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  #1  
Old 05-09-2008, 10:32 PM
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m104 airflow meter change help (wiring)

hey
in my c280 with m104 i want to change my airflow meter to a larger one, because im running out of voltage with my turbo.
i have a nissan one which should be big enough but it is only a 3 wire one and the stock one is a 4 wire one,
what are the 4 wires for? does anyone have a wiring diagram?
cheers
i saw a few other wiring diagrams for these around the forum but each one was diferent and i wanted to confirm with my one.

my new airflow meter has ignition, earth and signal (0-5v) output

VIN WDB2020282F068665

Last edited by c280nz; 05-10-2008 at 02:08 AM.
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  #2  
Old 05-10-2008, 11:57 AM
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IF I were you.... I wouldn't try to use a 3-wire sensor. I would locate a larger 4-wire sensor, or better yet.... pull your 4-wire insert out of its housing and make a larger housing for it. That way you can experiment with different diameters and get it dialed in for your application. After all the difference between Mercedes flow sensors is the size of it's housing, they share the same insert. As long as you have a method of matching fuel delivery to the new signal you will be golden. Remember that with a larger housing you will read less air flow than before and will have a smaller pulsewidth, which will allow you to run a higher fuel pressure or higher flow injectors (or both). Combined this will give you a larger window on the top end, which is where I assume you are running out of voltage.
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  #3  
Old 05-10-2008, 08:12 PM
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Quote:
Originally Posted by duxthe1 View Post
IF I were you.... I wouldn't try to use a 3-wire sensor. I would locate a larger 4-wire sensor, or better yet.... pull your 4-wire insert out of its housing and make a larger housing for it. That way you can experiment with different diameters and get it dialed in for your application. After all the difference between Mercedes flow sensors is the size of it's housing, they share the same insert. As long as you have a method of matching fuel delivery to the new signal you will be golden. Remember that with a larger housing you will read less air flow than before and will have a smaller pulsewidth, which will allow you to run a higher fuel pressure or higher flow injectors (or both). Combined this will give you a larger window on the top end, which is where I assume you are running out of voltage.
yea thats another idea i had to just make a larger housing. so the airflow meters in the bigger cars around 1994 ish all used the same sensor in bigger housings did they? i didnt know that.
your bottom comment is dead on what i was thinking but i was just debating changing to a larger airflow meter instead but ur right.
i have installed larger injectors but im running out of voltage at about 2psi boost which is around 4500rpm in 3rd gear, ( i havent set the boost higher yet because i cant map it cos after that its just pegged at 5v)
i will probebly get a rising rate fpr so i can turn the fuel pressure down(only slightly say 10psi) at idle/ no boost for better idleing and cold starting and have it ramping up under boost.

at present at idle its reading about 1v so u can easily see why i run out of room.
thanks for the input!!!

oh yea also i have a wideband o2 installed for a/r tuning
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  #4  
Old 05-11-2008, 12:30 AM
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Good that we are on the same page. I've not done this type mod on an air mass car but did a very similar mod on a speed density setup.

In your setup running 10 psi on a 2.8 is the equivalent of adding 1.9L of displacement.
(if my math is right)
10psi=.689bar
2.8*.689=1.9~
2.8+1.9=4.7 Liters of disp @10psi
(current injector size)*.689=X
(current injector size)+(X)=(new injector size)

So in theory you would want to increase your injector size by the same ratio as the boost, .689% , and keep the same fuel pressure. With your fuel delivery (+.689%) matched to the boost level (+.689%) then you can incrementaly increase your housing size to get your full load 5V reading at 10psi at max RPM. This should allow you to run well with the stock fuel maps. If you tune it this way you should start out rich with the smaller housings and lean it out to your target as you increase the housing size. Your boosted motor will thank you for this approach.

Your stock FPR is rising rate though I'm not sure how they respond under boost. Exactly matching your injector size isn't likely so you will still probably need to be able to tweak you fuel pressure a little bit
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  #5  
Old 05-11-2008, 05:46 AM
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Quote:
Originally Posted by duxthe1 View Post
Good that we are on the same page. I've not done this type mod on an air mass car but did a very similar mod on a speed density setup.

