Trigger System problem Link G4 Atom BMW S38 B36 engine

Hello,

i have a BMW from a customer in our workshop for ecu mapping.

Specs: BMW S38 B36 engine

6 cylinder inline 3.5L

Ecu: Link G4 Atom OEM Engine Harness

Trigger System: Multi Tooth 60 -2 reluctor OEM mounted on crankshaft pulley

No Sync Sensor

Distributor Ignition and Multi Point Group Injection

While i have done the setup of the TDC offset Angle (Ignition locked @10BTDC) i have recognized that the Ignition Angle advances 6°-7°(to 16-17° reading with the timing light) @ 4700 rpm and above, and when the rpm is slowed down below these point the ignition retarded back to 10°BTDC as previously.

When the ignition visible advances the sound of a retarded ignition (TDC or ATDC) is hearable from the exhaust.

I have tryed all the filter stages (RPM and Trigger) and raiseing the Trigger Arming voltage but the issue is allways present and no Trigger Error counted.

I also have checked the signal with an ossiloscope but nothing strange is visible.

When i do not use the trigger calibration Function and fix the timing with the values in the Ignition Map and reduce the timing 6° @ 5000rpm and above the timing readed with the timing light stays constant.

The Angle between two trigger tooth on that Trigger type is 6°.

Is it possible that the ECU looses the trigger tooth @ this rpm point and uses the next earlier tooth?

Or could a worn damper on the crank pulley causing that kind of problem?

Had anyone had this kind issue and can help me?

Thank´s and greetings from Austria

Can you attach a picture of the oscilloscope capture.

Hello Adam

i have attached 2 pictures from the signal measured on the sensor connector.

I also have a video but it is too large data for Upload.

I could send you via We transfer if you wish.

Crank sensor is wired with incorrect polarity. Swap the sensor +/- pins and re-check offset.

Hello Adam

i have already done that the result was exactly the same

Please attach a scope capture with the wires swapped. Preferably a close up of the missing tooth area and another zoomed out so we can see all 60 teeth

Hello Adam

i have attached the pictures with the wires swapped as you would like too see

Ok, the trigger waveform looks good and is correct polarity now. What do you have for an ignitor? Is the spark edge set to falling? Can you attach a copy of your tune.

Hello Adam

the customer has installed the Link ECU in the OEM BMW ECU Case and has used the OEM BMW Igniter. I have opend the ECU and attached a picture about it.

Spark edge is set to falling edge. I have also attached a map of the actual ecu configuration

Your settings in the tune and the scope capture of the trigger waveform look good, so I would expect rock-solid ignition timing when checking with it locked.

I guess the biggest unknown at this point is the ignitor. Who knows how that was originally driven and what type of signal it was designed for. I guess you could confirm it is driving the coil correctly by scoping the primary on the coil. You should see the primary sitting at 12V most of the time, then a short drop to 0V for the dwell period just before the large ~400V spike. Typical primary waveform below as an example. Otherwise you could just try swapping the spark edge to rising to see if the drift improves (watch coil doesn't get hot).

Hello Adam,

yes the coil is correctly driven like the example picture you have attached.

I had a new aftermarket ignitor in stock were the characteristics are known. I have installed it and checked again but the issue was still the same.

I have made some tests and i have recognized that when i lock the Ignition timing @ 25 degrees BTDC (and retard it at the timing light by the same amount to match the TDC mark) the ignition stays constant across the rpm range like it should be.

When i retard the lock timing back to 10 degrees BTDC the problem occurs again.

Is it possible that @ 10 degrees there is a interference on higher rpm (from the distributor or so) which is displayed throw the timing light?

Im not sure Im fully understanding your statement, but sounds like possibly a rotor phasing issue and the spark is jumping to the wrong post inside the distributor cap?

Turn the engine to 10BTDC by hand and remove distributor cap, the rotor should just be leaving the post.

Hello Adam

yes you have understood that right.

I have turned the engine to 10 degrees BTDC removed the distributor cap and the rotor is leaving the post @ this point.

When i lock the Ignition timing to 15 degrees BTDC the issue is gone and everything works fine.

I think that Valvetrain harmonics and timing chain deflection causes that issue with 10° BTDC Timing (edge of the rotor) and higher rpm.

The distributor is driven by the exhaust cam which is on the tensioner side of the timing chain.

Now everything work as expected thank you for your great support and help.