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Discussion Starter #1
I heard you can read the output voltage of the maf with the SAFC2 right? If so, can you guys please "0" out your settings and please give me the voltage you are getting at idle?

The reason I ask is because I'm a 97 NA, and I plan on using a TT maf. Let's pretend that a TT car with TT maf will read 5.00 volts, I heard that an NA with TT maf will read less (i.e. 3.5??).

So can someone please do me a quick favor and check their voltage for me with the stock MAF and the SAFC2 "0-ed" out?
 

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If no one helps you, and you already have a TT maf, hook the TT maf up in line with your stock maf and idle your car. Give the TT maf power and ground, and measure its output voltage. It might be somewhat erratic at idle, but it'll give you some idea of what you're looking for. There are wiring diagrams on mkiv.com that'll tell you which wires on the MAF to hook up and which one to measure from.

Also, MAF sensor transfer functions are not linear by any means, and going from a smaller MAF to a bigger one won't simply shift the curve upwards. So if you see 1v from your MAF at idle, and .85v from the TT MAF at idle, adding 15% fuel across the board with an AFC or just using 15% larger injectors might not work too well. Just keep in mind that whatever you find out will be a very approximate baseline, and that tuning should be done carefully. The % difference should be considerably higher at high loads than it is at idle. If you have easy access to a dyno, maybe you could hook up the TT maf inline, and measure the voltage diff at higher loads too instead of just at idle.

Shiva
 

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My safc2 displays a percentage number for the air flow reading, not the actual voltage. I assume it reads 0% for 0 voltage and 100% for 5 volts. I can't find any way for it to display a voltage number. You could maybe split the signal and wire it to the O2 or knock input if they display voltage. I'd have to take a look at the manual since I don't have either of them hooked up. Take a look at the manual or you can download it from apexi if you don't have one and see what those other two funcctions display.
 

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Discussion Starter #5
Let's assume that the NA maf puts out a voltage of 1 at idle and the TT maf puts out 3 at idle. That makes it a 1:3 ratio (na to tt). So is it safe to assume that throughout the rpm range it'll still be 1:3?
 

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The TT should put out slightly less than the NA.... but in any case, no, it is not safe to assume that the ratio will be constant. At higher flows (higher pressure, higher RPM), the ratio will probably be higher, meaning

TT voltage @ 30lbs/min / NA voltage @ 30 lbs/min > TT voltage @ idle load / NA voltage @ idle load

Try what supra400hptt suggested if you have an AFC. Hook both MAFs up, hook the TT one to the TPS or o2 or whatever you can on the AFC, find a hill or better yet go to a dyno, and get some data to see what you're getting into.

Is this a common mod? What size injectors do they use, how does it work out

Shiva

michaelvanle said:
Let's assume that the NA maf puts out a voltage of 1 at idle and the TT maf puts out 3 at idle. That makes it a 1:3 ratio (na to tt). So is it safe to assume that throughout the rpm range it'll still be 1:3?
 

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The TT should put out slightly less than the NA.... but in any case, no, it is not safe to assume that the ratio will be constant. At higher flows (higher pressure, higher RPM), the ratio will probably be higher, meaning

TT voltage @ 30lbs/min / NA voltage @ 30 lbs/min > TT voltage @ idle load / NA voltage @ idle load

Try what supra400hptt suggested if you have an AFC. Hook both MAFs up, hook the TT one to the TPS or o2 or whatever you can on the AFC, find a hill or better yet go to a dyno, and get some data to see what you're getting into.

Is this a common mod? What size injectors do they use, how does it work out

Shiva

michaelvanle said:
Let's assume that the NA maf puts out a voltage of 1 at idle and the TT maf puts out 3 at idle. That makes it a 1:3 ratio (na to tt). So is it safe to assume that throughout the rpm range it'll still be 1:3?
 

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Discussion Starter #8
supra400hptt said:
My safc2 displays a percentage number for the air flow reading, not the actual voltage. I assume it reads 0% for 0 voltage and 100% for 5 volts. I can't find any way for it to display a voltage number. You could maybe split the signal and wire it to the O2 or knock input if they display voltage. I'd have to take a look at the manual since I don't have either of them hooked up. Take a look at the manual or you can download it from apexi if you don't have one and see what those other two funcctions display.

IC, so it reads in %. Would the NA maf have 5 volts too then, or would the NA have less than 5 since it is smaller than the TT maf?
 

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I don't know anything about the NA, but I would guess it's 0~5 volts. Most sensors are. I tried to dig up some info in the NA section for you but it looks like you've already posted in a lot of the MAF threads. Didn't you already try this last year? If you really need it, I can test the voltage at idle tomorrow when I get home from work.
 

