michaelj

Hello all,

I have an unexpected solution to share regarding reduced fuel economy on a 2002 Civic LX automatic:

My wife’s Civic had previously gotten great gas mileage for her daily commute, around the 30-34 mpg range, for entirely city driving. I had recently discovered that it had dropped, drastically… like down to 15mpg (!!!) with no ECM/OBD2 codes showing.

Given that the car is currently at 104,000 miles or so, I decided it was time to get the 110,000 mile service over with. Here is what I did, all OEM Honda parts from Honda Parts Wholesale Direct (Honda of Dartmouth, MA?):

• Valve adjustment
• New Timing Belt
• New Timing Belt Idler
• New Plugs
• New Water Pump
• New Water Hoses
• (Alternator/AC & PS belts had previously been changed)

I performed the timing belt before doing the valve adjustment. While doing the valves, I spun the engine many many times to check and re-check the clearances, and then one last check of the timing marks. Everything went great and timing was bang on. The only downside came when removing the alternator, as the (+) positive terminal lug snapped off. I ended up replacing the alternator, and I will repair/rebuild the OEM unit for future just-in-case usage (the OEM unit spun freely, btw… it was on my list of things to double check.)

Button everything up, with new alternator and fresh plugs… but after filling up (tank was basically empty) and running through that tank, I discovered that fuel economy had only improved to 18mpg, still no ECM codes. I had been searching this site and elsewhere for inspiration on what to check/do next when…

Fast forward to this past Friday night. My wife called panicked because she was experiencing weird electrical issues (headlights seemed dim, engine had very little power, defroster would intermittently stop working, odometer would flash on and off.) Of course it was nighttime and raining, so the electrical draw was HUGE with lights, defroster, and wipers. My thought was that the new alternator was bad and that her battery was dying. She was almost here so she decided to try to get all the way home. She made it. I immediately checked the charging system with a multimeter. Engine running, but all other load off, I saw 12.2v at the battery.

Saturday/yesterday morning, I went out to diagnose again. I tested the battery first after its overnight rest and found it at 2.5v! That is when the light went off in my head. This battery was dated October, 2011. It has been abused by being fully drained (lights left on) multiple times. I’ve been able to pull it and recharge it each time, but have begun to wonder if it would survive the coming winter having been so abused. I decided that it was the best to replace it this go around, and did. Now with engine running I see a system voltage of 14v, which tells me the replacement alternator is working.

We took the car for a long highway drive yesterday, with some city driving and stop and go traffic thrown in. My wife said right off the bat, that the car “felt better” and that the engine felt like it was strong again. We did a fill up before and after the trip, to find that we drove 81 miles and burned 2.3 gallons. That’s a fuel economy returned to its former glory of 35mpg. The sticker says that 42mpg highway can be expected, however my wife’s driving style is somewhat aggressive and we did suffer stop and go and city driving in that mix… so I’m happy with the 35mpg.

Long story short: If you have reduced fuel economy and you’ve tried everything else, check your battery and/or alternator.

sdaidoji

iTrader: (1)

thanks for the info
yes, not enough electrical feed could make things go crazy, including MPG, but actual data is good

michaelj

Now that we have just under 100 miles on the Civic post-battery-change, and interesting thing has occurred, my wife sent the attached photo after her morning drive to work! Check engine light! Not sure what the code(s) are yet, but I will check it out when she's home tonight.

Spit-balling here: I'm thinking that a full, happy, and CONSISTENT electrical supply has revealed an underlying issue that has been there for a while. The dying nature of the previous battery may have been resetting the ECM occasionally. Maybe. I don't know.