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Discussion Starter #1
Is there a way of replacing the flapper AFM and still using the Motronic ECU, or would I need to go for a full programmeable one?
 

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Weren't the 24V ECUs all hot wire AFM Chris? Mind you, looking at the figures from my 12V RR session, the flapper maybe isn't as restrictive as we thought it might be. It didn't cross my mind until now, but I could have taken one along and fitted it temproaraily to see jsut how much difference it makes. I'll try(!) to remember to do this next time I take the car to the RR. We wouldn't have had the time at the last session anyway, but I can do it next time.
 

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Earlier 24v had flap AFM (like all US 24v models), while later 24v had hot wire AFM.
Jes
 

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Discussion Starter #4
Weren't the 24V ECUs all hot wire AFM Chris? Mind you, looking at the figures from my 12V RR session, the flapper maybe isn't as restrictive as we thought it might be. It didn't cross my mind until now, but I could have taken one along and fitted it temproaraily to see jsut how much difference it makes. I'll try(!) to remember to do this next time I take the car to the RR. We wouldn't have had the time at the last session anyway, but I can do it next time.
My 1994 engine has a flapper AFM. I was wondering if one of the later hot wire ones would speak the right numbers to the ECU so as to be a plug in substitute, but that seems intuitively optimistic!
It should be restrictive - the cross sectional area of the flap section is 2990 mm2, the c.s.a. of the tubing/plenum intake is 5024 mm2
 

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Ah, OK - wasn't sure. What's the c.s.a. of an inlet runner compared to the AFM?? That'll be the limiting factor won't it?

If we can find some data on the 2 AFMs & ECUs, that might give us a clue if they would be interchangeable....I'll see what I can dig up....so, can anyone tell me definitively which ECU goes with which AFM type please?
 

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Discussion Starter #6
the inlet runners are going to be approx 1275sq.mm each. There'll be flow in more than just one at a time though.
Do you need some numbers off the ECUs?
 

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True..it'll be more than 1 at a time, but not as much as we might think. Complicated, but it'll relate to cam overlap and durations. Wouldn't know where to start to work it out, but I will do that notion of putting a flappy AFM on my car next time it's on the rollers.

If you have ECU numbers for the early & later types, that would be a good start. The flappy AFM is simply a pot (with a few tweaks), the hot wire AFM is a more complex device, but could well have been designed to provide the same output signal to the ECU. I've never investigated this before.
 

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I am working on that challenge right now for my US spec 1995 164 LS 24 valve - it still has the flapper AFM. I purchased a generic hot-wire pass-through MAS sensor tube and will be running the UniChip product from South Africa to deal with the added fuel and timing requirements of the 3.45 litre rebuild.

You need a converter box of sorts that will convert the digital frequency from the hot-wire to the analogue voltage that the stock AFM is going to be looking for. I thought about upgrading to the European-spec 164 Q4 all-wheel drive electronics since that runs a MAS tube (on Bosch version 3.7 I think it is), but the ECU is different, the harness pin-outs are different so I scrapped that idea.

The UniChip is a piggy-back and a seperate issue - worth mentioning though since it goes with the conversation about keeping Bosch Motronic's relatively smooth maps and cold-start programs, but gaining programmability. With the removal of the restrictive flapper AFM, it is conceivable that the motor could use a bit more fuel and you can always use a bit more timing.

Add some of our GTA Stage I or GTA Stage II cams, 44mm GTA/Q intake runners and now the UniChip becomes even more important. I don't sell the product, but I love it - it works. With the Stage I cams, the Q/GTA runners and the UniChip my otherwise stock standard 164 LS (Super) kicked out 212-213-214 horses at the wheels through an automatic slush-box and still with the flapper-crapper installed!
 

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Discussion Starter #9
I pass on the following from another Alfisti fiddler.

I can say for certain that you cannot use the wrong type of flow meter with a standard ECU that was not meant for it. The newer (and much better) hot-wire types need a different supply and the output signal is not directly compatible with the potentiometer from a flap type. (The hot-wire types do not restrict the air flow like a flap does, but the signal is much harder to interpret.)
 

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It is very do-able though! Just need somebody - better than me - with electronics...
 

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Thanks JJ, Chris. Saves me some effort reinventing the wheel! Frequency to voltage is easy enough....but getting the right conversion law could be a tad tricky I suspect. Best way would be with a flow bench I suppose. Anyone got one handy along with a couple of AFMs?? Plot the relationships of flow to volts/frequency and I'll see if I can come up with a converter.
 

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Discussion Starter #12
I've got a spare flapper AFM that I can lend for the cause Chris. Sorry, no flow bench, and I can't think what medical equipment i could cannibalise either!
 

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I've a surplus of flappy AFMs myself. Dont have a hot wire type, nor a flow bench. I know someone who does...but suspect they won't be interested in this particular topic. Another path might be manufacturers data for the devices?? Anyone??
 

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Discussion Starter #15
Looks like hot wire AFMs are voltage too - easier to convert?
I wouldn't have thought that I need all the other gizmos these provide.
 

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Didn't think we where trying to design an ECU Barry, just wondering if the hot wire AFM could be adapted for use with a flapper type ECU. Aftermarket systems are many and varied of course, and a different topic entirely. The text on that website implies certain hot wire AFMs output an analogue voltage, but either way, if we can get the output characterisitics for both types in question, then a converter isn't that tough a job. Personally, I've no interest other than helping out, as my car runs and aftermarket system in Alpha/n, with MAP coming along as soon as I install the blower. MAP sensor is alrady installed in fact. The ECU I chose offers boost control in each gear, launch control, flat shifting, etc etc etc. Most of which I probably won't ever use. Our profiles (Jimmystratos & mine) don't indicate we are UK based, so I don't see us opting for a US product anyway, as support over here might be a bit lacking. Thanks for the thought though :)
 

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I do not know what the montronc is but the L-jet has the map in the AFM
it is not a pot. it has a bunch of LASER trimed resistors that are selected one at a time as the flap moves.

but I have to say reworking and pigybacks systems cost more or as much as a new programable ECU. I would only go that way if you need the OEM for smog inspection or somthing. I guess there is somthing for plug 'n' play if you can not work with wires.
 

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I do not know what the montronc is but the L-jet has the map in the AFM
it is not a pot. it has a bunch of LASER trimed resistors that are selected one at a time as the flap moves.

but I have to say reworking and pigybacks systems cost more or as much as a new programable ECU. I would only go that way if you need the OEM for smog inspection or somthing. I guess there is somthing for plug 'n' play if you can not work with wires.
The laser-trimmed discrete resistors are still a pot - potentiometer. It doesn't have to be a stepless device to qualify as being a pot. ..and gain, I don't think we are looking to redesign the ECU here, just adapt (if practical) the hot wire AFM to a flap-type ECU. If the hot-wire outputs a PWM signal dependant on flow, then given the transfer characterisitc of both types, I can probably come up with a small and inexpensive box that will allow the use of the hot wire AFM. For it to work, no ECU mods will be involved.
 
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