Question about shifting ignition order VEMS

by **nmerrill** » Sat Feb 23, 2019 9:24 pm

Well, now I'm stumped.

5 cylinder, VAG Hall 60-2 trigger, and distributor secondary- all set to factory alignment.
TDC after trigger set to 78, corresponding with Hall at tooth 14 (13 after FTT).

Triggerlog looks clean without errors.

Timing light on #1 plug wire flashes at #4 TDC (with ignition lock on 1Deg)

I shifted the reference tooth table three different times, maintaining the order, but shifting the locations
0, 24, 48, 72, 96
24, 48, 72, 96, 0
96, 0, 24, 48, 72 etc.

The timing light still flashes at #4 TDC - no change. I don't understand this!

Rotating in the ignition visual makes no change either, as it shouldn't, according to the help files.

Shifting FTT moves timing of light flash as expected. This isn't an option for this problem though.

I can't shift the ignition outputs because they are all the same pin = one coil on pin 35.

So, how do I get it to fire on #1 instead of 4?

by **varia** » Sat Feb 23, 2019 10:48 pm

here is mine

: 1vems.jpg (313.59 KiB) Viewed 32330 times

: 2vems.jpg (201.62 KiB) Viewed 32330 times

tomorrow i will have time to explain it.
htwh

by **nmerrill** » Sun Feb 24, 2019 10:07 am

OK! please do! trying to wrap my brain around what you've done...

by **nmerrill** » Sun Feb 24, 2019 11:10 am

Well, experiments this morning had good results...
Shifting FTT is an option for this problem! I was thinking I needed to shift it 24 teeth to get far enough, but that was incorrect.

I shifted FTT to 12 (from 0) and timing light now fires correctly at #1 TDC, and all cylinders.

I think what this does is;
moving FTT to 12 adds 72 deg. of crank rotation, which is the distance beetween #4 TDC, and #1, so the ecu waits 72 degrees (12 teeth) before starting its count, which delays the Ignition trigger to the proper timing.
TDC after the TT still stays at 78 deg.

I don't understand why shifting the reference tooth table does not affect the ignition timing in this case. I clearly don't actually understand the reference tooth table!

by **nmerrill** » Sat Apr 13, 2019 6:59 pm

I'm still puzzling over this, and wonder if anyone can enlighten me. The VEMs forum seems pretty quiet, so I'm posting here too.

To recap - the issue is that the VAG 60-2 wheel set up as per factory settings (trigger at 14th tooth after missing) results in A timing light firing at marks on my crank pulley basically at #4, or almost 72 Deg early.

I can't shift ignition outputs, because I'm running a distributor off 1 output, thus, nothing to shift, I think.

I moved FTT to 12, from 0, and left TDC after trigger at 78 deg.
Now it flashes #1 TDC correctly.

So, Id like to understand this! Just reading the help pages about TDC after trigger setting, and FTT, would lead me to conclude that moving FTT to 12 would reduce the TDC after Trigger degrees to just 2 teeth, since TDC after 0 tooth was 78 deg (13 teeth)- mechanically fixed.

As a test, I was able to use the ignition lock to set the ignition to advance all the way to 63 (it's maximum), it fired #1 almost all the way back to #4.

So, the ECU still is able to advance timing, meaning that the TDC after trigger is still large, presumably still 78 deg.

My *guess* is that moving FTT actually just shifts when the ECU begins its count, but it still counts based on the trigger reference table- that is tooth 0, 24, 48, it just starts someplace other than 0...?

Any thoughts appreciated!

by **audifreakjim** » Sat Apr 13, 2019 11:18 pm

I honestly still don’t understand how it works. I added stickers to my crank damper at each cyl tdc so I could see which cyl was actually firing where with atiming lightThen I shuffled them around till the coils were firing in the correct cylinders. Do this with the fuel disconnected so you don’t wash down the walls while fucking with it.

by **nmerrill** » Sun Apr 14, 2019 1:18 pm

yea, I've got all the TDCs marked on the crank pulley too.
I could swap distributor wires, but not really interested in a mechanical botch to help out my fancy EFI!

changing FTT tooth gets the results, but I just don't understand why...

by **audifreakjim** » Sun Apr 14, 2019 6:23 pm

This was the best thing about 034 EFI. The phases and angles were super easy and intuitive to setup.

by **Lucky** » Fri Apr 19, 2019 11:48 am

nmerrill wrote: My *guess* is that moving FTT actually just shifts when the ECU begins its count, but it still counts based on the trigger reference table- that is tooth 0, 24, 48, it just starts someplace other than 0...?

Any thoughts appreciated!

*edit * some information changed to prevent misinformation.

From my experience you pretty much have it. Since your using a 60-2 everything starts from the two missing teeth regardless if the 60-2 was installed with the engine at tdc1 or tdc 5. (If its a crank pulley 60-2 it can almost be in any position and a flywheel 60-2 is pretty much guaranteed to be in a set position.)

The reference chart is just that, a reference for where the other cylinders are located on the 60 tooth wheel. But remember 2 rotations for each firing event of cyl 1, so 120 teeth between each event.
Tdc 1 at tooth 8 as an example

Cyl 1 @ 8,
Cyl 2 @ 32
Cyl 4 @ 56
Cyl 5 @ 80
Cyl 3 @ 104 then back to 8 again

Each tooth is 6 degrees on the 360 degree rotation. So the 24 teeth between each cylinder is 144 degrees of crank rotation. Once you have tdc set anything else can be programmed in the ignition table for ign advance etc.

You want a tdc after trigger (ftt) to be between 60-80degrees
Example:
12 teeth and 78 degrees is the same as 11 teeth and 84 degrees however the 12 teeth setting is more favourable because it is in the 60-80 range.

Just my thoughts, and I've probably just repeated what you've already mentioned. If anyone sees anything I've mentioned is wrong please correct me.

Cheers

by **nmerrill** » Wed Apr 24, 2019 1:26 pm

"If you set 8 teeth then it will think tdc is at 8 teeth etc"

Hmm, in all my reading, I never got the impression that this was the case.
It's was my understanding that the combination of "TDC after trigger" and FTT told the ecu where TDC for cyl 1 is.
But, then, that's why I'm confused about my config producing the correct result (timing light flashing on #1 correctly) with FTT = 12 and TDC after trigger = 78 degress, when the rear main seal trigger is set to "factory" specs - tooth 14 after missing teeth...

by **Lucky** » Fri Apr 26, 2019 3:45 pm

You were correct, I made a mistake. It's been a while since I messed with vems lol. I was looking at my vems program today. the ftt is where the count starts from. Your tdc from the ftt should be roughly between 60 and 80 degrees and you are at 78 so all should be good.

It would seem that a setting of 14 ftt and 66 tdc would have the same results.
I will edit the above so future searchers dont follow bad info.