I did a lot of searching and have seen this bantered about a lot, but I could not find how anyone has solved this problem.
I would like to increase the air flow in the ecm so that the 0-5volt signal represents about 0-350 grams/sec.

 

There isnt much point in 'solving' the problem... not unless you can post me up a log showing a maxed MAF reading at a fairly low RPM and even then its only at WOT you're having a problem, part throttle its not maxing it out.

 

The MAF sensor is being modified for a substantial increase in air flow, so it will have to be recalibrated. I would guess it will hit the 255 limit at about 3+ vdc. TIme will tell.

This will be used on an engine setup for about 500hp.

I take it from your comment you believe we will not reach the 255 g/s limit before the MAF sensor is no longer in use???

At what point is the MAF no longer used?? I have seen many post that claim it is not used in open loop. But I thought open loop only meant the O2 sensor was no longer used, but the MAF sensor was still used for load calculations to determine fuel demand. Can anyone confirm when the MAF is NOT used??

 

What you will end up with you'll have to tune the vs. RPM table to add fuel past the point where the MAF maxes out. I have not found this to be a problem going past that point. If you really wanted, you could rescale the tables and adjust injector flow rate accordingly to fool the ECM into reading past what is 255 gm/sec but then you run into the 'lost resolution' and LV8 (load variable) issues with doing that.

The stock MAF reports 255 somewhere other than 3V, so unless you modify the MAF electronics with something like what Granatelli did or use their MAF, it will not read 255 gm/sec at 3V. If the airflow across the MAF increases in a way that it doesnt read the extra air, like in an excessively large housing, it will still be looking for 4.5+V for 255 gm/sec at the ecm. Not sure what exactly you're up to though, so I'm just guessing here.

Someone posted up on the PROM board a nice chart of what a MAF does at WOT and where other things take over the fuel curve. Its not out of the realm of reality to have the fuel curve you want beyond what the MAF can read, the question that remains is do you want to do that? Its just another way of providing fuel, most people do not need the added capability at points where the MAF is reading max aside of adding fuel that can easily be taken care of elsewhere. Once you venture beyond that and really want/need more than adding some fuel, its time to ditch the MAF altogether IMO as the stock code just isnt friendly to make the type of change you're asking it to. You could change things to where you're essentially reading 512 gm/sec (but the ecm wont be able to tell you that) but as some have argued, the number of data points from 1-512 is the same as 1-255 and you've 'lost resolution'. I cant say thats such a big deal but the amount of work involved just isnt worth it if you ask me. If you're really set on fooling the ecm into 350 gm/sec (keep in mind it cant tell you anything other than 1-255, the 255 gm/sec-350 gm/sec is something you'll have on paper), look into rescaling the MAF tables on the PROM board and you'll find all the information you need on how to do that.

 

Thanks for the help. WIll look on the prom board for info.

Yes the MAF sensor is being modified. The stock sensor is being placed into a much larger housing, so the actual air flow per voltage reading would be much larger than the stock unit. Therefore I was hoping to recalibrate the ecm tables to match the characteristic of the modified MAF sensor configuration.

 

Many have tried that, few have succeeded. It doesn't increase in a linear type of way, or even in a percentage kind of way. It's..... well, go ask some guys about the zillion different things that have already been tried and failed. I have not tried.

Even modest changes like removing the heat sink fins and the screens can have an affect on the MAF calibration (usually it's fairly small, I've done this myself several times without a problem). Bigger changes cause bigger problems, from what I'm told.

FYI- On a ~400HP engine the stock, gutted, MAF was just about pegged against the 255 limit in the last 500 RPMs. At 500HP you're definitely going to have a mildly modified stock unit bury the pin at 255 (probably for the last couple thousand RPMs on the top end, I would think).

Aside from actually mapping out a custom MAF calibration table (which has been done but not easily!) you'll be doing that fuel enrichment vs. RPM table thing once you hit the 255 limit. That 255 limit can not be broken in the programming- they only give you 8 bits to describe the air flow and 255 is the highest number you can describe with 8 binary bits.

 

255 cant be broken but it doesnt mean much. 255 is just a number, the ecm doesnt know what it means until you tell it so... you just lie.

 

From looking at the code the 255 is not just a number. The ecm uses the table value and the table scalar to calulate g/s. Due to the way it is handled in the code there is a definite 255 g/s limit in ecm calculated values.

