I have given my 85 a complete tune up, changed just about every sensor, hose and filter. I was also "Given" another Posi rearend in which I put 2.41 gear in and replaced my 3.08 Posi, hoping to get the gas mileage back. Nothing. Rochester was rebuilt 7 years ago, seems to be running rich. Could my 160 degree Thermostat make it run rich? should I put the 195 Degree back in. My other thought is the ECM took a Doo-Doo on me.......Help!!!!!!

Is your check engine light on?

O2 sensor bad, not connected or broken wire?

Catalytic converter completely plugged?

Assuming you have the electronic carb like my 87 Olds,

Is the float level too high in the carb or float valve stuck open?

Fuel metering solenoid on the carb bad, disconnected, or not working for some reason?

Is the engine temp or inlet air temp sensor is bad or not connected?

When you observe the timing with a timing light, does the timing mark jump around when you rev the throttle or is it stuck in one place?

If none of the above, then sounds like something's wrong in the computer or your brakes are really locked up.

Hope this helps your diagnosis a little.

Check Engine Light goes on almost always, unless I step on the gas a couple of times real hard, then it might not come on. But for the most part, it is always on. Changed the O2 sensor and made sure it is connected, I have not checked the engine temp or inlet air temp....because I don't know wher they are at. She has a crate 350 with a RV cam runs good and strong, even passed smog last month, how when it's running so rich, makes me wonder. Any how, is my guess on the thermosat wrong? and is there a way I can check the ECM? I took a little trip to the Pick n Pull and found 7 ECM's that I kinda hid, what #'s do I make sure of? I'm sure only 1 fits.

Why don't you check to see what codes the computer is throwing. You can do that by following this linkRetrieving Computer Control Trouble Codes (http://elcaminocentral.com/article-55--0-0.html). Once you have that information, you will be better informed as to what is possibly wrong. When you changed these sensors, did you clear the computer memory by disconnecting the battery for a few minutes? If not, try doing this as well.

Another thing to look for is any vacuum leaks. Check all of the vacuum hoses for cracks, any disconnected hoses, any breaks, etc. Also check the intake gaskets for any leaks. Vacuum leaks will cause you to have increased fuel consumption, but not necessarily a check engine light. Good luck!

I don't know how stringent the smog laws are there, but the real long term solution might be to ditch the rudimentary computer in the car and install the Holley projection fuel injection system---the only other thing you would need is an early model HEI distributor so you will have a vacuum advance---my Monte carlo with a 383 th700r4 and 373 rear gets over 20 to a gallon plus all the other benefits of fuel injection---like cold starts and able to compensate for altitude easily---I'm not a salesman for them but I sure do talk good about their system dur to the ease of installation and the way it has been trouble free since day one----I did install the larger fuel injectors due to the size and power of my engine..............Dan

Yes, running a 160 degree thermostat can keep the computer from going into closed loop. It thinks the engine is not up to operating temp and uses preset fuel tables that are set rich. This is the electronic version of a choke. Once the computer see the temp is at 195 the Os sensor takes over control of the fuel circuit and constantly tries to maintain a 14.7-1 air/fuel ratio.

Unless you get the computer reflashed to run closed loop at 160 your better off to return to a 195 thermostat. I have found out thru my own testing, that different areas of the engine run at different temps. Try putting the temp sender in the head between the #4/6 cylinder. This seems to be the hottest part of the engine which will send the computer into closed loop the fastest during warm-up.

I did reset the ECM and alo went through and changed every vacum hose I could find, even though that was a pain, it was done. Smog laws in California are pretty strict. I do not think that at this point I want to change to an FI, it is the challenge of fixing what is wrong first. I think I will replace the Thermostat this weekend and see if that is it. As always thank you all for the info....this is a great site..........Jp

Resetting the computer is not the same as clearing the codes and rebooting and disconnecting the battery. I don't know if the computer in your elky can even be reprogrammed. You have a VERY basic form of fuel injection with that carb. It's basically providing a small amount of feedback to regulate the air/fuel ratio. I think it does that by regulating the fuel rods inthe jets. Now that I think about it, I'm not even sure about the choke setup. Do you have a choke cap?

I'm sure Elkypete could shed some light on the subject.

Yes, those carbs use the standard choke, with the electric heater. Once the engine has run for a few minutes, open the air cleaner and see if the choke is full open.

With mileage that bad, it sounds like the mixture has defaulted to full rich, with the rods completly out of the jets. That happens when the mixture control solenoid is unplugged, or if the solenoid just goes bad.

As others have suggested, check the codes first. Otherwise you are just chasing your tail and throwing away good money.