Major sync loss under 1500 RPM
 

Just swapped from MS1 to MS2 on a v3 board. It will fire up and run OK as long as I keep the rpms above 1500, as soon as it dips below that I get massive bucking, sputtering, misfiring and raw unburnt fuel out the tailpipe.

I think I always had a small amount of this misfiring occurring (see my other thread https://www.rx7club.com/megasquirt-f...-idle-1090632/) but this is orders of magnitude worse now.

I'm assuming this has to do with the secondary VR conditioner mis-reading somehow but I'm not sure where to start troubleshooting. I did modify the LM1815 as per Aaron's site to change from 'R/C timer' to 'zero crossing' mode but to be honest I'm not sure exactly what that change does. Should I try going back to the original 'R/C' mode or does that not work at all with MS2?

I've attached a zip with a .msl log and a .csv 'composite' log, which is what was requested in my other thread (and I can now provide since upgrading to the ms2 :D) near the end of the MSL you can really see it happening

Any help or suggestions are appreciated!

i adjusted the gap on the sensors in the CAS to pretty tight tolerance (used a paper folded in half as a 'spacer') and the problem is like 85% fixed. i can bring the idle down close to 1000 rpm now, but it still randomly throws a 'sync loss' or two. it also seems to chug and sputter for a few seconds after startup before evening out.

is it normal for the ms2 to be THIS MUCH more sensitive to the VR signals compared to MS1? or did I break something?

Do you have another CAS to try? Adjusting the gaps tells me that there is an issue with the CAS. Or possibly a wiring issue at the CAS connector/DB37.

The difference between zero crossing and R/C timer is this: Zero crossing mode causes the chip to actually look for the input sine wave to pass zero by a threshold (which can be set) then start its internal one shot timer to produce the output pulse. In this way, the timer is "armed' to ignore any further zero crossings until the wave has also passed another threshold on the positive side. When it's in R/C timer mode, I believe this arming is done by the decay of an resistor/capacitor network connected to the timing pin. The datasheet has a fairly good explanation.

You can go back to the original R/C timer mode and give it a try, then adjust the MS2 noise filter.

According to the composite log you lose the 2 tooth signal when you experience the sync losses. Something is wrong with the CAS, wiring, or LM1815 circuit.

Cool, thanks for the explanation. Is the MS2 'expecting' a different type of signal vs MS1 then? or what's the reason for the two methods of building the circuit here: http://www.aaroncake.net/rx-7/megasq...onditioner.gif ?

I do have a spare CAS but it's pretty crusty looking inside. Guess it doesn't hurt to try, but I was worried about not being able to re-time the engine if it wont run at an idle RPM

The two methods come from the original LM1815 circuit way back in the day on MSExtra, I think. At the time I think it was due to a firmware difference. Interrupt vs. timer calculation on the trigger signal maybe. Ken or James would know.

But since the MS1 and MS2 share a board with the same basic VR circuit used on the NE wheel, I see no reason why it wouldn't work both ways.

As for swapping the CAS, as long as you have the thing on the correct tooth and place the CAS in the middle position, the engine will start and run. 10 degrees back or forward isn't going to make much of a difference.

MS1 required a pulse of a specific length for the ECU to catch it since it was polling driven instead of interrupt driven. MS2 was interrupt driven so we just used zero crossing mode.

Holy crap I was right! Yay for the memory of obscure things.

looks like my adjusted CAS was only 'fixed' at idle, it started crapping out again when i tried to drive the car. swapped to a spare one (which is super crusty and has rust inside) and it runs great now. went for a drive right away and auto-tuned to the point of drivability out of boost. guess it's good for now!

Excellent, glad to hear it.