My 2004 CRV is getting 75 miles less per gallon. My mechanic has replaced my spark plugs, cleaned fuel line, and new oxygen sensor. Car still runs rough intermittenly and gas milage no better. Any suggestions? Could it have something to do with the real time 4 wheel drive?

I am thinking you mean 75 miles less per tank?
But you can’t judge MPG by the tank.
You need to divide the miles by gallons that you put in.

Indeed, the OP apparently means 75 fewer miles per tank of gas.

Instead of attempting to estimate gas mileage “by the tank”, the OP needs to do actual calculations based on odometer mileage and the exact number of gallons used over the course of those miles.

As to the “real time” AWD, Honda’s system causes the vehicle to normally operate as a FWD vehicle, with the AWD only being engaged after it detects that the front wheels have lost traction. If the system is operating as it should, your gas mileage is not impacted by Honda’s partial AWD system.

On the other hand, if the AWD system is no longer operating as it should, then it is possible that it is “stuck” in AWD permanently, thus reducing gas mileage. However, the OP still needs to do an accurate (miles and gallons) calculation of gas mileage, rather than the very inexact “miles per tank” estimate.

Like the other poster said, divide mile traveled by gallons to return to fill(first stop/click).

It could simply be your fuel gauge. Has there been a check engine light or is your mechanic guessing at replacing the O2 sensor etc?

I think some back story on “Car still runs rough intermittently and gas mileage no better” would help. Did the apparent drop in mpg start when the engine started running rough? Did the rough running start gradually over time or after a single event (i.e. fill-up, repair work, changing gas brands, etc)?

As for tracking mpg, I calculate it every 3 to 4 tanks of gas (~1k miles).

Ed B.

“runs rough intermittently” suggests one cylinder is misfiring intermittently, which could cause a drop in gas mileage. When does it run intermittently? If in wet conditions, you may need a new set of spark plug wires. Could also be a faulty igniton coil, a cracked/arcing distributor cap, or a worn distributor rotor. All of those are fairly simple to inspect/replace.

Also, you should be having the valves adjusted every 30k miles. If you haven’t had the valves checked in a long time, one or more valves may be out of adjustment just enough to cause intermittent misfiring.

Has the ECU been scanned for stored “fault codes”? If not, it should ba as s good place to start.

Jesmed may be right, but can you describe specific conditions under which it runs rough?

Also, do you routinely have your AC or your defroster on?
And yes, it may have something to do with the real time 4WD. But that’s premature. Engine operating possibilities should be eliminated first.

I think the OP is gone…