87 305 TPI: MAF Issues....

[Peter Fenske]

Craig

The MAF appears to get good power supply voltage (coincident with
initial firing of fuel relay and steady 12-14v after startup), and the
MAF seems to give good readings (ballpark 400-700mV @ 700-1200rpm)
initially. However, if I monitor the signal voltage from the MAF, a
bauble occurs at seemingly random times (often very soon after
start-up), where the voltage jumps up to 3.2v or so (or was it 2.8v or
so, similar to voltage measured with MAF power supply cut off). This is
quickly followed by a Code33 set. To eliminate, the ignition usually
must be cut off for 10 seconds or so prior to restart. Once it sets, the
voltage stays around the 3+v level (if I remember correctly...it may
still vary with engine speed, though). I've gone 2-3 days without
coding, other times it's every start-up event. Sometimes as it codes, it
gets real rough and rich till the code sets, then it smooths out.


Well have you tried the 10 LB hammer tap test..

The bosch MAF uses a open collector style pulldown transistor.
If the circuit opens somewhere for a sec then the voltage will instantly
be pulled high..
The early versions had notorious solder failures.. Also any open in the
wire connecting
the MAF can cause your error.

gl:peter

PS you can defeat the code but bad things could happen.