Now Here's A Thought

[C_W 3 1 Cars]

The mi16 has a throttle switch not a throttle pot so it only uses it for idling and WOT enrichment. The afm as it is measures engine load.

 

That's what I mean; to replace the AFM you'd need the a MAP sensor along with a proper throttle potentiometer.

[hman205 1]

also the cold start valve get its air before the throttle body so would then make for un metered air

 

Thus Generating another list of problems with a AFM and MAP less system

[KRISKARRERA 2 1 Cars]

So in other words you might as well try to run the engine on the MP3.1 from the later 405 sri.

[PumaRacing 1]

No you can't, but you can replace it with a MAP sensor if you make them appear "electrically" the same. A MAP sensor changes resistance with engine load, as does the AFM.

 

No it doesn't. This thread is turning into a right mishmash of misinformation.

 

The MAP sensor registers the inlet manifold pressure but that can be the same figure at any number of rpm and throttle position values. At full throttle it will be more or less the same at any rpm but the total airflow will be completely different. Without knowing rpm it's as meaningless as just the throttle position. Let's try and get this straight once and for all.

 

An AFM, flap or hotwire, measures total airflow. Assuming a fixed air/fuel ratio that's all the system needs to know to add the right amount of fuel other than for full throttle enrichment purposes. With an AFM the system isn't worried about rpm or throttle position. The TPS can be a simple device that just registers full throttle so the system can adjust A/F ratio from 14.7 to something a bit richer when full power is required.

 

Without an AFM there are only two ways to calculate total airflow. Rpm and thottle position or rpm and manifold pressure. If the engine has forced induction then you always need to know manifold pressure. Rpm and throttle position isn't enough.

[petert 554]

The MAP sensor registers the inlet manifold pressure but that can be the same figure at any number of rpm and throttle position values. At full throttle it will be more or less the same at any rpm but the total airflow will be completely different. Without knowing rpm it's as meaningless as just the throttle position. Let's try and get this straight once and for all.

 

No. you're wrong, I'm afraid. It's possible to totally map an engine with just RPM and a MAP sensor. I've done it many times. I'll try and spell it out again.

 

205 AFM - is a variable resistor

GM MAP sensor - is a variable resistor

205/405 TPS - is a 3 position switch

RPM - comes from coil or crank sensor

 

The GM MAP sensor is very responsive to changes in load, just like the AFM.

[PumaRacing 1]

No. you're wrong, I'm afraid. It's possible to totally map an engine with just RPM and a MAP sensor. I've done it many times. I'll try and spell it out again.

 

Struth, which is exactly what I said above if you read my post properly and not what the OP was told he could do or what your previous post indicated. He was told the AFM, on the standard control system, could be replaced by a throttle pot - no mention of fitting a mappable ecu or measuring or mapping against rpm which is why it wouldn't work. Nor would replacing the AFM with a MAP sensor unless again rpm is measured and mapped against and you absolutely didn't say that first time round.

 

You said "A MAP sensor changes resistance with engine load, as does the AFM". It doesn't. It changes resistance with changing manifold pressure which can be the same at many different engine loads. The only thing which measures engine load is an AFM which is why that's the only thing that doesn't also need rpm or thottle position to be measured to calibrate the fuel properly.

[DrSeuss 0]

What still slightly confuses me is the use of a MAP sensor in conjunction with a throttle pot and a CAS, you can either use the throttle pot or the map for fuelling. I presume you use the map for the steady state fuelling and throttle position to calculate transient enrichment?

[petert 554]

Dave, the guy was looking for a cheap solution to try. I suggested that he would have to experiment with the values and try to make them electrically the same. You're saying flat out, it can't be done. I'm saying maybe it can. If everyone took one point of view we'd never progress. Young people need to experiment in order to find out how and why things work.

 

What Dave is saying, is that the 2500 and 5000 full load values for a MAP sensor will be indentical. Whereas for an AFM they will be different. This is absolutely correct. But if I were young and had plenty of time, with an interest in electronics, I'd make it work.

[Rippthrough 98]

Dave, the guy was looking for a cheap solution to try. I suggested that he would have to experiment with the values and try to make them electrically the same. You're saying flat out, it can't be done. I'm saying maybe it can. If everyone took one point of view we'd never progress. Young people need to experiment in order to find out how and why things work.

 

What Dave is saying, is that the 2500 and 5000 full load values for a MAP sensor will be indentical. Whereas for an AFM they will be different. This is absolutely correct. But if I were young and had plenty of time, with an interest in electronics, I'd make it work.

