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I bet the cruise control doesn't know to open the throttle more slowly because the engine is making more power though

I find the cruise control to be fairly accurate and react fairly quickly to change the throttle depending on load requirements. Where I live we don't have flat roads and the cruise control is constantly adjusting to maintain set speed. Cruise control wouldn't care about the volumetric efficiency of the engine, it simply controls the throttle to achieve target speed.

IT may even be as simple as at much colder air temps it may be dropping below the point where the lean cruise actually works? Unfortunately I won't know until we get some cold weather again.

Can someone please confirm that the V6 engines use the Hot wire MAF?

Just having a look back over the most recent datalog, warm afternoon ~23°C ambient air temp, cruising down the motorway with cruise set ~100km/h. Cylair is hovering around the 200+milligrams/sec per cylinder depending on load (going up or down hills etc). Sometimes climbing to ~300mg/s. The lean cruise table is zero'd out below 200mg/s so it's hovering on the edge of the lean cruise window on a warm day.

Now on a much cooler day with increased air density would the engine not see less cylair than a warm day? If so when cruising on a cold night the lean cruise would be doing absolutely nothing? I currently have lean cruise turned off, average fuel usage is currently only 0.1l/h more that it was before doing the LIM gaskets etc

It'll be interesting to see what the MAT sensor says when ambient temps are much cooler. MAT sensor was showing ~59°C in the LIM on the above run.

for a given TPS% and RPM you should see a higher cylinder air mass at lower air temperature.

charlay86 wrote:for a given TPS% and RPM you should see a higher cylinder air mass at lower air temperature.

I agree with that and you would be using more fuel to maintain the same AFR but you would also be traveling faster so then you would reduce throttle %age to get back to the same cruise speed?

I guess once we hit winter and we have a datalog from a nice chilly morning we'll be able to compare the data.

immortality wrote:

charlay86 wrote:for a given TPS% and RPM you should see a higher cylinder air mass at lower air temperature.

I agree with that and you would be using more fuel to maintain the same AFR but you would also be traveling faster so then you would reduce throttle %age to get back to the same cruise speed?

I guess once we hit winter and we have a datalog from a nice chilly morning we'll be able to compare the data.

You are spot on there, that's exactly how it works and why you should see a slight improvement, minimum no change not worse economy.

immortality wrote: Can someone please confirm that the V6 engines use the Hot wire MAF?

Yes they do.
These MAFs heat the hot wires to a fixed temperature above the ambient temperature (there 2 heated wires and a temperature sensor).
Mass airflow is then related to the amount of power used to heat the hot wires to maintain that temperature.

vlad01 wrote:

immortality wrote:

charlay86 wrote:for a given TPS% and RPM you should see a higher cylinder air mass at lower air temperature.

I agree with that and you would be using more fuel to maintain the same AFR but you would also be traveling faster so then you would reduce throttle %age to get back to the same cruise speed?

I guess once we hit winter and we have a datalog from a nice chilly morning we'll be able to compare the data.

You are spot on there, that's exactly how it works and why you should see a slight improvement, minimum no change not worse economy.

OK think about this, if two identical cars both travel 1km, they both take off from a stand still and accelerate to 100km/h. one car accelerates slowly and the other accelerates quickly. Which car uses more fuel?

The slower one of course assuming both WOT.

Just been looking at that datalog some more. Engine idle, in gear 14.7 AFR 184mg/s Cylair, idle mode, 15.1 AFR 168mg/s Cylair, idle in park, 15.1 AFR 160mg/s Cylair.

Cruising down the motorway it's really only just consuming more air than idle......

edit:i'm quiet intrigued to see what it does in winter now.....

If your engine temps stay as they should, its won't change much amusing you fix this problem first.

If your car is massive tank with a pissy little shit jap engine like my company car, it will suffer horrendously due to the car struggling to push through the denser air of winter lol.


If the public were so concerned with fuel economy, they should not fuel the market for big cars with small engine and instead demand small light cars with large displacement engines.