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Cylinder identification 
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LQFP112 - Up with the play

Joined: Thu May 01, 2008 6:30 pm
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Location: Ann Arbor, MI
I am trying to come up with a way to identify the cylinder where the action is - i.e. which cylinder is ready for spark.
The sensors i have is a couple of hall effect sensors on the cam (disty) - one is the SGC/G signal and the other is the SGT/ne1 signal.
So for one camshaft turn (two crankshaft turns) the SGC pulses 4 times (for 4 cyl) and the SGT has one short pulse and one (relatively) long pulse.
The ECU sends a trigger pulse to trigger the spark at the right time - normally the distributor takes care of routing the HV pulse to the correct cylinder - i want to do it electronically using COP or coilpacks. So basically i want to identify which cylinder needs to be sparked next based on SGC and SGT signal - and i want to do it without any complicated uprocessor stuff - basically i want to build a simple EDIS module.
I am going to dive deep into the MS code to see how its done - but if anybody knows off the top of their head how its done or have any ideas how to do it - please jump in.....


Thu Jun 26, 2008 7:35 am
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That sounds like an early Miata signal, can you identify the car and give us accurate timing diagrams for it? Where are the leading edges of the two secondary slots? If they line up you can just call it wasted spark and use one edge. If not I can't think of a way to do it without "fancy micro stuff", but maybe someone else can? :-)

Fred.

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Thu Jun 26, 2008 7:45 am
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LQFP112 - Up with the play

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Location: Ann Arbor, MI
It is very similar to a miata - but miatas already have DIS - I am trying to do this for my mx-3 (which has cam sensors and no crank sensor - just like the early miatas...)

http://www.rivercityroad.com/garage/cas.htm

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Thu Jun 26, 2008 7:58 am
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LQFP112 - Up with the play

Joined: Thu May 01, 2008 6:30 pm
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Location: Ann Arbor, MI
Also i am not trying to calculate "when" to send the spark - the ECU already does that - i am just trying to route it to the correct cylinder - the "where" part of the question......


Thu Jun 26, 2008 8:03 am
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Which engine does your mx3 have? One of our members has a KL-DET mx3 up in the mountains in the states. It's fast with 400whp :-)

Some astinas came with the fwd BP and wasted spark with a CAS stock. Perhaps you could swap to one of those ecus in the mean time, or is it a "do it to prove i can" experiment?

I'm just thinking that it will be a lot of effort for little gain, that's all.

Fred.

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Thu Jun 26, 2008 8:23 am
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LQFP112 - Up with the play

Joined: Thu May 01, 2008 6:30 pm
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Location: Ann Arbor, MI
It came with a 1.6 DOHC - i swapped in a 1.8 BP from a protege - the protege is a 95 model - so with the engine/harness swap i am partially obd2 - i can use scantool and laptop to read most of what is going on. I am trying to talk to a mazda engineer to see if i can get the "special" software to "access" the core ECU functions.

Back to the point - My original idea was - if i could figure out #1 TDC then the next spark trigger sent by the ECU should go to #3 and the next one to #4 and then #2 (or whatever the firing order is). So if i could just start a counter and start counting after #1 TDC and use the last cylinder as reset then it should work as a simple routing device....
I want to keep this obd2 ecu and still have a EDIS system without going through the trouble of swapping ECU/Harness and doing all the splicing to get it to work.....

EDIT: adding this link - http://forums.probetalk.com/showthread. ... 333&page=2


Thu Jun 26, 2008 8:52 am
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LQFP112 - Up with the play

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Location: Ann Arbor, MI
Just had a vision - do most modern (1992+) ECMs use sequential fuel injection? If yes i can use the injector pulse as cylinder id method instead of mucking around with the cam sensor.....

Any thoughts?


Mon Jun 30, 2008 11:06 am
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The fe3 ecu from 88 - 98 has batch with two separate wires to power two injectors each. I'm unsure if it is timed in a staged/semi sequential way, but that would also do the trick for you anyway provided it was timed consistently with respect to ignition at all rpms. Some ecus switch strategies at different rpms.

Fred.

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Mon Jun 30, 2008 1:00 pm
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shameem wrote:
It is very similar to a miata - but miatas already have DIS - I am trying to do this for my mx-3 (which has cam sensors and no crank sensor - just like the early miatas...)

http://www.rivercityroad.com/garage/cas.htm

Image

Based on the signals above, it can be done with some 74HC logic if you want. I can list some parts, or make a drawing if I have time.

A necessary piece of information though. The rising and falling edge of the CAS signal, what are the relative cylinder positions for the SGT edges? I mean, 4 (of the for 8 repeating) edges of the SGT signal must precede TDC sufficient to use as a timing mark for ignition advance. Which edges, rising or falling?

Which points up a question. Say the SGT and SGC signals are converted to 4 discrete signals, one per cylinder, preceding each cylinder TDC by a sufficient amount. What device is controlling the spark advance?

- Jim


Mon Jun 30, 2008 10:15 pm
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LQFP112 - Up with the play

Joined: Thu May 01, 2008 6:30 pm
Posts: 135
Location: Ann Arbor, MI
Thanks for the help. I havent scoped the signals yet - i am planning to use my labjack u12 (http://www.labjack.com/labjack_u12.php) to acquire some of those timing diagrams - once i get some free time.

From the website - http://www.rivercityroad.com/garage/cas.htm
Quote:
You can see the two unequal pulses from the SGC. The engine computer uses the unequal length of SGC to tell when the cylinder #1 of the motor is at top dead center (TDC). The SGT pulses are all the same. The computer knows it is time to fire a spark plug when an SGT pulse occurs.


I cant find anymore info on the timing of these sensors......


Mon Jun 30, 2008 11:25 pm
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