Jim85IROC

iTrader: (2)

I want to start getting some in-depth information on MAF's, specifically the TPI units. The MAF on my GTA is tanked and the parts store wants over $250 for a new one. For now I'm going to grab a used one, but I want to start investigating other options (besides converting to speed density).

Basically all I know about the MAFs is that it measures the mass of the air by the amount of current it takes to keep a heated wire at a specific temperature. Does anybody care to share with me how other styles work? I believe that the V6 MAFs (such as the one on my 2.8 and many other GM cars) works in a somewhat different manner. I have no idea how the LT1 and LS1 units work. I'd like to find out though.

Next. I've heard that a certain porsche MAF will work on the TPI cars, but due to its insane cost, nobody is running it. This made me think though. Bosch is making MAFs for all sorts of cars from Porches to Volvos. Some of these have got to work the same as ours. Bosch had a very large hand in the majority of the early mpfi systems regardless of car make/model, so there has to be a lot of simularity between our MAF and other units.

If anybody can point me to some good MAF resources, I'd appreciate it. I'm hell-bent on figuring out how these work because there are a few experiments I want to do:

1. Find a different MAF to use on my car. Those used Volvo jobs sell cheaply on Ebay.
2. Retrofit a newer style MAF to work. This would open the doors for all sorts of good stuff to happen, but I looked into this briefly in the past with the LT1 units and recall that neither their operation nor signals were anything alike, but hopefully there's a different model's MAF out there that can be worked on
3. Run a pair of MAFs. This will help overcome their flow limitations. I know I can make this work with a simple op-amp circuit, but I need the time and resources to experiment.

Anyway, if anybody has some real good in-depth information, I'd love to hear it. Thanks!

Z28DJP1987

Buy a new Well's Maf that flows 750 cfm for about $180. And get
rid of the hot wire system. Check with Wells Mfg customer service
for a sales location. Also do a seach on this subject.

smokin87iroc

on the flow problem.
my question is can you not run 2 tubes in parallel one with the MAF and one without and say that the flow that the maf is picking up is actually twice what it reads and then adjust accordingly in the prom. so that when you run boost or nitrous you can overcome the 255 g/s limitations?
Andrew

Jim85IROC

iTrader: (2)

Well... so far from what I've uncovered it seems that the 255g/s limitation is shared both by the MAF output and the ECM's input. Even if you had a MAF that could output more than that, the ECM wouldn't know what to do with it.

Here's another question: It seems that the 85s ran a more reliable digital unit instead of the Bosch piece (This explains why my 85 is still on its original MAF). Now... I wonder what would happen with a Grand National MAF that could handle up to 510g/s. Too bad the computer still couldn't handle more. I thought about running the GN computer, but it's sequential-fire, so I couldn't just piggy-back 2 more injector plugs and expect it to work.

88TPI406GTA

My suggestion is exactly what Smokin87 suggested. My father is an electrical engineer and works with sensor inputs all the time.

Here is what it would be. Simply have an air filter, then branch the air inlet into two tubes with two MAF sensors...one is the active one and the other is not used (electronically) but is merely there to have ensure the same airflow as the functional one and then join the tubes back together again before the TB.

Then go in and modify the MAF scalar tables so that 255 gm/sec is now 128 gm/sec...effectively halve the signal from the MAF that is plugged in. So what would happen is that you would never have to worry about exceeding the 255 gm/sec limit of the MAF sensor...now when it was reading 255, the airflow would be double that or 510 gm/sec. There would be no circuit needed to mod the signal from the MAF sensor as the interpretation of the sensor counts would be done in the MAF table. It still would be reading the airflow, but only half of it...that is the reason for having another dummy sensor, to ensure it pulled EXACTLY the same amount of air through the other tube.

The downside to this is that the "resolution" of the sensor would be a bit grainier and each "step" in the sensor counts would be not as fine...but it still should be able to run effectively. One is effictively scaling the input from the sensor. This is what the stock tables do anyway, so this concept isn't anything too radical.

I hope this is making sense to others as well. I am sure that one would have to also tweak the fuel tables and the LV8 tables as well to compensate for twice the air flow.

If anyone has a reason why this WOULDN"T work, please state it...This is theory, of course, but it could work if you adjusted the tables accordingly. The downside is that one would need to tweak each table accordingly and that would take some time. I am not ready to go MAP yet

Guest

The 85 MAF was far from more reliable as the later units, and required an expensive (and somewhat failure prone) MAF module to operate. The MAF used on 85's was a Bosch unit as well, so theres no difference in the brand either. If yours is different, someone changed it somewhere along the line.

Jim85IROC

iTrader: (2)

I was under the impression that you could use the newer style MAF in the 85s with no problem, and I've also seen Mike Davis' site where he ran the 165 ECM with the stock 165 MAF burnoff relay setup on his original 85 MAF. The expensive Burnoff module doesn't seem to need to go along with the 85 MAF. All that crap got rolled into the 165 ECM except for the relay.

88TPI406GTA

So...what about evaluating the validity of my theory? :>

This, I think, would be the only way to do it as retrofitting a newer MAF wouldn't work due to differing signal types, as well as the computer not knowing what to do with the signal larger than 255 gm/sec...

I await responses...

Matt87GTA

Well, I like your idea Adam, but I am not so sure you can just half the scaler tables and the rest will follow.... It may run, but I think more tweaking of things like the P/E tables will need to be worked over as well. You might well spend more time and $$$$ on getting it to work than setting up a SD setup would cost you.

