Field Service Mode

[Kurek, Larry]

> 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.  
> 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.

That confirms it then :)  I had a similiar problem with a 2.8 MPFI I swapped
into an S10. It ran great under *most* circumstances, but every once in a
while...especially under load...I'd get a SES, which was indicating MAF
voltage low. Since you mention getting a new block...here is your problem
(I'd bet):

Bad ground :)

What happened in my case, was I mounted the MAF relay on the radiator
support, and grounded it to the mounting bolt there. I guess that even with
everything bolted together, the body would flex just a tad and the ground to
the support would go to hell...and the relay would open and bingo...SES!
Make SURE you have reconnected the grounding strap between the engine and
the frame/body/raditor support. It didn't take much in my case to cause this
problem. A short wire from the battery ground to the rad support and haven't
had this problem since.

As for the field diag mode...I think the ECM substitutes some fixed values
for sensors, such as the MAF. I could be wrong....

Larry