420A I'm at a loss on why my MPG is so bad

[1997gs]

Ok I've no idea what's going on but I filled my tank 4 days ago and I e already used half a tank and I only go to and from work what all can affect fuel efficiency

 

[C'LO]

Maybe it’s the level sensor perhaps if it’s not actually empty, or could be a bad oxygen sensor

 

[AWD-Tony]

Fill it up again and see how many gallons it takes. That will rule out the sending unit.

 

[1997gs]

Wouldn't the sensors trip a engine code

 

[rabenne]

If you are asking if the fuel level sensor reading incorrectly would trip a malfunction indicator lamp: No, it would not.

If you are asking if a bad oxygen sensor would trip the MIL, yes, it could. But I doubt you are actually consuming as much fuel as your gauge says.

 

[rabenne]

Fill it up again and see how many gallons it takes. That will rule out the sending unit.

Let us know how this goes...

 

[ThunderChild]

Could also check the oil to make sure it's not fuel saturated. Other option is to hook up a code scanner and see what the fuel trims say.

Oherwise do the proper fuel calculation when you fill up: miles traveled ÷ gallons filled.

 

[Lilslmj]

Check your actual mpg and get back to us. We can't help you if you tell us you drive to work and home but we don't know if you work 40miles away or 100 miles away so get your actual MPG

 

[miguelmcv]

Most of the time a front oxygen sensor doesn’t throw a code, it just runs rich without noticing.
The only way to see is a obd2 reader and Monitor the from o2 sensor.

But like other ones says, fill the tank and see how many gallons you are putting in, drive it and do the math.
When the gauge shows low and you fill it again see how many galones it takes, maybe it has half tank and it will not take more then 5 gallons.

 

[randman2011]

My GSX takes about 150 miles to drop from full to 1/4 tank. Then it stays on 1/4 tank for another 150-200 miles before the fuel light comes on. I have learned to not trust the fuel gauge on any of these DSMs. It's not that difficult to fix assuming that you can get the fuel supply line unscrewed from the sending unit but as far as I can tell calibrating the sending units is a matter of guess, test, and revise.

Coolant temp sensor, front O2 sensor, MAF sensor influence fuel economy. If it's running just fine you could rule out the MAF, but as everyone else has stated, verify your actual mileage before digging into anything else.

 

[ThunderChild]

OP has a GS, so no MAF, but good reference that if the map is clogged up that's another thing that could be contributing to poor mileage.

We still need to know miles to the gallon so OP need to do some driving and fill up once or twice still.

 

[Clipsoe]

Fill it up and reset the trip counter, get a 1 gallon gas can and fill that up, drive it till its empty and runs out, use the gas can when it does to get back to the gas station. Once you fill up check the cost and gallons. You can get a lot of info: Total of how much it takes to fill, how many miles you can get on a tank, how many miles you can get once the gas light comes on, and if your needle if working properly. Once you have that (Trip count from last full tank divided by gallons filled) you can calculate mpg, as well as using your trip counter to know exactly how much gas you have.

 

[Cherry]

Usually if its an O2 sensor and it runs rich your car will produce black smoke out of the exhaust. At least thats my experience with my dads van.

 

[BLACK'98DSM]

I get 360-ish miles before my gauge says empty. I bet I could push it to 380 before I actually run out. (running premium)

 

[Vegas Smith]

Have you gotten under the car and checked for leaks?

 

[spyderdrifter]

Since this topic is here, my scanner reads live data and fuel trims, but I've never understood how to read the data. Can someone explain that?

 

[miguelmcv]

Since this topic is here, my scanner reads live data and fuel trims, but I've never understood how to read the data. Can someone explain that?

Trims has to be between +5 and -5. It jumps up and down but the average is 0, so +5, -5 is good.
If it goes over +5 or below -5 then you are not in parameters, so you have a leak or some sore of.

 

[spyderdrifter]

Thanks.

 

[spyderdrifter]

This is the only data I have that could be referring to fuel trim that isn't open or closed loop, is this correct?

You must be logged in to view this image or video.

This was taken while at idle if that helps.