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The best position for trigger wheel gap. 
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LQFP112 - Up with the play
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Joined: Thu Feb 10, 2011 12:27 am
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Location: Auckland, NZ
I am about to mount my trigger pick-up and I need to know the best position to put it in.

I only have an 8-1 trigger wheel.

Image

When I built my own wasted spark system I had it set up so that I had one trigger just before TDC. That way the software would start the timer on that pulse and the spark would fire some time before TDC.

With FreeEMS will the same apply?

It is going to be easier for my to mount the trigger pick-up so that the gap is just before TDC but that might not be any good for the software.


Sat Jul 09, 2011 6:20 am
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Spudmn, although there probably is an optimal position, it only becomes important with ultra low res inputs such as single and double edge distributors. With 14 events per engine cycle and only 4 cylinders, you'll be well covered. If you imagine that instead of one missing tooth, you have 4 missing, ie, just 4, on the crank, that's equivalent to 8 on the cam, which is effectively what my truck ran on with its CAS unit. (it actually had 10, but that doesn't matter much)

With the current software the optimal position is the one where the beginning of desired dwell (during cranking) occurs as close to an event as possible. Later when I improve it, the optimal position will be when the spark event itself (during cranking) occurs as close to an event as possible. The latter is easier to calculate, but the former is what is currently done.

For the record, with the old dwell stretch code, and improper starting etiquette, my hyundai started pretty smoothly on just 8 cam events per cycle, or 4 per crank revolution. Your worst case situation is that one of the channels, for one of its cycles, for one or two cycles worst case, while cranking only, will be a little inaccurate. At all other RPMs it doesn't matter at all :-)

In other words, don't worry about it. Reality is that the software has to handle this properly, and thus having it positioned badly is better for testing. As such positioning it randomly is optimal :-) Make sense?

Fred.

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Sat Jul 09, 2011 9:04 am
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Spudmn, and others, there are notes in this file about wheel selection and mounting:

https://github.com/fredcooke/freeems-va ... s?raw=true

Fred.

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n00bs, do NOT PM or email tech questions! Use the forum!
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Sat Oct 01, 2011 3:26 pm
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Joined: Thu Nov 10, 2011 8:01 am
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I have a strange request for information. I need the dimensions of the reluctor for the crankshaft speed sensor.

I'm working on a '00 Jetta with the ALH engine. The customer had run a lot of Biodiesel and it had plugged up the intake manifold with carbon. Another mechanic tried to clean it out on the motor and got carbon into the cylinders. The rods bent so severely that the crankshaft counterweights took the bottoms off the pistons. It also mashed the pickup wheel for the crank sensor. I'm trying to repair it rather than pull the block out of the car.

I have got the wheel back to round using a lot of patience, but one of the cutouts that the sensor looks for is messed up. I think I can measure the distance from the other slots and use some feeler gauges to set the gap, but I don't know if all four gaps are uniform or if one is supposed to be a different size. I have three slots the same and then the buggered one.

Are all four slots the same size? Does the ECU just look at that sensor for engine speed or is it using it for crank angle too?

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Fri Nov 11, 2011 7:25 am
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If you're talking about a Jetta part, you need a thread of your own. Let me know and I'll split it.

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DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!


Fri Nov 11, 2011 1:05 pm
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