Motronic question

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handpaper
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Location: Newport, South Wales

Post Sun Oct 19, 2008 9:49 pm

OK, it's doesn't involve an engine swap, nor any FI (yet :twisted: ), but here be Those That Knows....
The prospective LPG track car has been attacked and is now missing a few bits. Some horrible little scrote tried to torch it by lighting the nearside tyres; the rear blew out and took the fire with it, but the front went up properly, burned through to the engine bay (via the ABS lead and brake line holes) and lit the PS fluid.
It was caught and extinguished shortly after, but the airbox and AFM, engine relays, fusebox and large parts of the engine and chassis wiring looms are gone.

The idea for this car was to remove the complete petrol fuel system and just leave Motronic to do the sparks; this is still the intention but I'm wondering if it's worth replacing the AFM.
It's a serious restriction and isn't needed for fuelling purposes, but what about sparks?
Does Motronic 1.3 have an ignition map based on air flow/engine load, and if so, what does it do when that info isn't there (i.e. broken/disconnected AFM)?
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Brianmoooore
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Post Mon Oct 20, 2008 12:45 am

I've heard, but not confirmed, that the AFM does have a small influence on timing, but since the ignition map isn't ideal for LPG (needs more initial advance and less total advance), it won't necessarily make things worse if it's not used.
When I first converted my 325 to LPG, I ran it for several months with the AFM wedged fully open, with no discernible ill effects.
handpaper
E30 Zone Regular
E30 Zone Regular
Posts: 883
Joined: Sun Apr 16, 2006 11:00 pm
Location: Newport, South Wales

Post Mon Oct 20, 2008 3:37 pm

Here's an ignition map from an M30 (Motronic 1.1, 059), click to show it on the original page.
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If the M20 is similar, simply leaving the WOT switch connected should give usable values?
StuBeeDoo
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Post Mon Oct 20, 2008 3:49 pm

Brianmoooore wrote: When I first converted my 325 to LPG, I ran it for several months with the AFM wedged fully open, with no discernible ill effects.
My LPG system has a vacuum operated device that holds the AFM flap fully open while running on gas.
HTH
Stuart.
This is why I no longer drive an E30......

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