Fuel economy keeps INCREASING. Need help or ?

[Kotrin]

What app would you suggest?

Fuelly with a gps app of your route (sorry so late on the response). My in car stereo does it for me and my ScangaugeII does also..lol

 

[PWD4R]

Ok so I figured out how I can get 459 miles or 738 kilometers per tank of fuel. Sorta...



If my ScanGauge is accurate in its reporting of real-time fuel mileage and if the conditions were just right, i.e., predominantly flat ground and a nice tail-wind, I could "in theory" drive 459 miles on one tank.



I set this experiment up so that with the cruise control on, I wouldn't be inadvertently affecting the throttle position with my foot either.



Also, I added the TPS sensor to my ScanGauge so that you could see if there were any shenanigans with how much throttle was being applied in that moment. At idle, the TPS sits at 10. With the cruise control engaged at the speed that netted the desired 27mpg — the TPS seemed to sit around 14-18 on flat ground and obviously more or less depending on incline/decline.



As you can see in the pic, if I drive on flat ground at 42 miles per hour with the cruise control set — I get 27~ mpg.



Now obviously the OP isn't driving 42 mph — but I could see with an engine that is running lean in conjunction with speed that was under 55 mph in addition to favorable road & wind conditions — the OP "might" approach 27 mpg and achieve 450+ mpg.



I only had short area of the road to note all this, so I wouldn't be surprised if there is a way to do this but at a higher speed as well.

So how stoned were you to do that? You're interesting but there's no way you didn't have better things to do lol


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[HighMiles]

The vacuum leak I had fixed before returned. Originally I had cut the split end off and stuck it back on, but have no idea when it split again.

The hose is from the black plastic box hanging off the intake between the air filter and plenum.

Replaced the vacuum line this time. Head out on my trip tomorrow after work. Will see what happens.

 

[jgue467]

Nice Problems!

Excessive fuel efficiency is a Nice problem to have. Really, really nice.

Only Nicer problem I can think of is Low cholesterol, had yours checked recently? :cowboy:

 

[HighMiles]

Finally...

For some reason I could not post from my phone, via the website or Tapatalk...

To recap the purpose of this thread: My fuel economy has been increasing and I am:

1. Concerned I may be harming the engine be somehow running too lean - although it has been going on long enough that I am feeling better about it, and

2. I want to find out what happened, so I can recreate it on other 3rd Gens, or at least know what parts I should swap out whenever this one dies.

I am not trying to say how great my T4R is, or that I get better economy than others. I do not care about that.

Last trip:

GPS says I am just over 3% slow on my odometer. When I compare the corrected odometer reading, it agrees with Google Maps, within a kilometer and a half.

There were no winds for or against me that were worth noting.

I filled up to spill before I left, did the same upon arrival.

This is an honest reading once out of the mountain pass. I know that it can be easily fudged by slightly letting up on the gas pedal. This is not that.

Arrival:

Fill up:

Math:

661km x 1.03 (correction for tires) = 681 km

Convert to miles: 681km / 1.62km per mile = 420 miles

Litres or fuel to gallons: 65.98 litres / 4.54 liters per gallon = 14.53 imperial gallons

420 miles / 14.53 gallons = 28.9 mpg, or 24 mpg, US gallons.

For me, this is about 150 km more than my old tank of gas while doing this trip over the years. It slowly changed over about 4 months.

RELATED NOTE: My friend's 99 3rd gen gets terrible economy. we went on the same trails while camping, both filled up before and after the trip and I used 17.44 litres, compared to his 29 litres. Another friend with a 3.4 litre in his 82 Toyota pickup used about 25 litres. All trucks went exactly the same place, in a line.

Where can I start looking for possible reasons for leaning out? there are no codes on the 99, but it is running rich. It may have 200 000 kms on it.

You can eat off the inside of my tail pipe, and his is black - like an old oil burner with no catalytic convertor.

Thank you for your feed back.

 

[OldManKamps]

For some reason I could not post from my phone, via the website or Tapatalk...

To recap the purpose of this thread: My fuel economy has been increasing and I am:

1. Concerned I may be harming the engine be somehow running too lean - although it has been going on long enough that I am feeling better about it, and

2. I want to find out what happened, so I can recreate it on other 3rd Gens, or at least know what parts I should swap out whenever this one dies.

I am not trying to say how great my T4R is, or that I get better economy than others. I do not care about that.

Last trip:

GPS says I am just over 3% slow on my odometer. When I compare the corrected odometer reading, it agrees with Google Maps, within a kilometer and a half.

There were no winds for or against me that were worth noting.

I filled up to spill before I left, did the same upon arrival.

This is an honest reading once out of the mountain pass. I know that it can be easily fudged by slightly letting up on the gas pedal. This is not that.

Arrival:

Fill up:

Math:

661km x 1.03 (correction for tires) = 681 km

Convert to miles: 681km / 1.62km per mile = 420 miles

Litres or fuel to gallons: 65.98 litres / 4.54 liters per gallon = 14.53 imperial gallons

420 miles / 14.53 gallons = 28.9 mpg, or 24 mpg, US gallons.

