losing RPM signal around 800rpm

fastfreddie · Post by **fastfreddie** » Fri Sep 15, 2006 3:08 pm

So..i got the car started and all that, but when idling in drive (rpm around 800) it seems to loose the rpm signal. Im using MS2 v3 and the vr sensor curcuit and direct coil control, and a MSD coil. Its' fine while driving and when idling in neutral (rpm about 1000) but i sense something is wrong with my settings. The timing also seems pretty erratic (gets more stable with RPM but still not to my liking) however this is on a small block mopar v8 so the slot drive distributor isnt' the most stable.

ive attached a picture of the data log.

Any input would be appreciated!

fastfreddie · Post by **fastfreddie** » Fri Sep 15, 2006 3:08 pm

So..i got the car started and all that, but when idling in drive (rpm around 800) it seems to loose the rpm signal. Im using MS2 v3 and the vr sensor curcuit and direct coil control, and a MSD coil. Its' fine while driving and when idling in neutral (rpm about 1000) but i sense something is wrong with my settings. The timing also seems pretty erratic (gets more stable with RPM but still not to my liking) however this is on a small block mopar v8 so the slot drive distributor isnt' the most stable. ive attached a picture of the data log. Any input would be appreciated!

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Bernard Fife · Post by **Bernard Fife** » Fri Sep 15, 2006 3:31 pm

fastfreddie,

Have you tried experimenting with the hysteresis pot on the VR input circuit? It is R52 on a V3 main board. You might have to also adjust R56 if there is an offset bias voltage as well. See: http://www.megamanual.com/ms2/vradjust.htm

Lance.

Bernard Fife · Post by **Bernard Fife** » Fri Sep 15, 2006 3:31 pm

fastfreddie, Have you tried experimenting with the hysteresis pot on the VR input circuit? It is R52 on a V3 main board. You might have to also adjust R56 if there is an offset bias voltage as well. See: http://www.megamanual.com/ms2/vradjust.htm Lance.
Forum Rules --- No responses to your posts? See this. MegaFAQ --- MegaManual

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fastfreddie · Post by **fastfreddie** » Fri Sep 15, 2006 3:43 pm

Yep, tried that, a few turns at a time, but no diffrence. Still seems to drop the signal. All is fine above say 900. For reference the a/c output is around 2V at 1000rpm, and it's a nice stable sinewave.

Also im having some issues with the whole VR sensor stuff. My tach input when measured with my oscilloscope from the VR sensor looks just like the attached picture, which looks like the polarity is reversed (negative when reluctor tooth is approaching) but it will not run at all if i set the trigger capture to rising edge? Its now set to falling edge and it runs fine, the advance checks ok (if a bit erratic) at various rpm's and when dwell is set to 1ms it runs rougher........

My head hurts...............

Thanks for the quick reply!!!!

fastfreddie · Post by **fastfreddie** » Fri Sep 15, 2006 3:43 pm

Yep, tried that, a few turns at a time, but no diffrence. Still seems to drop the signal. All is fine above say 900. For reference the a/c output is around 2V at 1000rpm, and it's a nice stable sinewave. Also im having some issues with the whole VR sensor stuff. My tach input when measured with my oscilloscope from the VR sensor looks just like the attached picture, which looks like the polarity is reversed (negative when reluctor tooth is approaching) but it will not run at all if i set the trigger capture to rising edge? Its now set to falling edge and it runs fine, the advance checks ok (if a bit erratic) at various rpm's and when dwell is set to 1ms it runs rougher........ My head hurts............... Thanks for the quick reply!!!!

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Bernard Fife · Post by **Bernard Fife** » Fri Sep 15, 2006 3:52 pm

fastfreddie,

There's a trick here. The VR circuit goes high on the falling zero-crossing event, and low on the falling zero-crossing event. The rising and falling edges in MegaTune refer to the edge as seen at the processor. So for the diagram above, the correct trigger is 'falling edge' as your experince shows.

If set to the rising edge, it still works (with an adjustment to the trigger offset), but the timing is variable depending on the rate of falloff on the signal.

2 Volts isn't much at 1000 rpm, the HEI VR puts out about 8-10+ Volts at that speed. Is the sensor to reluctor gap adjustable, and can you move it closer?

1.0 millisecond is pretty low for a dwell setting, they are more typically between 2.0 and 4.0 milliseconds.

Lance.

Bernard Fife · Post by **Bernard Fife** » Fri Sep 15, 2006 3:52 pm

fastfreddie, There's a trick here. The VR circuit goes high on the falling zero-crossing event, and low on the falling zero-crossing event. The rising and falling edges in MegaTune refer to the edge as seen at the processor. So for the diagram above, the correct trigger is 'falling edge' as your experince shows. If set to the rising edge, it still works (with an adjustment to the trigger offset), but the timing is variable depending on the rate of falloff on the signal. 2 Volts isn't much at 1000 rpm, the HEI VR puts out about 8-10+ Volts at that speed. Is the sensor to reluctor gap adjustable, and can you move it closer? 1.0 millisecond is pretty low for a dwell setting, they are more typically between 2.0 and 4.0 milliseconds. Lance.
Forum Rules --- No responses to your posts? See this. MegaFAQ --- MegaManual

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fastfreddie · Post by **fastfreddie** » Fri Sep 15, 2006 4:05 pm

Thanks again for the info!

Ok, so im not crazy after all, since the vr sensor page says the sensor should go positive when the reluctor tooth is approaching... so i guess this is a faulty statement?

I run the dwell at 2.5ms normally, i was just trying to see if i had the settings wrong so dwell would become part of the timing.

The sensor is already real close to the reluctor. (about one dust particle from colliding) so not much improvement there. How come it still seems stable when cranking? The output voltage should be super low at cranking speeds (about 170rpm) but i do indeed have problems starting it, it hovers a sputters for a while, but when it catches it revs up fast and clean. Obviously could be my cranking pulsewidths screwing that up also.

Brgds

Freddie

fastfreddie · Post by **fastfreddie** » Fri Sep 15, 2006 4:05 pm

Thanks again for the info! Ok, so im not crazy after all, since the vr sensor page says the sensor should go positive when the reluctor tooth is approaching... so i guess this is a faulty statement? I run the dwell at 2.5ms normally, i was just trying to see if i had the settings wrong so dwell would become part of the timing. The sensor is already real close to the reluctor. (about one dust particle from colliding) so not much improvement there. How come it still seems stable when cranking? The output voltage should be super low at cranking speeds (about 170rpm) but i do indeed have problems starting it, it hovers a sputters for a while, but when it catches it revs up fast and clean. Obviously could be my cranking pulsewidths screwing that up also. Brgds Freddie

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