[darkpuppet]

Hmm... I posted a question about the physical limits of the stock MAF... and after a lot of back-and-forth posts, SCT weighed in with their take on it:

Quote:FACT: The MAF WILL output voltage up to it;s operating voltage of 12V.

FACT: a divider circuit can and has worked before

FACT: the MAF curve is a 6th order polynomial (mostly) so the extra range can be calculated

FACT: The EEC can only handle 5V max input.

We will be marketing an extender at some point, I think

you can follow the thread here, or continue the discussion at this board.

very interesting information regardless.

[naz]

very nice info!

so that means

GIVEN: PCM can only handle 5V input
ASSUME: there is no extender on the market yet



GIVEN: there is no circuit between your bone stock MAF and your PCM with the SCT module

therefore, your MAF output signal must be less than 5V since that's all the PCM can handle and therefore you must not be flowing enough air for the stock MAF to output more than 5V

do you think that reasoning makes sense?

you really should get on the dyno and verify things... while you are there might be interesting to get your injector duty cycles and also splice into the MAF output wire and find out what is going on there to verify the hypothesis

[darkpuppet]

I think your reasoning makes sense.

I find it interesting that everyone views that 5V cutoff at the PCM as a hard ceiling, and that everything connecting to it runs the same.

The fact that the MAF can send a signal up to the full 12V sorta opens up other possibilities I think...which makes me wonder why this question wasn't asked before....

Regardless, I do agree that I need to hit a dyno... I've been dragging my ass, waiting for the colder sparkplugs to come in, but they should be in before next weekend, so I hope to get to a dyno no later than Thursday next week.

Might be a good chance to get some empirical evidence. :)

[naz]

darkpuppet,Mar 31 2004, 11:44 PM Wrote:I find it interesting that everyone views that 5V cutoff at the PCM as a hard ceiling, and that everything connecting to it runs the same.

The fact that the MAF can send a signal up to the full 12V sorta opens up other possibilities I think...which makes me wonder why this question wasn't asked before....

well.. isn't it sort of a hard ceiling though? maybe not a "stuff stops working after 5V" but for all intents and purposes it might as well

if the PCM tables only have values for up to 5V how are you going to control the engine properly when the MAF signal goes above 5V

you can build a circuit to apply a transfer function or use an interceptor thingy like those Apex-i SAFC but those still won't do load calculations for you, and therefore can't adjust the ignition timing properly. i don't completely understand the load calculation process but i do know that it takes more than just the MAF signal as an input.

and so now instead of just repopulating the PCM tables with different values, you need to use some device to rescale the MAF signal, and you still need to repopulate the PCM table with different values anyway, so you get the load calcs and other stuff right

i think that's why using a recalibrated MAF together with its appropriate flow bench test sheet is the 'prefered' way to go because you don't have to do 2 sets of calculations, only 1, and because you are using the PCM directly, you don't add possibility of failure by using another component..

IMHO bro, why don't you just pony up for the recalibrated cobra MAF, and go with the proven solution instead of being a pioneer and experiencing the crap that comes with that

if you can afford that bling bling headunit.. you can pony up $250usd for the MAF man...

[darkpuppet]

haha.. yeah, I'm not trying to do anything new or different. This question popped up just out of plain old curiosity... I wasn't planning on doing anything with the information except learn how everything works a bit more fully.

But knowing that the MAF goes higher in voltage, wouldn't you agree that instead of ponying up $250+ for a new MAF, a $30 connector would be nice... especially since you can apply the newly mapped (calibrated) values into a custom tune. It allows the possibility of knowing the flow characteristics with a $30 part if anyone ever bothered to take the time to test/market such a beast.

It would be like calibrating your MAF without spending hundreds of dollars to do it. So you can do your custom tuning for it, get a proper tune, etc. No extra tuning would be required outside what you'd normally do for a callibrated MAF.

By absolutely no means have I ever suggested that just a calibrated MAF and injectors are enough... anything I've proposed, I've taken a custom tune as a pre-requisite.

But I digress..that's not what I'm going to do, it's more to just satisfy my curiosity. Considering all the costs involved, I would be getting a calibrated Pro-M or Cobra MAF when I move to SCT. It's proven to work, and I can live with that.

To be honest, I would have probably ordered that stuff by now, if I wasn't still waiting for Steeda to get back to me....

But since then, I've had a good chat with EFF, and if I can solve my stumble problems safely (and get it dyno-approved) with the stock computer, I might hold off a bit, so I don't drive myself into the poor house (at least I can watch movies in my car when I get kicked out :P )...

[darkpuppet]

I know there was some talk before about which MAF is best to use with the SCT package.

from the mouths of SCT:

Quote:bela, a GT MAF should be plenty for you car anyway. For the Focus this isn't really a huge issue like it is for the V8s. For those you have to go to Pro-M or something, and those are different calibrations from MAF to MAF, making it real hard for us to send a mail order calibration that works right the first time. The Ford MAFs are very consistent from unit to unit, so we'd prefer to use one of those and extend it's range. Since a Lightning MAF is good up to about 450rwhp you should be able to find a Ford MAF for 4 banger use

If the car will be dyno tuned then the Pro-M option is also perfectly viable. They are good MAFs and are consistent from run to run, just not between MAFs.

looks like Ford MAFs are preferred for their consistency, while a Pro-M will suffice for dyno tuning.

