Mikes3.0cabturbo

Car is a 90 model 944s2 cabrio, turbo conversion, with a EMS 4424 standalone engine mangement system. All installed and wired correctly but stumped by a simple offset value...

The 4424 needs to be told the 'index' tooth location in number of teeth after the missing 2 (60-2 wheel), its from this index tooth that the timing is set.

I cant find any reference to where this is, I have experimented with putting in values of 1 to 5 which I found in a BMW/motonic forum, but have horrible backfires and kickbacks when trying to get it started.

To test that I had everything else done right, I used the stock motronic to control ignition and the 4424 everthing else (like a piggy back mode) - it fires and runs, so it is a simple matter of getting this 'index' value right and entered into the 4424, then I'm onto the tuning.

Can anyone tell me what this offset to the 'index' tooth should be please?

thanks
mike

Zero10

Umm, I am no expert in this matter, but when I read the description, I think this would be the seperation (in teeth) between the missing teeth and TDC for #1?.... Am I completely out to lunch here?

If TDC is in time with themissing teeth, I'd try from -2 to 0?

gregeast

You might search under 'Megasquirt' as I think they've struggled with the same issues.

I found this on one of those threads:

"We have 132 teeth on the flywheel and no missing teeth. The reference sensor is how the DME knows the position of the engine. Essentialy it's a dual wheel setup and would need to be decoded appropriately with one wheel having 132 teeth and the other having 1. I think once the router board is built, plug and play will be much closer to reality. Another option is to use the the current software with stock wiring and build a circuit that would flatten a couple teeth every time the reference sensor came past. This would essentially create a 132-2 wheel."

Hopefully that will make more sense to you than it does to me.


Click Here for the whole thread.

Mikes3.0cabturbo

Umm, I am no expert in this matter, but when I read the description, I think this would be the seperation (in teeth) between the missing teeth and TDC for #1?.... Am I completely out to lunch here?

If TDC is in time with themissing teeth, I'd try from -2 to 0?
__________________



Hi Zero10, I think the TDC mark is the signal generated by the missing teeth, the index tooth is independant but critical to the 4424. This is one area of the EMS that I dont have much information or knowledge on, the manual is a little light on for information too. The company has never done a Porsche before, so this is all a bit new..
rgds
mike

Mikes3.0cabturbo

Hi Greg, thanks for your suggestion I will do some searching, what I have seen so far is mostly 951 guys with megasquirts, mine is a 3.0 16v turbo so quite different.

thanks
mike

Raceboy

On S2 60-2 trigger wheel the missing tooth is 58.5 degrees BTDC. And it's NEVER on TDC because TDC after the trigger degrees determines the maximum ignition advance.
You should paste here all the variables you can put on the fields of primary trigger and I can give you pretty accurate values. They're all calculable.

Trigger tooth
Tooth numbering begins at zero on the first tooth past the missing tooth, in the direction that the toothed wheel is rotating.

Next trigger tooth
Normally one event is required per cylinder on an engine. This value reflects that. It can be calculated using the following formula:

Next trigger tooth = imaginary teeth * 2 / number of cylinders
On 60-2 wheel, 4 cylinders
Next trigger tooth = 60 * 2 / 4 = 30

Crank min. period
In order to filter out noise from the trigger the 'Crank min. period' value must be determined. It is very important that the configured value is higher that what is expected during normal running conditions near the rev limiter.

Using the formula below it is possible calculate a reasonable 'crank min. period' value:
Crank min. period = 60 sec / max RPM / number of engine events * 2

VERY IMPORTANT:
Tooth width
Wheel type: 60-2, Ang. width of tooth: 2, Ang. width of missing tooth: 6, Engine phase: 240

All of this applies to 60-2 trigger wheel on the car that has 4 cylinders.

And if something is misunderstood, please post the value fields of your primary trigger settings.

Mikes3.0cabturbo

Raceboy, thanks for your reply, all I am asked for in the setup page for sensor/ignition is the following and my current settings;

trigger sensor = magnetic
trigger edge = positive
trigger pullup resistor = none
synch sensor = not used
ignition type = multi tooth
teeth per cam cycle = 120
teeth after missing = 1

from your comments on the location of the trigger tooth, it is set right at tooth after missing = 1, and yet the ignition is very wrong at this setting, unless I have missed interpreted something.

This is the page of EMS stinger http://www.enginemanagementsystem.com/downloads.htm

thanks
mike

Raceboy

First, determining ign. event from the cam teeth when cam sync is not used, is suspicious. But the setting is correct.
But, as I read from the manual, this ECU will not work on multitooth trigger arrangements without cam sync.
So, you have to install this since S2 don't have it.

Mikes3.0cabturbo

Racerboy, I just re-read the manual for the 4424 with what you shared on the 60-2 information, the 'index' tooth is actually = to the static timing tooth, so I believe that the static timing of the S2 3.0 is 12.5 BTDC, so then number of teeth after missing would it be 58.5-12.5 = 46, tooth per degree = 2, so index/static tooth is 46/2 = 23 teeth after missing.

I am out of my depth on this so please correct my assumptions if I have this wrong.

rgds
mike

Raceboy

Actually, it's a bit the other way.
Assuming the ECU works without cam sync (which the manual says it does not), and the setting you defined as index tooth, should be 10 teeth. Because 60-2 wheels every tooth is 6 degrees wide (these are absolute degrees) and 58,5 degrees BTDC means 9,75 teeth BTDC. You have to make it 10.

Mikes3.0cabturbo

I am getting the picture now thanks, what about the 60-2 being crank degrees so that it takes two complete crank turns for an engine cycle - would this then make each of the teeth 3 degrees, then it would be 20?

I was told I only needed cam synch if I wanted multi igniters, anyway I do have a cam synch hall sensor on the car as standard so could add it to the 4424 if needed.

jbrill

This is a bit off topic, but i would love to see pictures of the car and the engine setup

Mikes3.0cabturbo

Hi jbrill, certainly will post some when finished, expect to do that in the next couple of weeks, I have been taking pics through the process, so hopefully it may help others who may wish to take the 'turbo' route, this has been 18 months of researching and collecting & fabricating parts.

jbrill

i am very, very interested! please keep me informed! if u want you can email me pics of where u r at now! jordb@dccnet.com i cannot wait to see this!

Raceboy

No, the ECU needs to know only crank degrees when in wasted spark mode. On sequential, it needs to know the exact engine phase when to reset the sequence. But the TDC-after-trigger point is strictly by crank.
But, since I'm not too familiar with that specific ECU, I can be wrong. You should try them both.