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Clarification of sync tooth and general trigger setup

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Hi all, 

I have a BMW M50B25TU engine, with a VR crank sensor and a hall cam sensor. ECU is a G4x Storm. 

I'm hoping you guys can give me some tips on configuring my triggers. 

While I'm aware there is a base map for my engine for the G4x, I need to be absolutely certain my understanding of the trigger setup is correct due to a suspected misaligned crank trigger wheel.

While making a mark with white paint where the TDC mark is on the crank trigger wheel (to use with a timing light), I noticed cylinder 1 was a long way off actual TDC (maybe 30 degrees or something).  I've since made my own mark to use at real TDC.  With this new TDC mark - I managed to establish a timing offset value of -261 degrees (not what's stated in the base map for my engine).

I've included a screen grab of my crank and cam sensor outputs on the Trigger Scope.  From other scope traces I've seen, mine is indeed offset (trigger wheel misaligned).   I assume this isn't a problem - it just needs setting up!

When it comes to setting up the cam sync, from what I've read in the help file I should be using Sync Mode = Cam Level.  I think this is because I have a hall cam sensor (steady state voltage on a square wave).

The question I have at the moment is what is the purpose of the Sync Tooth in the Trigger 1 setup?   I thought this was where the ECU looks for a cam pulse (e.g. if you have a VR cam sensor generating a single short pulse).  

For Sync Mode = Cam Level, the help file indicates that only the 1st tooth on the crank after the missing tooth is used to sample the cam sensor state. So setting the Sync Tooth does nothing in this case??

I've no doubt missed the point here. 

Just to throw in additional complication, to ensure the Vanos cam angle shift won't affect things surely I want the ECU to sample the cam level pretty much bang in the middle of the square wave? (give maximum movement each direction)  That would be roughly on the 20th tooth after the gap on the crank trigger. BUT - apparently only the 1st tooth is used?

The map currently uses a Sync Tooth value of 49 which is where the cam level goes high, low.  This was a stab in the dark and probably wrong. Clearly sampling here will be on the cam sensor transition, and not on a steady state value. 

Map, Trigger Scope log and screenshots attached. 

Thanks guys!

(p.s. I am aware about the need for igniters with this ECU. Audi R8 coils standing by. I'll measure base timing again once fitted)









map_3.pclx trigger_scope_2.llgx

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Here's the section of the help file that states only the 1st tooth after the gap is used to check the cam sensor state:


The level of the sync signal is sampled only on the tooth after the gap on the crank signal. This means that the level of the sync signal at other crank positions is irrelevant. For this reason a signal with more than one tooth can be used on the cam as long as the signal level is high at the tooth after the gap on the crank signal on one crank revolution and low on the next crank revolution.


·When the tooth after the gap occurs on the crank signal, if the sync signal is low, engine position is set to 0 degrees plus the trigger offset. If the sync level is sampled high on the tooth after the gap then engine position is set to 360 degrees plus the trigger offset."

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So this is a new thing on the G4X you can tell it where to check the cam level / crank reference point.

With the sync tooth set to 49 it will look at the level at the 49th tooth after the gap. 

We need to correct the help file for this 

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I would suggest setting the sync tooth to "1" in this case.  The ecu will then look at the exhaust cam level just after the missing teeth go past the sensor on the crank.  This is a nice place to do the sync test as it is well away from any edge on the cam even when the cam is fully advanced (cam scope trace will move towards the left as the cam advances).  Im pretty sure it will also sync the fastest with this set to 1 as it will have all the info it needs to sync sooner.

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  • 2 weeks later...

Hi all.  I really need some more help to get this engine to fire up.  (thanks in advance!)

It's a M50B25TU single Vanos (if that changes anything about base timing).  See trigger scope above, trigger sensors look 'ok'. 

Following review of my trigger scope, @Adamw recommended Sync Tooth = 1.  Both triggers show active during cranking, no errors (or only when I stop cranking).

I just fitted some VW ignition coils (built in igniters) that deliver a strong spark and these haven't altered the base timing at all.  I just checked this with a timing light.

Each coil pack fires a decent spark when tested (so wiring numbering correct, and they appear to be powered correctly).  Injectors fire too when tested individually. 

