Miks15
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| posted on 20/4/10 at 07:58 PM |
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edis checks
Hi Guys,
Im going to give my engine another go tomorrow. I just want to make sure ive connected everything up for the edis right.
From what i believe the sensor lines up with the missing tooth on the trigger wheel when the engine is 90 degrees BTDC on cylinder 1. So this means
that when the engine is at TDC, the missing tooth is 90 degrees beyond the sensor?
Also am i right in thinking that it should spark 10 degrees before TDC when no ecu is connected?
Thanks
Mikkel
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norfolkluego
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| posted on 20/4/10 at 08:12 PM |
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Miks, right on both counts, the easy way to think about it is as the MJ manual describes it.
Engine at TDC
Missing tooth at 12 o'clock
VR sensor at 9 o'clock
Obviously that's with the sensor on the left as you look from the front, if on the right
Missing tooth at 6 o'clock
VR sensor at 3 o'clock
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Miks15
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| posted on 20/4/10 at 08:23 PM |
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OK thanks for that. well mine are more like 8 and 5 oclock but they are at 90 degrees apart.
One thing i dont quite understand is how if it fires before tdc how it can work? I always thought they fired slighty after tdc.
Could someone explain how this works?
Sorry if this is a dumb question 
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mediabloke
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| posted on 20/4/10 at 08:44 PM |
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quote:
Originally posted by Miks15
OK thanks for that. well mine are more like 8 and 5 oclock but they are at 90 degrees apart.
One thing i dont quite understand is how if it fires before tdc how it can work? I always thought they fired slighty after tdc.
Could someone explain how this works?
Sorry if this is a dumb question
Not a dumb question. I should know - I've asked a few... 
EDIS expects the missing tooth to pass the VR sensor at 90 deg BTDC. In theory, this would allow up to 90 deg. of advance. EDIS uses this as a
reference point.
Kept going back to this pic to sense-check when I was building mine.
With no PIP/SAW signal from the MJ, the EDIS system fires at 10 deg BTDC - static timing. Or to put it another way, 80 deg. after the missing tooth
passes the VR sensor.
Think that makes sense. Or I might just've confused myself...
HTH anyway. 
[Edited on 20/4/10 by mediabloke]
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Miks15
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| posted on 20/4/10 at 09:09 PM |
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I do just about understand that.
what im more confused about is why firing 10 degrees BTDC would work. The way im thinking is if it fires BTDC then wont it try and force the piston
back down the way it came trying to rotate to crank the wrong way? In my head i always thought it had to fire after TDC?
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t16turbotone
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| posted on 20/4/10 at 09:26 PM |
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Timing advance is required because it takes time to burn the air-fuel mixture. Igniting the mixture before the piston reaches top dead center (TDC)
will allow the mixture to fully burn soon after the piston reaches TDC.
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mediabloke
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| posted on 20/4/10 at 09:38 PM |
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quote:
Originally posted by Miks15
I do just about understand that.
what im more confused about is why firing 10 degrees BTDC would work. The way im thinking is if it fires BTDC then wont it try and force the piston
back down the way it came trying to rotate to crank the wrong way? In my head i always thought it had to fire after TDC?
No offence meant, Mikkel.
As the explosion takes an amount of time, the fuel/air would always have to be ignited BTDC, so as to be fully burnt by ~10deg ATDC, and to
extract the most power from the stroke.
Some 70s engines were tuned to fire after TDC, but they are few.
Francis.
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Miks15
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| posted on 20/4/10 at 09:55 PM |
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Ahh that makes sense! Thanks for that guys!
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snapper
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| posted on 21/4/10 at 08:49 AM |
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As the engine turns faster (more revs) the burn time for the mixture stays the same so the spark is advanced to fire earlier thus the point at which
the mixture exerts maximum preasure is still at the correct point.
This works on the Pinto engine upto 3700 rpm when maximum advance is "All in"
Vacuum advance in a distributor then swings the timing in relation to load
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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MikeRJ
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| posted on 21/4/10 at 12:20 PM |
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quote:
Originally posted by mediabloke
As the explosion takes an amount of time, the fuel/air would always have to be ignited BTDC, so as to be fully burnt by ~10deg ATDC, and to
extract the most power from the stroke.
The aim is to produce peak cylinder pressure at ~15 degrees ATDC, the mixture will not necessarily be fully burnt by this point.
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