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Old 10-14-2011, 12:50 AM   #1
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Unhappy Mspnp, 36-1, sporadic misfire

hey folks I'm putting this out here to see if anyone has had a similar experience or knowledge that may help my situation. Im going to just list facts to trim the fat. This is not a consistant misfire it runs in all setups, but running 36-1 somtimes it drops 1000 RPM

using a timing light the timing doesn't look as steady as the CAS timing and when the misfire occurs the timing jumps back (advanced) a few degrees.

Trigger & tooth Logs look fine. I sent them to [email protected] DiY. nothing out of the ordinary he says its something on the output side, but what? The Cas is using the same Dwell & signal and output

MSPNP, 10g hi res, AEM Twinfire, 300M cops.

it has and still runs fine though the CAS @ fixed 50% dwell with the Twinfire & cops for almost a year.
I've used VR sensors ( used & new) ,fixed 50% dwell, 9th tooth,wheel decoder settings correct, Pots all the way counterclock- wise, correct polarity, shielded signal wire grounded @ Ecu, different sensor air gaps .035-.060 , it still has a habitual misfire.

I used the hall effect sensor from DiyAUtoTune, I ran the signal wire through the one I used for the VR sensor every so often it misfires, I ran the signal wire through the signal wire for the CAS to the same result.

Thanks,



Last edited by EvilMiata; 10-14-2011 at 01:05 AM.
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Old 10-14-2011, 08:39 AM   #2
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looks very similar to what mine would do when my TB was loose and allowing the inigtion timing to wander.
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Old 10-14-2011, 09:28 AM   #3
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looks very similar to what mine would do when my TB was loose and allowing the inigtion timing to wander.
But the OP is using a 36-1 crank trigger, a loose timing belt wouldn't effect ignition timing.

Could cam timing slightly varying cause such extreme problems?
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Old 10-14-2011, 09:36 AM   #4
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Where did you get your 36-1 wheel from? Joe Perez had an issue with his, the wheel wasn't precision cut and would sometimes not give out proper signaling.
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Old 10-14-2011, 09:40 AM   #5
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If you command a fixed spark angle, does the observed spark angle still "glitch" when the tach input glitches?

I'm on board so far with Reverant's idea of the wheel being imperfect (uneven teeth or off center).
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Old 10-14-2011, 09:41 AM   #6
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But the OP is using a 36-1 crank trigger, a loose timing belt wouldn't effect ignition timing.

Could cam timing slightly varying cause such extreme problems?
it's early, haven't have coffee yet. I also dont read.

But the jitter on the crank looks about the same too, holding fairly tight to target and then just drifting off. This shouldn't happen on a crank wheel.
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Old 10-14-2011, 09:52 AM   #7
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yeah I'm having the problem with the crank driven 36-1. The timing is solid with the CAS.

The trigger wheel is from DIY. Its properly cut and professionally mounted and installed, but that would affect the input signal and the teeth & triggers appear fine.
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Old 10-14-2011, 10:03 AM   #8
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If you command a fixed spark angle, does the observed spark angle still "glitch" when the tach input glitches?

I'm on board so far with Reverant's idea of the wheel being imperfect (uneven teeth or off center).
yeah set to a commanded 10 degrees it still jumps.it was drilled and cut out on a CNC . If that where the case wouldln't it be off at the same point everytime and jump or misfire at regular intervals? THis may run for a solid minute fine, then suddenly skip. It may skip once or mabe twice back to back. It's an unpredictable miss
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Old 10-14-2011, 11:28 AM   #9
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The trigger wheel is from DIY.
Joe's 36-1 wheel was also from DIY; you might want to contact him.
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Old 10-14-2011, 11:35 AM   #10
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oh yes, the ninja throwing star.
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Old 10-14-2011, 12:46 PM   #11
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oh yes, the ninja throwing star.
ok, If that's the case wouldn't the tooth logger be off in some way ? I'm just trying to think through this logically...

I thought about magnetic field interference , due to it being right by my alternator, but to me it seems that also would show up in the tooth logger.

