Recently I've been getting really bad gas mileage. It didn't happen until I changed the spark plugs with new ones. The plugs are gapped correctly to .54 mm . The engine does have 270K miles on it so. I've cleaned the air filter, and inspected the plug wires and theirs no visible cracks or marks. Anyone have any ideas on what it could be?
it's rated for 17 city / 25 highway
but 12 to 21 is more average.
If you are going to keep the vehicle, get some mechanic to put an OBD II analyzer on it. It will find the problem.
@man_w_2003_66000_miles_van I have a scanner and there's no codes that's noticeable that triggers anything. I've even looked at data streams of everything and everything seems to be fine. I have photos to show if needed.
Logic would dictate that you got bad spark plugs. Which brand did you use? Are they the same part number which is recommended for your car?
Are there any trouble codes? Are your tyres inflated at the correct cold tyre pressure? Try installing a brand new air filter & check if it goes away?
Is the car misfiring at all and check for any loose hoses.
@inthrustwetrust I bought motorcraft sp-432 spark plugs and bought and replaced all 8 and still had the same issue. I couldn't find the original plugs for the car but matched them as close as could be and this one is the closest i could find that had the same half thread design they had back than. The gap is set to .54mm which is recommended for the vehicle.
@inthrustwetrust i put 35 psi in all 4 tires the recommended amount they say to put . Nothing is misfiring i tried a test with spark plug wires and their was no arching so their good. I havent gotten a new air filter but i can still see through it. Maybe the Mass air flow sensor? I checked it and looked to be dirty .
Ok try the steps in Scotty’s video on how to make your car run better with a little spray cleaner. If that doesn’t fix it, then it’s time to look at the live data. Did you already check all hoses for any vacuum leaks?
@inthrustwetrust I did check to see if theirs any vacuum leaks theirs none. the engine is not going up and down on rpms when idle neither so its not vacuum hoses . I do have a scanner that does have live data.
Great, test the fuel pressure and look at the data for the oxygen sensors & MAF sensor.
@inthrustwetrust Oxygen Sensor Read at: 0.5.85V at idle, Air flow rate MAF sensor: 7.01g/s, Short term fuel Trim (B1-S2): 99.2%, Short Term Fuel Trim (B2-S1): -1.6%,
Look at long term trim, ideally should be 0 but +-4 is good. I suspect you'll find an issue on bank 1.
@HillBilly When idling the long term trim is 0.0% it stays like that as well.
Well, the computer has your a/f ratio perfect (or thinks it does). Make sure it's going into closed loop operation after warm up. Putting in new (OEM) upstream O2's will insure most accurate data from them along with new (OEM) maf giving ecm the most accurate data it can get to adjust injectors...and with 0 ltft, it's doing that very well.
Now I wouldn't do that as I think it's age and wear on the engine causing your reduction including ageing trans power loss.
Is this a used car you bought, or original owner?
have u tried using 93 octane or better.
Always fill up with 93 octane 1x per month to help keep valves clean.