CPTN

My 2000 Civic EX (AT, 96K) seems to have suffered from a noticeable decline in gas mileage for no apparent reason. I was due for an oil change, but it had never happened before because my oil was so bad (I change it myself every 4k and use synthetic). I was averaging about 27 Combined (probably about 65/35 highway to city on a normal tank) and that has dropped to almost 22.

No clue why.

Also threw a new air filter in when I changed the oil yesterday (had been about 10k).

Has anyone else experienced this?

Former User

Any CEL codes?

How old are the plugs, wires, cap, and rotor?

Is the ignition timing set to spec?

CPTN

No codes.

Plugs, wires were changed about 17k ago. Not sure about cap and rotor.

Not sure about the last one? Had the TBelt replaced at a reputable Honda dealer in town, so I'd assume so.

Former User

Definitely inspect the contact points of the cap and rotor for wear and corrosion. If they are old, just replace them with OEM parts.

As the plugs have almost 20K miles on them, inspect and/or replace them too. They're cheap.

You may be able to get a free rental on a timing gun at an auto parts store.

CPTN

Thank you.

thorvick

I just want to share my experience with the same issue.
I was recently troubleshooting a problem with my Civic EX 1997 (D16Y8) and ended up replacing the distributor cap, rotor and ignition coil (Part# TC-08A). I bought only cheap parts from Napa. 4 full gas tank after the switch, my gas milage dropped from 34-38 MPG to 25-28 MPG!!!!! 30% drop!!!!
I decided to test whether the new ignition coil (Napa Echlin 1101017A RUF89CS RA0111) was the culprit and put the old one back (TEC Honda OEM). I also reset the ECM/PCM.
Problem solved! Got back to my 35+ MPG.
CONCLUSION: as RonJ@HT said, OEM only!

Izo

Other stuff to check out:
Temperature stable after a 5-10 min drive? If not it could be a stuck open thermostat.
PCV: Test the PCV and replace if necessary.

fleabag

Redo your electrical grounds (scrub the bolts, washers, eyelits thoroughly!, blow out the holes for the bolts with air), check the ohms value of your grounds to the battery cable so that they're as close to zero as possible, lightly scrub hole for o2 sensor and or check ohms value of o2 sensor to battery ground to make sure ohms value is zero, give the car a tuneup, replace PCV valve, check for vacuum leaks, etc.

If he hasn't replaced the PCV valve or can't remember when he last replaced it, he needs to replace it..