High tooth count wheel not reving over 2900

[SQLGUY]

Sorry to hear that that didn't help.

One other thing to look at is the dwell you're seeing when the engine starts to stumble. Microsquirt doesn't start charging the coils until after the tach pulse occurs, so, if the tach pulse is happening to soon before firing, there may not be enough time to charge the coils as ignition advances at higher RPMs.

If this is the problem, you'll actually see the dwell getting reduced suddenly as ignition advance pushes into your charging time. The solution would be to change your delay teeth and ignition offset to allow more time between the tach pulse and the start of dwell.

[jlturpin]

Yesterday I tried 22K resistors on each VR input with no success. I also tried setting skip teeth with no luck.

My current thought is to try using the Cam sync dual spark option and changing the offset of the crank sync trigger to reflect 1/2 the 58.6 btdc crank sync stud. Not sure if I am on the right path, but nothing else seems to be working. If I understand the factory bosch dme, it uses the crank sync to set tdc for cranking and then checks sync of the 132 teeth flywheel occasionally during steady speed to make sure both are in sync. Since this is not an option with M-0, an it checks on every revolution for sync, this may be causing the ms to be overrun. Opinions please...


1 of the main reasons I feel that the timing is wondering all over the place is my timing map seems to be fine for the first few seconds of normal running, but once I start to accelerate, it seems to start misfiring. Also, I did notice as SQLguy stated that I my dwell is falling off quickly when I try to accelerate, no matter what the skip teeth is set to.

I know there is a solution, I just have to find the right combination.... Oh, I think I blew my turbo hotside seal with the lean running over the past several day, 99% of it in my drive way. I have burned $70 in gas, but I still have most of what little hair I started with. Once I get this sorted out, I get to pull the turbo, which is a huge pain on the 944. Probably 10-14 hours labor, good thing I have more time than $$..

If anyone can help this would be appreciated.

[grippo]

You can't experiment with skip teeth - that number is set by the number of cylinders you have. If timing is wandering you have to find out why - don't try to accelerate. With the engine idling the timing should be very steady. Then move to a higher rpm slowly and stay at that rpm. The timing should again be steady. If it is, but it misfires when you go rapidly from one rpm to another, then this should show up in the tooth +/- counter.

Also, what SQL said about dwell is very important. If the dwell starts to shrink as you increase speed, then you have to change your trigger offset and number of delay teeth so you get the same timing but the dwell time no longer shrinks. (Dwell can shrink as you get to really high rpm, but you are not at really high rpm.)

[jlturpin]

Sorry, I did mean delay teeth, I was not changing skip teeth. I have not used or found the tooth counter, so I'll have to locate it and figure out how to use it.

[SQLGUY]

So, what are your offset and delay teeth set to now, and what did you try changing them to?

[jlturpin]

Well, -301.4, and I set the delay teeth to 6-10. I guess I may have been confused about setting the offset. Even though the physical stud on the flywheel can not be move, I need to set the offset to 280'ish or do I need to raise it to 330ish or somewhere in between?

[SQLGUY]

Your stock setup seems like it should allow almost 300 degrees for dwell and advance (If I'm understanding things correctly). That should be plenty.

Please post an msq and a datalog if possible.

Thanks,
Paul

[jlturpin]

OK, I made some headway tonight. I set the offset at -300 and set delay teeth to 17 (I think). Now it is time to work out my timing table, seems that the factory table I tried to transpose from tps% to MAP is wrong....

I don't have the .msq file on this pc, but I'll try to put a copy of it out tomorrow with a data log.

Thanks,

Jonathan

[jlturpin]

EDIT. I changed to using an old Toughbook laptop for megatune and it seems that resets have improved. I also did some more work on my .msq and have the car running, idling and accelerating great, until around 2700 RPM. At this point, the tach counter starts counting down. Up until that point, it revs wonderful, and my AFR's and timing seem to be dialed in.

I tried 22K resistors on both VR1 and VR2, then moved to 44K on both. It actually ran better with no resistance, and rev'ed a few hundred rpm higher. It seems like 2680 point where it starts counting down, up to this point there are NO lost signals. No dwell loss.

I have tried VR delay, delay teeth in every combination I can come up with (so far), and have made minor changes to Base offset in .1 increments.

Since the reference mark is at -58.6 and does not allow for an equal number of delay teeth, it actually comes up to be 21.48 teeth. What next?

22 teeth gets me 60 degrees, if I change the polarity of the reference sensor, is it possible for it to make up the 1.4 degree difference? Then I could change my offset to -60 and set delay teeth to 22. This should get me spot on.


132 teeth ring gear Factory VR Sensor is same offset as the Reference sensor
1 tooth Reference stud on Flywheel at -58.6
2.7273 degrees per tooth

[jlturpin]

No change with polarity change on VR sensor. Ing output shilded. Good ground, good power supply.

Attached is the MSQ that seems to run near perfect below 2700 RPM where I start dropping triggers.

The attachment 2 951-RUNNING good missing triggers above 2700 -60 22delay hard start.msq is no longer available

2 951-RUNNING good missing triggers above 2700 -60 22delay hard start.msq

Good running .msq up to 2700 rpm, 3bar map, 55# injectors, MSD coil, 944 turbo S, K26/8 Hot start issue to be worked on later

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datalog200807081917.xls

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