You are right Madmax in saying you should be able to lie to the ecm about the fueling to end up with the right a/f ratio, but then all the ecm calulated air and fuel values are incorrect and could lead to other problems.

I have done extentive searches and have not come up with anything where someone has been able to get the ecm to handle airflow values greater than 255g/s. Or if they have they have, they have chosen not shared the info. From looking at the code I have not been able to find a convenient way of rescaling the airflow values (short of a major code rewrite).

If I chose to go the route of faking the fueling to compensate for the added airflow, what is the best way to handle this?
- decrease the injector size in the ecm
- or recalibrate the MAF tables to match the reconfigured MAF sensor and use the PE vs RPM tables to get the correct a/f ratio above 255g/s

It seems to me the first method would be the easier, but I am sure there are problems with both.

Would appreciate comments from others as to which method will work best.

 

Your from Dyer?

I'm in Schererville :-)

Whaddup neighbor.

We have an entire NW Indiana/South Chicago Board here uner regionals.

Option #3 would be best bet.

Lie to the ecm as little as possible, the more you have "correct" the better fudging for the 255g/s limit is.

If everything is correct up to and including the 255 limit, you can guesstimate and accurately confirm it with a wideband 02.

That or dump it and convert to speed density. Not much $$ and easy enough to do.

later
Jeremy

 

Don't the LSX MAFs go to 512 G/s? I thought that's why the Buick community used them. Honestly, if the MAF maxes out on a '7148 (GN box) then they must be using some sort of Alpha-N configuration after that. The MAP sensor (1 bar) in a GN gets used by the boost gauge if the ECM has one, but does not run to the ECM. While it doesn't speak for garunteed reference to the TPI box, it would be a logical guess IMO, if someone could check the schematic of the engine harness in a manual then it would be confirmed. I guess where I'm going with this is that if you really want to keep the MAF (long story short go SD and don't look back IMHO) you may look into the MAF translator especially if you can recalibrate your own MAF tables.

 

Its all relative, the ecm is told what to convert its signal to, and thats the only limitation involved. If you want to put forth the effort to get around that, you can... its not impossible, however its not easy either. IMO its not worth the effort like I said before. Anyway, you'll see lots of banned user ID's and locked posts but start here

https://www.thirdgen.org/forums/tpi/...sec-limit.html

https://www.thirdgen.org/forums/diy-...uper-arap.html

Read this

https://www.thirdgen.org/forums/diy-...uestion-s.html

There's a bunch more. There is also some SERIOUS misinformation floating around in those posts and others so... try to not get confused. Only advice I can give on that is when you see people talking in absolutes, take their advice with a glass full of salt. I'll leave it at that or next thing you know this post will turn into a flamefest.

 

Sorry, but why not just go with MAP instead?

 

Stubborn?

 

Thanks for the info guys. From following some of the links it certainly seems this is a controversial subject. Certainly not looking to provoke problems here or flame anyone, but the differences of opinion are helpful to me in trying to determine how to attack this problem.

Hi Jeremy. Good to hear from a local. I have followed the NW Indiana Board some over the last year, just have not jumped in on the fun. My son and I spent more than a year and a half building the 91 Camaro. We tried to get it complete (well, never really complete) for thirdgen fest in Crete, but we did not make it. Took nearly 6 months on the ecm tune to get it ready for emmisions test and licence. Our next goal was the Ridgeway show, which we just made in time and was the first we had the camaro out. It was not really built as a show car (just a nice driver) but used these events to push us along to get it done. My son is back to college now so the camaro has not been driven much lately. Maybe I'll post a picture and introduce myself on the NW indiana board so you will know the car if you see it around.

Anyway, sorry guys for going off subject. Back to the project at hand. Just a little background. The questions about the MAF is actually for my nephews 89 Firebird Formula. It has a 383 ci, about 12.5:1 compr, Trickflow heads, Holly SteathRam, and quite a radical cam (I don't have the exact spec with me). He runs it strictly on 100+ racing fuel due to the comp ratio. He was shooting for about 500 hp with this build and from what I know about it I would think it is good for about 7000rpm. So you can see that air flow is a concern on this motor. Up until now it has been running with the stock TB and MAF. I have done only minor tuning on it for him to get the BLM and timing setup. In this config it idled and ran remarkable well.

He is in the process of changing to a 58mm TB and is molding the MAF sensor into I believe a 4" tube. Hence the interest in how to setup the MAF.

