Can anyone clarify ODB1 MAF function...and PE? Example for discussion: Set MAF to 1V=11gms/sec, 2V=34gms/sec, 3V =78gms/sec and 4.8V [and higher] = 254gms/sec
I am eliminating LOTS of rows. I pick these for clarification.

Questions:

• Does a measurement of 1V from the "wire" in the MAF tell the ECM to deliver 11gm/sec via the injectors? And, the correspondingly higer amounts with more air flow?
• Does 254gms/sec represent 100% PW or something lower? Seems like 100% isn't something it should hit so maybe it figures the PW from injector size to deliver that amount?
• 254gms/sec must be the limit for the "cell(s)" that make the numeric calculation. Thought it's not 256, it's close enough to make sense in that regard.
• If 254 represents 100% fueling how could "PE Temp" and "PE RPM" add additional percentage [fuel] if it already "thinks" its at the limit?

Goal:
I'm considering a change in engine configuration with 100fwhp potential gain. Currently I'm at 370fwhp, looking to jump between 450 and 500fwhp (375-425rwhp). In doing so, I'd probably swap from a stock TB to an aftermarket 1000cfm unit. For example, that's 1 of 2 offered with an FFI intake. For it to "receive" unrestricted air "input", I'd think the MAF would need to be increase from 3" to 3.5" or 4" -- assuming Blowerworks still sells those units?

From this, you should be able to see why I need a refresher and complete understanding of the parms I'd need to change/convert MAF values in my BIN. Note: I COULD ask if it's a fairly straight conversion? Say...if a 4" is 50% bigger than a 3", would the values be multiplied by 1.5 in my current table -- as a starting point? I'm pretty sure Blowerworks offers some guidance, but I still like to know my challenges up front.

Thanks for any insight!

 

Greg,
The number in the MAF tables are grams of air the engine consumes per second not fuel, and 254 g/s is the largest number that the computer can read. PE is independent of the MAF reading, what happens in PE, is the MAF is reading 250 g/s and the computer then adds in an additional 15% more fuel to move from stoich fueling of 14.7 lbs of air per 1 lb of fuel to the commanded PE air fuel number of lets say 12.5 to 1. Once you max what the MAF can read, no more additional fuel will be added and as the engine airflow keeps going higher the car will get progressively leaner. To deal with this there are tables in the program that allow you to add additional fuel based on RPM so if the car engine runs lean you can force the computer to add in additional fuel. This is sort of crude but can be made to work OK in most situations but has it limitations.

 

Interesting. My first thought was the MAF would measure air...but grams/sec seemed more likely to be a measurement of fuel -- for any given VOLUME of air. Yeah...air has weight but it didn't seem intuitive that gms/sec was an air measurement. Plus, the ability to adjust how much fuel per specific reading of the MAF made more sense to provide the ability to set mixture before allowing the O2 to enrich/enlean that "base" tune.

 

If you are modifying to try and achieve 450 ho then throw out the prom chip. Of course you could use it but it’s not anywhere ideal. You could go to a programmable ECM, they range in price depending on which one you get. I am using a Holley HP mine. The cool thing about the Holley is you can go coil per cylinder as well.

 

Thinking a bit more....So you're probably saying when the MAF measures say....14.7 gms/sec of air input, it would deliver 1 gram (or 1 gram / 8 cylinders) worth of fuel? Then, of course, when in PE, the ratio raises to get 12.5....or whatever's commanded.

On the limitation side, additional fuel can be added until the injectors go "static"....wide open.

I might see if I can find some very good, detailed comments on MAF systems posted by SuperL98 or Tequilaboy or ??? 12yrs ago. It was a great thread. Beyond that, I'm kinda curious (especially with the post above) what the 89 ECM limitations are? Probably depends a bit on injector size but I'm thinking SkiDwnIt hit 500HP IIRC. And, I think that might have been RWHP. My memory tells me he did it with 24# SVO injectors too? If I guessed, it was running an 85 Corvette -- one of the oddest and hardest to tune.