[naz]

if you got your stock MAF flow bench tested and you know the CFM of air for all the output values and you made your own circuit so you knew exactly what the transfer function was.. then yes i agree it would be a lot cheaper than getting a recalibrated MAF

but i'm thinking.. what is the cost of getting the MAF flow benched.. and you also get some performance gain from getting the larger diameter MAF too.. so that should be factored into the cost equation

as for that ford MAF v. proM MAF.. i'm not so sure its a big deal.. if you have a flow bench test sheet for both then what is the difference? i think its more like.. we already have flow bench sheets for the standard ford MAFs and we don't want to do any more work recalculating anything

on an off topic note.. proM wants to know what size injectors you are going to be using with the MAF.. and that seems to affect how they calibrate it. no clue how or why though. i'm thinking that gives them a rough idea of your HP needs so they scale the airflow into the 0-5V range properly

i thought you got all your gear for free man? what's the deal.. spending $$ to fix up mistakes they made and stuff? or are you just bitten hard by the mod bug and upgrading everything all in one shot :)

[darkpuppet]

there are bugs I want to fix,

Things that would work just fine, but I want to make better (ie, SCT and upgraded MAF, IAT instead of autologic),

and things that are just frivolous personal taste issues (ie headunit).

I wish I got everything for free, but I can't complain of what I did get for free :P.. I'm on my own now, and with such a headstart, it's hard doing just one thing at a time...

I still need a better exhaust, and if possible, new wheels (or at least rubber)

[naz]

on a side note.. i wish more guys like boost til boost or berinG or P51 or Jay would weigh in on threads like this.......

or else i might as well talk to you on ICQ steve hahaha

btw.. check your pm bro

[darkpuppet]

naz,Apr 1 2004, 08:07 PM Wrote:on a side note.. i wish more guys like boost til boost or berinG or P51 or Jay would weigh in on threads like this.......

or else i might as well talk to you on ICQ steve hahaha

btw.. check your pm bro

got the PM.. and right back at ya... (and thanks for the offer btw, I'll keep it in mind as I shop around)...

As for the other guys, you're totally right. I'm a sucker for tech, and am always looking forward to their next posts..but they never come :(

p51 did post in the [fj] thread about the question.. wasn't the most serious post I've read tho.. :P

[funny_canuck]

What type of signal is being sent from the MAF to the PCM?

If it's digital then the reason for max 5V should be obvious, considering the PCM likely uses something like TTL logic. YES, with TTL inputs higher then 5V will work but they will not do anything more. TTL devices have a tolerance and differnet voltage ranges reperesent the inputs.

I've never metered the outputs form the MAF but if they are digital then increasing voltage beyond 5 V will be useless. Varying the frequency/ pulse width would be a differnet issue.

Increasing the voltage could also have the reverse effect when you look at what is happening at the receive end of the PCM. If the input voltage is higher then designed for the electronic components in the PCM could heat up. HEat in electronics = bad performance, more power loss and ineffciencies.

Just my $0.02 on a few other things to consider.

If someone is serious about doing this sort of modification they should be looking at more then whether or not something physically burns out o doesn't turn on at a higher voltage.

[darkpuppet]

funny_canuck,Apr 1 2004, 10:49 PM Wrote:What type of signal is being sent from the MAF to the PCM?

If it's digital then the reason for max 5V should be obvious, considering the PCM likely uses something like TTL logic. YES, with TTL inputs higher then 5V will work but they will not do anything more. TTL devices have a tolerance and differnet voltage ranges reperesent the inputs.

I've never metered the outputs form the MAF but if they are digital then increasing voltage beyond 5 V will be useless. Varying the frequency/ pulse width would be a differnet issue.

Increasing the voltage could also have the reverse effect when you look at what is happening at the receive end of the PCM. If the input voltage is higher then designed for the electronic components in the PCM could heat up. HEat in electronics = bad performance, more power loss and ineffciencies.

Just my $0.02 on a few other things to consider.

If someone is serious about doing this sort of modification they should be looking at more then whether or not something physically burns out o doesn't turn on at a higher voltage.

the 5V cutoff is a limitation of the PCM, and the digital/analog converter that feeds it.

The PCM tables only hold values up to about 4.76V (apparently), with 30 spots in the table, and the last spot being 15V, which is considered an infinite value (15V is definitely higher than the system voltage while the car is running).

that, and the digital/analog converter will only allow up to 5V before it clips the signal from the sounds of things, so there's another limitation.

The MAF itself is capable of 12V max.. it's an analog cicuit, that appears to incorporate a thermoresistor, wheatstone bridge, etc to make it run (all analog).

What this means is that it is theoretically possible to make a divider circuit to basically 'calibrate' te stock MAF so that anything over 5V is translated below 5V, and then you can get your custom tuned solution to plot the extra airflow in the MAF translation tables.

The trick is to create a MAF translator to cut the voltage, and to translate that 6th degree polynomial function of the MAF sensor to the increased airflows so you can enter the proper information into the MAF translation tables.

In short, the MAF probably won't burn out at higher airflows, it's just a matter to get the signal below 5V so your custom tune can pull values out of the translation tables.

or something like that :P