missfire at higher RPM (4800+) and no trigger errors

[Daniel2345]

Hi,

i have a problem with the VEMS in an Volvo 850 Turbo. Sparking is fine until 4800..5000 rpm. At this point, there are missfires and exhaust temp rises up to 950°C.

I tryed nearly everything which can be configured in software. Different Trigger points, ignition values from 0 to 25 degrees at this point. lambda values 0.85, 0.80, 0.75 and 0.70 were tryed before missfire occoures.

Im running distributer irgnition with original ignition coil or MSD Blaster, both with original power stage attatched to the coil.

Can be seen here:

http://www.daytonagblimited.co.uk/ignition-coils/314-volvo-ignition-coil-850-c70-s70-v70-0221601012.html


i use standard IGBT from the shop on the vems board to drive the final power stage from the coil.


it seems, that this does not occur under very low boost like 150kPa. engine can do more, tested with original ecu (motronic).


coil charge time was tested between 1.0ms and 10ms.


is there anything which can limit the ignition coil current on the vems board?





logs and monitoring shows that injection, ignition, triggers, dwell - everything stable...


i use 1.1.98 firmware and latest vemstune.




i think, there must be something on the board. too large Resistor or something like that?



Any help or ideas? Thanks.

[GintsK]

What exactly connection you use for driving original power stage? It is not doable from IGBT transistor. Because OEM output stage is triggered from positive impulse. But from IGBT you can get just negative impulse or floating.

Does your unit has free stepper chip outputs? You can try drive output stage from there.

Gints

[fphil]

Good enough Vems grounds? Lot of current there at high rpm should flow.