 

So I do have this data on the ECU. I have a new laptop though and my definition files are licensed. I will figure out how to get them loaded and I can tell you what the ceiling of the g/sec is. GM uses airflow to calculate everything so the g/sec is airflow, from there it will figure out fuel flow. The PE is just a mode the ECU is in during a certain TPS position. What you see is the A/F ratio it will change to say from a 14.7/1 to a 12.5/1 and you can change this to what every you want. It is just a calculation that to the ECM and it will add the appropriate amount of fuel to achieve that assuming the g/sec is correct. This is what you would use your W/B for and you would adjust the g/sec based on the feedback from the wideband. Now on his ECU for every change you have to reprogram the prom chip. If it is an original then you are 30 minutes in a UV eraser. If using a adapter to a 512 chip you can electronically erase which is much easier. However the ECM I was talking about earlier is called a EBL and it will remove the MAF and change the car over to a MAP system like the 90/91. This ECM can also receive direct input from a wideband and while it does not "self tune" it does create a new self tuned bin file that you can load each time you are out tuning the car. It will help get it close for you, but it is still best to fine tune yourself. The Holley will also turn it into a MAP system and it is just allot more elaborate and it will tune on the fly and self tune if you are not sure what you are doing.

 

Yeah...I'm using an adapter with a 512 chip. I feel like I learned how to adjust it fairly well but couldn't remember how it used/calcuated MAF data. I like the idea of something newer but can't say I'm pumped about $500 (or more) to convert -- on top of any physical conversion/wiring necessary. Can't hurt to hear the costs involved though.

BTW...254gms/sec is the highest the 89 BIN goes.

I'm thinking back to the first thing another member helped me with 13 yrs ago....Adjusting my descreened MAF tables. I ended up RAISING most of the values in each of the 7 MAF tables. If it JUST measures air, I wouldn't think that would be necessary from engine-to-engine. Yeah...air is more dense at sea level versus Denver but I'm at 100ft above sea level. I wouldn't expect much change (like I did) to be necessary. In fact, I gave me BIN to another builder creating a similar combo in 2010. The difference was he ran a MR vs my mega SLP TPI. It was PIG RICH in his car. That means I was (is) getting TONS more air. Last year, I swapped to another screened MAF which runs fine.

In short, I'm not sure why mine didn't also end up pig-rich. Air is air -- for the most part (setting aside barometric pressures). Almost makes me want to overlay original MAF values for an 89 to see what happens!

Back then (30k miles ago), I used narrow band feedback for MAF "tuning". This time, I want to install a wideband in my extra header bung.,.,. and be more precise.

 

Wideband is definitely the way to go. Narrow band just tells you if you're over or under 14.7 - good for tuning your cruising AFR but not much else, IMO. For what you want to do, you could grab that blowerworks MAF for sale in the classifieds. I think only 1 wire needs to me moved over the ECM connection and you're GTG with a new bin. The MAF and bin get rid of the 254gm/sec limit, and the MAF has a much higher range than the old TPI Bosch sensors.

I'm using the EBL, which is a modified factory ECM that converts you to speed density. As mentioned, the big advantage of the EBL over the blowerworks MAF is that wideband data is integrated into the data stream, and it will give you 'suggested' new VE tables based on the wideband data. Oh yeah, and it's flashable, so no chips. The wiring is more involved but still pretty easy - something like 5 wires moved around at the ECM and a MAP pigtail under the hood (I made a jumper so it's reversible, if desired).

MAF should not need adjustments for altitude, temperature, etc. because it's measuring the MASS (not volume) of air entering the engine. The mass is the mass and does not need to be corrected (as it does with speed density). Removing the screens from the old TPI MAF should not require changing the tables in theory, but it does impact how that airflow is being measured. There is more airflow in the center and less near the sides, and the screens were there to sort of equalize that center to outside flow differential (not for protection of the thin wire from mechanical damage; your air filter takes care of that).

With MAF, even though it's measuring air mass entering the engine, you can see differences required in the tables from engine to engine due to reversion. I think what happens, particularly at idle and low rpm, is that air moves across the MAF sensor in both directions, and a false higher airflow is registered making the ecm think the engine is under more load than it actually is. As a result, more fuel is added, and the engine runs pig rich. With big cams, you'll see this more with short-runner intakes than long as that air stack has farther to revert and gets dampened somewhat.

