mx5cartalk.com

Hi everyone

Looking to refine the AFR now that I've fitted CAI, extractors and cat back soon to come, I'm not looking at force induction anytime soon so staying away from exy options like ECU or even branded piggy-back but would consider a Megasquirt if someone's looking to get rid of one, otherwise a simple Jaycar DFA sounds like the go. Just a couple of questions before I drive in....

1. Has anyone try the Jaycar DFA (Digital Fuel Adjuster)?
2. How did you find it?
3. Were there anything about it that you find lacking/could be better?

https://secure4.vivid-design.com.au/ele ... &SUBCATID=

Cheers
Minh

i've got one and i LOVE it. it's awesome, i think this is one of the best mods you can do, especially considerring how cheap it is.

a few other guys on the forum have fitted them recently too, to more stock set ups. mine is currently running 460cc injectors on a naturally aspirated engine, and it runs like stock except for a bit of an idle issue.

i had it on the car before fitting the bigger injectors, and definately noticed a performance increase and better fuel economy with the stock injectors.

seems like there are a few hand sets floating around on the forum now as well, so you might be able to save yourself some cash and borrow a hand controller for a couple of weeks to get your tune right, instead of buying one.

i can't think of anything i don't like about it, except for the relay fitted to the board ( it's best to omit it) and the size of the heatsink. it's a good idea to fit a bigger heatsink (or just bolt a thin sheet of aluminium onto the existing heatsink), as they changed the display on the hand controller to a backlit one, and as this draws more current sometimes it can get a bit overheated. this does not affect the performance of the dfa but until it cools down (10 , 15 minutes), you can't make any tuning changes.

Does this get rid of the need for the AFM???
Because if so this seems like the cheapest options for a few cold horsies...

no, it does not replace the afm, it modifies the existing afm signal.

a lot of people (myself included) seem to have a hard-on for ditching the afm. there is a lot of unfounded talk on the 'net that the afm is \"restrictive\". there is no actual evidence to support this that i know of. the only 2 actual tests of the afm that i know of were done by adaptronic (australia) and norman garrett, for the miata club of the usa. both found no benefit in removing the afm, except in extremely high horsepower, highly modified engines applications.

so, if you're looking for cheap power gains, stick with the afm. it works, and it is not restrictive. i do however agree that cosmetically, the engine bay looks nicer without the afm. hey, i am ditching mine after all

Fatty wrote:no, it does not replace the afm, it modifies the existing afm signal.

a lot of people (myself included) seem to have a hard-on for ditching the afm. there is a lot of unfounded talk on the 'net that the afm is "restrictive". there is no actual evidence to support this that i know of. the only 2 actual tests of the afm that i know of were done by adaptronic (australia) and norman garrett, for the miata club of the usa. both found no benefit in removing the afm, except in extremely high horsepower, highly modified engines applications.

so, if you're looking for cheap power gains, stick with the afm. it works, and it is not restrictive. i do however agree that cosmetically, the engine bay looks nicer without the afm. hey, i am ditching mine after all

I'm sure Matty on here did the hard work and has actually tested all pieces of the NA intake system for restriction and the numbers are definately floating around a few places on the net...

I'm just too lazy to be assed finding them...

You might be able emulate the current AFM with a less restrictive type. If we could work out the actual airflow with-respect-to signal for the current and then the less resctrictive alternative, then you could use an interceptor to emulate the stock AFM signal but with the added free flow and response.

Just a thought....

...you can even go one step better with the above thought and replace AFM with a MAP/Vacuum sensor. So a MAP sensor which output signal to an interceptor (Jaycar DFA) which then outputs \"AFM emulated\" signal to the ECU.

This could be really interesting, might start off by mounting a vacuum/MAP sensor somewhere close to the AFM then simutaneously log data from the two (AFM and MAP) sensor with the engine at work. Then by comparing the response curve, should be able to work out where within the MAP sensor response function needs changing to match the reference AFM signal. Then all that's needed is dialing in the changes on the DFA to closely match the load characteristics of the AFM signal. You then logs the final signals (AFM and \"MAP emulated AFM\") and fine tune until they're spot on...then remove AFM and voila!!!...feel the response!!!!

Is there anything I've overlooked?...is there more to the AFM then just potentiometer that is turned by the action of the flap? does it measure anything else...air temp maybe? what's the signal range? 0-5V?...any on/off switch? if so for what reason?

I've got a vacuum sensor of a Starlet Life somewhere I might put in action sometime soon.

Cheers
Minh

Sean wrote:

Fatty wrote:no, it does not replace the afm, it modifies the existing afm signal.

a lot of people (myself included) seem to have a hard-on for ditching the afm. there is a lot of unfounded talk on the 'net that the afm is "restrictive". there is no actual evidence to support this that i know of. the only 2 actual tests of the afm that i know of were done by adaptronic (australia) and norman garrett, for the miata club of the usa. both found no benefit in removing the afm, except in extremely high horsepower, highly modified engines applications.

so, if you're looking for cheap power gains, stick with the afm. it works, and it is not restrictive. i do however agree that cosmetically, the engine bay looks nicer without the afm. hey, i am ditching mine after all

I'm sure Matty on here did the hard work and has actually tested all pieces of the NA intake system for restriction and the numbers are definately floating around a few places on the net...

I'm just too lazy to be assed finding them...

