Ive noticed that my 2004 MCS is starting to consume much more gas than normal. Its gotten to the point where its going thru a half tank in about three days off of just regular driving, less than ten miles a day.... Is it time for new injectors? Or fuel filter?

 

The injectors could be leaking, but that seems like an awlful lot to not have noticed a drivability issue to go with it. I would look for other leaks in the system. Does it smoke (black) alot?

 

Usually filters or injectors won't show in a reduction of fuel economy, but I can see a loss in leaks. Do you notice any odors or water spots where you park? The computer could be choking the car more not reading something right and pushing more fuel into the combustion chamber? Dirty air filters? Do you have an ODB log reader to tap into the computer and see how the numbers are flowing?

 

Is there gas in the oil?

Does the car start ok?

 

I highly doubt there is gas in the oil since the car runs fine...

 

No black smoke.. Ran seafoam in the summer too

 

Well I restarted the mpg consumption and the numbers seem to be jumping around... No gas smell around the car either

 

Has this been going on for several tanks? Could it be that you're just having an fuel-quantity indication problem, rather than actually only getting 5 MPG?

 

Well it's been like this for a couple tanks, idk what it could be because at times the distance to empty actually coincides with odometer, but not always. Also normally when it gets down to below 70 miles to empty, it will only have one tick. However it is still showing two ticks

 

I have the one ball exhaust mod and it's great on power and I have been getting on it lately, but it's been doing it before I did the mod

 

Well i will check the air filter as i havent changed it all year (since i bought it used in feb) hopefully thats the thing. Will also check injectors

 

Maybe some D-bag is stealing your gas.

 

The obc is pretty inaccurate...and running the fuel tank to almost empty is VERY BAD FOR THE PUMP...IT IS COOLED BY THE REMAINING FUEL IN THE TANK....hot pump= failure in less time.
Injectors can get drippy...usually results in a hard start...or stuck open..motpr stoppage...if they were spraying too little fuel, you would get lean codes, and better mpg...worse mpg may mean you are getting close to needed a pair of o2 sensors....
A bottle of injector cleaner will not hurt....
In some parts of the country the change over to winter fuels, and folks idling a bit to warm up kills mpg....

 

I hate to admit defeat when it comes to troubleshooting, but I'm at a loss. If you're really down to 5 MPG, but the car feels like it's running fine,then it's not anything as simple as a dirty air filter or the new one-ball exhaust mod.

Frankly, HRM's idea that someone is siphoning gas makes more sense than anything else I can think of.

 

If you haven't replaced the 02 sensors yet, that could be part of the problem - especially the one before the catalytic converter. Often, a failing 02 sensor will give you a SES light though.

 

Does your kid steal it after you've gone to bed? I used to do that. lol

 

Well I usually fill up when the counter gets to 40 miles to empty... As for hard starts, it's always turned a few times more than what I'm used to.. The idle used to get a little lumpy in the summer, but hasn't happened for a few months now. At the shop they're saying maybe switch to a better grade of gas

 

Update: checked spark plugs. They're fine
Air filter is slightly dirty but nothing serious, haven't been able to find a place that sources these filters... Tire pressures look good.. Car ran extremely well this morning.. No evidence of a leak.. And I lock my doors do the gas isn't stolen, also accOrding to the obc this fuel is being consumed... IDK WHAT'S GOING ON

 

Has the fuel filter ever been changed?

Jim

 

Not to my knowledge.. But im hearing that wont cause a drop in fuel economy

 

Lol hahahaha im only 20 myself

 

Don't trust the OBC for calculating fuel use....it is notoriously inaccurate. Get a calculator and do the math yourself when you fill it up.

 

True. I'm OCD about mileage - the OBC on mine has ranged between 1% and 19% too high, with an average of 11% too high.

6 gallons over 30 miles makes no sense at all. You should be seeing or smelling that type of usage.

 

Hmmm so i made a thanksgiving drive and got about 400 to the whole tank.. Ran injector cleaner but I'm still seeing the range jump around at the slightest change of speed

 

^+1 for this...The Pre Cat sensor could be the problem,have you tried to get the car scanned for codes?My pre-cat sensor failed and showed codes even tho the SES/CEL light didnt come up at all...