jayboydog

I used to get 18 MPG in city driving. Now the mileage is 14 MPG. no Check Engine Light. idles fine. accelerates well. have replaced some of the fuel injectors, new spark plugs. replaced 02 sensors. was getting check engine light for EGR solenoid and that has been taken care of. what would cause my gas mileage to drop to 14 MPG and no check engine light?

vqmaxman

The fuel filter needs to be changed and the tires need to be rotated and balanced and ect ect. If the tires are improperly inflated the car will give you bad MPG. The fuel filter is really dirty or clogged that will also give you the bad MPG. The other things to check is the IACV and the TB and the get them cleaned. The other things that will have to be done is get a new PCV valve. The MPG is really low and bad.

The Wizard

iTrader: (43)

Tires for sure play a role in gas mileage

I'll add the following:
1. Check for the ghost KS code.
2. Injector(s) are bad/leaking under pressure
3. One or more O2 sensors is tired. Did you replace them all?
4. Now that it's summer, is your AC on all the time now?
5. Dirty air filter
6. Driving habits
7. Are you carrying around a lot of extra weight all the time?
8. Excessive idling
9. What oil/weight do you use?

Quickywd01

iTrader: (16)

Everyone else forgot about that one.

dwapenyi

iTrader: (3)

Which O2 sensors were replaced? A bad KS won't cause that big of a drop in MPGs. My KS was bad for half a year yet still managed to average 23-24 mpg per tank.

max ride 41

iTrader: (4)

i had a bad knock sensor for 3 years and did'nt notice a big change in gas mileage after replacing it. fuel filter and a seafoam and i bet you get better gas mileage.

Turbobink

iTrader: (2)

A tad more info would be helpful on accounta I'm not seeing a clear timeline.

Are you saying that you noted reduced MPG and made all of the listed changes but MPG didn't improve?

Are you saying that you completed the listed maintenance recently and those changes have resulted in or at least corresponded to the reduced MPG?

Or are you saying that at some point during your ownership those things have all gotten done and recently your MPG has nose-dived?

Quickywd01

iTrader: (16)

You can't just drop a line like "have replaced some of the fuel injectors" and expect to get away with it...

CMax03

iTrader: (3)

Damaged fuel injector oring, Or defective FPR, or def MAF....I would swap out some with known good parts not necessarily new but good!

jayboydog

I am wondering if a temperature sensor which sends signal to ECU might be bad causing a rich fuel mixture. is 14MPG considered to be "limp home" mode?

Quickywd01

iTrader: (16)

I'm wondering what kind of plugs you got? I'm wondering if you messed up the injectors?

jayboydog

I suppose an injector might be leaky but I am more focused on the computer getting a signal which causes the computer to manage the engine in a rich fuel mode. Replaced the two upstream O2 sensors. Fan comes on when engine gets too hot.

Quickywd01

iTrader: (16)

Cool, good luck.

2000i30ca

if you check eng light is not on, coolant temp sensor would be on my top of list to check. this is only sensor that the ecm could not "test" or double check with input from other sensor. ecm will be able to tell if a o2 sensor is lazy or if a spark plug is missing, but if a coolant temp sensor is bad, and it usually goes bad on rich side ecm will believe the engine is cold and kept putting in more fuel. you can verify by try smelling eng oil to see if there is excess gas. and you don't have to buy new ones, you can pull the old one and measure the resistance and check against spec.

one other thing you could check is binding brake calipers, the symptom would be that one rotor is hotter than others, you can check with a infrad gun. or you can jack up each wheel and give it a spin. one thing you will feel is that brake is working too well, just barely touch it and car slows, it is because the clearance in brake pad and rotor is already taken up in the stuck caliper.

jayboydog

I changed the two upstream O2 sensors, tested the MAF signal wire (0.58v at idle, voltage increases as engine revs faster). the mechanic said if the temp sensor to ECU were bad, the radiator fan would not turn on. (apparently the fan is turning on). I had tested the resistance of the fuel injectors several months ago. two had no continuity, the others did have resistance so I replaced the two which showed no continuity. The mechanic replaced some of the fuel injectors with used injectors, I have no way of knowing which ones. when he finished I was getting 7 MPG. so one of the used injectors was leaking. that injector was replaced and the car is again getting 14MPG. still shy of my expected 18MPG.

The Wizard

iTrader: (43)

IMO, you're dancing around the issue. Get all new injectors, or send yours out for professional cleaning.

And you only expect 18mpg? Why? You should be capable of getting 22 to 25mpg's no problem.

dwapenyi

iTrader: (3)

What is the situation with all other basic maintenance of the car? Plugs, air filter etc? Are they regularly changed?

Also, has the fuel filter been changed? It needs to be done every 30K miles. If it is long overdue then that could contribute significantly to bad gas mileage.

2000i30ca

check your pcv hose connection. first remove pcv valve from the valve cover and then try to rotate it by hand. you should not be able to do that. also shake the valve to be sure it rattles. my guess is this hose is hardened and is leaking vacuum. I have replaced one, and I could tell a difference in throttle response. bad hose could cause low vacuum and low manifold vacuum could cause fuel pressure regulator to increase injector pressure and waste more fuel

Frank Fontaine

When my car was new I tracked mpgs religiously, and I always found this one to have a major impact, even after only 10k sometimes.

I'm looking now--my android only has 3 years of data, but the avg. mpg is 21.5, and that's a combination of some highway, but mostly city.

jayboydog

had the engine rebuilt after found water and oil mixing. but the Mileage is still 14 per gallon. the idle fluctuates rhythmically from 750 dropping to 650 for an instant and rebounding to 750. the engine has to be cranked two or three times to start. (although today I turned the key to on position and waited five seconds. the car started on the first crank). took the car to a dealer for diagnosis. was told the MAF sensor needs to be replaced.