I thought that since it does show up coming in well it maybe some thing going wrong in the processing in between the input and output, because they ( the CAS settings & 36-1 settings ) both should be putting out the same signal running @ 50% fixed on dwell. so In my mind that X's out anything outside the ECU. Unless there is some other setting I'm over looking that may change the output...I'm not new, but I should be learning forever, enlighten me...
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Old 10-15-2011, 09:41 PM   #12
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on a pnp if this step was missing could it have this affect? :

Get a 330 ohm 1/4w resistor and cut the leads down to about 1/2" at each end. Maybe a bit less.
Tin each end of the resistor with a bit of solder.
Cut a 5" piece of hookup wire (22ga is fine) and strip just a 1/8" or so. Tin the stripped wire with solder.
Melt the tinned wire tip to one end of the tinned 330 ohm resistor tip and let it cool.
Use this wire/resistor combo to jumper the 'top' (top as in when you facing the silkscreen side of the PCB, with the text so that you can read it normally) lead of R26 to IGBTIN on the opposite side of the PCB.
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Old 10-17-2011, 02:39 AM   #13
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I've come to a conclusion , That this must be a problem with a different signal leaving the Megasquirt when when the output is inverted, but this is the only way ive got it to run on the 36-1 settings. The twinfire must not agree with what ever the difference is. Watching the trigger output light on the twinfire I can see it skip whenever this stumble occurs.
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Old 10-17-2011, 03:02 PM   #14
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Quote:
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Joe's 36-1 wheel was also from DIY; you might want to contact him.
I had a couple of different issues with my 36-1 setup.

The first was that the wheel itself was not perfectly round. Mine was the smallest of the three, with the triangular teeth, and the tips of the teeth were not all at precisely the same height. I solved this by placing the entire assembly of wheel / crank adapter into a lathe and trimming down the teeth by about 2mm, which not only caused them to all become true, but also put a flat spot on the ends which greatly improved the output voltage from the sensor (more metal near the sensor = more output voltage.)

I believe that DIY is going to change the design of this wheel, to make it similar to what I did and give it flattened teeth. This alone will probably fix most of the problems people have with this wheel by simply increasing the output voltage you get from using one.


I also went through several revisions of the decoding circuit. The LM1815 turned out to be very poor at dealing with the aforementioned tooth irregularities. I then switched to the "stock" VR circuit from the 3.0 schematic, and that was good, but still gave a very occasional misfire.

Finally, I went to a MAX9924 circuit, and this made the system rock-solid.
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Old 10-17-2011, 03:14 PM   #15
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I had a couple of different issues with my 36-1 setup.

The first was that the wheel itself was not perfectly round. Mine was the smallest of the three, with the triangular teeth, and the tips of the teeth were not all at precisely the same height. I solved this by placing the entire assembly of wheel / crank adapter into a lathe and trimming down the teeth by about 2mm, which not only caused them to all become true, but also put a flat spot on the ends which greatly improved the output voltage from the sensor (more metal near the sensor = more output voltage.)

I believe that DIY is going to change the design of this wheel, to make it similar to what I did and give it flattened teeth. This alone will probably fix most of the problems people have with this wheel by simply increasing the output voltage you get from using one.


I also went through several revisions of the decoding circuit. The LM1815 turned out to be very poor at dealing with the aforementioned tooth irregularities. I then switched to the "stock" VR circuit from the 3.0 schematic, and that was good, but still gave a very occasional misfire.

Finally, I went to a MAX9924 circuit, and this made the system rock-solid.
ok mine is the 6.75, but I think they have a different manufacturer now. Im leaning towards the Twinfire not agreeing with the inverted signal from the pnp, But it will not run anyother way, and yeah I could see that being in the code. why couldn't it run off the 36-1 yet output the same signal as when it's using the CAS? I'll put the rest off that "LM1815" and MAX9924 circuit into google translate lol...oh and the teeth are flat and laser cut .
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Old 10-18-2011, 10:28 AM   #16
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Thumbs up 36-1 trigger wheel baaby yeah! it helps set the timing is that enough for you?

OK, Matt told me to switch back to inverted "no" and adjust the trigger angle. I adjusted and adjusted with no effect, it went from cranking like it was to advanced to popping loudly through the exhaust. so I turned off the fuel pump (no flooding or sonic booms), and using a remote starter cranked it while watching with a timing light and saw no marks. I figured it must be 180-out, so i swapped my out puts to the Twinfire and there they were. with the fuel still off I adjusted the trigger angle til it was @ 10 BTDC with the map at a fixed 10 then started her up. no stumble. nothing. I realize i may have been able to swap my A & B trigger numbers in the Wheel decoder settings also. the CDI definitely didn't agree with the output " inverted " setting signal for some reason. the Timing mark is rock solid and steady, Thanks for all the info folks! Big thanks to Matt, Russ, and Ben 10 @ DIYAUTOTUNE for always having patience when dealing with all my emails, ignorance and occasional guest appearances .

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