[Diy_efi] What Injector Is This?

[Mike]

Its very similar, the bosch element in mine is not
that small - looks like the wire length is some 60mm
arranged in a loop.

I dont think its a design issue (read flaw) wich means
the Bosch 'needs' a large clean current as might be
implied. Bosch seem to go to some trouble with
issues like cal and an automatic clean as such is
bound to be more reliable than relying on people to
do it - which I still find perplexing.

Have you ever looked into the throat of one of these
ford MAFs and watched if it does or doesnt apply a
current pulse - maybe it does but its not enough to
make the wire glow.

Yes, I would like to see a schema of the ford MAF,
the 'clean' may well be supplied by the ecu and not
be inherent in the MAF as it is for bosch, as far
as I can determine from all I've read on these
issues - some sort of 'clean' burn is very helpful...

rgds

mike



At 03:24 AM 4/3/03 -0800, you wrote:
>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
>
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