ZB Commodore high fuel consumption reading, or high fuel consumption

[J_D 2.0]

I would expect that first gear takeoff instantaneous fuel readings of 40L/100kms would be quite normal. Every car I’ve ever had with instantaneous fuel readings does this as it’s an calculation based on that exact point in time, ie: If you continue doing 3000rpm in first gear at high load (accelerating up to speed) for 100 kms you will burn 40 litres of fuel to travel that 100kms.

 

[stooge]

i finally remembered to look at that screen in my zb and it does the same.
it jumps up high when in the low ratio gears and levels out as it changes, so it is just normal operation.

 

[MattSAU2XR8]

Similar thing with my previous VE SS - admittedly bigger engine of course. If you go into diagnostic mode it will tell you fuel burn per hour, and generate very high numbers when accelerating away from a standing start.

Interestingly petrol engines are supposed to use around half a pound (so 220g or about 300 mls) of fuel per hour per horsepower developed.

How to Estimate Your Engine's Required Fuel Flow.

Fuel filters need to be able to flow a certain amount to make your power goals a reality. This is how you calculate the GPM needed to hit your goal.

blog.cantonracingproducts.com

So if accelerating reasonably hard an an RSV, perhaps using 2/3 of the available 300 odd HP then 200 HP X 300 mls could be 60 litres per hour...

Or on the other hand if cruising at 100 km/h and using 8 litres per 100 km this would suggest that only 28 HP is required (8l / 300 mls)...

That said the V6 engines aren't the most economical around town. But then being able to get to 100 km/h in 6 point something seconds in a relatively heavy car was never going to be economical...

 

[Utetopia2015]

i finally remembered to look at that screen in my zb and it does the same.
it jumps up high when in the low ratio gears and levels out as it changes, so it is just normal operation.

So... i was still concerned that if it wasn't excessive fuel usage, it was a readout error, especially since it didn't really fluctuate, it just hit 39.9l/100km and sat on that before coming back down.

But here's the thing. It is normal. Here's why....

At idle, not moving, you use 2l/hr. At 5km/h, you're probably not using any more fuel than idle, especially if you're not accelerating and just rolling forward. At 5km/h, the readout switches to (x)l/100km because you're now moving forward, but you're still only using 2l/hr, but it takes you 20 hours to go 100km distance. 2l/hr for 20 hours is 40 litres. So at 5km/h, its using 40 litres to go 100km, because its taking 20 hours to do it.

At 10km/h rolling forward with no acceleration, its taking 10 hours to go that same 100km, so at 2l/hr, the readout is 20l/100km.

Hindsight is a wonderful thing! In all fairness, though, the Colorado has the virtually the same cluster information, but doesn't read an instant fuel consumption like that... it just drops to 0 as you decelerate (I'm lead to believe).

 

[ZB_Driver]

Yesterday afternoon, i started my ZB RS, 3.6L, AWD.
Idle fuel consumption was normal, at about 1.8-2.0 L/hr.

Rolling off with no immediate acceleration, the fuel consumption readout jumped to 16L/100, to 26L/100 and then eventually to 39.9L/100, until i accelerated properly up to speed, where it then dropped to normal acceleration consumption (14L/100 - 21L/100) before settling in to 5L/100 - 8L/100 at cruise. The same high reading of 39.9L showed again when slowing at an intersection just before coming to a complete halt, which the reading then switched to the normal 1.8L/hr idle reading. There's no abnormal fuel consumption reading when accelerating from 80km/h to 100km/h.

It seems to be a 1st gear issue - both taking off and slowing down. I don't think there's a short term drivability issue, and I'll have to call Warrnambool Holden Monday.

Anyone else experience this? Thoughts whether there is a definite fuel consumption issue, or computer gliche?

Link to video footage I took on my phone. Jump to around 2:20 :

There is nothing wrong with your car. I am a former GM engine engineer and I can tell you that is completely normal operation. Most GM cars clip the instanteous fuel consumption reading at 39.9litres per 100km in the Instrument Cluster (eventhough the fuel consumption may be reading higher in the Engine Control Module) and it is not unusual to hit this fuel consumption rate at higher loads when accelerating (especially at higher rpm where extra fuel is added, i.e. running rich mixture, to protect components like turbos and catalysts). On deceleration, the fuel consumption goes to zero as the fuel injectors are disabled (named DFCO - decel fuel cut off) this is to save fuel and avoid poor combustion/poor emissions at light engine loads, and as you approach low rpm/vehicle speed the injectors are reenabled and when you are travelling at such a low speed your actual litres per 100km will be really high: i.e. fuel consumption is 2 litres per hour consumption at idle, you are travelling at 5 km/h speed meaning that it will take you 20 hours to travel 100km, which equates to 2 litres/hr x 20 hours = 39.9litres/100km. Does that make sense?

Enjoy your LGX V6 they sound great!

 

[Anthony121]

The Mitsubishi 380 used to show 99.9 lts /100 when accelerating from standing start

 

[Brettly-2008]

... and as you approach low rpm/vehicle speed the injectors are reenabled ...

My SS makes a lovely crackle/burble when this happens at around 1200rpm following a zero throttle decel.

 

[ZB_Driver]

My SS makes a lovely crackle/burble when this happens at around 1200rpm following a zero throttle decel.

That was tuned by the engine team at the Holden Proving Ground to give as much exhaust character as possible. You should have heard the fuel cut shifts on our V6 turbo Cadillacs (like a gun shot) . This example is quite tame at lower rpm. Click on YouTube link: CT5-V upshift

 

[Anthony121]

That was tuned by the engine team at the Holden Proving Ground to give as much exhaust character as possible. You should have heard the fuel cut shifts on our V6 turbo Cadillacs (like a gun shot) . This example is quite tame at lower rpm. Click on YouTube link: CT5-V upshift

That was one of the last Cadillacs imported too for Holden

 

[Derekthetree]

That was tuned by the engine team at the Holden Proving Ground to give as much exhaust character as possible. You should have heard the fuel cut shifts on our V6 turbo Cadillacs (like a gun shot) . This example is quite tame at lower rpm. Click on YouTube link: CT5-V upshift

See to me that sounds really fake. All the VAG DSG systems do it, but more farty.

Now when I lift off the throttle after a squirt I get a much better sounding rumble.