Discussion Forum - Northstar Chevelle Club

Steven, I started a new thread for the topic on your mileage here.

You might also check something that seems obvious but I think I figured it out on mine this week.  Last week when the alternator went out, I checked the battery when I got home and it was just over 11 volts.  Of course, I had driven it 40 miles or so without being charged, so it was draining a little as I drove it.

After I put the new alternator in, the battery voltage is now 13.5 volts, and steady at that whether the headlights are on or not, so I believe the regulator is doing it's job, otherwise, it would dip below 13 volts if it wasn't with a load.

Long story short, check the battery voltage when running, as that will impact your HEI distributor module if it doesn't have a full 12V to operate on (you can check the voltage at the HEI module pin too, but the battery is easier), resulting in less spark, resulting in less engine efficiency, resulting in sucky gas mileage because you have to give it more throttle to go.

All I can say is after changing the alternator this week, the engine seems more responsive, and I know I used WAY less gas yesterday.  I only used a quarter tank of gas from Rosemount to Fridley to Ham Lake and back to Route 65 after the cruise.  This was on par with my buddies '10 Camaro, and I think I even have a smaller tank.

Sometimes it's the simple things, and not always mechanically related and can be electrical in nature.  Something quick and easy to check with a voltmeter.