Timing advancing under RPM

[walbuck]

Hi - Hoping someone can help with this

Running a MS3 on a 3VZFE Turbo engine in an MR2

Car runs nice - but has timing advance when revved
Has a 24 tooth triggerwheel distributor in it - missing tooth of course and at cam speed - no mechanical advance in those dizzy's

Have the software set at FIXED ADVANCE - yet still getting timing increase whenever revving - and not a small amount either
Have done the usual checks - running it at falling edge and rising edge
Prefers falling edge as no need for any filtering - needs filtering on rising edge but still advances both ways

Checked the Spark summary gauges - no interference from idle advance, Mat advance, Clt advance or anything else

Tried it with spark tables set at 5' and fixed advance off - but exact same scenario
Distributor cap, rotor, leads, coil etc are all brand new

It's odd - as done plenty of these engines before (although always on MS1) and never had issues before

Got the MSQ file, a short datalog and the CSV composite logger - but they all look ok to me.

Tried 3 seperate timing lights - so not that either

The alternator isn't running at the moment (next job) but shouldn't make a difference on FIXED ADVANCE?

Definitely a headscratcher

If you find time - can you have a quick look at the files- make sure it's not something REALLY basic I've overlooked

Thanks
Jared

[gboezio]

If you run a VR sensor and get 2-4 degrees, it usually comes from the trim pots that are misadjusted, the best neutral position is to get the trigger to 0V, but sometimes due to noise you need to raise the treshold to get a clear signal.
Doing so will add or remove timing as the sine wave stretch, 0 crossing won't change as much, on my actual build I used the spark trim to bring flat the timing curve.

[billr]

How much is the timing changing? Retarding or advancing?

[MegaSlant6]

I am a complete novice at this, but had the exact same issue ,timing advancing even with fixed timing selected

got a tip from Matt Cramer, he had me set the dwell type to fixed dwell.

that resolved the timing advancing issue for me.

[jsmcortina]

I am a complete novice at this, but had the exact same issue ,timing advancing even with fixed timing selected

got a tip from Matt Cramer, he had me set the dwell type to fixed dwell.

that resolved the timing advancing issue for me.

That means that your spark output polarity setting is backwards. Setting fixed dwell covers it up but the timing will be less accurate.

James

[MegaSlant6]

fixed dwell covers it up but the timing will be less accurate

I certainly do not want to clog up the original posters log,'
however, when one clicks on the ? mark button next to the Dwell Type drop down box
there is a statement that says
"Fixed Duty locks the spark output to a constant duty cycle instead of controlling dwell.
eg Fords Push Start ,... Bosch Smart Modul,... or MSD or other CD boxes."

that comment indicates that a Fixed Duty selection is intended for a MSD CD box, like the one I have.
I was only passing on to the original poster on how I resolved an issues similar to his. I do not know if he has a CD ignition, but it appears that he
is using a similar distributor trigger.

[walbuck]

Thanks Guys
All sorted
Yes - Spark output was inverted - that was the issue

Seems the ECU was using the early 2n222a transistors rather than the later Mosfet drivers we're used to
Swapped the Spark polarity and the timing is now super stable

The igniter (stock) and coil wasn't heating up and the engine ran perfectly fine - so didn't think there was an issue
Knew it would be something basic I overlooked
Cheers again
Jared