 

 

Err how? You can't just magically transform the signal so it suddenly takes account of RPM without remapping the entire thing anyway.

[petert 554]

What about using a 555 timer to count the RPM, the output of which is a variable duty cycle square wave, which is used to turn on a transistor, varying it's voltage output.

 

There's a 100 other ways, that one just sprung to mind.

[karlo 1]

What still slightly confuses me is the use of a MAP sensor in conjunction with a throttle pot and a CAS, you can either use the throttle pot or the map for fuelling. I presume you use the map for the steady state fuelling and throttle position to calculate transient enrichment?

Yep, throttle pot is just used for acceleration and deceleration enrichment. In some cases you can use mapdot (watch for rapid increase or decrease in vacuum, ie. map) instead and just drop the TPS, especially when you have a large throttle body and just cracking it slightly open will cause a large drop in vacuum. In most cases, the TPS will be more precise, though.

[DrSeuss 0]

you'd never bother with a map sensor to replace the AFM. A hotwire maf sensor would be a million times easier. As for using 555 timers in car electronics, get a grip. You'd write code to burn onto a microcontroller.

[MartinR 0]

you can use a MAF, but you need to build a circuit which can send a burn signal to the MAF, I know because I have tried as I have a nice MAF I "borrowed" from a Volvo S60 T5 when I worked for Volvo

 

I would love to be able to use the MAF instead of the AFM, but I dont know how to make a circuit which will send this burn signal. Whats also worth noting is that the majority of modern MAF sensors use 0 - 5v whereas the AFMs use 0 - 12? (could be wrong there, so if someone could correct me without crapping down my throat that would be cool)

 

Need someone to graph the input and output of a MAF sensor so you can see how big and how frequent the burn signal is.

[MartinR 0]

just been doing some reading.

 

Apparantly the burn off signal only happens after engine shut down and heats the wire to 1000 degrees C for 1 second.

 

found a lovely link describing how to test one

 

MAF Testing

 

So if someone knows how the AFM should be tested and how it works then great, coz if this is similar to how the MAF sensor works then I can sense a possible replacement coming on!

[Rob_the_Sparky 9]

To replace a Motronic AFM with a Hotwire sensor should be relatively easy as Motronic uses it to measure air flow then uses a map to determine the fuel. On Jectronic it will be more interesting as there is a fuel "map" designed into the AFM, hence the laser trimmed resistance track. Its output is a base fuel map, not air flow. Hence they are different for every car.

 

It certainly is not impossible but it will take quite a bit of work to sort out the details. Personally if I were going down this road I just fit an aftermarket ECU and have full control of fuel and ignition.

 

Rob

[Toddman 0]

Now I may not have appreciated all the aspects of what was needed but the last couple of pages have been VERY helpfull

I was and still am of the opinion that you can get the system to work without the flap although it may need several additions which I did not fully appreciate.

Like Peter says it is this type of banding about of ideas that helps craete new projects and there is no better experience than actually doing it and finding out why it won't or why it does work.

 

Cheers

Luke

[madspikes 41 1 Cars]

Bugger, there gones my idea!

 

I have been working for the last 18months a system of replacing the flap with a hot wire meter. I'm currently in the process of building a prototype after much testing and development. So would people be intrested in such a system?

 

Mad

[M3Evo 0]

Bugger, there gones my idea!

 

I have been working for the last 18months a system of replacing the flap with a hot wire meter. I'm currently in the process of building a prototype after much testing and development. So would people be intrested in such a system?

 

Mad

 

Guess it really depends on how much it'd cost.

 

There's talk of the conversion costing about £800 on the E30 site I'm on, for which you could build a megasquirt and have ignition control etc. aswell!

[madspikes 41 1 Cars]

I was think more of £50 - £100 plus the hotwire cost.

[dee205 3]

While reading an old Retro Cars magazine last night at work I came across a Lancia Scorpion with a Lancia Beta engine running a Bosch L-Jetronic set-up with a hot wire conversion instead of an AFm. The got a MAF convertor to allow the fueling to be mapped from Split Second Performance in California.

 

Damien

[taffycrook 2]

You said "A MAP sensor changes resistance with engine load, as does the AFM". It doesn't. It changes resistance with changing manifold pressure which can be the same at many different engine loads. The only thing which measures engine load is an AFM which is why that's the only thing that doesn't also need rpm or thottle position to be measured to calibrate the fuel properly.

 

The Jetronic set up does use a rpm signal.

Engine load can be any one of Throttle pot, AFM, MAP AirMass ECU's look at all signals to calculate fuel requirements of an engine.

Load is calculated not so much measured.