But FYI, this 255 g/sec 'limit' is really not a limit. That's right folks!! Just because the sensor does not read above that g/sec doesn't mean the car will simply shut down... You still have control of the fuel up to 6400 rpm in a 165 ECM and if you don't have all of your timing in by the time you are maxing out the MAF, you either have something totally FUBAR'd, you have a HUGE engine (cubic inch wise), or you are turning some BIG TIME rpms and have an intake that will allow you to do so (pretty much not gonna happen for virtually all of us)..... So you really have full control of the engine up to 6400rpm. The table to use for the fuel up to 6400rpm is the 'P/E % change to Fuel/Air ratio vs RPM' in TunerCat..... It requires more tuning to get it to work correctly as the ECM won't be able to correct for MAF input, but it will work if you use this table to set the fuel all the way up to 6400rpm.

And if you get that Wells MAF (or do the poor man mods to the MAF sensor itself) you will flow more than enough air to support most small blocks.... I would guess that a 400 or larger (depending on intake setup) may well need more flow than a Wells SU-145 or modded Bosch MAF will allow if you spin it up above say 5500rpm, but if you spent the $$$$ and work on that kind of engine setup, swapping to a SD setup shouldn't be a big deal...... Bottom line is there are only a few out there with concrete reasons to worry about the limitations of the MAF sensor and maxing it out.

jwscab

to give some info to help answer the original question and maybe clear up some things or maybe confuse them....the original 85 bosch unit is apparently a voltage output proportional to airflow, that is ex)0 g/s=0V, 255g/s=5v. The 86-89 units were a frequency output proportional to airflow, 30 hz to 120hz or something like that. The newer vortec and lt1/ls1 units are also frequency output proportional to airflow, but much higher, like 1kHz to 12kHz, so they don't interchange. One other thing is a problem, as far as i can tell, is the frequency responses between the two later versions isn't linear, so adapting one to another isn't a plug and play, and would require remapping of the tables, for instance if you could make an adapter that directly rescales 30-120 hz to 1k to 12 khz, you would still need to rescale the tables to make them linear. Those who know more about this, is this correct?

88TPI406GTA

I agree with you Matt. I definitely know of Glenn's efforts in tuning the MAF setup with the built 383, and I have those tables saved somewhere too. That would probably take a bit less time than what I am proposing, but it would allow someone with higher HP to retain the MAF sensor.

Hypothetically, running a MAF sensor would be more accurate than running a MAP setup simply due to its ability to actually measure airflow. On my 406, I will probably hit the max gm/sec with my redline of about 5500.

This discussion is merely to see IF there is an option to keeping a high HP MAF setup, while having it accurately measure airflow. Changing the PE tables is still a manual way to do it and it would support a limited HP level. I am wondering if this would support a 575-600 HP engine WITH being able to measure/monitor MAF signals up to power limit, unlike what is available now.

That is really the key is to see how to get the ECM to react to the changing load/RPM/MAF signal dynamically, instead of just changing the PE table manually to compensate.

Greg '85 T/A

True. The '85 burnoff module does the same thing the two relays do with the '165. The difference is that the '85 unit accepts a serial signal from the ecm to control the burn-off cycle while the '165 burn-off relay has its own, discrete output. The MAF doesn't care which scheme your car has. I've plugged a MAF from an '89 car into mine and it worked fine.

RMK

Does anyone know the bst place to get one of these or another MAF on line????

Robert

ImportsRsloths

I really want to get a Well's maf to.... i remember the part # being (off the top of my head??!!?) SU-145 one more thing the wells i was told has a LIFETIME WARRANTY!!!

Jim85IROC

iTrader: (2)

I ordered a Wells on Friday.

Instead of replacing the ailing GTA sensor, I'm going to put it on the IROC and cross my fingers that the 85-style MAF works on the 88. I've been told that the newer ones will work on the 85, but no word on vise-versa. I think the guys that converted to the 165 ECM in their 85s kept using the same MAF, so hopefully it'll work.

ImportsRsloths

Where and HOW did you order a wells maf????

ImportsRsloths

Called em and they have them in stock!!!!

World Discounts
800-288-6728
Part # SU-145
$166.45

ImportsRsloths

Check out the sig!!!

grumpygreaseape

although delco has 3 part #'s for the mass air sensor i have freely interchanged all 3 numbers with the one on my 85 and have never had any comebacks or problems.the easiest way to diagnose a bad maf is the old bottom of the trouble tree "replace with known good unit" desperation plea from the engineers who put these things together. k.g.u. happens to be the one on my car. cuts down on the diagnostic time. works for me. unless someone can give a definative answer concerning the differences i gotta say different #'s-yes, different functionally -no. the different part #'s may even be related to mounting holes or the lack thereof and how it attaches to a particular chassis pontiacs and vettes and camaros all have a different mounting scheme some use bolts some use clips and some use clamps. two pennies :rockon:

Greg '85 T/A

That's what I've found. Some have the "nipples" on the base tapped for screws. (oops, I said nipples )

grumpygreaseape

nipples-huhuhhhahuhaunhhuh-beavis and bunghole laughter noises. he said nipples. seeya round




:rockon: :lala:

RMK

Butthead: Yeah....and we all know what nipples are attached too

Beavis: Yeah, Yeah...*****!!! *****!!! NNHHAAA

With regards to the MAF, I'll give them a call.
Thanks

Robert