In your setup running 10 psi on a 2.8 is the equivalent of adding 1.9L of displacement.
(if my math is right)
10psi=.689bar
2.8*.689=1.9~
2.8+1.9=4.7 Liters of disp @10psi
(current injector size)*.689=X
(current injector size)+(X)=(new injector size)

So in theory you would want to increase your injector size by the same ratio as the boost, .689% , and keep the same fuel pressure. With your fuel delivery (+.689%) matched to the boost level (+.689%) then you can incrementaly increase your housing size to get your full load 5V reading at 10psi at max RPM. This should allow you to run well with the stock fuel maps. If you tune it this way you should start out rich with the smaller housings and lean it out to your target as you increase the housing size. Your boosted motor will thank you for this approach.

Your stock FPR is rising rate though I'm not sure how they respond under boost. Exactly matching your injector size isn't likely so you will still probably need to be able to tweak you fuel pressure a little bit
all very helpful information :-)
my stock injectors wer approx 200cc *6
i have changed them to 310cc
so if i tweak up the fuel pressure slightly they should just flow enough.
i also have a piggyback ecu to adjust the airflow signal in relation to rpm and throttle position so this helps alot. it is a greddy emanage.
2 questions for you
do you know if i can buy larger airflow meter housings so i can just swap my meter into it eg from a c43?
and also do u know how much flow the mercedes fuel pumps have?
im hooking up a fp guage to monitor if its holding pressure with the bigger injectors but havent got it hooked in yet.
and il probrbly only run 8psi unless i get either water meth injection or get the ignition timing hooked into this unit also.

thankyou for your help so far dux
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  #6  
Old 05-13-2008, 07:53 PM
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I do not think the equivalant 4-wire V8 flow meters will fit your insert. The later models insert is smaller in diameter so I don't think there is a direct bolt in that will work for you. I'd source a few junk meters and cut the section that houses the insert off of the flow meter and epoxy that to a larger section of pipe such as PVC. Once you have determined the proper diameter for your app. then you could build a more solid version with the proper dimensions. I doubt the PVC would hold up long to the under hood heat.

I don't know off the top of my head what the fuel pumps flow but I know of people running more boost than you are planning on stock pumps. It would be a good idea though to put a guage on it to watch the pressure to ensure it is ok. Even if it is only temporary. Peace of mind is priceless.
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  #7  
Old 05-13-2008, 11:27 PM
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Dont know exactly what your talking about but a S500 MAF will fit your car if you have the four pin rectangle type connector. Also, if its just the housing, the S500 housing will transfer over and bolt onto your sensor if thats all you need.

I have a SAFC NEO on my MAF, all i do is punch a few buttons and i can readjust the fuel settings in conjunction with the MAF.
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  #8  
Old 05-13-2008, 11:36 PM
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Hmm im on my old computer, pro60modman never worked when i made it.....any way back on my regular account and heres the diagram for a 3.2l M104 if that helps
The MAF is B2/5
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  #9  
Old 05-14-2008, 12:12 PM
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Here's a good article on enlarging an airflow meter housing.

http://autospeed.com/cms/A_2631/article.html

Autospeed is a great online magazine. They have tons of articles on stuff like this. You have to be a member to get most of them though you can purchase single issues.
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  #10  
Old 05-28-2008, 06:24 AM
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Does the Greddy ECU not adjust for MAF sensor voltages?
I use the Apexi SAFC with 320cc injectors on my 2.8 M104 using around 5.5psi boost.
This increases the MAF output voltage by upto 50%.
It all works fine except hot starting which needs some throttle applying.
I use the standard FPR but may change this soon.
I also read a trick about squashing the top of the standard FPR to increase the internal spring pressure. I partly tried it with not noticable results although maybe I didn't squash it enough. I need to get a pressure guage to test the results.
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