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BMW S50 intake backfire when ignition turned on


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I have a 1995 M3 with an S50US (basically a bigger m50 vanos) with a G4x plug'n'play. Im having an issue where the engine is backfiring out the intake when I turn on the ignition and wait for the tachometer sweep. It also has a hard time starting if i attempt to start it while the tach sweep is in progress.  It doesnt happen every time. Does the G4x do a spark test when the ignition is turned on? Im not sure how else this backfire would be happening, but it keeps blowing up my idle control valve hose and its really annoying and im not sure what to look for. Thanks!


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Another couple notes on this topic:

1. The G4+ did not seem to do this

2. The base map has the start prime set to fire the injectors at Key-on -- this is obviously the source of fuel causing the backfire.  

Since there is no start signal to the ecu to provide an alternative prime signal source, on a couple of cars with the same no-start signal pinout I've done the following:   Set up a virtual aux output to engage when RPM > 0 AND RPM < 400 RPM AND Engine run time is < 5 sec.  I then use this output as the activation for the Start signal digital input.  The G4x has the ability to do this, but the G4+ does not it seems.


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A similar issue has popped up with other ecu's in the past. A sort of fix was to wire the supply for the ignition coils via the fuel pump relay or trigger.


The slight delay in coils turning on with key on, prevented the initial fire some hear/feel. I highly doubt changing anything relating to fuel injected will make any difference, although the user feeling anything probably does relate to some degree about residual fuel already left in any cylinder. Which can often be down to tuning too.

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