Ditching the AFM

Check it out! wrote: TPS on the motronic system is just a W.O.T. for those who havnt looked into engine management. This is basically a throttle on/off switch, it doesnt tell the ecu where the throttle is merly if it is on or off of idle.

Nonsense! It also has a full load switch!

Drew540i wrote: Check it out! wrote: TPS on the motronic system is just a W.O.T. for those who havnt looked into engine management. This is basically a throttle on/off switch, it doesnt tell the ecu where the throttle is merly if it is on or off of idle.   Nonsense! It also has a full load switch!

I would suggest taking the tps (w.o.t) apart and looking.

Check it out! wrote: I would suggest taking the tps (w.o.t) apart and looking.

What's all these TLA's?

Thought you said you didn't know much about Sixes?

Drew540i wrote: It also drops straight into where an M30 came from because the blocks are similar. I'm sure even Andy 335 (thanks for the quality info mate!) would have condidered this if he knew how far he'd be going!

I know what you mean mate, the M5 lump would make an excellent swap, though it's a more involved and expensive one to start off with.

The extra things over and above the M30 swap is the height of the M5 engine can cause problems so i've read,(custom ?)exhaust manifolds and swapping over to an old brake booster set up to allow enough room for the plenum or smaller servo and chop a small lump out of the plenum. Nothing to difficult though.

Check it out! wrote: I would suggest taking the tps (w.o.t) apart and looking.

And I would suggest you actually know what it is
you're talking about. It's amazing how much of a fool
you look when you make a glib comment which is
oblivious to the facts!

A throttle position switch does three things:

1.) At rest, the tiny microswitch (often referred to as a
Burgess microswitch after the company that makes
it for Bosch) is depressed. This tells the ECU that
the engine is at idle.

2.) Just off idle, the microswitch is released which
then switches the ECU into part throttle mode,
accessing the part throttle maps.

3.) When the throttle switch is fully wound around,
two contacts are closed together which sends a
signal to the ECU to access the full throttle maps.


Maybe you'd care to argue with BMW and Robert
Bosch about this? If you like, I can photocopy and
send you the relevant pages from the BMW Motronic
service information manual?

Just to expand a little and see if my understanding is correct or not ?

1.) At rest, the tiny microswitch (often referred to as a
Burgess microswitch after the company that makes
it for Bosch) is depressed. This tells the ECU that
the engine is at idle.

At tick over the AFM flap is closed(?), the air by-passes the flap, the by-pass area is adjusted by the tick over mixture adjustment screw ?

2.) Just off idle, the microswitch is released which
then switches the ECU into part throttle mode,
accessing the part throttle maps.

Part throttle, the ECU referances the AFM(air flow),CPS(rpm), IAT and coolant temp sensor and works out the timing and the fueling from the part throttle maps, further adjustments are added on for IAT and coolant temp. Coolant temp needs a bigger adjustment than IAT ?

3.) When the throttle switch is fully wound around,
two contacts are closed together which sends a
signal to the ECU to access the full throttle maps.

WOT, the AFM flap is pinned open by he force of the air(depending on RPM ?), ECU ignores the AFM and reverts to an RPM based WOT map but will still be affected by IAT and coolant temp corrections ?

Of the E30 generation Motronic only the M3 had a baromic sensor which is located inside the ECU casing ???

As i said i'm just kind of testing out my understanding of Motronic management from the E30 era, have i got it right ?

Drew540i wrote: Check it out! wrote: Its the same part as on the e30. a car i know a fair bit about. Actually it's not the same. M20 and M30 throttle position switches work the other way round from each other and do not interchange....

Another area of the AFM which is a bit u/s is the routing of the "cold" air feed right above the exhaust manifold! Not only that, but it changes diameter a couple of times too.

James Sohl engineered a better system which proved it's worth on the TBMW rolling road day.

Why didn't the air feed come from the n/s of the engine bay? Surely it would have only entailed turning the AFM around 180 degrees.