My car has a dual personality...great

[porshuh]

Consider the following:

1) I drive my car on route back and forth from work and to client sites. I feel great lean burn power at 75mpg, which is the most throttle I have to give her to keep at any pace I have to go. Mixed city/highway mpg is 66-70mpg per trip in this condition.

2) Find loud music to cover my cursing voice to the car. I have to do everything in my power short of kicking out the driver's side floor board to flinstones the thing to keep her out of ASSIST. Driving at a lean burn 75mpg feels like I am rolling on flat tires over fly tape. If I do every hypermileing technique in the book, I can keep the car at or around the 50mpg mark...just barely out of assist. Of course (even with adjusting down to as low as 15mph below the speed limit) I dip in to regen, which makes things even worse.

Can you guess the difference in situations between #1 and #2? Day and Night. Literally. #1 is on a bright sunny day, and #2 is at night.


Now...as seeing that the car (as far as I know) can't tell the difference between brightness...I can only think that the difference is due to ambient temperatures. Situation #1 is about 75*F, and situation #2 is about 55*F. I can't imagine that a mere 20 degree F difference in temperature would warrant such an amazing (and hair pulling aggravating) experience.

Here are my only thoughts:

1) Both cats are throwing codes...is there a chance they are not heating up enough? Though cold cats flow more than hot cats...nvm
2) Damnit, I don't have any other thoughts

If I only drove this car during the day, I can get 70mpg all day long. But at times (almost always at night), the car drives like it needs every bit of 50mpg just to struggle at the speed limit down the highway.

Any thoughts for me to get started on???

[mikeeech]

Ambient temperature would be my guess. There is a cardboard box winter modification on the threads here which makes a surprising difference at this time of year.

[Eli]

Nah, temperature wouldn't explain that....unless maybe you're going from 70F to -10F.

That's what happens when you have a head wind, or are climbing up a hard to perceive incline. I know the feeling well.

That's why I have a GPS elevation profile readout on my phone(so I can tell if I'm ascending or descending) and look at the wind/weather patterns before taking a road trip so I know if I'm going to be fighting against it. Even a few MPH headwind can make a huge difference.

This helps alleviate what I call "MPG anxiety". It's really frustrating when you don't know why, but not so much when you do.

[aisbell]

With the headlights on, background IMA battery charging is likely occurring much (all?) of the time. This additional drag (i.e., the IMA motor-generator in generator mode) might explain the difficulty in maintaining lean burn.

With the headlights off, background IMA battery charging would occur only if the IMA battery charge level is below a certain level (depending on which BCM version one has).

If one has MIMA, one could disable background IMA battery charging to test my hypothesis.

[Eli]

I've taken many road trips at night and was never able to detect a difference in MPG with the headlights on vs. off, though I know one must exist.

With the headlights off, the automatic background charge won't come on until the SoC is low, but with them on it appears to start in the 64-68% range, which is just a few bars from the top.

That's a good lead overall; try topping the battery to 20 bars and then doing the drive at night. The loss seems excessive overall though.. Another thing that will cause this feeling is a single or multiple tires being very low.

Could be a combination of everything.. tires, wind, an incline and a background charge! Oh the horror!

[porshuh]

Originally Posted by Eli

Nah, temperature wouldn't explain that....unless maybe you're going from 70F to -10F.

That's what happens when you have a head wind, or are climbing up a hard to perceive incline. I know the feeling well.

That's why I have a GPS elevation profile readout on my phone(so I can tell if I'm ascending or descending) and look at the wind/weather patterns before taking a road trip so I know if I'm going to be fighting against it. Even a few MPH headwind can make a huge difference.

This helps alleviate what I call "MPG anxiety". It's really frustrating when you don't know why, but not so much when you do.

I like your thinking, Eli...but these are on identical round trips...so elevation change wouldn't play into it. Headwind sounds good - but none of these evenings are particularly windy, and wind is usually lower at night anyways.

[Eli]

Hmm... I guess it could be temperature? I've never noticed an impact that profound though. I took a 400mi road trip last winter with temps ranging from 30F to below zero and managed 76MPG...

EDIT: Unless this is a very short commute?

With my 2 mile commute, winter conspires to lower my average fuel economy from 60 to 40.

[TopFuelTim]

Dunno about the codes thing. I had to pick up my daughter from work in North Georgia for a week at 2:00am, and had a heck of a time with mileage. Normally 68-70 average, it dropped to around 61-62 average for those trips. Figured it was the generator causing a slight drag to keep the headlights going. Also wondered about the high humidity that time of morning. Winds were not a factor.

In the meantime, I did the Calpod clutch switch modification, so I can enable or disable assist at any time I want to. It was not hard at all to do.

Does yours already have the Calpod mod?

How to disable Assist/Regen

My .02 cents worth,
Tim Glover

[porshuh]

Thanks for all the thoughts, guys and gals.

I don't think the headlights have anything to do with it, as I don't see the regens coming on that much sooner.

The biggest difference I see is that during the day, I can slowly give it the 'ole right foot, and as the instant mpg gauge slowly drops down the scale, I can actually feel (butt dyno) nice power pulling the car along at 75mpg (instant gauge). At night - I'll slowly give it gas, watch the bar slowly go down the instant mpg scale, and wait for any sort of power....125mpg - nothing...100mpg nothing...75mpg - just barely more than nothing. It takes consistent 50-55mpg (instant) to keep the car going down the road.

At this point, I'm leaning towards the "combination of issues" that Eli pointed out as the culprit...it was cooler, humid, damp ground, and very well could have been a head wind...

[thedhgroup]

How old is your 12v accessory battery? The combo of an old battery and the background charge could be putting more drag on the engine. I replaced my 12v battery and it helped my situation. There may be as much as 15 amps of current flowing without any of the charge lights indicating such.