I have tried to start with a trigger offset of -261 (the value I determined using the timing light, while locking timing to 0 degrees) and also 99 degrees (-261+360).

With 99 it seems to do very little, but at -261 it spits and bangs a bit. 

The Master Fuel for the base map for the plug in 'BMWLink' ECU, is 20ms.  My injectors are around double the flow rate (ish) of standard ones,  so I have set Master Fuel =10ms as a first guess.

I suspect a massive mistake made on my part with the timing, but I have no idea what that could be.  I found TDC using a rod into cylinder 1, made a mark, used a light and adjusted the offest until I hit that mark while at  0 degrees fixed timing. Timing light sensor is clamped around a short HT lead with a small spark chamber (so you can see the spark) in it.  So it's coil pack -> HT lead with spark chamber (+ clamp for timing light after spark chamber) -> spark plug.  I assume clamping the timing light sensor after the spark chamber would not add any delay / error? See picture of the HT lead / spark chamber tester. 

I have attached logs for trying to start the engine with -261 degrees timing offset, and for +99 degrees.

Also attached is the map file. 

Also I consistently get a Fault Code 8 -  settings overflow. That sounds really bad - like the config isn't loaded properly. I'm using a fresh install of Windows 10, and the latest PCLink and ECU firmware (G4x Storm).

Pleas also note I have a problem with my ICV at the moment, so those lines are cut and the system is inactive. I have cracked the throttle open to around 10% for both starting attempts (log files).

Please take a good look at my maps and log files. There's something fundamental that's wrong here, I just can't figure it out. 

Thanks in advance!!!







ecu firmware version.PNG

pclink version.PNG

spark tester.PNG

trigger settings.PNG

map_4.pclx start_attempt +99 timing.llgx start_attempt -261 timing.llgx

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9 hours ago, RobinHodges said:

Also I consistently get a Fault Code 8 -  settings overflow.

Im pretty sure there is a bug in the latest firmware causing this, I see it on mine as well but it doesnt seem to effect anything.


9 hours ago, RobinHodges said:

I assume clamping the timing light sensor after the spark chamber would not add any delay / error? See picture of the HT lead / spark chamber tester. 

Yeah that will be fine provided the timing light still picks up the spark ok which it sounds like it has.  You are correct in that if the timing mark aligns with an offset of -261 then 99 is the other possible correct offset.


I dont see anything obviously wrong in your setup.  Although your inj PW looks about right at cranking, just as a reality check I would give it a try with the master fuel value doubled and if no different then try it halved - this just covers bases such as injector size being completely different to what you believe or low fuel press etc.  Have you confirmed there is fuel pressure?  You can also try spraying some WD40 or brakleen or similar into the intake to see if that gives any signs of life.

I tried your tune loaded in an ecu on a simulator and all injectors/ign etc is working.

Your coils are wired ign1 = cyl 1, ign2 =cyl 2 etc right?

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Thanks Adam.  Good to know the overflow error isn't an issue. 

I have tried different master fuels a few times (from 2ms to a 20ms).  

Ignition coils are wired into the correct outputs. The first test last night was coil testing one by one, then the injectors (but without observing the flow  - only tested by feel).

One observation that I forgot to mention that could be really important is that sometimes on cranking it sounds like the engine jams (accompanied with a large voltage drop).  Could this be attempting to fire at completely the wrong moment forcing the engine back?  Could it be WAY too much fuel entering the cylinders causing some kind of hydro-lock (I hope not!).

Sorry if this is pretty basic stuff. It's just so frustrating that I know what I should be doing with all the control tuning once the engine fires up - its just getting to that point!





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Yeah I noticed in the -261 log there are a couple of drops to zero RPM.  That is a kick back by the sounds of it - that usually means the timing is way too advanced. It might pay to check that ign timing again.  Looking at some other info I have around, the E36 plug-in base map has its offset at -328 and info from a s54 and S52 has their offset is around 276, so that -261 just seems a bit weird.  

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  • 2 weeks later...

Hi guys.  Just reporting back on this topic. 

So it turns out the trigger wheel had come loose.  Don't ask! It's a sore topic in our house at the moment.  After tightening it up, setting base timing and guessing some numbers for master fuel, it started up first time!! Woohoo!

Thanks again for the advice so far. Now on with the fun part!




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