1995 350 ecm (?) problem

I have a 1995 chevy 350 engine that WAS giving me about 17mpg. Suddenly, it
drops to 10 mpg. I do the usual (plugs, wires, dist & cap, injector cleaner,
o2 sensor, etc), with NO change. There is NO code stored in the ecm, no
check engine lite. I gave up and took it to a GM dealer, who charged me $150
to hook it to the computer. I was told that the engine was running too cool,
so it never goes into closed loop. They said change the thermostat, the
coolant sensor, and possibly the ecm module (they wanted $900). I changed
the thermostat (195 degree) and the coolant temp sensor, with no change at
all. I even checked the wiring to the ecm module, thinking maybe I had a
broken wire, but all checked well. I changed the ecm module. No change. I
changed the Knock sensor, no change.
How can I tell if the ecm is going into closed loop? I monitored the O2
sensor, which after a minute or so (coming up to temperature) shows about .85
to .9 volts at idle (which is quite rich). At driving speed, it jumps so
much I cant tell.
There must be some voltage measurement to tell me if the ecm goes into closed
loop!
Anyone have any ideas whats up with this monster?
I am thinking about putting in a higher temp thermostat to see if it does
anything, but am not sure that this is even in the ballpark of the problem.
There is no smoke, doesnt burn oil, no coolant leakage, but the exhaust
smells rich.
Thanks

On Sat, 29 Apr 2006 05:50:29 GMT, "Bornloser" wrote:

There are two coolant sensors, on for ECM and one for gauge, might
sure you change the right one. The one you want is on side of engine
mounted in head. You might check MAP sensor too.
-----------------
The SnoMan
www.thesnoman.com