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
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
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
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
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
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?
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.
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?
Ahh that makes sense! Thanks for that guys!
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
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.