My Coil Packs Keep Melting! Audi ABZ V8 Running VEMS Ver 3.3.

[Siena]

Hi guys, not sure if this is in the right place, so please bear with me.

I am running an Audi S8 4,2L V8 32V, in my '96 A4 quattro.

The problem I have right now is, if the ignition is left on for any length of time, (from 2 minutes onwards) the coilpacks start to melt. It doesn't seem to be an issue when the engine is running. Right now, only one cylinder bank is running, the right-hand bank, as viewed from the driving seat.

I have changed the coilpacks over from the running bank, to the non-running bank, but the problem remains - no spark on the left-hand bank. I believe the EMS may have a blown driver for the left-hand bank. I have spoken to someone else, who's having the same issues, it's a bit of a puzzle.

Does anyone have any ideas? I spent yesterday scratching my head, and getting nowhere. I've ordered a new set of coilpacks, but will of course still have the issue with melting, if ignition is on without engine running. Thanks in advance.

[Siena]

Sorry guys - I forgot to add.

My firmware version is 1.0.78.

Thanks.

[PeepPaadam]

How much is the dwell time?

[Siena]

Coil chargetime @ 14V [ms] 2.3
Coil chargetime added @ 6V [ms] 1.2

I've even dropped lower, and the problem still persists. It only melts the coils if ignition is left on, and engine's not running. If the engin'e running, or ignition's turned off, it's not an issue.

I thought the dwell time would be more of an issue on a running engine, but clearly, it's not the case here.

[rob@vems.co.uk]

We're looking at the various possabilities, and will let you know what we find.

Rob

[Siena]

Thanks a million, Rob!

[dundersmurfen]

as a safety wire your relay supplying coilpacks with 12v+ via fuelpump.

[Siena]

^^^ That's a good idea, thanks. 

[hilly]

Been looking into this tonight and the ignition outputs are all cleared at the same time as the fuel pump inactivity timeout (eg if locked on after a stall) so hooking up a relay to the fuel line won't help.
If it is set to something sensible (such as 1 second) it will still fry a low impedance coil pack in pretty short order, as Siena has discovered

Rob has come up with a solution using an extra relay and output, but it requires mods to the loom, I am hoping to find a more elegant solution.
Still investigating the best way around this at the moment while replacement parts come in ...

Hilly

[Siena]

I've ordered the later coils, same as on the Lotus Esprit ABZ, which is currently running fine.

Hopefully, this may cure the problem.

[Siena]

Any thoughts on running the coilpacks ground via a seperate oil pressure switch? At least if the engine stalls, the earth would be cut off as pressure drops.

[Sprocket]

I carried over the wiring logic that Rover used on their original loom. The mian power feeding both the coils and the injectors comes from the main relay which is energised via VEMS on RPM >100. This drops the power to the coils and injectors on stall almost instantly and remains off untill the the engine is turned over. Seems to work a treat.

I was under the impression that the FETs and IGTBs fail closed, so if there is 12v on the coils and the IGTB has failed the coils will fry. The question would be why the IGTB failed if this is the case. I use IGTBs for the injectors as the FETS kept dieing, where the IGTBs are quite happy so they are a tough bit of electrickery. Mind you when i first started with the VEMS, I tried the 'inverted output' setting in ignition settings, STUPIDLY and it very audiably popped the fuse. what sort of fuse rating are you using for the coil feed?

[Siena]

^^^ I believe the fuse is a 15amp, but I'll check to make sure.