Sudden drop on MPG causes?

[DamonOwner]

I have not used my 2008 Windsport 34B with a Ford V10 as much as I would like. However, I recently noticed on the last few trips out, my MPG has dropped significantly. Where I was averaging 6-7 MPG, I am now consistently getting about 3mpg (over a few trips of 200-800 mile ranges).

I know this is not much information to go on but any suggestions?

[Belgique]

Mine is in the shop today. Per Scan Gauge, I'm struggling to get 4MPG when I used to get 7.

The owner, an old friend and great mechanic, said he doubted his computer would show anything because there was no "check engine" light and Scan Gauge shows no codes. He commented too that the winter blend was cutting mileage for his clients.

Do different shops have different equipment...i.e., equipment that can scan deeper?

[rgatijnet1]

tderonne wrote:
You are missing my point. The engine controller doesn't know the air fuel ratio. The information is not there for the Scan Gauge to monitor.
Maybe you are watching the short and long term fuel trims?

Perhaps you need to take it up with the folks at ScanGauge. As the link I gave you shows, it monitors the air fuel ratio and shows it as the optimal 14.7 during normal cruise on my GM 8.1L. This drops when I am accelerating or climbing a hill as the engine is fed more fuel for the additional load.
Are the short and long term fuel trims given as 14.7??? NO, They should be close to "0" or less than 10% plus or minus for each.
Perhaps the ScanGauge is taking all of the information available and calculating the A/F ratio.
If you read what is on this link, it shows that on some vehicles, it gives the fuel trims AND air fuel ratio. Scan Gauge X commands

[tderonne]

You are missing my point. The engine controller doesn't know the air fuel ratio. The information is not there for the Scan Gauge to monitor.

Maybe you are watching the short and long term fuel trims?

[rgatijnet1]

tderonne wrote:

rgatijnet1 wrote:
That is why I continuously monitor my air fuel ratio with my ScanGauge.

Scan Gauge can't show air fuel ratio. There is no air fuel sensor to display.

In fact, commanded air fuel isn't even a standard parameter, did you add that with X gauge? Maybe that's what you are looking at?

I have a newer ScanGauge with all of the x gauge upgrades. It does show A/F ratio as well as transmission fluid temp. Here is the link: ScanGauge

[tderonne]

rgatijnet1 wrote:
That is why I continuously monitor my air fuel ratio with my ScanGauge.

Scan Gauge can't show air fuel ratio. There is no air fuel sensor to display.

In fact, commanded air fuel isn't even a standard parameter, did you add that with X gauge? Maybe that's what you are looking at?

[jplante4]

I like to make a request that the OP post the resolution.

[rgatijnet1]

That is why I continuously monitor my air fuel ratio with my ScanGauge. If something was changing in my fuel delivery system, it would change my air fuel ratio from the normal of 14.7(for a gas engine) at cruise to some reading that would indicate my engine was burning more fuel than normal.
It takes a period of time to accurately monitor fuel mileage but my air fuel ratio is displayed instantaneously so if a problem develops I will know it right away.

[John_Joey]

More vote is for one or more bad coils.

[J-Rooster]

Mr.Mark wrote:
This is a good example for checking fuel mileage. I have done it at every tank on our coach (even though it's diesel). If a person didn't check their mileage do you think this would have been caught?

MM.

X-2, I check my mileage like Mark at a minimum of at least once a year! Very good practice!

[wa8yxm]

Thought it was summer blend that dropped due to higher vapor temp.. Oh well, what do I know.

I know they used to tell us Gas and Booze do not mix, but now the government insists we buy a mixture.. Those "Do not mix" folks knew their stuff (Save for a small amount in the winter)
E01 Good, E02 Good (in winter) e more than 5, not so good.

[Big_Katuna]

Winter blend fuel will drop. Definetly get an analyzer on it.

[tderonne]

Are you sure it's 3 MPG? Short trips can kill mileage.

You do mention an 800 mile trip though. Did you really have to stop every 150 or 200 miles (50 - 70 gallons) and fill up? If you were running that rich (double) you'd be pouring black smoke out the exhaust pipe.

(And the whine is the cooling fan, I'd bet money on that.)

[DamonOwner]

I appreciate all the ideas... Regarding stealing my gas, not likely, I have measured the MPG from fill-up to fill-up while on the road, not after storage.

I am not sure if it is related but sometimes when pulling really hard on an incline I hear a high pitched whine that continues until I let up on the throttle.

Thanks again for the help.

[topflite51]

Defective O2 sensors can cause this to happen, but should set check engine light. Have seen some that did not however.

[Ivylog]

Is it possible someone is taking 5 gallons out of it when in storage?