As a mechanic, if this job was presented to you and you were told the customer would judge the sucess or failure of your work based on the method of mpg calculation described how would you feel?
I can say the contacts on the fuel sender do change resistance over time, I can’t see why the OP won’t even consider testing his mileage by the more accepted method. I decline this job, my box needs to be re-organized.
Some O2 sensors are easy to get to and some are not…They are located in the exhaust pipe near it’s joint with the exhaust manifold, upstream from the converter. They look similar to a spark plug and it usually takes a 22mm open end wrench to change them…price range $40-$85.
They send a signal to the ECM telling the computer if the engine is running rich or lean. The computer then adjusts fuel flow to the injectors as needed…If an oxygen sensor starts getting tired, it can cause the computer to think the engine is running lean and it will then inject more fuel to correct the problem when there really was no problem…
3 years ago we had the head gaskets, timing belt, thermostat and all that replaced…ever since then it has run cooler than it did before 190 vs 160 now…can a coolent temp sensor affect gas mileage?
If recently we have been hearing a slite rattle from the converter…if the stuff in the converter is loose and changing exhaust flow a bit will that change the sensors signal?
im listening how do you want me to test it now?
we had a lot of work done on it at once tuning it up and the shop said they replaced the spark plugs or at least i was charged for it … so when i looked at them later they were very black and pretty much no electrode left…they all looked very old and used
It absolutely does - that’s why it was the first thing on my initial list way up top.
When the car is cold it must run richer - more fuel. In the old days it was called “choke” and was done on carburetors by restricting air with the choke plate. Nowadays the computers commands more fuel from the injectors.
If your car always runs cool (thermostat) or if the computer thinks the car is running cool (coolant temp sensor) then it will continue to send a rich fuel mixture.
Thermostat and coolant temp sensors are prime suspects any time there is a noticeable drop in fuel economy.
they were very black
That’s evidence of running rich.
I’d suspect O2 sensor, thermostat or temp sensor.
Well, its all now buried in this lengthy thread by now - but we know that:
a) your car is running cooler than normal and
b) your old plugs probably showed that you’re running rich.
Replace your thermostat with an OEM rated part and put a multimeter on your coolant temp sensor (you need resistances as the coolant temp rises and falls - you can probably find the specs via Autozone’s online repair info).
Fix those two things and I’ll bet you’re close to back to where you were with mpg.
thanks that sounds good
No, not everyone. I won’t and don’t use. Ethanol cuts into my fuel mileage too much for the penny or two I save at the pump.
My opinions are subject to change with new facts.
It is probably gas related. If the mileage went down suddenly late last year, you might see it inccrease about now as the gas stations run out of their winter blend. That’s what happened to my cars. My mileage just started going back up within the last two weeks.
You are not the only one. Since the beginning of the Arab Spring in December 2010, both my husband and I have noticed a drop in our gas mileage. We drive two different well maintained cars: 2006 Mazda 3 and 2004 Honda Civic, but we both fill up at the cheap WalMart and Kangaroo Express gas stations in Huntsville, AL. My gas mileage dropped from a 30-33 mpg (steady for the past 4 years) to 24 mpg. The oxygen sensor was replaced a year ago, the spark plugs are in good shape, the tire pressure is normal, and the alignment is good. My husband also saw a precipitous drop in his gas mileage. This points to bad gas to me (more ethanol in the mix?). Since December, I have been filling up the tank at more expensive gas stations eg. Texaco, Chevron and have gradually seen the gas mileage come back up to 30 mpg. My husband continues to fill up at WalMart/Kangaroo and has seen only a slight improvement. Could be just coincidence, but also could be bad gas.