I have a 1998 honda civic EX coupe with only 83000 miles. i have had a new cap and rotor, timing belt, aem short ram intake. Irun mobil 1 senthetic, and have had two fuel injection cleanings (done by a shop through the vaccum lines) in the last 6 months. I have new brake pads, drums, drum breaks and rotors. I run 17 inch rims with 205 40 17 tires on them. I can not for the life of me figure out what else i can do to get this gas mileage thing under control. Everyone i talk to just says WOW and thinks I am making this up. Please help!
Thanks

 

The most common culprits are worn spark plugs or a dirty air filter. There could possibly be a leak some where, but if it was leaking gas you would most likely smell it. What's up with a 1998 Civic with only 88k miles on it? Was it sitting for a long time or you just don't drive it often?

If I were having your problem I would take the throttle body apart, clean it. Take out the injectors, and clean them too. I'd check all the fuel lines for any sign that they are compromised. I'd check my fuel pressure, and spark plugs. I'd inspect and clean the fuel rail. It never hurts to check and adjust the valve clearances if needed. Although I've never heard of valves causing fuel consumption problems. Fouled or worn ignition parts can make all sorts of problems although with 88k that engine should be fine. Unless it was sitting for a long time and the internals corroded or something.

It's difficult to adjust the fuel mixture on a fuel injected engine, but there is a small (very very small) chance that the chipset is bad. Do you know if the car has always had this consumption problem? Normally when computer chips are faulty they simply don't work, but with the info you gave I am considering everything.

The ugly option: You could pay Honda to diagnose it... And they will probably tell you nothing is wrong and then charge you $100 or something ridiculous.

 

Sorry I forgot to metion. Also check your engine timing. I would be iterested to know when your fuel problems started to happen.

 

The first thing I would check is your o2 sensor. It sounds about the right time for that unit to fail. Since it's winter, I'd also remove your cold air intake and use your stock intake. I believe CAI can hurt mileage when it's really cold out.

Those vacuum line treatments did not clean your injectors. If vacuum lines connected to your injectors, there'd be gas running in them, not vacuum. It might have cleaned your intake and your injector tips a little, but try running some gas cleaner in your gas for the lazy way to clean the injectors. I highly highly highly highly highly recommend the product "Seafoam". It can be harsh, but it's very effective at removing carbon deposits and cleaning buildup. You can probably find some at an Autozone or Kragen. I'd put 1/3 can in your fuel, 1/3 can in your oil about 200-400 miles before an oil change, and I'd run the remaining 1/3 up through a vacuum line (though a shop probably already did this).

About half the things you mentioned don't affect mileage. Your new timing belt and brake pads/drums don't modify your mileage. You could check your tire pressure to make sure they're up to spec. Low tire pressure can drop your mileage by about 5%. I agree with EJ8 about checking your timing. If you got a new timing belt, it's VERY possible that the mechanic who did it set your timing incorrectly. It may even be possible that he installed it one tooth off (and perhaps you're running really retarded, which wouldn't produce weird sounds, but it would kill your power and your mileage).

BTW, I have an '87 civic with 188k miles on it. It's never had a brake drum job done. I've checked it numerous times and there's still decent life on them. The rear drum brakes are very low wear items and shouldn't need replacement at 88k. I only mention this because it sounds kind of fishy that you've listed several maintenance items that are irrelevant to fuel mileage. It almost sounds as if your mechanic is trying to sell you these mileage improvers. Is that the case or am I just paranoid?

 

Ya I agree with Jamned that the mechanics may be trying to scam you on things that you don't need. This is the sole reason why I do everything myself. Also I believe "If you want something done right do it yourself". Mechanics will not respect your car like you do, and will never do the little extra finishing touches that I always find myself doing everytime I work on my car.

As for going 188k on one set of drums I've never heard of that many miles on a set of pads before. When's the last time you bled your rears and adjusted them? If you really got 188k on a set of pads and their working properly that's awesome. I had to change out mine on my 95 LX around 100k.

One more thing to note using injector cleaner by putting additives in the gas normally clogs the fuel filter. I always clean directly through the throttle body, or by removing the injectors completely. But Jamned is correct in that it is good to clean the lines at some point. I'd do this right around the time the fuel filter is needing to be changed though.

 

Hmm, I'll keep that in mind next time I try running cleaner. I'm also a DIY maintenance guy. I got the car around 120k and I started learning how to do routine maintenance around 150-160k, so the brake fluid was old and possibly the original for a while My brakes were underpowered and I suppose that could've stretched the life out a lot. Don't worry, I bled the system with new fluid around 170k, so I'm not driving around like that anymore[&:]