Field Service Mode

[Shannen Durphey]

David Mulvey wrote:
> 
> My 87 IROC 5.0 has a ping problem when I get on it hard. Error codes light up indicating a bad MAF or MAF relays or wires inbetween.
Check out this code, see if it needs correcting.  No sense chasing
other problems until this one's fxed.
> I tested and cleaned and check all componants best I know how.  Everything seemed OK.  MAF gives a voltage of .7 Volts at idle, and
> when I gas it in the driveway it jumps to about 2 Volts. It's got a new block.

> 
> One thing that I don't understand is why does my car run perfect with no pinging with the ECM in Field Service Mode (Pins A and B
> shorted)?  
Field service fixes the timing and fuel delivery.  There's no ecm
controlled advance, and fuel delivery rates won't adjust for rich or
lean conditions.

Should I leave it in Field Service Mode?  No.  You risk running too
lean/too hot.

Does the computer take sensors out of line in this mode and then
somehow keeps
> the car running through a backup mode??? Very close to that.  The o2 sensor is disabled.  The tps, map and IIRC the cts are used.
> 
> I am currently working on a diagnostic hookup so that I can fit right in on this list, hopefully that too will help out. I will be
> sure to post on my web site any software that I may develope.  Thinking of realtime window based displays of what ever word I would
> like to look at.  I have been doing this sort of thing at work on Military Aircraft, but this will be my own time, equipment, and
> serial based instead of 1553 bus.
That would be cool.
> 
> Thanks
> 
> David
> Lancaster, CA
Shannen