Disclaimer: That last paragraph is just my understanding and may not be based entirely on facts. I just took a stab at answering your question and thought it might spark more discussion.

 

Its easy to integrate a WBO2 signal into the datastream. See example log below. Its a medium injector (48 lb/hr) car with a mid-range 3500 kg/hr sensor on a Superflow dyno with WBO2 data included.

https://datazap.me/u/tequilaboy/test...ark=215-21-142

D1 Procharger without intercooler and custom tuning (triple range). As you can see, its about out of injector here, but the car does have water/methanol injection capability. I don't think the water/methanol was used during this pull. If so, it should have been considerably richer for my taste.

Data from the Superflow dyno itself:

https://datazap.me/u/tequilaboy/test...-3-5-6&mark=96

 

I'm not sure a 3" Blowerworks MAF (even if it's smooth) has huge advantage over stock 3" MAF. I get the stock Bosch has internal obstacles that impede flow. At least I descreened mine. I've even heard suggestions to remove EVERYTHING except the element OR even tranfer the "guts" to a larger PVC pipe (which someone in 3rd gen did). If I bought a Blowerworks MAF, I'd go at least 3.5" and maybe 4". (Assuming larger is always going to have lower pressure drops across the tube).

The EBL idea (conversion to SD) sounds like a good idea at a similar price point? It would take some time for me to learn speed density logic/tuning, but I'm sure I could get it...And, I like that it provides hints/suggestions.

It's probably exhaust vs engine that requires differences in tables from car to car but I like your theory how error might occur at the lowest rpms.....especially on short-runner engines.

Got any link(s) to EBL stuff?

 

I have to admit I'm no idea what I'm looking at (in either link). They look like AFR data though the scale isn't clear. Even if it was clear, I admit I can't determine how it helps me learn or see how to assure a 375-425rwhp "limit" is reachable using stock ECM...or if I'd need new hardware?

 

OK...So far, I've gotten that the stock 89 MAF (or ECM?) has a limit of reading 254gms/sec of air. Through additional reading, I see posts suggesting the stock setup can support 360-390rwhp...then a poster saying he's a hair above 400rwhp with stock equipment. Can't determine if that's with an aftermarket or DIY MAF housing though. I also see one suggested solution using an LS7 MAF -- as well as blowerworks MAFs. (BTW...No clue as to what SIZE is needed for what power levels).

I also THINK I'm reading that the stock BIN needs to be replaced to break said limits? AFAIK, everything I've done until now has only been the alteration of PARAMETERS in the BIN. In short, nothing to do with instructions...only changing values it reads (upon loading?) that get used by the stock BIN "logic". So....people are saying when a stock MAF is "outgrown" that a new BIN (meaning the logic part of our 89 "software" get's replaced?

I don't know if the 512 chips I burn/use include software to interpret BIN values...or if it's JUST the parms? If the software (instructions) need replacing, then I have to assume the need for a different or modified ECM?

I've also seen posts leading me to believe my stock ECM can be converted to SD by changing a few pinouts. And, if this is true (and/or easy enough) does it completely eliminate the ceiling on rwhp? Or...move it up considerably?

On a side note, I seem to remember member 0ski_dwn_it hitting 500hp with his 85 Corvette years ago -- using 24# SVO fuel injectors. And, that the reason he was able to do this is because batch fire enters "double fire" mode when demand is high enough. In doing so, fuel gets "injected" with every revolution of the crankshaft (vs every other revolution for the combustion stroke).

Overall, I'm trying to figure out how to accomplish the next step in addressing limits of the stock ECM/MAF? Before now, I pretty much understood all the "parms" though I wasn't sure if the MAF was calibrated to send appropriate fuel OR just "read" airflow. At least THAT question has been answered in this thread. I get it now...and Thank you!

