5.7 idle fuel consumption per hour?

is this the proper point in time that we inject:

if you use 0w-20 you could probably lower your idle GPH?

or is it too soon?


move along....nothing to see here....

 

5.85 g/sec * 3.6 kg-sec/g-hr / (14.5 afr * 0.7 kg/L * 3.785 L/gal) = 0.548 gal/hr

rough calculation it doesn’t take into account the fluctuation in afr and maf.

 

That would be a very frugal 2.1L per hour.

 

45F ambient, sitting at stop light, HVAC off, mine reads 0.42 gallons per hour.

 

I pulled MAF data this morning and used this equation and the one linked. Both indicate .4 gph. This was engine at operating temp hvac off.


https://www.windmill.co.uk/fuel.html

 

All this math makes my head hurt.
Very cool regardless.

All I can really say is my truck is a thirsty bitch.

 

That’s 1.5 l an hour. Much less than my initial estimate, although hvac off as you noted.

 

Ah yes the maths work. Now someone should check AC on and try to capture maf and afr when the compressor is cycling.

 

Heat didn’t seem to have much impact. A/C full blast bumped it to just over .6gph. Again, engine was at full operating temp. Consumption seems to nearly double while warming up.

 

The hunt for answers continues...

I got out my laptop with a copy of Techstream and started data logging on my truck through Toyotas software.
Here is the log screen in Techstream. I logged Coolant Temp, RPM, Injector Fuel Volume in Cylinder #1, Injector Port time, and MAF



Here is the same data in a spreadsheet. I logged 5 minutes worth of data and show the avg value for each at the bottom of the list. This photo shows the last 15 or so seconds of data. As you can see almost all values are stable at this point.



The truck was warmed up at normal operating temp when I started logging. Coolant temp was 187 the entire time. RPM 600-700 Rpm.
Fuel flow into cylinder #1 was pretty steady at 0.110 ml per second. That would mean 0.880 ml per second across all 8 cylinders every second.

52.8 Ml per Minute
3168 Ml per Hour which equates to 0.85 Gallons per Hour

I have read online that the factory fuel injectors are in the range of 370 CC/min. This would mean at idle and 0.85 gallons per hour the injectors are operating at 1.7% of total capacity.

I found a second source to try to verify the data further. Using the fuel consumption logger inside Techstream I logged that it took 6 minutes and 35 seconds at warmed up idle to burn 0.1 gallons of gas. This was at the same 600-700 Rpm and about 0.115 ml per second on Injector #1.



If it takes 6 minutes 35 seconds to burn 0.10 gallons then total gallons burned in an hour would be about 0.90 Gallons per hour very close to the number above including minimal error.

 

A few other things to note from my newly logged data.

On startup and a cold engine the truck defiantly burns 1.6 - 2.0 gallons per hour, however as the truck starts to warm up this number comes down significantly to stabilize about 0.80 gal/hr. I know at 3 minutes into warmup the truck was down to 1.1 gallons per hour. (This was from an earlier log today when the truck was started cold)

The other interesting thing was that using the MAF values as others have suggested in the post doesn't seem to give accurate results. However I’m not entirely sure as to why yet.

My MAF was steady at 4.77 Gm/Sec, according to the math calculations this would be about 0.40 gallons per hour. However the raw data from the fuel injector is telling me the real number is significantly higher than this. Seems most people with Scangauge are calculating fuel burn based on MAF values and I am not convinced this is giving accurate results.

 

0.90 US gallons is 3.42 liters. Which also was my post 1 napkin math.

 

Can you send the TSE file? I have Techstream too and I’m curious to see. Technically, maf*afr is correct… the ECM judges injection amount based on maf and afr.

 

My head hurts, time to Unwatch this thread.

 

Just for fun.

I logged the entire startup fuel curve on my truck just now. Truck had been parked for over 24Hrs here in Texas. Outside Air Temp about 70F. I just turned on the data logger and THEN started the truck. You can clearly see a spike it fuel flow on start up and as the engine warms up it starts to plane out.

Coolant Temps were 70F on startup and I turned the logger off at about 170F.

I logged a data signal on the CAN (communication network) bus coming from the Engine ECU to the Cluster, this is the value used to calculate MPG info on your instrument cluster. (Shown in Orange)

At the same time I logged fuel use data through an OBD2 software. It uses MAF readings to calculate what it thinks the fuel rate is assuming 14.7 grams of air to every gram of gasoline. (Shown in blue)



Both signals spike up to just over 2 gallons per hour on start up. Then they both slowly start to come down.

The CAN ECU signal level off about .71 Gal/Hr and when I turned the AC on at the end it jumped to about .81 Gal/Hr.

The OBD MAF signal level off about .45 Gal/Hr and when I turned the AC on at the end it jumped to about .58 Gal/Hr.

Personally, I really think the MAF values are too low. The other logs I did in Techstream line up really well with the CAN ECU signal. (Orange Line). Assuming it is accurate, In the 12 Mins of running to warm up the truck burned 0.18 gallons of fuel. As stated already avg burn rate is 0.80-0.90 Gal/Hr with AC on but now you can see the actual curve as the truck adds fuel for cold starts.

 

This is good to know. I sit in the parking lot with the engine running when I'm at the mountain waiting for the lifts to open. Not sure if the colder temps effect the GPH but its usually between 20-30°f

 

My first thought is the colder air is more dense, more oxygen. I would think the colder it is the more fuel added earlier, harder cold start. When the truck is warm it might still burn a little more fuel with thicker air but next time a cold front blows through and it’s 30 F here I will log it again.

I think from here on out I will only log the ECU signal on the CAN bus. I really don’t trust the error in the MAF calculations. This is what Scangauge is doing btw.

I think I’m about to go do a quick log at highway speed for fun. Set the cruise at 70Mph then turn the logger on. It’s a nice day for a drive.

 

Same time, you'll be removing heat from the cooling circuit to keep cabin temp up. This might cause the engine to possible increase fuel consumption to make up for lack of "operating temp" coolant temp.

 

Similarly, I watched MAF data towing through the mountains last weekend. In 3rd gear at 4,500ish RPM it was pulling 220 grams of air per second - nearly half a pound. That works out to 20gallons/hour.

 

Hahaha I went ahead and logged the MAF and Coolant Temp also via OBD. Here is the graph, MAF in Green using the vertical axis on the right.

MAF spiked to 17 G/Sec on start up, leveled out at about 5 G/Sec and jumped to 6.5 G/Sec when the AC came on. Funny thing is Toyota uses the MAF signal and several other sensors to calculate injector pulse time. It seems using MAF calculation only is not accurate for fuel consumption as it is ignoring the Short and Long term fuel trim values the ECU is calculating and factoring into fuel rate.

 

Do it

 

3.42L/hr? I don’t think so. I used to be a trucker, and the 15L Caterpillar engine in my tractor would burn about a gallon an hour idling. There’s no way a Tundra burns that much idling.

 

I have a OBDlink MX+ and it shows the fuel rate. Its .4-.5 gal/hr at idle.