91 Bravada ECM to Fuel Pump Relay Problem

[snoopybear]

Doing the steps you suggested I found the short to ground in the light green wire where the wire exited the harness in the engine compartment.
All resisitance is now within the specs you mentioned.

After putting it back together: with the engine off, ignition off, MAP sensor unplugged, the resistance to ground on the light green wire is 52K Ohms, light green to purple wire is 52K Ohms, and purple wire to ground is <1ohm. With the ignition on grey wire to ground is 5 volts.

With the engine running, on the light green wire, voltage to ground at idle is around 1100 millivolts and as I increase the revs the voltage on the same wire decreases to around 900 millivolts. When I disconnect the vacuum line to the MAP sensor, the voltage rises to about 4+ volts and the engine sputters. Still showing code 34.

[old_master]

Good piece of work finding and fixing the short! Now the ECM is receiving the signal. Sputtering when unplugging the vacuum, and voltage rise is a normal result however, voltage at idle on the light green wire is too low, and that's what's setting the DTC 34 at this point. The MAP sensor may have been damaged from the short to ground in the signal wire. Some of the auto parts stores have testers for the MAP sensor, check around. You might have to install a new MAP sensor though.