drifting timing with rpm
 

I have a 99 turbo runing MS3 Basic stock triger and GM coils, i see an increasing timing discrepancy as rpm rise when i look at timing on the engine with a timing light, i could see it on the dyno when i set all the timing numbers to 12 deg on timing table 1 and did a run and i can see it reving the engine after setting timing to 10deg fixed timing (not the timing table) the timing shift is about 14 deg at 6000RPM and aroud 16 at 7000rpm.
I will test a different cranck sensor tomorrow to see if that changes anything.
Any ideas of what can cause this?

Here is a utube video of what i see with a timing light when reving the engine with fixed timing set at 19 deg

What do you have the spark hardware latency set to?

--Ian

it is set to 0, can i put a negative number there?

Start with 100, see what happens. That's what rev used for a 32-1 wheel I've used.

The exact number varies from car to car, but it will always be a positive number (representing electrical delay from crankshaft to ECU) and will generally be in the tens to lower hundreds.

It's a trial-and-error setting.

Thanks, i will test it tonight

I progresevelly changed and burned with each change the spark latancy from 0 to 255 (the maximum) with fixed timing set to 10 BTDC, the timing still advances with rpm from 10 at idle to arownd 20 BTDC at 6000rpm, there did not seem to be a difference as i changed the latency number, my tuner said that some cars have this issue and is caused by sensor variation, he dos say that this is the only Miata he has seen with this issue.

Chiming in, as it's definitely the first time I see it as well.

I would start by updating to the latest stable firmware, which is 1.4.0.

The latency is only used if the timing retards, not if it advances.

Also, this might seem silly, but do try with a different timing light as well.

Just noticed that myself.

Strange happenings afoot. Prediction?

Thanks everybody, i will try a diferent timing light, pickup sensor, and the latest firmwere, i am still runing 1.4 alpha 9 that Scott Clark from DYI installed before tuning my car earlier this year.

Reverant, I think that the engine is getting the timing i see with the timing light, take a look at the timing table we ended up with (only tuned to 15PSI and it makes 300HP at 14 on 93 octane) but it would have ended up in some big negative numbers timing wise if we would have gone to 18 or 20 PSI.
We were going to tune with the flex fuel sensor and E85 but desided to wait until i can figure out what is going on with the timing.

The spark latency setting is to help control timing retard induced by the vehicle's electronics. It will not correct self advancing ignition in relation to RPM.

You may be triggering off the wrong edge of the tooth. I have seen cases where an unstable edge will cause timing advance with increased RPM.

Ben, i am runing OEM triger wheel and sensor, i see that you reccomend 2mm tall teeth and thicker steel with your sensors.
Do you reccoment i install one of your wheels? I dont see a bolt on wheel on your website but would like to know if you have one that you reccomend.
Thanks

Why?

Just try different input capture edges and see if you find a combo that works better than current.

All my units work with rising edge and going high. Setting to falling edge will cause the edges to overlap and the car won't start. These units use optocouplers, and I've never seen this issue before.

Which firmware are you on right now?

I am runing 1.4 alpha 9 that Scott installed before tuning the car earlier this year

Alpha firmware should NEVER be installed if you don't have a reason to try it. Scott should know that. Upgrade to 1.4.0 or downgrade to 1.3.4.

The reason for loading it before the tuning was that we wanted to run the flex fuel sensor and E85 blending maps during that session and 1.4 had some new features in this area.
I will load 1.4.0 and see if that changes anything

Is this true with your MS2's as well?

Mine is showing falling edge and going high (inverted) and I've had issues cranking forever but once it starts it runs ok. That is what it was on default when I got it.