For me, this is about 150 km more than my old tank of gas while doing this trip over the years. It slowly changed over about 4 months.

RELATED NOTE: My friend's 99 3rd gen gets terrible economy. we went on the same trails while camping, both filled up before and after the trip and I used 17.44 litres, compared to his 29 litres. Another friend with a 3.4 litre in his 82 Toyota pickup used about 25 litres. All trucks went exactly the same place, in a line.

Where can I start looking for possible reasons for leaning out? there are no codes on the 99, but it is running rich. It may have 200 000 kms on it.

You can eat off the inside of my tail pipe, and his is black - like an old oil burner with no catalytic convertor.

Thank you for your feed back.

Set the cruise at 100km/h GPS and measure the CC/min of fuel that the engine is using with the torque app. Make sure to measure on a straight and flat road. From my measurements, I think my truck gets 160-190 cc/min. Roughly 13 L/100km

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[phattyduck]

24 mpg going ~55mph? Sounds about right...

That, along with 'fill-to-spill' instead of just filling 'til the pump stops will get you the range you are seeing there.

If the truck isn't bucking or running oddly, I'd probably just go with it. Maybe check your fuel trims with a scangauge or the torque app or whatever, just to make sure you are near 0?

-Charlie

 

[kball]

You didn't name your truck Christine did you?

 

[Victor_inox]

It`s running slightly lean, nothing too extreme.
You can replace that O2 sensor if you want to fix that code, or you can keep great gas mileage. I`d keep that mileage.

 

[frodiesel]

24 mpg going ~55mph? Sounds about right...

That, along with 'fill-to-spill' instead of just filling 'til the pump stops will get you the range you are seeing there.

If the truck isn't bucking or running oddly, I'd probably just go with it. Maybe check your fuel trims with a scangauge or the torque app or whatever, just to make sure you are near 0?

-Charlie

I have consistently pulled 24.x mpg at 55-62 on long flat backroads. 99 3.4l v6 254,000 miles. Also i have seen 25 with the right wind more than once. Scangauge2

 

[kolelt]

I'm scratching my head because I filled up and when to PA, pennhurst asylum and back to NJ. think it was roughly 180-200 mike trip. Was basically on E.

 

[smerhej]

I regularly get ~10l/100km city driving (roughly 23-24 mpg), so ~8l/100km at 95 kmph doesn't seem that ridiculous, and that's after I replaced the u/s O2 sensor as well. I'm also running stock size tires/rims.

Still missing the 550km to 35l fill up I use to get with my echo though...

 

[TXLX1]

Speed has a ton to do with it. On a recent trip going 75-80mph, I got 12mpg. Coming back going 60-65mph, 19.5.

Is the scangauge 2 the one to get? Been looking at them.

 

[HighMiles]

Thanks for the feedback! I do not like it when a vehicle changes behaviour and I don't know why.

I enjoy the extra 5 or so mpg I am getting, and will check the fuel flow rate at 100 and compare with OldManKamps' and check the fuel trims as PattyDuck suggested. That may also shed some light on my buddy's 99 running so rich. Will pull a spark plug and check the colour as well.

Glad to hear that some others are getting in the 8 - 9 l/100km, and glad that I am getting that now. In the past, 24 miles per imperial gallon was tops for me on the highway, so 29 - 33 is a welcome change!

 

[trplpwr]

Might be low fuel pressure, I had a small block chevy that for some reason went from
16 mpg to 25, then the fuel pump fell off the block! I tried to reduce fuel pressure after
that but couldn't get the same results...

 

[HighMiles]

Might be low fuel pressure, I had a small block chevy that for some reason went from
16 mpg to 25, then the fuel pump fell off the block!

It is the original pump... Hmmm. It does not starve for fuel when I step on it, though.

 

[HighMiles]

Set the cruise at 100km/h GPS and measure the CC/min of fuel that the engine is using with the torque app. Make sure to measure on a straight and flat road.

From my measurements, I think my truck gets 160-190 cc/min. Roughly 13 L/100km

Here are the results:

Even with the cruise control set, there was a bit of variation, the fuel trim would bounce between low positive and low negative numbers.

 

[HighMiles]

I pulled 2 spark plugs, and the plug wires had deteriorated off in the plastic tube where the metal end that snaps to the spark plug was crimped to the spark plug wire, so I had to replace the wires.

30 years ago, I was taught that the spark plug should be a chocolate brown. Now this was for carbureted engines that were gas pigs.

These were white, which seems to be old school for lean. Is it new school for efficient?

The electrodes look worn, probably should replace them soon, but does anyone know if this colour is ok?

I really appreciate all the help you guys give.

 

[thegipper]

I'm no spark plug visual expert but I'd definitely say you are running lean with the plugs looking that white.

 

[HighMiles]

I'm no spark plug visual expert but I'd definitely say you are running lean with the plugs looking that white.

And if I remember correctly, lean means hot, which can be a problem.