Red Devil - I hope you got the hint.

You asked for some info?

I've found both published and printed information on MAFs that list the output both ways. The key is how the ECM uses the signal from the MAF. After all the hunting, here's the information I found that I believe is correct:


MASS AIR FLOW METERS -

The Past

* 1985 - CAFE/CARB rules graduated the emissions limits downward.

* 1985 - Early (½ year)1985 2.8 MPFI and V-8 TPI used AC/Delco FM MAFs. The entire system couldn't perform to meet emissions standards due to use with older 8-bit ECM. AC/Delco rushed to upgrade the ECM to 16-bit and sharply curtailed or dropped all MAF R&D efforts.

The 1985 AC/Delco MAF generates a 5VDC square-wave output that is modulated in output frequency based upon the measured air flow. If measured with a voltmeter, the voltage will vary due to the RMS averaging of the meter and duty-cycling of the output. This would give the appearance of an analog output. If you use a true RMS DMM (like a Fluke 8026B), the voltage will remain steady at around 3.0-4.0 VDC. But the ECM input ignores the apparent voltage variation and counts the number of pulses directly, rather than converting them to "counts" internally. If the MAF output is checked with an oscilloscope, the waveform is a variable frequency square wave at about 50% duty cycle that peaks around 5VDC.

* 1985-1/2 - AC/Delco released new 16-bit ECM with internal A/D converters to accommodate purchased Bosch analog output MAFs.

The 1985-1/2-1989 Bosch MAF generates a variable voltage signal (analog 0-5VDC) that the ECM accepts and translates into a digital number of "counts" using an internal A-D converter. The MAF output voltage increases as the measured air flow increases. If the output signal is measured with an oscilloscope, the trace is a pure DC line that varies in voltage with sensor measurement. The Bosch MAF uses a open collector style pulldown transistor. If the circuit opens somewhere for 600mS then the voltage will instantly be pulled high.. The early versions had notorious solder failures.. Also any open in the wire connecting the MAF can cause an ECM error.

* 1985-1/2 through 1989 - all V-6 & V-8 used Bosch analog MAFs (0-5VDC output).

* Late 1989 (1990 Model Year) - All V-8 engines used speed-density fuel control and new ECM.

* 1989 - 3.8L Buick V-6 in Buick/Olds/Cadillac products (BOC Group) switched from analog Bosch to AC/Delco FM MAF on high-performance engines only. All other 3.8L and V-6 engines used speed-density systems.

* 1990 - 3.8L Buick V-6 in Chevrolet/Pontiac/Canada products (CPC) switched from analog Bosch to AC/Delco FM MAF on high-performance engines only. All other 3.8L and V-6 engines used speed-density systems.

1990 saw the and of MAF's and the beginning of speed-density systems on V-8 engines.

* 1992-1993 Hitachi was a partner with AC/Delco for SFI MAF design and development for OBDII cars.

1992 models brought back the MAF on LT1's, and it is also a FM output. The newer PCM's again have the A-D converter for most other analog sensors. This newer MAF can be used on older FM systems by using an external converter to create a digital output based upon the analog signal. The key is in the scaling and zero point of the output. The "MAF Translator" has already done the homework and scaled the output correctly for the older ECM's.

To find a translator, check http://www.ModernMusclecar.com or the Motorsport Technologies, Inc. Sites.

The GM P/N for a 1985 TPI MAF is 14081243. 1986-1989 use P/N 10055877 or 14094712, all years. I'm STILL confused...


The Present

* 1993-2001 cars have higher frequency output FM MAFs Produced by Delphi (former AC/Delco division) for use with the newer PCMs.

The Future

* 2002 - Delphi development for OBDIII systems is severly behind schedule, and Hitachi may once again be enlisted as a partner in design and development for the PCM and sensor devices. It is also possible that the Denso Division of Toyota (formerly Nippondenso) may be an ally in this design and supply the PCM and sensors for 2002 GM vehicles. GM already has a limited partnership with Toyota in California production facilities and some foreign marketing.

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

[This message has been edited by Vader (edited October 16, 2000).]

 

And then some.
Y'know, you may want to add to that nice little web site of yours. Yu do no justice to the almighty T/A, but I really like the fiero stuff. I think I'm hooked.
Now what in my wonderful world can I do to pass on my gratitude? You got looks (can't go wrong with black, nope, ya can't), stunning intellectual capacity (can't have the force without it), and almost limitless power (for a mortal). What else?

 

RD,

It's time to update the site a bit. The truck is wrinkled, the Fiero is wrinkled (both while parked) and the T/A needs a little more attention. The hockey team is older and slower, and the boat is in storage. The kids are older, and the older Impala has had a few changes since the last view. Coupled with a new job and "takin' care of bidness" at home just isn't as easy as it used to be.

Still, I'm finding time to sit here and bang the keys, AND play with that old ECM. Sooner or later...

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

 

Interesting... so my 3-wire frequency film MAF is a Bosch? The GM manual for '86 eludes to only the v8 hot-wire unit being Bosch... unless I misread your info.


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards

 

Tom,

I'm not sure of that one. The data I have was mostly for TPI V-8 ThirdGens and 'Y' bodies. I threw in the 231 Buick data due to the interest from the GN and TTA people. The 2.8 may well have continued to use the FM output MAF, as did many other GM V-6 vehicles during those years. If that's the case, consider yourself a pacesetter, since all GMs went back to FM MAF outputs by 1993.

Thanks for the clarification.

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

 

Okay, cool. Yeah the f-body 2.8's all used the orange 'frequency film' MAF's, not the hot-wires. However, I've noticed my dad's 2.8 A-body's MAF has 5 wires going to it.

'Fact, his car had a TSB out, taken care of by the previous owner. It covered replacement of the computer chip. From what someone told me, it seems the MAF's on those models acted flaky, and GM was replacing them all the time. They got sick of that, and released a chip that either ignored the MAF signal, or treated it differently.

Thanks for the "frequency film MAF" terminology (FM MAF)!


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards

 

When the MAF on my 86 2.8 took a dump, I went to a pick-n-pull and found a 2.8 buick or olds with a MAF that looked identical to mine except it had an elbow on it. A little creativity with a screwdriver got the elbow detached and what I was left with was a 100% carbon copy of the MAF on my camaro. I believe it was the 4 wire. I pulled the screens and installed it and it's been working just peachy.

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The IROC Homepage
<A HREF="http://www.rit.edu/~jli4307/camaro" TARGET=_blank>
View the restoration of an 85 IROC</A>
"I didn't know a bored out Ford could go so slow" -Shenandoah

 

Screens, as in plural? The '86 2.8 just has one screen, "before" the orange frequency film. Unless that was something used on the a-body cars, but all the junkyard'd 2.8 f-body cars I've seen have the 3-wire connector MAF. Hell of a mystery, eh?

And I guess I jinxed my dad's A-body, he got an MAF code this morning. Oops!


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards

 

Vader, just a thought, but why not package up your msg. and put it up as a tech article for future reference??