In response to those suggesting changing to SD/map, I think this would be an extremely tough engine to tune using SD since the cam is so radical and produces very little vacuum. From my experience with tuning idle, AE, and PE on the 91 camaro TBI system ( which has much less cam) I just believe this engine will be nearly impossible to tame using MAP.

 

Whats the cam specs?

I sorta kinda agree. MAP is a littel harder to tune a big cam, and closed loop might make the car run worse, but I absolutely HATE the way the OEM does the maf tables. It's just dumb.

-- Joe

 

LOL @ just dumb. Good choice of words.

Might want to read up on the OBDII thread down below this one somewhere. Running a late model MAF system, although far from an easy swap from what I read, will get rid of that pesky tiny MAF and 255 problem all at once.

 

Anesthes, I don't have the cam spec's. I'll have to ask my nephew the next time I see him.
Are you running SD or MAF?? What have you run into with tuning your setup?

 

I'm running speed density with a '730 ecm. My cam is a cc-306 cam which is not huge (230/244, .510/.540, 112lsa 110ctr) but it's rairly lumpy. I can run in closed loop, but I get surges here and there. I've played with the o2 constants but it really just likes running in open loop better. (why not, carbs work fine in open loop ).

I idle around 800rpm and about 11" of vac. I max the map sensor + vac gauge out at about 20% throttle (free flowing miniram with 58mm tb I guess?).

After figuring out the right amount of advance, how much ae the car needed, etc I got it dialed in pretty damn good. MAF might make it run a hair better in closed loop, but I prefer to tune map.

tpi_roc has a much bigger cam than me running map, but slightly higher compression (I think 11:1 vs my 10.1:1) which helps smooth the cam out a bit.

ski_dwn_it on corvetteforum ran a huge solid cam for a few years with MAF before he finally switched to MAP, and I think he's running a F.A.S.T ECM now. If you are dead set on using MAF you can contact him, or if you want to repin to speed density feel free to ask myself any questions.

-- Joe

 

The LT1 stuff is the bomb, but like you said the conversion sounds tricky.

-- Joe

 

Thanks for the info Anesthes, it is very helpful knowing what others have done. I guess I was not ready yet to make some of these compromises (that may not be the best word, sounds like a bad thing and I don't mean it that way) i.e. changing to SD and running open loop. But, with time I may well learn that this is the only practical way short of spending tons of time and money.

 

The biggest limitation with the '165 ecm(and '730 if it isn't fixed in the updated .bins) is the 6375rpm data stream limit on rpms. I shift at 6500-6600, but the aldl data stream stops and flatlines at 6375 so you don't know what's going on above that rpm. I think that's why some switch to the aftermarket ecm's.

My 383 miniram car maxes the maf at around 4500 rpms, but then you just add more fuel in the pe vs rpm table. My afr is 12.6:1 from the dyno wideband. The car runs fine in closed loop other than an idle blm of 160, where I can't fix a lean blm problem which I think has to do with overlap on the cam (107lsa) and my low compression(10.5:1). Open loop would be a better solution.

I can tell you from the seat of the pants dyno that a bigger maf will make more power. Don't have any solid evidence, but when the wells 750cfm maf was on the car it felt much faster thru the rpms compared to the stocker with no screens I have on it now. Airflow gm/s at idle used to be around 16-17 with the Wells maf, now they are around 14.5 at idle, so the aftermarket maf was sucking more air. I can't remember the cfm's on the stock maf(maybe 658?), someone correct me if I'm wrong.

I've emailed and called various places over the years but nobody was ever interested in making a larger maf sensor for a car that has been out of production since '89(maf-wise) so you kind of work with what you have or switch to something else. I would buy another wells maf, but I have the stuff to do the sd swap in the garage so it looks like I will be another maf-sd convert myself.

 

89gta383 when you used the 750cfm Wells MAF sensor what did you do to bring your BLMs bad in alignment or is the calibration of the Wells identical to the OEM?

Good luck on your change to SD. Let me know how things work out.

 

Before I had the radical cams that pinned the blm's at 160 (first one was 242-254 110lsa, 2nd is 230 107lsa) all I had to do was adjust the first 4 entries in the 1st maf table. Now it doesn't matter what I put in the 1st maf table, the blm's stay at 160 at idle. The car drives fine and the blms jump back to 128 once you give it throttle.

 

The easy way out is to use a late model MAF and a converter. Some minor tweaks to the code in the ECM, or some fiddling with the calibration will be all thats needed on the computer side. The resolution isnt that good due to the fact that its still an 8-bit system, but it does work fairly well.