uneffective "delay teeth"

[The Benz Master]

Hi, i've been using my MS2 v3 all summer on my mercedes 190e 2.3-16 1986. Everything went prety straight forward except that the "dellay teeth" in megatune has absolutely no effect on ignition timing !? I belive i have 2.86 or 2.88 code.. it was still the latest code last september.

So what i did is compensate with "trigger offset" so it runs prety fine and ignition advance is good too but i still get a hard time to start the motor. It kicks back a lot when i try to start it and i'm prety sure it could be related.

My missing tooth is 55* BTDC so i put 5 in the "delay teeth" box, which should give me arround 5* of base timing but when i check while cranking, it still sits arround 55*. So i then checked the effect of the "delay teeth" parameter while the engine was running (resetting and restarting the engine every time) and what ever i did, timing never moved, it's like if "delay teeth" was always at zero. With "trigger offset", it works, timing can be adjusted at will but i still cant start the engine easily.

any ideas what it could be or did anyone encounter this specific problem already??

thanks

[insanezane]

i think during cranking it uses whatever you have cranking trigger in ignition setup set too you may be set on trigger rise if so you could try trigger fall and maybe get a better responce and there is also calculated if the trigger fall doesn't help. Zane

[grippo]

Delay teeth only has an effect during synch at the very beginning. If you change it while the car is running, it will have no effect. As far as your starting problem, you should be able to get 5 deg advance using the delay teeth.
I would have to see your msq to go further as to why you aren't getting it. It could be your trigger offset isn't right.

[The Benz Master]

i restarted the car after the "dellay teeth" changes and it did nothing.

Trigger offset is spot on... i tuned it to give me TDC. I even checked my trigger wheel timing with the camshaft timing marks to be sure it was properly positioned.

just took a look to my msq and even with dellay teeth at 6, i needed to set trigger offset at 55 in order to get proper timing.

thanks guys

[grippo]

Delay teeth defines the start of the first tach pulse relative to the first tooth after the missing tooth. (If 0 the tach pulse starts at this first tooth after the missing one.) Trigger offset defines where this tach tooth is relative to compression TDC. So in your case, with a delay of 5 teeth (50 deg) your trigger offset should be 5 deg, since this tach tooth is 5 deg BTDC.

[The Benz Master]

that's exactly what i tought... but it does not work. i currently run "6" on dellay teeth and still need to put 55 in trigger offset to get ignition at tdc.

[grippo]

I am currently on travel and won't be back until the end of the month. I have your msq and will look at and test it when I get back.

[The Benz Master]

allright, no problem. Car is in storrage for winter anyway.

thanks

[grippo]

I looked at your msq without any changes on the scope with the toothed wheel on the bottom and the ignition on the top. If you label tooth 1 as the first one after missing and count to the right, that is what I call the first(leading) spark. If you take the missing tooth as -1 and count to the left, that is the second (trailing) spark. Here is what I saw:

-------Delay Teeth-----------TrigOffset-------------trailing spark-----------------leading spark
------------6----------------------55------------------------T-8------------------------------T+11
------------0----------------------55------------------------T-14-----------------------------T+5
------------0-----------------------5-------------------------T-19-----------------------------T-1

The advance for all was about 15 deg btdc. T-8 is the 8th tooth counting from T-1 = the missing tooth, T+11 is the eleventh tooth counting from T1 = the first tooth after the missing one.

There is definitely a change exactly as one would expect. I determined which edge was the spark by matching the section before the spark to the dwell shown in MT.

[The Benz Master]

that's strange... When i used Dellay teeth 6 or 0 with trigger offset 55, i always got the same T+5.

I ran all summer long with Delay = 6 and trigger offset 55 and it gives me T+5 spark timing. At T+6 it's 5* ATDC so it's totaly imposible that i ran at T+11.. Not with the performance and fuel economy i was getting from my engine and besides it was running quite smooth (a lot beter than with original injection system).

