Miata Mailing List: December 1997, Message #110
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From: 	"Will Brown" <wbrown@rlc.net>

Subject: re:OBDII thought 

Date: 	Mon, 1 Dec 1997 18:17:02 +0000



In a nutshell:

	You would need to dial in the circuit for different max boost

	I don't like active clipping (but the premise is good)

	Neither will help, from what I've since deduced

	Some sort of mechanical pressure reducer is needed



Now for the verbose:



Barry, after a long walk in the woods, logged on and said:



> Interesting idea. Would the variable gain and/or offset need to be

> compensated for variations in max boost level? Some run 8-9 psi;

> others run 12 psi.



Yes - tho if this 'gadget' ever made it to 'production', it would be 

fairly easy to get a nice graduated adjustment knob.



>   I still prefer the "active-clamp" circuit because it can be preset before 

> shipping but I'm open to new ideas. 



As I think I stated in an earlier post, I frown on the clamping

thing, because then the ECU has no real feedback as to what's going

on with the engine - if all the sensors stayed flat lined, the

engine would appear to not be running? ;-) I see your point - as

always, simplicity is the best way to go if at all possible - less

to screw up (but the feds beat us to the punch on that one - a

little thing called OBDII?)



> Is there anyone out there with the service manual for an

> OBD-II-equipped car? 



Ummm, me  (I have access to a scanner too, if that matters)



> Any other volunteers wish to help resolve this problem? I can get

> access to a 96M to get outputs from the air-flow meter and EGR but

> I need to know where to tie into the harness. 



I could tell you that, but then I'd have to kill you - no, really -

when I made the original post, I started thinking after I sent it

off (always bad to think about your posts after the fact) - between

some of Paul's initial data taking, and from the sensor sensitivity

I derived from the test procedure in the shop manual, my educated

guestimate is that the sensor maxes out at about 1-2 psi... nothing 

electronic will help, IMO - I am thinking some sort of mechanical 

pressure reducer/divider/somethingorother is needed to put inline 

with the pressure line feed, so the actual air pressure getting to 

the sensor gets knocked down to a range it can handle.  Now, this is 

an area where I don't even know enough to get myself into trouble - 

which means not a lot!  Or maybe another sensor altogether?  I've 

seen them in electronic data books, but never paid them much mind.



Somebody please step up and prove me wrong, and say that the world 

(at least *charged OBDII Miatas) _can_ be set right with $2 worth of 

electronic parts... pleeeze



Until then - the battle still appears uphill...



\/\/    ---->    Will Brown    ---->    '96M in Charlottesville VA



http://www.geocities.com/MotorCity/Downs/7061