 

Greg,
You need to replace the stock bin file with a modified bin file that will work with the blowerworks MAF and you need a modified tuning program to then tune the car. You also need to repin the wiring harness. I have a 4" blowerworks MAF and the modified bin and program. You could get those items from Blowerworks if they are still around or from Tequilaboy.

As far as the double fire vs single fire that does not work as you are suggesting. Double fire only works at low RPM and light load and then it reverts back to single fire mode because single fire mode will supply more fuel then double fire mode, since you do not have to start and stop the injector and loss the injector open and close time from the total injector flow. Double fire does not allow you to make more power and double the amount of fuel that flows. A 24 lb injector that never shuts off can flow 24 lbs of fuel per hour at a BSFC of .4 which is quite lean a set of 8 can support 480 engine HP not wheel HP.

Someone telling you they can run 500 HP at the tires on 24 lb injectors is probably confused.

24/.4 x.8 x 8 = 384 HP at the engine with 24 lb injectors. assuming 100% duty cycle gets you to 480 engine HP but you should size injectors at 80% to be safe and provide some head room.

 

I'm not talking about 24# "GM injectors". I'm talking about 24# FORD SVO intectors which flow 25.5# in a GM fuel rail and at least 27# with an AFPR raising it a bit more. That's what ski_dwn_it had in his 85. I'm 99% sure he pumped them up with more fuel pressure. @ 27 pound "performance", it sounds like your saying 432fwhp at 80% pw...up to 540fwhp at 100%. At 100% duty cycle, you're saying the injector never really closes?

So...if he claimed 500hp...maybe he was measuring it at the flywheel?

If I tried hard enough, I might be able to find a thread on it...from 12-13yrs ago. I think his actually name is Jessie Azzado (or something like that). In case that rings a bell.

 

You are changing the givens, it is no longer a 24lb injector if you run at higher pressure or different ratings, 24lbs means 24 not raise pressure and use a lower rated injector. Gm rates injector flow for the tpi at 3 bar.

 

If my injectors flow 25.5# at 43.5psi, and probably 27# around 50psi, what would you estimate they'd support? I'm seeing something like 420rwhp? What's the highest FP that's stable with an AFPR on an 89 Corvette fuel rail?

At what point do you think a large MAF (e.g., Blowerworks) is warranted? This post from Orr89rocZ suggests 400rwhp is still possible with stock equipment and even that he didn't see any difference with a MAF conversion (sort of hard to believe). With PE required above 4500rpms, is that a "problem" or perfectly OK? I'm going to assume someone will say it's not ideal -- so I'm curious what AND WHERE (HP level) does aftermarket applications prove beneficial? I'm thinking someone suggested above 300rwhp 2-3 yrs ago. If 400rwhp is possible (or maybe more), my question revolves around what they are/where missing by not abandoning the stock GM equipment above 300rwhp?

 

MAF GM computer is maxed around 500chp (will be hard to tune-likely won’t be optimized). If you want more power then that you have to go with SD and a stand alone system. An Accel system is cheap these days as it’s archaic but it will work. I used a FAST Classic system for my 421 and I was able to tune it in the car or siting at my kitchen table.

The quick C4’s back in the day typically ran SD with an Accel or a FAST(classic) firing all cylinders. These days are in my rear view mirror but fun at the time none the less’

Put a miniram on (and a cam suitable) and it will be an entirely different beast! You will forget all about the long runners trust me!

I realize that you were married to that intake but it really holds any engine back that’s bigger than 305 cubes and even that it holds it back.

Ah the good ole days! I will be purchasing another C4 however the C6 Z06 won’t be sold. It really is the complete package-love it……

But always a soft spot for the C4’s! 👍🏼

 

