Re: High Freq MAF Problem

["Bruce Plecan" <nacelp@bright.net>]

Just as another way to do it, how would this sound.
Use the MAF, and wire in a second ecm.
Hook enough up to it to wake it up, and disable what ever flags it codes.
Then use a diacom, and record one ecm,  and then on a simuliar drive record
the other ecm.  Then compare what things look like.
Not anywhere as slick as what you got, but jus an idea.
Grumpy




| > To see if the signal is getting through, hook your scope to pin 16 of
| > the '34984/'79435.  That's the output of an inverter.  Pin 17 is the
| > input.  The counting is done in a different chip.
|
| Yes, I did not explain exactly when/where I connected the probe very
| well.  I was at both the counter and the fuel chip.  No pulses at all on
| the counter.  The input conditioning expained the problem when probed at
| pin 17 of the 9435 chip.
|
|
| > The frequency MAF in the 727/730/749 has an RC filter on the input of
| > the inverter mentioned above.  R is 100K.  The C looks like many of
| > the other surface mount capacitors.
|
| The C is .01 micro farad.
|
|
| > The 8253 ECM (used with the 3800) has a different RC filter.  The R is
| > 48.7K (1%).  The capacitor looks different from any other cap on the
| > circuit board.
|
| The C is 120 pF (measured in-circuit).
|
|
| > Hmmm, is the high frequency MAF also used on the Buick 3300 V6?
|
| Yes.  The 3300 is just a "batch" version of the 1228253 code.
| The 1228706 also uses the 48.7k resistor, but the C would not
| read right in-circuit.
|
|
| > This would explain why it uses an ECM (1228706) that doesn't
| > interchange yet looks just like the 1227730.
|
| Exactly. I did not understand the difference either, but now
| it is clear. So if one wants to use the high freq MAF in
| a 1227730 app, you have to find the 1228706 ECM.  This
| might turn out to be the easiest way to get the high freq
| MAF in an earlier application, changing chip caps is not
| for the timid.  ;-)
|
| Scot Sealander
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