how important is it to reset the computer after making changes? I am getting poor mpg arount 8 to 10 hwy and city. i changed plugs wires dist cap fotor button o2 sensor air filter and st the timing 10 deg btc.
truck runs good but still appears to be running rich, burns a lot of fuel and exhaust smells like unburnt fuel. the one thing i havent done is try to reset the computer
I'm not familiar with the '90 in particular, but most newer Ford engines have a gray plug in a wiring harness connector (called a Spout Connector) that needs to be removed before setting the timing. Did you do that? Also, the computer relearns the fuel corrections within 80 miles or so on it's own if the engine is running right. I would double check everything then troubleshoot for a rich condition plus check the KOER codes, if you can do that on your model engine/EEC.
The computer has some adaptive learning modes. Resetting the computer removes any learned adjustments and restores the default parameters. This is a different than resetting any fault codes that may be stored in memory.
If there is not an active code (the 'check engine' light is not On), then there will be no 'limp home' strategies in effect, no matter which faults are stored in historical memory.
Not sure how much adaptive learning was done on our vintage of truck. At any rate, the computer should eventually re-learn its way back to where it should be.
However, pulling the ground cable off the battery for about 20-30 minutes effectively 'zeroes' the computer offsets, and hopefully results in a shorter, faster learning curve.
I forgot to mention that on my 4.9, the timing mark was for the probe not a timing light. I had to find TDC then make a mark on the damper with a cold chisel so I could use my timing light. I had a Chevy once that had spun the damper so every time I checked timing I had to make a new mark with a felt tip pen! Verifying the mark might be good for you to.
ECT= coolant sensor that feeds the PCM or ECM. It tells the computer how warm the engine is so it knows how much fuel to give. If this engine is fuel injected, you can do an injector leak down test to see if it's a bad injector. Re-pulling the plugs at this point might reveal a sooty plug helping you localize it to one cylinder too.