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Discussion Starter #10
Yea I tried this last year. I thought it was linear until I was told it wasn't so I took it out. I didn't want to run it untuned. I guess I can dyno tune the TT maf, but only above 4000rpm. Anything below 4k I would have to guess.

I don't want to be running around too lean or too rich below 4k. And could you please test out the voltage or air for me with the SAFC2? I guess you would have to "0" out the SAFC, thanks.

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Originally I thought the TT maf would just be rated at 550cc's. And since I have 440cc's, I thought I would just richen the SAFC/SAFR 20% and everything would be cool (since the 440cc's (injectors) are 20% smaller than the 550cc (maf) ). I guess that's not how it works, so here I am trying to figure it out.

Like I mentioned, I guess I can only tune above 4000rpm, so anything from idle to 4000 I would have to "guess". So I just need to know a basic guideline and I'll set it at that.
 

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Ok, pure signal, no processing, 1.6V at start up and 1.5V after idle settles down. What I think you are going to have to do is put a meter on the output wire of the safc once you get TT MAF installed. Start the car and add or take out full while reading the voltage until you see about 1.5V from the safc to the ecu.

What you are trying to do is possible as long as the curves of both mafs are similar. I run 720cc with the maf, taking out 25% as a base, then do finer tuning at wot above 4K rpms.
 

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Discussion Starter #12
So, you were able to get a voltage signal then? Good, I'll compare that to mine when my SAFC comes (hopefully soon RYAN), lol.

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You seem to know a lot about electronics. According to mkiv.com we should set it to "hotwire", but my friend told me he ran "pressure" and it's better. I have an HKS SAFR right now, and I set it to "pressure" and there seems to be no side effects much. Can you tell me what's the diff?

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And can you give me the steps how to get the SAFC2 to display the voltage of the maf? I played with a friend of mine's SAFC, and it seems complicated.
 

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Oh yea, also there were 5 wires on the MAF harness. I was able to get a reading with a voltmeter using the middle one. No matter what I did, I still get a ~2.5volts reading on tehe na and tt maf, no matter how much I leaned/riched or the RPM I was at.
 

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I count the wires from front to back. On the TT the connector sits sort of like the cylinders of the engine. From the front of the car I consider the first wire #1 and the one furthest back towards the firewall wall #5. Wires 2 and 3 go to the intake air temperature sensor so don't mess with those. You want wire #4.

I measured the voltage directly with a digital volt meter. One trick I use is to get a sewing needle. When you test the wire, hold the sewing needle to the probe of the meter. Then press the sharp tip of the needle to the wire until you get a reading. This way you do minimum damage to the wire and insulation. As far as I know you can not use the safc to read maf voltage. Like I said, it gives you a %, not the actual voltage. You will need to use a meter.

I would leave the setting at hotwire rather than pressure. The reality of it is both sensors are 0~5V, close enough to work it seems, but I wouldn't complicate things until you have things set up and working the way you want. Then experiment.

A good majority of what I know comes from the factory service manual. It should be the first mod everyone buys. The rest of it is 6 yrs of experience and what I've learned from others.
 

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OK, I guess I should try the #4 wire. So you said that you got about 1.5volts right? But won't that mean that 1.5volts is set for 550cc's, so if I have 440cc's I should try to get the voltage to read 1.2v somehow?

I have an analog voltmeter and it's not the most exact one, it was a cheap 20 one. Can you tell me what's a good cheap digital voltmeter?
 

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I think it will be the opposite way. At 1.5V more air will be going through the TT maf than the NA maf at 1.5V. So I'd say you need to increase the voltage. I've got bigger injectors with the maf and take out fuel, you've got smaller injectors so you should have to add. You are dealing with a 25% difference between 550 and 440cc injectors. Keep in mine I've never tried this and don't know how the NA ecu is going to react. You're actually messing with one of the most critical sensors related to fueling. When you get it running, driveability will seem ok if it's rich. If it's lean, the car will stumble and hesitate.

I've always gotten my meters from radio shack and not had any problems. They are pretty cheap and serve my purpose.
 

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Another thing I was just thinking about. A lot depends on the fuel programming of the factory computer. Technically, you could have a TT size maf on the factory NA computer, and the computer be programmed to use that size maf and run perfect. It may not be a simple matter at changing the signal 25%, then again maybe it is. Still say you need a wideband :) I tried taking the hotwire part of my maf out of the sensor one time and putting it in a bigger pipe. Did not work well at all.
 

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The curve is not linear, especially down in the idle and low power portion, so trying the get a good tune with the SAFC or any other two-dimentional piggyback is going to be difficult. It might be impossible if the NA curve is very different. If it is the same curve shifted up, it should be possible to get it close.

good luck
 
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