# maf voltage clamp?



## vrSpoon95 (Jan 31, 2005)

is is possable to make a voltage clamp if so how i need one for my s/c vr i'm going to make a bigger maf housing or just use that clamp but i dont know how to make one any help please!!!


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## C2Motorsports (Nov 25, 2003)

*Re: maf voltage clamp? (vrSpoon95)*

Wanna just buy a larger MAF housing? We have them in stock....

chris
C2


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## DUB_4_LIFE (Aug 8, 2003)

*Re: maf voltage clamp? (vrSpoon95)*

what pulley are you running? and how much boost loss do you see with all that piping for the intercooler?


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## vrSpoon95 (Jan 31, 2005)

about 3 psi with the belt slipping a bit but will the larger maf housing stop the ecu from going into the retard mode from it going over 5v


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## JPLengineer (Jul 7, 2005)

*Re: (vrSpoon95)*

as far as I know, yes . .it does.
With a bigger housing, the air velocity will be less as it passes the MAF sensor. As it does, the MAF sensor will not will cool a much, and thus giving a lower output.
Put on a bigger MAF http://****************.com/smile/emthup.gif . . .if that doesn't work, THEN do a clap.
It can be done, and it is a simple circuit. If the larger MAF doesn't work, IM me and I can help you . ..


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## mechsoldier (Aug 14, 2004)

*Re: (JPLengineer)*

the clamp is just a 4.7v zener diode, you can find them at radio snack


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## AnotherA2VR6 (Jun 20, 2002)

*Re: maf voltage clamp? (vrSpoon95)*

The problem with a clamp is that you will not sense any airflow past a certain point so how does the ECU really know how much fuel to add? The best solution is to go with a larger MAF housing along with new software to take this change into account. This way you get a better/smoother running car that is consistent through various supported boost levels and weather variations.


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## mechsoldier (Aug 14, 2004)

*Re: maf voltage clamp? (AnotherA2VR6)*

Well maybe, but the dodge/dsm/honda/etc have been doing it forever.....this isn't REALLY a good argument because even with a bigger maf, you're going to throw off the readings at a lower RPMS.
For example, if 200 cfm used to put out 3 volts, with the bigger maf it could now put out 2.5, making the ECU think it's getting less air than it really is...


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## AnotherA2VR6 (Jun 20, 2002)

*Re: maf voltage clamp? (mechsoldier)*

Just because everyone else does it is it the best solution?
That's why you update the software to take into account the larger MAF housing. So in your example the axis point on the fuel table is shifted down due to the drop in velocity, (MAF output voltage drops), so you compensate by adding more fuel at this point, you basically re-tune to car to suit the new housing, shifting the table down. You might loose some resolution on the low end but you can make up for this by adjusting the table, etc.
If you clamp the voltage you cannot read changes in airflow above a certain point, it's the same thing as running off the last column in the table where you cannot get the proper amount of fuel you need. Changes in weather really affect how the car runs, rich one day, lean the next, there's no consistency.


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## JPLengineer (Jul 7, 2005)

*Re: (mechsoldier)*

I would think you'd want to clamp it right at 5.0V, so tat you can get the best possible accuacy.
You can also do it my saturating a mosfet, which is probably the best way, but a zener will work too.
The best way to do it is to get a large MAF man . .just do it this way, and you'll by happy . .


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## Corradovr6sc (Nov 8, 2002)

*Re: (JPLengineer)*

If you are obd1 with a hotwire maf you have no choice but to go for a voltage clamp. Split second sell them btw.


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## mechsoldier (Aug 14, 2004)

*Re: (JPLengineer)*


_Quote, originally posted by *JPLengineer* »_I would think you'd want to clamp it right at 5.0V, so tat you can get the best possible accuacy.


You don't want a 5v, most systems are setup so that they never go over 4.7, if it GOES over that then the computer may throw up a code for maf overvoltage. I have NEVER heard of somebody using a 5v.
Anyways, he didn't ASK what the best choice was, he asked about zener diodes....This WHOLE forum is full of people who have these theories about **** and are DETERMINED to get people to spend money when they don't need to. 
How much is a zener diode? a couple bucks? Run the ****ing thing and THEN if that doesn't work spend your money.


_Modified by mechsoldier at 11:24 AM 2-7-2006_


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## AnotherA2VR6 (Jun 20, 2002)

*Re: (Corradovr6sc)*

That could be a problem, but possibly not.
First I heard of someone who had made or found a large MAF housing for a hot wire MAF.
Second I believe it's possible to retrofit a late style, (MK3 VR6), MAF into the hot wire MAF cars. This would require software changes as well as testing to make sure this will work, (i.e. does not having the burn off wire connected affect anything?)


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## mechsoldier (Aug 14, 2004)

*Re: (AnotherA2VR6)*


_Quote, originally posted by *AnotherA2VR6* »_ (i.e. does not having the burn off wire connected affect anything?)

Yes, it will get dirty and the readings will start to vary.


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## AnotherA2VR6 (Jun 20, 2002)

*Re: (mechsoldier)*

He asked about both.
I think we are just pointing out the positives and negatives about each possible option. 
You're free to run whatever you want, but should people not give opinions? Isn't this how things get discovered, by people trying things and not just following the norm? Besides the large MAF housing option has been used and is shown to be very effective, and in my opinion, is the best choice for the reasons I've stated.
What are your reasons for recommending a clamp? Is it just possible $ spent? I want to understand where you are coming from and I don't want any opinions to not be stated.