-Greg with 27 lb injectors you could support around 400 to 420 RWHP. This assumes a BSFC of .4 which is actually pretty good and may not happen and a injector duty cycle of 90%.
-The fuel pressure being stable is all related to your pump, if you have the correct pump it will be stable.
-The stock MAF sensor will be out of range at 254 g/s at around 350 engine HP, that means all additional fueling will need to be added by the RPM vs fuel adder table. (The MAF will not be able to detect any additional airflow)
-Sure you can run 400 RWHP with a stock MAF but as explained the fueling will no longer be controlled by the additional airflow seen by the MAF but instead by the RPM vs fuel adder table
-The point of the 3" blowerworks MAF is to allow you to read the actual air entering the engine and have accurate fueling across the entire RPM range
-The only way to know if your 3" MAF (even a blowerworks MAF) is holding you back is to see how much intake vacuum you have at WOT. If the entire air intake system shows an intake reading of 95 KPA or less at WOT I consider that fairly restrictive. (My 3" system on my 434 CID reads 88 KPA at WOT which is terrible, this car makes around 400 RWHP and would benefit greatly from a 4" system) Just have not got around to building it yet.

I do have a 4" blowerworks MAF laying around and may consider selling it. You still need to get the correct definition file on your laptop to tune the car and the correct bin file. You could use my bin as a start point but the definition file for tunerpro I do not have. (I use Tunercat). You may want to talk with the forum member I mentioned earlier he may be able to help you.

 

1986-1989 TPI MAF system limitations above 350 hp

Note: much of this is redundant to what has already been discussed above. Solutions are available. BSFC and injector %DC values were selected for convenience/consistency across both examples, but should be reasonable for this discussion.

Factory TPI MAF sensor limitations (1986-1989):

• Failure-prone Bosch sensor
• Potential flow restriction/pressure drop due to screens, heat sinks and housing diameter
• Limited sensing range
• Open element design is susceptible to reversion
• Temperature sensitive (not suitable for high inlet temperature and pressure)
• Calibration variation
• Sketchy replacement quality in the aftermarket

Factory fuel system limitations:

• Fuel injector capacity 23 lb/hr
• Fuel pressure regulator variation
• Fuel pump capacity

Converting fuel flow rate to power example: (23 lb/hr) * 8 injectors = 184 lb/hr fuel flow rate @ 100% DC or 158.24 lb/hr @ 86% DC. Factory injectors support
approximately 359 hp (assuming 86% DC and 0.44 BSFC).

Factory ECM software limitations:

• 255 gm/sec air flow range
• Calculated PW is mathematically limited at very rich target AFR settings limiting PE effectiveness. Sorry $6E users.
• DTC sensitivity (Codes 33, 34 and 36)
• Limited load range
• Random scanning/connectivity issues

Converting Mass air flow rate to power example: Based upon proportional fuel flow rate at 12.8:1 AFR: 255 gm/sec air * (60 sec/min) * (60 min/hr) * (1 kg/1000 gm) /
(12.8 AFR) * (2.20462 lb/kg) = 158.11 lb/hr mass fuel flow rate. ECM software supports approximately 359 hp @ 0.44 BSFC.

Factory ECM hardware limitations:

• Eprom/Memcal programming
• 8 bit A/D converter

 

Suggested solutions to the limitations noted above:

MAF sensor solutions:

• Use a modern and reliable sensor design such as an analog slot-style sensor.
• Choose a housing diameter appropriate for the application in order to minimize flow restriction/pressure drop
• Choose a sensor with appropriate sensing range for the application considering housing diameter
• Use a sensor that is robust with respect to reversion
• Use a sensor and housing that is suitable for high inlet temperature and pressure
• Use a sensor with a stable calibration
• Use a sensor that is readily available in the aftermarket

Fuel system solutions:

• Fuel injector capacity: Simply choose the correct injector for the application
• Fuel pressure regulator variation: Use an adjustable pressure regulator or tune for the car's known fuel pressure
• Fuel pump capacity: Simply choose the correct fuel pump for the application

Custom software solutions:

• Desired air flow range can be selected for the application
• PW calculation can be corrected to permit very rich target AFR settings, earlier cars can alternatively use bpw vs load table, but unnecessary with range extension
• DTC tuning can be adjusted to fit the application and hardware (Codes 33, 34 and 36)
• ​​​​​​Load range can be extended along with air flow range
• And more

ECM hardware solutions:

• Electronically erasable chips, adapters, and emulators are available to ease programming woes
• 8 bit A/D converter provides sufficient resolution for accurate fuel control. No solution is necessary.