Yes Matty did do some work in this area and found that the standard 1.6l AFM is restrictive, which was one reason why he (and others) have looked to replace the standard AFM with a RX-7 type. I think he did a write up that appeared in the Vic Club magazine, and/or an online Auto magazine.
Before I fitted my turbo I ran the FM-Link ECU in NA mode. I took out the AFM and used the map sensor. I was still running the original injectors and exhaust, but (purely seat-of-pants) the engine reved so much smoother and there was mucho Zoom Zoom.

J

Juffa wrote:Yes Matty did do some work in this area and found that the standard 1.6l AFM is restrictive, which was one reason why he (and others) have looked to replace the standard AFM with a RX-7 type. I think he did a write up that appeared in the Vic Club magazine, and/or an online Auto magazine.
Before I fitted my turbo I ran the FM-Link ECU in NA mode. I took out the AFM and used the map sensor. I was still running the original injectors and exhaust, but (purely seat-of-pants) the engine reved so much smoother and there was mucho Zoom Zoom.

J

Yeah I came across his work in the past...great work!!! it was in the Autospeed magazine I think. Thought about the RX7 AFM mod but at the end of the day it's still a restriction. What I'm thinking is something similar to your FM-Link piggyback, but hopefully abit more affordable with the use of the Jaycar DFA (~$80) and a vacuum (MAP) sensor you could pickup almost next to nothing off a wreckyard, obviously plenty of time spent on prototyping, testing, tuning and more tuning, but good learn experience in the end.

Apart from going exy piggy or full ECU, are there any other method(s) of replacing the AFM?

Before you say \"all AFMs are a restriction\" please go do some real testing to justify that statement.

I don't think you'll achieve what you want because airflow is dependent on both MAP and rpm, you can't just create a 1:1 conversion between airflow and MAP... and then you still need the air temp signal from the AFM so the ECU doesn't get confused.

Easiest way would be a HKS VPC. Cheapest way would be a Megasquirt...

yep, matty is correct (as always). you can't just use a map sensor, you need map and rpm to simulate the afm signal. astroboysoup is using the hks vpc in conjunction with a dfa on his car. i'm not sure if he's had a chance to get it on the dyno yet to test the results.

we had a big discussion a while ago to try and figure out someway of using a map sensor with the stock ecu... eventually i put the idea in the \"too hard basket\" and bought a megasquirt, but i didn't know about the vpc at that time. there is also the map-ecu and spilt second thingo, both of these will do it but both are more expensive than a megasquirt.
anyway at the time i was thinking of data-logging and then programming this data into some kind of progammable pic microchip kinda thing, but it was beyond my capabilites. dick bipes (creator of the bipes acu) was doing some research into this idea as well a few years ago and actually has some charts on his website of map and rpm values. but he stopped working on any miata projects a while ago, i think he sold his miata and bought a mercedes slk.

also, in regard to the the afm being restrictive thing, from what i understand of the tests , yes technically it is restrictive, but in practice there is not enough airflow in a naturally aspirated system for the restriction to have any effect on power. it only becomes a problem when you are flowing lots of air, such in a turbo or supercharged system. but there could be other benefits of ditching it such as throttle response, smoother running etc etc, as juffa found.

Mr Starlet wrote:...

Is there anything I've overlooked?...is there more to the AFM then just potentiometer that is turned by the action of the flap? does it measure anything else...air temp maybe? what's the signal range? 0-5V?...any on/off switch? if so for what reason?

Cheers
Minh

yes there is also a temp sensor in there.
the the signal range is 0-5v, voltage descends as airflow increases. eg at idle it's roughly 4v at wide open throttle it's roughly 0v.
yes there is also a safety switch in there that will shut off power to the fuel pump when the flapper is shut completely (no airflow, hence engine is not running). it's there to stop the pump in case of an accident. this feature can be bypassed in the diagnostics box in the engine bay.

luckily i have a HKS VPC that did away with the AFM by using a MAP and a temp sensor..

its great... i've tuned out the idle bugs but its still very rich since i still haven't take the car on to a dyno.

also have the DFA here too all hooked up. I'm just waiting to get it tuned. then i can tell ya all how many more ponies i have

Fatty wrote:

Mr Starlet wrote:...

Is there anything I've overlooked?...is there more to the AFM then just potentiometer that is turned by the action of the flap? does it measure anything else...air temp maybe? what's the signal range? 0-5V?...any on/off switch? if so for what reason?

Cheers
Minh

yes there is also a temp sensor in there.
the the signal range is 0-5v, voltage descends as airflow increases. eg at idle it's roughly 4v at wide open throttle it's roughly 0v.
yes there is also a safety switch in there that will shut off power to the fuel pump when the flapper is shut completely (no airflow, hence engine is not running). it's there to stop the pump in case of an accident. this feature can be bypassed in the diagnostics box in the engine bay.

Agh found your previous thread...
http://www.aus-cartalk.com/viewtopic.ph ... m&start=15

The Pupat wrote:

Fatty wrote:ok thank for the detailed info.

but the curve can be corrected, thats not a problem. the biggest problem, as i see it, is this :
from what you are saying, the map sensor MAY output the same reading at , say for example, 1000rpm and 5000rpm, depending on throttle position.

if this is the case, i'm screwed

Not may will. And yes unless you can get an RPM correction you are screwed.

Ahhh crap!!! this was what I overlooked...
Yep "too hard basket" it goes. MegaSquirt would be the easier answer.