ECU / Airflow Meter question

Fatty · Postby **Fatty** » Mon Sep 11, 2006 11:58 am

so the airflow meter sends a signal to the ecu. there are 3 common types of meters. which one does the na6 use?:
0v to 1v
0v to 5v
0v to 12v

also, which wire carries this signal to the ecu ? if someone could post a pic with a big arrow pointing to the correct wire in the ecu harness, that would be great :mrgreen:

the reason i am asking is that i have purchased a digital fuel adjuster so i can fiddle with the air/fuel ratios. i need to know this info so i can set it up and install it correctly.

Matty · Postby **Matty** » Mon Sep 11, 2006 12:25 pm

The NA6 uses a 0-5V signal, however it's reversed in that the signal at idle is about 3-3.5 V, and falls as the load increases (ends at about 1V IIRC)

Fatty · Postby **Fatty** » Mon Sep 11, 2006 12:55 pm

thanks matty. hmm ok the voltage decreases as the load increases.

i was planning on eventually replacing the airflow meter with a map sensor, this might throw a spanner in the works. Am i right in saying that MAP sensors operate in the 0-5V range, but are not reversed like the airflow meter?

Matty · Postby **Matty** » Mon Sep 11, 2006 2:30 pm

ahahaha, MAP sensors I think mostly work in the 0-5V range, with increasing voltage as the pressure increases.

However, there's not a linear relationship between the two, since MAP has no correlation to actual air flow rate (except when calculated in combination with rpm).

Fatty · Postby **Fatty** » Mon Sep 11, 2006 2:40 pm

yeah figured as much matty.

thing is tho, the digital fuel adjuster (DFA) has 128 \"load\" points that can be adjusted, (each point corresponding to 39mV on the 0V to 5V range). each of these points can be adjusted by +/- 2.5V.

so, if the ecu is expecting to see a signal in the range of 1V to 3.5V, the range is 2.5V from top to bottom. This corresponds exactly with the maximum offset adjustment that the DFA can perform. So if your map sensor is outputting ,say, 4V for example, the dfa can modify this as far down as 1.5V to \"trick\" the ecu. i'm not convinced that 2.5V is enough room of a range ... it doesn't leave much of a safety margin at the top and bottom of the scale does it ...

Fatty · Postby **Fatty** » Mon Sep 11, 2006 2:50 pm

or, here's a crazy thought, 2 DFA's in series will allow me to modify each load point by up to 5V's! but that's getting a bit silly isn't it. at $80 per dfa, it's probly better to stick with an airflow meter , like the rx7 one for example (as suggested by boags)

Boags · Postby **Boags** » Mon Sep 11, 2006 3:35 pm

Speaking of the rx7 air flow meter. What series is suggested for turbo application? I have a friend of a friend who runs a rotory mechanics shop, so i'm sure they'll have a few to sell...

Boags

adamjp · Postby **adamjp** » Mon Sep 11, 2006 10:49 pm

The Series 4 NA RX7 AFM.

Postby **Okibi** » Tue Sep 12, 2006 12:00 am

How much was the \"digital fuel adjuster\" since you have the 1.6 ecu, why not just save the pennies for the plug in Wolf ecu and ditch the AFM?

Fatty · Postby **Fatty** » Tue Sep 12, 2006 1:05 am

i paid $127 for the DFA and hand controller.the hand controller can be used to control several other jaycar kits as well.

i went this way coz i enjoy building electronic things, and it seemed like a good cheap option.

Fatty · Postby **Fatty** » Tue Sep 12, 2006 11:20 am

so i still need to know which wire i need to intercept . i guess i can follow it back from the airflow meter ,using my multimeter and some trial and error, but if someone has a chart or diagram showing what is what, that would save me a lot of stuffing around. even just a hint on the wire colour would help.

Fatty · Postby **Fatty** » Tue Sep 12, 2006 2:33 pm

well that's exactly what i'm trying to accomplish here slugoid, using the dfa to tweak the meter signal.

Matty · Postby **Matty** » Tue Sep 12, 2006 2:46 pm

I have more recently installed the RX-7 AFM body, but with the MX-5's internals (including the much softer spring). I don't have any electronics mods apart from that (and softening the flapper about 6 clicks). It seems to run OK most of the time, but has a slight lean spot in the midrange under light acceleration.

The DFA would be a good addition to my setup.

93_Clubman · Postby **93_Clubman** » Sat Sep 16, 2006 8:07 am

Fatty wrote:so i still need to know which wire i need to intercept . i guess i can follow it back from the airflow meter ,using my multimeter and some trial and error, but if someone has a chart or diagram showing what is what, that would save me a lot of stuffing around. even just a hint on the wire colour would help.

not sure if you found the answer you were looking for, or if this helps, but fwiw the miata performance handbook by norm garrett shows the following looking from left to right facing the male plug on the afm:

FC = fuel pump lead
E1 = fuel pump ground
E2 = ground
VC = +5 volts
E2 = ground
VS = air flow signal
THAA = air temp signal

by way of confirmation, the male plug on the afm in the diagram shows two ridges at the top & three ridges at the bottom providing oneway fitting. unfortunately no wire colours are mentioned, but i'm sure russellb has posted a wirng & ecu connector block diagram a few times this year.