Chris Lockhart

I know this may be a stupid question, and may have been discussed before (if it has, I couldn't find it). From what little I know about it, the only choice for a modified/boosted engine is the Super MAF, which of course uses the same housing. Why not use a newer cartridge style MAF sensor like what's in lots of modern cars? From my minimal research on the subject they appear to operate within the same 0-5 Volt spectrum, and have pigtails to use them in universal applications. It seems to me that packaging the MAF in a custom application such as supercharged or turbo 928's, would be much easier with one of these. The aftermarket support for them is pretty big, with various universal housings and mount plates that can be installed in virtually any intake pipe as long as the MAF is properly sized to the pipe diameter. This place has virtually everything you can think of for them:

http://www.pmas-maf.com/product/hpx-...sm-6pin-style/

hans14914

Chris,

I am using the Hitachi style sensors with my kit. The reason most people have not used them is they require additional electronic hardware to function with our LH. The Stock MAF sensor works in a (nominal) 2.2-6.5v range. Its probably actually closer to 2.3-6.4 usable though.

I have measured the transfer functions of both the stock and SMAF and have that data, along with the hardware and profiles to make a Hitachi sensor track that curve.

GPA951s

When I was at the PRI show I saw a MAF that looked allot like the $1600 dollar ones at the time. (Im a 951 Guy but same difference) the Company is Pro-Flow Technologies, They made me one calibrated to the original "vane" from Bosh.. had an altitude sensor built in, idle rich\lean and throttle rich\lean, \nice unit for 350 bucks.. Might want to look them up.. I ran mine on 3 different cars over the years..

hans14914

I dont believe that sensor, or the Abbaco (EFI Systems) products are available any more. They were both good products, but still had a 5v upper threshold.

Chris Lockhart

So what exactly does it need in order to talk to the Bosch brain? I'm not very proficient in the electronics world. Thanks.

hans14914

At a minimum you will need a voltage offset. The factory brain goes into a limp condition if it does not see a lower threshold voltage of ~2.2v

Randy V

I'm sure Zeisco has one in development - soon to be released to the public!

PorKen

I am not much of an electron wrangler myself but as much as I have figured, there is a ~48% voltage divider on the {LH2.3 board} to work with the 928 MAF (carried over from the S2/S3 LH2.2), essentially cutting the signal in half. Since it is not practical to modify the board, the voltage has to match.

The 'limp home' mode threshold could be programmatically lowered or deleted, but the divider makes the resolution a coarse 0-2.5v.




Tech note: MAF voltage is read in two ways. Primarily it is converted to a frequency which is counted by the (8051) ECU for load calculations. Secondly, it is combined with the TPS idle input* and converted to a digital value which is used to determine the acceleration pump.

*For the LH, both the WOT and idle inputs could be variable resistance/voltage. EZ is WOT variable, idle is digital.

928NOOBIE

https://splitsec.com

Look at model PSC 1-003. It allows changes up to 5V in either direction of incoming MAF signal. I have one and will be installing it on my car once exhaust is done.

hans14914

003 is +/- 2.5v with a 0-5v total range. You may want to us a different module for full resolution in the LH, or plan on modifying the base table columns.

928NOOBIE

I spoke with the guys that make it...it goes on top of whatever is coming in..what he told me is that the way they built it is for 5.5V and higher it will add whatever you put in the table at the 5.5V value...so if you add a volt...you get 6.5...if you are bringing 6 in...it adds another..you get 7..etc.. the table in the software won't go all the way up to 7V but he said the unit can accept 7V input..and would add/remove whatever the value is in the farthest right column..I think it's 5.5 V..but I'd have to crank up the laptop to check the software...

There is that limitation..anything over 5.5V you can't customize...

PorKen

Took a fresh look underneath the S4-up {LH2.3 board}. There are two square (test?) points on the board not connected to anything (on either side), pre and post voltage divider that would be easier and safer(?) to solder onto. I calculate a 2K ohm 1% resistor across those points would convert a MAF input voltage of 5.0V => 3.019V vs. the stock 6.4V => 3.048V

As I understand it, this resistor bridge would allow a 0-5V MAF? (With some map tweaking.)


2K + 5.62K in parallel = 3.35K (+) against 5.11K (-)
http://www.ohmslawcalculator.com/vol...der-calculator
http://www.sengpielaudio.com/calculator-paralresist.htm



I am fairly certain a stock-ish X-piped S3 (or S4) won't draw enough air to go over 5.5V

928NOOBIE

Quote:
Originally Posted by 928NOOBIE View Post
There is that limitation..anything over 5.5V you can't customize...
I am fairly certain a stock-ish X-piped S3 (or S4) won't draw enough air to go over 5.5V

That is good news for me.

PorKen

Perhaps not surprisingly, the S2/S3 {LH2.2_86.5 board} has the same voltage divider (earlier boards are green, have a different layout, but the same components).

I also looked at a '87 Volvo LH2.2 board which is very similar to the '86.5 928 board. It has a 4.42K(+) and 6.82K(-) divider which translates to a 3.034V input using the 5.0V MAF the Volvo uses.

SMTCapeCod

Are these the blinker fluid folks?