Really Bad Gas Mileage???

so i hooked up my volt meter to the o2 sensor and ran a lead into the cab so i could see the out put at all times....turns out that when the engine warms up and im at cruising speed the out put is around 0.91

is that too high??

Yeah, too rich. That explains the bad gas mileage.

The mixture control solenoid on the feedback Nikki carburetor fails to open position by spring action.
So it looks like it is constantly open that is why you are running rich.
A good mixture control solenoid will show an O2 sensor output between 0.4 - 0.8 Volts DC while cruising and always crossing the 0.5 VDC.

Test it for resistance with a multimeter. In the picture, follow the wire to the round yellowish plastic connector. Disconnect the plug and test it there.

Good luck.

One question.
Did you umplug the O2 sensor or you just backprobed it through the plug?
If you unplug it, it will go into open loop and default to running rich.
If you left it plugged and just backprobed it for the meter that is the correct way so it's still in closed loop. Then you are really running rich and the carb is defective.

the 02 senesor is still pluged in i just probed ther line to get a reading out of it.....

when I pull the vacuum line off my dist. the idle doesn't change either. Does that mean it needs to be replaced? I have noticed a change in gas mileage here lately. I know I have the orignal 02 sensor I'll need to replace that with it.

ok guys i have an update on my old 88 b220 that was getting terrible gas milage and idles like a drag racer.

on recomendations from several member i set out with my volt meter in hand to do some testing of a few different sensors.

like i said before i tested the 02 sensor and found it to be outputing about .9 volts....a little high.

So i then disconected the mixture control solenoid. I followed the wires down and found the yellow connector and unpluged it. I then started the truck with this conector unpluged thinking i should test it while the engine is running. Well when i started the truck it started and idle like it was brand new. No kidding i started it up and the idle was stready and smooth.

So the reason why it took me so long to post is ....i wanted to run a tank of gas to see if my mileage improved.... well i am happy to say that my milage is right back where it was ... ihave no put on just over 300km and have over a 1/4 tank left.

So i gues my question is now is it harmfull to run with that soleniod unpluged..

im just so happy that the truck is running great again and not chugging gas...but i dont want anything harmful to happen by running it with that plug undone....

eric

that solenoid being unplugged may cause it to lean the mixture out, which is not good either

test the O2 readings again and see what you get

im positive you can't buy that solenoid from a parts store, may have to get another carb