Stupid VRef GM 8pin question

[Army of Six]

im getting ready to go to ign timing control with my MS 3.0 v2.885

i was reading about the relay to supply 5 volts to the "B" pin during run but NOT cranking. that way the timing isnt controlled until after the engine starts. here is the stupid question. why cant you just run 5 V to the "B" pin during crank and run and MS controls the timing while it is cranking?

Thanks,
Vic

[Bernard Fife]

Vic,

You can try that, but the engine speed when cranking is quite unstable, and this leads to large errors in the cranking timing with HEI. If you set-up is marginal, this can make starting hard, or even break the starter. By using the bypass, the timing is set entirely in the module based on the geometry, and there is effectively no error in the timing advance while cranking.

If the HEI had more teeth to determine the crank position, the timing could be more accurate under cranking conditions, and you could use the table.

Lance.

[Army of Six]

hhhm...ok.

thank you for the response. I think i will try it. im not sure how easy it will be to find a wire that is not hot when cranking and hot when not cranking in my 67 econoline.

i was wondering how something like this would/could work. basically at cranking 12V will start the timer and in 5, 6, 10, whatever seconds later (after the motor starts) the timer will send 5V to the "B" terminal and start to control timing.

http://www.google.com/products/catalog? ... CG8Q8wIwBQ

thanks again,
Vic

[WASyL]

i tried this on my camaro and havn't found any that would work as you want to do

best reagds

[convertables_10]

I have 5v on my Vref wire all the time. My cranking rpm is the same everytime though. I havent had any issues as of late with it being done this way. I pull my 5v from my tps sensor. I use 10* in the top 2 cells in the 1st row on the timing table.

[Army of Six]

ok thanks for the replies. i guess i will just try and run 5V off the VRef during crank. hopefully i can get a clean tach signal

thanks,
Vic

[Army of Six]

I have 5v on my Vref wire all the time. My cranking rpm is the same everytime though. I havent had any issues as of late with it being done this way. I pull my 5v from my tps sensor. I use 10* in the top 2 cells in the 1st row on the timing table.

what have you done to insure a good clean tach signal during cranking?

[convertables_10]

Im running the DIYAutoTune mk-hei setup on mine. So far its working flawless. I lowered my cranking timing today and it fires on just a touch more than a bump of the key.

[drholl]

I used a relay for the V Ref voltage that was controlled by the stereo. The stereo turned off during cranking. I suppose the heater blower motor probably does the same thing. When the key is returned to the "Run" position the stereo and the "V Ref" both come back on.

Holl