Sudden drop in MPG

[iwatchyoupark]

Hi Guys,

Car : 2004 1.4vvti corolla

Roughly 3 weeks ago my car took a nose drive in MPG, going from about 340miles to a tank to struggling to reach 260. The extra fuel usage is very evident when travelling at speeds around or above 60mph (2800rpm+ in 5th gear) I've been told this could be caused by clogged air filter, faulty MAF or damaged O2 sensors. There is no EML on and the car drives fine but feels a little more sluggish than normal/

I've checked the air filter and its clean (relatively speaking) i cleaned some dirt and oil residue from the MAF and neither seemed to have changed the MPG issue.

After looking online and speaking to a mechanic friend i was told you can test the o2 sensor by measuring the resistance, i checked the pre-cat o2 sensor (been told the pre-cat sensor is the one that usually fails) and got a reading of around 8.1 ohms, which i believe is within tolerance (can someone confirm this?)

I've yet to test or check the post cat o2 sensor as i've had limited time to crawl under the car. 

What would be your recommendation for the next step to find the issue? 

 

[DeTomato]

Some supermarket petrol can wax up the fuel injectors. Put a bottle of fuel injector cleaner into 1/2 a tank of fuel. Run it for a few days and see if the problem persists then top up with clean fuel. Could also be a leaking fuel injector if it's running badly also? How long ago were the Spark Plugs replaced? If worn and the gap is to much then it will also cause excessive fuel consumption.

[iwatchyoupark]

Funny you mention it, i never said on the post but i noticed the dive in fuel efficiency after i filled up at a recently opened manless "go" petrol station. 

The car starts, runs and drives fine, just feels a little more docile than normal, especially in lower pre-vvti rpm. 

Another friend suggested it could be a dirty fuel filter, i don't see how this could cause the issue but i'll replace it anyway for all they cost. 

I don't believe its a maintenance thing such as spark plugs or air filter as the fuel drop was immediate, not something thats gotten worse, but the plugs are around 15k miles old so will replace them while i'm there.

[Catlover]

What is a "go" petrol station.

The only unmanned petrol station around Chester that I know of is Costco and I been using their 95 petrol on and off for 2 years and dont notice any difference.

[FROSTYBALLS]

Go is a fuel brand sold in Ireland - some sites are 'pay at pump' only.

[Dread2zz]

Check your tyre pressures!!!