Is this normal?

Does this indicate a faulty computer?

To make a long story short, my gas mileage has sucked for the past 2 years. (15 city 23 highway in 2008, to 11.75 city 14 highway now), and I've racked my brains trying to figure out what is wrong.

When I put the GM key in the computer port to run the diagnostic, nothing happens. The computer doesn't kick on or anything, and it used to.

I also heard that if your computer is bad, it will leave your metering rods wide open to let in all kinds of fuel.

Is this true?

Thanks yall for the help, any is helpful.

 

Without the computer, the rods will be continuously in the rich position, and there will be no timing control. Mileage and performance will both suffer greatly, but it'll run.

 

Is there any way to test the computer?? That may already be happening because my gas mileage SUCKS bad

My problem is that I think I may have a faulty ECM, but the electronic timing advance DOES work, however the ECM will not flash any codes when you put the GM test key in the computer port... like the computer doesn't even turn on, and I know it should.
Perhaps the computer could be going bad little by little? That's what I'm leaning towards

 

You will still get some rudimentary advance with the computer not connected or working. The ignition control module will step the timing up a bit at a set RPM, somewhere around 1500-2000 (I don't remember). This is a built in limp home mode and you can see this with a timing light with the ESC to the dist disconnected.

In my experience ECMs either work or don't. Intermittent problems or partial function usually track down to some other component. Yours is likely just bad or not connected properly. Verify power to it. The dedicated ECM power wire that runs from the battery terminal alongside the fuel lines has a fusible link and is the most likely culprit. There's also a fuse for 'engine controls' that provides power to the pieces/parts that the ECM controls or receives data from. It this fuse is gone the ECM may still have power but nothing it wants to talk to can listen.

Loss of the diagnostic port isn't necessarily an indication of a failed or unpowered ECM. I've seen plenty of ECMs that functioned fine but wouldn't light the test light, usually from loss of ground at the ALDL. A properly functioning computer (AND mixture control solenoid) will cycle the solenoid 10 times a second when the key is first placed in 'Run' or when the engine is running. That's the clicking you should hear from the carburetor and is the MCS controlling the rods going into and out of the primary jets. If it's not clicking the rods are stuck up, out of the jets.

 

The fuse to the ECM was blown. All this time I've been saying... "the computer us bad.." and never checked the fuse. I amaze myself

 

if the fuse blows again,check over the engine wiring
harness for any wires worn through and grounding
out..