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## AnotherA2VR6 (Jun 20, 2002)

*Re: (mechsoldier)*


_Quote, originally posted by *mechsoldier* »_
Yes, it will get dirty and the readings will start to vary.

The hot wire MAF needs the burn off, not the MK3 style MAF which would be retrofitted in. The MK3 hot film MAF does not need a burn off period.


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## mechsoldier (Aug 14, 2004)

*Re: (AnotherA2VR6)*

ahh I had it backwards.....The burn off only operates for a few seconds, you may need to run a resistor inline with it to trick the computer if the ecu is advanced enough.


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## vrSpoon95 (Jan 31, 2005)

ok i got a 4" peice of pipe (ya ya getto) and installed it by drillng a hole and installing the MAF sensor into it i drove the car a bit the first time i started it up it ran good air/fuel and so fourth. but the second time i started it it run super rich i got to drive it more tomorrow well see i also thing i'm going ot take off the EGR valve also i read that it helps if you install some diodes.....


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## ArcticFox (Nov 4, 2005)

*Re: (vrSpoon95)*

Home Depot Motorsports http://****************.com/smile/emthup.gif http://****************.com/smile/emthup.gif http://****************.com/smile/emthup.gif http://****************.com/smile/emthup.gif http://****************.com/smile/emthup.gif 

_Quote, originally posted by *vrSpoon95* »_ok i got a 4" peice of pipe (ya ya getto) and installed it by drillng a hole and installing the MAF sensor into it i drove the car a bit the first time i started it up it ran good air/fuel and so fourth. but the second time i started it it run super rich i got to drive it more tomorrow well see i also thing i'm going ot take off the EGR valve also i read that it helps if you install some diodes.....


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## vrSpoon95 (Jan 31, 2005)

i'd spend 10$ instead of 100 for a thing that might work


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## JPLengineer (Jul 7, 2005)

*Re: (mechsoldier)*

I didn't know the max was 4.7V.
If so, that is sort a poor design b/c that kill ADC resolution when you're 
0.3/5 = 6% more of a signal, which in a way means 6% more fuel.


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## darkVR6 (Feb 11, 2005)

*Re: (JPLengineer)*


_Quote, originally posted by *JPLengineer* »_I didn't know the max was 4.7V.
If so, that is sort a poor design b/c that kill ADC resolution when you're 
0.3/5 = 6% more of a signal, which in a way means 6% more fuel.

It only says the FSV (Full Scale Voltage) is at 4.7 Volts = max airflow. This allows for 16 states of leeway (assuming 8 bit ADC) to detect a bad sensor in case of voltage fluctuations...this is GOOD fault tolerant design. I bet if you remove the MAF, the signal line is pulled up to 5V, so if no sensor is present it will default to limp mode as well.
It also makes sense as 16 is 0x10 or 10 base 16, so the software would say something like 
while (MAF > 0xEF){
LimpMode():
}

Makes sense.....
Anyone else verify that when the ECU reads 4.7V (or 0xEF or greater) the ECU trips the limp mode? I am desinging a cheap solution that will maximise the quantization levels available for MAF sensing.....
Someone could do a test by removing the signal line and putting a voltage divided pot on there to slowly increase the voltage...then see where it limps out at. I am guessing to detect limp mode, you have to be running at WOT though, so I think it would take a co-pilot as well.
Anyone else know the EXACT voltage for limp mode turn on for the MAF output? Also, anyone have the pinout or wiring diagram for the MAF in a MKIV?



_Modified by darkVR6 at 3:31 PM 2-8-2006_


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## JPLengineer (Jul 7, 2005)

*Re: (darkVR6)*

WOW, 
that was a good post my friend . .
I didn't know that they used an 8-bit ADC, I figured they would use a 10-bit.
I also never knew about the limp mode engauging in if it goes over a certain amount . [email protected] were talking about that a few night ago . . about ECU cutting back do to quick signal rise rates due to turbo kick-in . .
GOOD POST 
PS: It is obvious which computer language you use










_Modified by JPLengineer at 4:03 PM 2-8-2006_


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## darkVR6 (Feb 11, 2005)

*Re: (JPLengineer)*

Hey, thanks
But these are all assumptions....not sure if it is a 8bit or a 10bit...8 bit is the norm in most microcontroller nowadays...but it could be 10 bit.
I would still like to get my hands on the pinout for the wiring harness and the limp mode trigger voltage....Its got to be less than 5V for sure.....almost all automotive systems are 5V due to the fault tolerant design parts are speced at this voltage.


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## mechsoldier (Aug 14, 2004)

*Re: (darkVR6)*

I don't think it will trigger limp mode, it'll just throw up a fault code. If it was in limp mode it'd redline at like 4k RPM and run pig rich after that. I think it may go to default table values though.
Anyway, you don't have to be at WOT to trigger a limpmode


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## darkVR6 (Feb 11, 2005)

*Re: (mechsoldier)*

IF it doesn't trigger limp mode, then what happens at MAF > 5V ? Why does it not run right? It might go in limp mode, but only temperally....
NOt sure though....anyone?


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## JPLengineer (Jul 7, 2005)

*Re: (mechsoldier)*

I just got the new version of the C2 stage 2 fuel kit for FI.
But the first version was brand new, and it had that problem, my motor would jerk right at 4K rpms or so . .which was caused by the turbo kicking in, and seeing just a huge increase . .just cut back violently.
but he fixed it, and now the software is great


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## darkVR6 (Feb 11, 2005)

*Re: (JPLengineer)*

I am thinking a capacitor on the signal line my fix that problem.


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