to
just read the 6 different width sync slots.

Regards

Alex

Hi All,
just my 2c worth. I will say that the crank trigger is the best idea but for anyone interested I found these guys http://www.triggerdisc.com/ who make a 24 tooth replacement disc, I'm pretty sure this is where AEM get them from.

I do not know anyone using one and don't know the price but at least this is a contact.

Hi All,

Here is what we made for Mitsubishi 4G63. As you can see the crank wheel is stamped so is fully compatible with the
stock engine. However on Evo 9 we have problem with slow VVT response. Not sure if it is related to the trigger wheel setup we use on this car or some other fault.

Also used made 24/1 laser cut trigger wheels for RB/SR engines.

Regards
Alex