Post-fix NMS mileage?

Hi All
What is the consensus about the likely mileage hit incurred by reflashing the ECM to behave all the time not just when on the test dyno?

Zero consensus. No...one...knows. No...one...can...possibly...know...

My take on it:

these run the hottest when under heavy load, and NOx production is at max level under these conditions.

The highway cruising at 65-75 is easier on the engine, as all you have to do is to maintain momentum by overcoming the rolling and aero resistance.

As long as fix is at its most aggressive when engines are under heavy loads - say climbing long grades, or driving at 85+ mph, folx that do mostly hwy cruising should see very little impact on avg mpgs. methinks

Mine barely consumes any DEF and even if I will have to refill it twice as frequently, no big deal at all.

Most of my driving is hwy cruising under 75 mph. If I loose 2-3 mpgs (my summer time avg is about 50mpg), well, I can live with that. If it is more like 10 mpg loss, combined with noticeable loss in power/torque, then there's always the buyback route.

Remember that settlement requires full disclosure of fix's impact on mpg etc

And I'd image we'd have folx reporting their post-fix #s, and quite possibly, cars will get dyno'd, post-fix, by indys as well

Since there is no fix yet, everything written is, at best, only a more or less likely outcome, at worst just pure speculation.

Thanks. I guess there may be some indicators in the data from the tests that revealed the cheat. It was a stark difference in mileage that tipped them off no? I don't think they were trying to sample NOx out on the road. Or am I mistaken?

Speculation on my part. If the SCR system is too far downstream to maintain the correct temperature for proper operation, they may have to increase the amount and frequency of fuel post-injection, which will result in reduced mileage in some conditions (likely city). At steady-state cruising, the exhaust temperature is both relatively high and stable, and it's unlikely that additional post-injection would be needed to increase temps.

So to summarize my prediction, if there is a reduction in fuel economy, it will be city fuel economy where the engine is frequently returning to idle. I think it would be unlikely that fuel economy will drop below the original EPA figures that were on the Monroney sticker when you bought the car.

The settlement mentions that the EPA and CARB will accept NOX emissions that are higher than the standard, but lower than they are now. If this is the case, the chances of a significant fuel economy hit are greatly reduced. I'm selling my car back, but I would be optimistic that you'll get a car you're happy with.