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Discussion Starter · #1 ·
Help! Crank sensor positioning and the effects on timing?

Question for you EDIS gurus: On our escorts (EDIS 4) the crank sensor is placed 90 degrees away from the missing tooth on the trigger wheel enabling the system to work as intended. Now, if you loose the PIP/SAW pulses the EDIS controller goes into lip mode and locks at 10 degrees BTDC… This brings me to the question: Being that the crank sensor is now the only form of input; if while in limp mode, the crank sensor were to move around the circumference of the trigger wheel (and still retain the correct clearance gap of course) clockwise and counterclockwise, would the timing advance and retard respectively?

Assuming it would, roughly how many degrees would each tooth equate to changing timing?

If you're wondering why:

I am thinking about cooking up low cost electronic ignition solution with a mechanical advance for a project of mine. Here is what I came up with: It would consist of an EDIS 4 module wired to power, ground, ignition coil, and crank sensor only. Variable timing would be taken care of by a circular plate with a bearing at its center mounted facing the trigger wheel (trigger wheel is mounted on the crank of the engine, accessory side). The plate would be mounted to the vehicle by one bolt through the bearing so the plate would be able to turn freely. A stand off would then be mounted on the outer circumference of the plate. The crank sensor would then be mounted on the stand off as to be in proper alignment with the crank trigger. An old turbo waste gate actuator would then be mounted to the vehicle and an adjustable linkage fabricated and attached to the plate 180 degrees from the crank trigger. Theoretically, once the waste gate actuator is plumbed in, it will react according to varying engine conditions, causing movement of the actuator arm and in effect moving the plate (and the crank sensors location around the circumference of the trigger wheel) thus advancing or retarding the timing. With a lot of experimenting with actuator linkage lengths, location, and the possible use of a return spring and or ball/spring valve to alter the vacuum signal, I am sue the desired timing advance under load could be reached.

…this crazy idea for a complete, adjustable, standalone ignition system for under $60 hinges on the principle: will the location of the crank sensor effect timing when EDIS module is in limp mode?

Thanks in advance!!! :D
 

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Discussion Starter · #3 ·
like2ride said:
The EDIS module itself controls the timing that is sent to the computer. If it cant send a signal to the computer then the computer cant send the timing needed back to the EDIS module to adjust the timing. When you are in "Limp Home Mode" you are at 10 degrees perminent fix not adjustable because the SAW coming out from the ecu to the EDIS is disconnected and therefore the edis wont have the timing adjustments from the ecu. Good thought on it but it isnt really going to work as easy as you think it is.
I'm not trying to sound smart, so please bear with me… I understand exactly what you're saying in regards to the ecu and its role in timing advance, as well as the pre programmed limp mode. I am not trying to get the edis module to advance timing for say, all I am trying to do is end up with advanced timing; for all proposes, the edis module will think nothing has changed and it will still be running at 10 degrees btdc. So according to what you're saying, the timing will not be affected at all by the movement of the crank sensor? I.E I could totally remove the crank sensor and some how the ignition will still fire at 10 degrees btdc? The only possible way that can happen is if the EDIS takes a signal from the crank sensor (closed loop) in order to set the base timing and figure out TDC of the engine, and as soon as a signal from the ECU is not found (in micro seconds), it jumps into an open loop mode where it relies purely from the saved information provided by the crank sensor during the first few revolutions of the engine. Some how I can't see that being how it is. But i dont know, im no expert by any means. I would have to say that the edis module knows the location of #1 piston at all times because the crank sensor is placed at a predefined location in relation to TDC on the circumference of the trigger wheel. The timing has to change as the crank sensor is the only form of input into the EDIS module.

What im getting at is, if I moved the crank sensor after the vehicle is started in one direction or another the edis module doesn't know the difference and still thinks the sensor is at its predefined location, but in reality the piston is at a different location. The edis module will keep firing at what it thinks is 10 degrees btdc, but due to the new location of the sensor it will be ether advanced or retarded.

Yay? Nay? Please point out the holes in my logic, im not very familiar with this system and hopefully you, or someone else can shed some light on the subject for me.
 

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Discussion Starter · #5 ·
I am not concerned with the cam sensor as it is not needed for the EDIS to work. Also the fuel management will be taken care of by individual carburetors for each cylinder (motorcycle side drafts). For that reason, I will not need information from any sensor on the engine (aside from the crank positision sensor); they will all be removed in effort to clean up the engine bay. I will be installing electronic senders for oil pressure and coolant temp to feed info to a set of auto meter gauges. I agree with the Megasquirt, or for my application MegaJolt specifically. But, as with the carburetor setup, im looking do something a little different :lol:
 

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Discussion Starter · #7 ·
Assuming the timing is on a linear curve, your equation should work. MegaJolt is fully programmable, its basically only the Megasquirt ignition control sans the fueling. That would be the more sensible way to go with the project. It would be a lot less problem, and far more tunable. BUT im looking to try something a little different, just to see if it would work... not because its a better option.
 
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