jimbo1111

What's the difference between chips for maf and chips for afm. I'm puzzled. Also has anybody tried a temp compensation sensor on there maf with good success.

fast951

The MAF output signal differs from the AFM signal. The signal mapping in the DME chip is different between MAF and AFM...

A while back there was a thread regarding the Air Temp attachement with the AFM. The thread calls for installing the Air Temp Sensor between Pin #1 and Pin#4 on the MAF connection. I don't think that's correct as Pin#4 in ground and Pin#1 is the ATS signal...

I'm not sure where all of this started, but the signal from the MAF already compensates for temp (AFM does not therefore you have the Temp Sensor with it).

Danno

"What's the difference between chips for maf and chips for afm."

It has to do with the difference in output voltages given the same airflow:

<img src="http://www.gururacing.net/ImagesMisc/MAFvsVAF.gif" alt=" - " />

As you can see, the voltage response is not the same. The whole idea behind these four-**** adjusters is to massage the voltage output of the MAF to appear like an AFM to the DME. The criss-cross at the beginning poses some problems as well (rich idle). The ideal solution is a set of chips mapped with an MAF-sensor's output in mind with no massaging of the voltage output. Such as the AutoThority MAF kits which comes with a MAF-specific chip. We've also got a MAF chip to retrofit MAF kits and lets you leave the ARC2 at zeros across the board (or with one or two clicks here and there). You can also select 4 injector sizes with our chips while leaving the ARC2 settings the same.

Here's the pertinent section of the air-temp sensor circuit:

<img src="http://www.gururacing.net/ImagesMisc/AirTempSensor1.gif" alt=" - " />

And the section out of the manual that deals with the AFM and air-temp sensor:

<img src="http://www.gururacing.net/ImagesMisc/AirTempSensor2.gif" alt=" - " />

The air-temp sensor actually provides TWO (2) functions:

I. Air-fuel ratio adjustment based upon air-temperature (density). The adjustment is actually very minor in order to maintain a 14.7:1 stochio. mixture. This is the function that most people think of when they hear 'air-temp sensor'. However, the altitude sensor will cause a 6.3% leaner mixture when triggered that will throw this adjustment completely out of whack anyway.

II. An even more important and more significant function of the air-temp sensor is cold-start enrichment beyond 14.7:1. This process goes as follows:</font>

• <font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Upon start-up, the engine-temp sensor triggers the DME to provide cold-start enrichement; this is a binary on/off value.</font></li>
• <font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">A separate cold-start enrichment map is referenced based upon the value of the air-temp sensor. The amount of enrichment above 14.7:1 can be from 6.3% to 12.6% depending upon the temperature of the outside air. Without an air-temp reading, the adjustment is 0%.</font></li>

<font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">The primary issue with MAFs and the lack of an air-temp sensor has to do with cold-start enrichment not air-fuel adjustment based upon air-density. While a MAF compensates for air-density & temperature to maintain a constant 14.7:1 ratio for stochio. mixtures, it cannot give you a richer mixture than that.


Without the air-temp sensor, you won't have a rich 10.0:1 to 12.0:1 mixture on startup. Thus, you have to do the manual-choke procedure of turning up the LOW **** on the ARC2 by two clicks or so to get a clean start. Then you have to dial it back down when the engine's warmed up.

special tool

In case anyone is interested, I was actually clocking the impedence on my stock afm for the sake of noting it on my maf potentiometer the other day in the ridiculously cold northeast. Btween the outer 2 pins at 70 dgrees you should have - around 2.6k ohms, at 10 degrees - around 10.3k ohms. I believe someone suggested that the stock afm's range stopped at 6.something, but it keeps on increasing.

Danno

Yup that's right. The NTC air-temp sensor will continue to increase in resistance as temps decrease. The actual fuel-enrichment table in the chips based upon air-temps goes down to -27F(-33C).

dand86951

Danno, for all you guys not dealing with the cold weather, it appears my chips would not have been able to compensate for a cold start a couple of days ago as it was -37C up here. My experience with the MAF without cold start temperature compensation is that the engine does have a tough time and it takes it a bit for the engine temps to get warm enough for things to smooth out. Trust me I didn't try to start it at -37C.

special tool

Jimbo - to answer your question, I pulled the stock temp sensor out of my afm and replaced my adjustable potentiometer with it this afternoon. It worked perfectly the first try - I didn't see how it couldn't being that they only exist to supply impedence, and I had been matching my ape potentiometer to the stock afm for a while.

Danno

" I pulled the stock temp sensor out of my afm and replaced my adjustable potentiometer with it this afternoon."

Does this mean you are simulating the air-temp sensor with a pot? So you turn the pot to the cold-air position to richen up the mixture for cold starts, then turn it down when the engine's warmed up?

special tool

Danno - yes, I was doing that. My ape mass air is older and has a screw adjustable potentiometer for the sake of adjusting CO. However, since I was plagued by cold start problems, I was constantly throwing my multimeter on the afm pins and adjusting the maf impedance to match. That always worked beautifully - but a pain in the ***. Yeasterday, I pulled the temp sensor out, pluged it into a teed-in section of fuel hose and soldered it up. Works perfectly now.
I will assume that ape did that to help with emissions, but on a track car...
By the way Danno, if you want that thing for examination, I will zip it out to you.