[Diy_efi] What Injector Is This?

[Perry Harrington]

On Thu, Apr 03, 2003 at 07:11:01PM +0800, Mike wrote:
> Perry,
> 
> mmmmm, Are you sure you're not confusing normal MAF
> operation with the 'clean' mode only at engine shutoff ?
> 
> All the (recent, last 15yrs) Bosch MAFs I have seen have
> the classic hotwire mechanism (duals as in the ford and with
> temperature compensaion) which runs a current through
> the wire so it dissipates a certain amount of heat, it is
> the removal of this heat by the mass air flow in concert
> with an internal wheatstone bridge which provides the
> measurement signal. Under these conditions the wire is
> not visibly hot but I wouldnt want to touch it.

The Ford MAFs are differential as well.  I have a schematic
of sorts around here somewhere.  The hidden element is for
ambient air temp correction and the exposed element is for
mass air flow.

> 
> Upon turning off the engine, the ECU sends a signal to
> the MAF electronics to provide a 'clean' to the main
> sensing wire - it passes a larger current for a few
> seconds to burn off any particulates, this is where it glows
> light red or as some have observed white hot.

The Ford MAFs do not have a "clean" signal.  This is unique to
Bosch MAFs, presuably due to a design issue.

> 
> This is essential because under normal operation for
> many hours when the sense wire is hot, particles tend
> to stick to it and upset the linearity of its output.
> 
> I would expect the ford MAF has a similar 'clean' mode
> otherwise it would need frequent cleaning manually...
> 
> It may be possible the ford MAF is not as robust to 'clean'
> cycles and these may be limited to a multiple of engine
> shutoffs or maybe its given a clean during a sec or so
> before cranking, either way I would be surprised there
> were no 'clean' mode as described above for the Bosch.

The Ford MAF is physically different than the Bosch MAF.  The
bosch maf uses a couple of different designs, with very small
elements.  The Ford MAFs use an element between a 1/8w resistor
and 1/4w resistor in size.  All the elements really are is
platinum resistors.  The Ford MAFs require cleaning from time to
time, but in general they do not get seem to get real dirty.

I would presume that the larger elements in the Ford MAFs draw
more current and thus are self cleaning.  The Bosch elements are
very small and require periodic cleaning with momentary high
current.

> 
> rgds
> 
> mike
> 

-- 
Perry Harrington			Data Acquisition & Instrumentation, Inc	
perry at dainst dot com					 http://www.dainst.com/

Those who would give up essential liberty to purchase a little temporary safety
deserve neither liberty or safety. Nor, are they likely to end up with either.
                             -- Benjamin Franklin

_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi