intermittent misfire at full acceleration

[turtle10]

• Car: 1993 Toyota Paseo race car
• ECM: MS-II v3 rev 2.905 assembled from a DIY Autotune kit
• Ignition: VR circuit controlling Toyota ignitor and mechanical distributor
• FI: Triumph TT600 individual throttle bodies, stock Toyota injectors

I started with a baseline tune from Wedge over at Toronto Paseo Club and now have the car running pretty well. With the four throttle bodies, the idle is high at between 1500 and 1700 rpm. I've got the throttles synced as close as I can by ear. I don't have a proper manifold vacuum gauge to test it. I made an analog gauge but the engine almost immediately tried to suck up all of the oil in the tubes. If I dial in the the throttles/fuel/ignition to a more stock 1000 to 1200 rpm idle there is no power until around 2500 rpm. So, I've left the idle high.

I think I am having problems with my ignition. At almost full throttle accerlation, there is an intermittent misfire and my stock tach becomes erratic. The timing is right on the mark on the engine at idle. I've installed new plugs, but that didn't make too much difference (though the engine runs a little better now). Could there be a problem with the ignitor or distributor?

MSQ file attached.

Thanks,
Michael

[drholl]

Misfire at higher RPMs. It is possibly the dwell time that you have set in the ignition setup.
I don't know your engine setup, 4 cyl, 6 cyl or 8 cyl. COP, Distributor?? If COP just ignore this post.

If distributor, keep reading.
Anyway you have the dwell set to 3.1 and the spark time to 2 ms. That's 5.1 ms per spark - - - if possible.
At 5,000 RPM on a V8 you only have 3 ms between sparks so with the computational power of the MegaSquirt the time to perform a spark at 5,000 on the V8 is cut to -
a dwell time to 1.82 ms and for the spark duration to 1.17 ms.
That's not very long for a dwell duration. Try setting the spark duration to 1 ms. That will change the dwell and spark duration to -
a dwell time to 2.26 ms and for the spark duration to 0.7 ms.
That's why EDIS, COP and the newer short dwell times on the high performance coils are so great.

Hope this helps.
Holl

[trakkies]

Did the dizzy originally have mechanical advance which has been locked? The relationship between rotor arm and plug lead contacts might be the problem. Can also be a problem on ones which didn't have mechanical advance if using a wilder advance curve. A quite easy way to check is to cut a hole in a spare cap and look at the position using a strobe light.

I'd consider ditching the dizzy and going wasted spark.

[Matt Cramer]

Could you post a data log of the issue? That will shine a lot more light on the problem.

[Bluehaze]

This problem is familiar to me as well. I also have a VR/Dissy?coil setup. Had intermittent missing at the mid 2k revs under hard accel, as well as at cruise sometimes. My datalog was showing the RPM diving to Zero from 2500 RPM for an instant, then coming back. I think I may have eliminted the problem by increasing my Next Pulse Tolerance. Perhaps I'm off the mark here, but the way I read it in the book, if the "Next Pulse" falls outside the percentage of tolerance (in my case it was only 15%), then it is ignored, and therefore an ignition event is skipped, and we have in essence a "miss". Increased the NPT at running to 25% and so far so good. Maybr if there is excessive chatter in your dissy, this may be a cause?
Or am I perhaps barking up the wrong tree?