Bad mpg. Idk why.
03-12-2012, 07:54 PM
#62
Like another commenter, my car is a '98 (auto) and it has rather poor mileage around town. On the highway I can get 25mpg if I stay under 75mph and have seen as high as 27mpg, but around town I'm only getting 16mpg lately. I think it's gotten slightly worse over the last several years too. The engine is unmodified and I replaced the driver's side pre-cat O2 when it threw a code a year or two ago. It actually just threw a low voltage code on the O2 after the cat on the same side just recently and I reset it and has yet to come back in the couple of months since. The car has new cats and I checked underneath and all the wires are safe.
I definitely need a new fuel filter as I have no idea how old the current one is. Actually the car just started doing this hard-start routine where it takes a few cranks and sometimes it will start right away, and sometimes it takes a couple of tries to start running--and the car always turned right over on the first try. It runs fine after that, but I'm hoping a new fuel filter might help. Cleaning the MAF would couldn't hurt either (although I'd think that would lead to a lean burn condition, if anything). I do smell gas, especially when the car starts running, but I don't see anything coming out the exhaust (though that is the source of the smell, the evap. is fine). I don't have any trouble codes.
I know with stuff like this, it could be a lot of things, but I'm open to suggestions. Cleaning is always good. I trust the plugs I put in there, so I don't expect they are to blame, nor has there been any kind of stumble or misfire. The fuel injectors could be a culprit and so too could the 02 sensors, but those are expensive to replace just in the hopes of better fuel economy.
I definitely need a new fuel filter as I have no idea how old the current one is. Actually the car just started doing this hard-start routine where it takes a few cranks and sometimes it will start right away, and sometimes it takes a couple of tries to start running--and the car always turned right over on the first try. It runs fine after that, but I'm hoping a new fuel filter might help. Cleaning the MAF would couldn't hurt either (although I'd think that would lead to a lean burn condition, if anything). I do smell gas, especially when the car starts running, but I don't see anything coming out the exhaust (though that is the source of the smell, the evap. is fine). I don't have any trouble codes.
I know with stuff like this, it could be a lot of things, but I'm open to suggestions. Cleaning is always good. I trust the plugs I put in there, so I don't expect they are to blame, nor has there been any kind of stumble or misfire. The fuel injectors could be a culprit and so too could the 02 sensors, but those are expensive to replace just in the hopes of better fuel economy.
You are correct there are so many sensors in there your 02 sensors could be fine and MAF is dirty. I am NO EXPERT lol only a 19 year old kid that has ideas and makes them happen. Always things to learn and when I think I m right sometimes I am wrong.
If your computer isn't throwing any CEL for the o2 sensors it means more than likely it is switching over to closed loop. You would have to monitor the voltage from them to actually determine if there good. The front ones under normal conditions range from .2 to .8 volts. The after cat seems to sit around .5 volts. Due to the fact you said the engine is running smooth I am more likely to think it could be something else.
You said the fuel filter, I would start there. Hard cranks are no good. Cheap and easy and maybe that could fix it. Maybe some of the other experts will chime in?
If your computer isn't throwing any CEL for the o2 sensors it means more than likely it is switching over to closed loop. You would have to monitor the voltage from them to actually determine if there good. The front ones under normal conditions range from .2 to .8 volts. The after cat seems to sit around .5 volts. Due to the fact you said the engine is running smooth I am more likely to think it could be something else.
You said the fuel filter, I would start there. Hard cranks are no good. Cheap and easy and maybe that could fix it. Maybe some of the other experts will chime in?
While I was soaking the fitting+old filter with WD40, I took apart my intake tract to clean the MAF. I used MAF cleaner and a Q-tip on the little wires. It was lightly covered in a thin layer of black dust, but not nearly as bad as most air ducting I've seen, especially at this mileage. I also threw in a new air filter for good measure.
The bad news was that with the intake hose off, I could see that the intake manifold was coated in engine oil (I also posted about it in this thread, note that I am not the OP with the photo). To me this says the PCV valve is bad, so I got a new one and put that in. The hose/fitting/grommet the PCV fits into was ripped, so I had to tape it up for now, but that's another part I should replace if I can get one.
I'm assuming with all that oil being ingested, that the plugs may have a coating on them as well which could be preventing a clean combustion cycle. I'd like to clean out the manifold, but I don't want to take it off if possible so that likely means top end foam. I should probably pull a spark plug to check the conditions inside, and to make sure they aren't ruined. I still have 3, O2 sensors on their way, so those go in next weekend. Unfortunately, the hard start is still present and the car seems to drive the same. I have a pressure gauge for the vacuum system that I believe can also check fuel pressure, or I can rent a dedicated gauge, so I should check if the fuel pump may be on its way out. A clogged fuel filter may have exacerbated the problem if that is the case. Not looking forward to dropping the tank due to rusted sway bar endlink bolts, rusted exhaust clamps, and in general, rust just waiting for me find it. Still, the car runs smoothly as it always has, and it's too soon to tell if gas mileage has improved yet.