Do you have any hints on what i should test to figure out my problem since it does not seem to be software related? I will most likely buy a new scope shortly or i could do some testing with a timing light for now.

This is very confusing.

Here's a picture of my trigger wheel set-up... maybe something's wrong with it? It's laser cut so it's very precise... Tooths are 5* wide and i use a OHB900 hall sensor from digikey. One thing i know is that the sensor will detect the tooth a bit before it reaches the center and keep detecting it a little bit after the tooth has passed the center too so it could actualy detect tooths 6* wide instead of 5* but i tought i could just correct timing with trigger offset if it ever had any incidence. Could this be causing my problem?







thanks a lot for your help

P.S. I'm not sure i understand what you mean about the spark/dwell thing.... I use an MSD6 on ignition so dwell is not important for me.

[grippo]

The bottom picture shows a 36 tooth wheel with no missing teeth, but your msq is 36 - 1 ? I'm guessing you just show the original wheel in the bottom photo but have removed one tooth in the car.

All I meant about dwell/ spark is that spark will be on a rising or falling edge, depending on your setup. If you have this wrong then the spark can move when dwell changes and this can play tricks. If you change the spark polarity in MT, set delay T = 0 and TO = 5, do you get correct spark on the timing light ?

If that isn't the problem, a scope would be the best way to resolve it - we aren't talking about a few degrees here, but 50 deg. But you may also need a stim for 36-1 wheel output to run on the bench.

[The Benz Master]

A bit late.... i got to work on the car lately and got back on tuning this week-end.

I have a MSD6 so i runn a fixed dwell and it's set on the right polarity. Yes, the wheel in the car has a missing teeth.

i've done some changes this winter and put the 1st tooth at TDC cuz i also had some start-up problems... i still get excessive timing at start-up (35-45*) even f it's set for 12* in the map.... this caused some kickbacks and eventualy killed the bendix... that's why there is not always RPM in the datalog when the starter is actualy cranking.

still have weird correlation between the wheel /advance map and real timing. I have 36-1 set with 0 dellay teeth (tooth at tdc, tripple checked with cam timing, front damper tdc mark and screwdriver in the spark plug hole) and i need to put 35* in trigger offset in order to get the timing where it's supposed to be...

[The Benz Master]

Sorry, i was wrong, there is no such thing as fixed dwell but the polarity is def right.

I think i'll start to look at buying a scope.

[grippo]

If when you are at tdc, no. 1 cylinder, the edge of the tooth after the missing tooth is right under the crank pos sensor, then you shouldn't need a trigger offset of 35 deg. I would need to see the msq to go any further with this. Another factor is whether you are looking at cranking rpm or above it.

As far as the tracking of ignition advance and your spark table, the plots seem to correlate with the table. As you go up in rpm and load, the table shows the timing gets less advance and there is a dip in the spark advance curve as you go from roughly 30 deg to 17 deg and the advance at steady rpm, map also agrees with the table. (I am only going by a rough eyeball - I didn't measure the graphs with a ruler.)

[The Benz Master]

yes, the edge of the tooth after the missing one is right under the sensor when at tdc... that's what i dont understand. Once the 35* error corrected with trigger offset, ignition timing seems prety much spot-on.Thinking about it, my advance spike would correlate with the 35* trigger offset cuz cranking was set at trigger rise... but it still does'nt explain the 35* error.

if i set cranking rpm at 10, i should get the advance shown in my map as soon as i hit the starter button right? if so, it should start a lot better, i will try this when i get my new bendix.

thanks for your help

[grippo]

I would leave the cranking rpm where it si and change trigger rise to "calculated" - that will have the same effect, but let you use the wider pulse tolerance during cranking, plus there may be other things affected by cranking rpm. The calculated option just means it immediately calculates the spark advance from the table rather than sparking when the tach pulse comes in.

[The Benz Master]

ok, i'll test that tomorow. I finished rebuilding my starter and installed it in the car this afternoon. It starts well with cranking rpm set at 10.

thanks