Can you talk to your ECU?

[TobyB]

So it has TXD and RXD pins...

but what does it say?

What does it want to hear?

I have this little hope that it says 'Hey, dummy, your AFM is out of spec'
but there's this great big suspicion that all it says is ACK ACK NACK.

t

[Hooffenstein HD]

1010011010

[agent]

1010011010

01010100011010000110000101110100001001110111001100 10000001101110011011110111010000100000011001010111 01100110010101101110001000000110001001101001011011 10011000010111001001111001

[nando]

if you're talking motronic, you're not going to get more out of it than you would by doing the stomp test. These things are so old I don't think any of the BMW software tools or cables even work on them anymore.

[TobyB]

Yeah, I know- and the old tools don't do much, either...

...it was like you had to actually WORK on the car to fix it back then!

t

[nando]

I'll take modern computers and diagnostic tools over "guess and replace" any day. :p

[jalopi]

yes, but it rarely replies

[ForcedFirebird]

I can see all the sensor values ;)

I'll take modern computers and diagnostic tools over "guess and replace" any day. :p

"Guess and replace" still isn't the answer. e30's can be diagnosed with a lot less than a scanner.

Even modern cars are subject to "guess and replace", specially when they have them scanned and think "oh, o2 out of range, must need to buy o2's" when they most likely have a vacuum leak.

[ST1G]

1010011010

[nando]

there's only 3 sensors that truly matter on the E30 anyway - CPS, AFM, and coolant temp. Technically, the only one required for the engine to run is the CPS. :p

[TobyB]

I can see all the sensor values

Awww, quit pullin' my dipstick- that's exactly what we need-

Pro3 has to run the stock flapper AFM, and seeing how the ECU's interpreting the flapper
is what I want to do. It's getting blamed for a bunch of stuff, and there's no way to
prove/disprove that without seeing how the ECU is seeing it

Tell me more, John!

t

[ForcedFirebird]

Awww, quit pullin' my dipstick- that's exactly what we need-

Pro3 has to run the stock flapper AFM, and seeing how the ECU's interpreting the flapper
is what I want to do. It's getting blamed for a bunch of stuff, and there's no way to
prove/disprove that without seeing how the ECU is seeing it

Tell me more, John!

t

Moates Ostrich emulator.

If you have a DMM, you can verify the AFM is functioning...

http://www.the944.com/afm.htm

To save space on the chip, the AFM tables are a function of one another (math formula). Back then, even 256k wasn't a lot of space for all the things needed.

[TobyB]

Ahh, the Ostrich. I had forgotten... TunerPro?

Yes, an analog voltmeter can tell even more/less, depending on the ECU. The thing is,
it's not just the resistance, it's the mechanical damping of the meter we're wondering about.
And wtf the ECU THINKS it's getting. I suspect a number of 'em have analog- side problems...
In THEORY, the AFM isn't doing much at WOT over 4k. In practice, that doesn't seem
to be true. What IS true doesn't seem to be written down in black and white, or 100%
repeatable from car to car. Which is just... more frustrating than carbs.

Thanks!

t

[varg]

Yes, an analog voltmeter can tell even more/less, depending on the ECU. The thing is,
it's not just the resistance, it's the mechanical damping of the meter we're wondering about.

Well the mechanical damping of the meter is part of the specification of the unit, and definitely something the engineers and tuners took into account when doing the OEM tuning. There is an acceptable tolerance just like any other device, and 20+ year old devices are probably mostly in excess of those limits, but they seem to work fine for most. You can see that there isn't much damping to speak of in one of these when you look at the output, with changes in throttle position the vane will sometimes oscillate briefly which is reflected in the signal, and if you ask me most of the damping here is done by the airflow and the mass of the flapper itself, some complicated fluid dynamics there for anyone who wants to attempt it (not me).

In THEORY, the AFM isn't doing much at WOT over 4k.

Whose theory is that? It's doing the same thing it would at any other engine speed. It's specced for a given application, it measures flow over a given range that is reasonable to expect from the engine it is fitted to. The maths that the ECU is doing may change at high engine speeds, John would know more about that than I would since he has actually tuned these ECUs and seen their contents, but the principals are the same as in any other engine management system so I have a good grasp of what's going on here.

Here's a thread containing some flow measurement done with a stock AFM on an M42:

http://www.r3vlimited.com/board/showthread.php?t=353875

Carbs are just analog computers ;)

[barbierij]

there's only 3 sensors that truly matter on the E30 anyway - CPS, AFM, and coolant temp. Technically, the only one required for the engine to run is the CPS. :p

I had to plug my 173 in after my MS quit on me today. I pulled the TPS plug and cut power from the wideband. Ran like super crap and no power below 3k. Just wanted to post some info.

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