Megasquirt Support Forum (MSEXTRA)

Hello,

I'm experiencing large timing errors on my car, that I think might be bad for it.
in the logs it can be +-50%.
If I understand it correctly, with a 24 tooth wheel on the crank each tooth corresponds to 30 degrees and 50% of that is 15 degrees.
Having 15 degrees of random timing error cant be good for a boosted high compression engine.

The engine seems healthy however, it made 240 whp from a supercharged 1.6 with 1 bar of boost. (log is from dynorun)

Should I worry?

Should I ditch the cam mounted wheel and go for a crank mounted 60-2 wheel?

Thanks! *EDIT:

Noted that i dint specify what hw/sw version I'm running, what a fail...
Its MS3.0 + MS3X, running fully sequential, with COP's
Software is v1.4.0 with a "Differential ITB" mod (Only effects fueling)
Engine is a 4age blacktop with a Toyota sc14 supercharger running E85...

Fixed original post with more info...

Are we taking a vote on this?

I say "yes, get rid of the CKP sensing on the cam, and go for as many teeth as practical on the real crank wheel". And, yes, use a missing-tooth wheel. They are so simple and offer the ability to run dizzy-less without a CMP sensor, it amazes me that anything else was ever used. Maybe an "NIH" or patent issue for some OEMs?

Ah, I do concede, though, that missing-tooth can't sync up as fast as some of the more goofy patterns. So, if bragging-rights about how fast your engine will fire up are especially important, then missing-tooth may not be your best choice...

A 50% timing error doesn't seem to actually work out to 15 degrees in the real world, even though the number suggests it should. Post up a tooth log and that will give a better idea of just how far off the timing is.

Right now, the timing error number isn't particularly useful.

Matt Cramer wrote:A 50% timing error doesn't seem to actually work out to 15 degrees in the real world, even though the number suggests it should. Post up a tooth log and that will give a better idea of just how far off the timing is.

Right now, the timing error number isn't particularly useful.

Thanks,
I'l put up a tooth log when I get to the garage later this week.
But its winter here and its in the middle of a twin charge conversion, so unfortunately I can only free rev it.

billr wrote:Are we taking a vote on this?

I say "yes, get rid of the CKP sensing on the cam, and go for as many teeth as practical on the real crank wheel". And, yes, use a missing-tooth wheel. They are so simple and offer the ability to run dizzy-less without a CMP sensor, it amazes me that anything else was ever used. Maybe an "NIH" or patent issue for some OEMs?

Ah, I do concede, though, that missing-tooth can't sync up as fast as some of the more goofy patterns. So, if bragging-rights about how fast your engine will fire up are especially important, then missing-tooth may not be your best choice...

That's what I'm considering, and I do prefer accurate timing to fast startup
It all depends how easily I can make a trigger wheel arrangement...

I made a tooth log: Definitely something strange going on. The pattern almost looks like "ringing", could the belt be vibrating? (the 4age blacktop belt pensioner is known to fail, but it is brand new, only 1 tank of fuel)

But I'm not getting any sync errors!
The frequency of 4 teeth is also strange as it does not divide evenly with a engine cycle.

Any ideas?

As you conclude, it looks like you have some kind of mechanical problem. With a "Dual wheel" configuration, this won't usually lead to sync-loss, but that tooth log shows wildly varying tooth intervals which will inherently cause real timing errors because the code cannot make an accurate prediction on what will happen next.

James

Not optimal, but not as bad as you feared. This is about a 12% variation in tooth timing, which would mean nearly 4 degrees of timing variation. This is going to hurt performance, but isn't nearly as scary as 15 degrees of scatter.