Occasional Fuel Economy Problem with my HCHII
 

Sometimes, my car really makes it difficult for me to get good fuel economy.

Normally, this is how my car responds. I can be cruising along at ~50 mpg. By slightly letting off the accelerator, I can get the fuel economy to increase to a variety of ranges between 50 and 100 mpg. If I let off some more, the ICE shuts off.

Here's the problem. On a few occasions, I have not been able to hit any of those ranges between 50 and 100 mpg. I will be cruising at ~50 mpg. By slowly letting off the accelerator, the FE does not increase until the ICE shuts off. This behavior has happened on my most common route that I drive so the problem is very obvious. It does not go away for the entire commute. Each time this has happened, the problem went away the next time I drove the car. Also, the car has been fully warmed up each time this problem has occurred.

Has anybody else experienced a problem like this? Does anybody know what could be causing this?

Thanks.

Re: Occasional Fuel Economy Problem with my HCHII
 

Can you correlate the problem to something like low battery SoC? It could be that you are getting a little bit of regen to trickle charge the battery, which would add a bit of resistance and force you to hold the throttle a little more open than normal. One way to deal with it might be to find a good time to add some regen manually to get that charge up and get back on your way. Of course, I'm just talking theory...

Re: Occasional Fuel Economy Problem with my HCHII
 

The problem last happened yesterday evening and the battery charge was at 7 bars when I started the particular drive. I cannot come up with any reason why this has happened. Early on in this commute, I had the fan on high. I turned it off during the commute and the problem persisted.

I hope this problem does not keep happening. It turns a commute that should give me mid 60s into a commute that gives me mid 50s.

Re: Occasional Fuel Economy Problem with my HCHII
 

I've had a "mild" forced regen with five or six SOC bars... but I don't recall seeing it with seven. Maybe it was just at the end of the regen stage? NOTE: I'm defining "mild" forced regen as driving on level road where one or two green charge bars never seem to go away (unless you take your foot completely off the gas). Happens to me occasionally.

Re: Occasional Fuel Economy Problem with my HCHII
 

The particular commute that I was on has me driving at the posted speed limits of 25 to 35mph. It is through residential areas. Under these conditions, I only get forced regen when the SOC hits 4 bars.

Driving at freeway speeds, I frequently get the mild regen that you are referring to. This is actually why the SOC was at seven bars. My wife had been driving it on the freeway just before this commute.

Re: Occasional Fuel Economy Problem with my HCHII
 

I experienced this "mild" forced regen yesterday and it kind of ticked me off. I was in the 5-6 bar range for SoC, so there was not a good (obvious) reason for it. Outside temps were in the high 90s, so maybe that had something to do with it.

Also, I think I have been seeng something similar to Mr. Kite's experience. It is very frustrating. I was on a slight downgrade and had my foot pretty much all the way off the accelerator and mpg was around 25-30, while normally it should have been in the 75-100 range. I don't have any explanation, but you are not alone.

Re: Occasional Fuel Economy Problem with my HCHII
 

My vote is on forced regen. I have had this happen and it almost always correlates to me not being able to get the last bar of regen charge off of the meter without kicking the ICE in more and dropping the mpg even further. This is really obvious with low SOC (4-5 bar range) as the car demands 3 or 4 bars of forced regen, but I also think the computer monitors you total inflow and outflow of current to the battery and prematurely stops the system from going into a negative sum game at higher SOC situations (ie forces regen to keep the SOC at the steady state high level). Most of the time this happens to me is when I am traveling without many breaking opportunities or if I am not using hills to regen, but to coast more.

The only other time I see a lower than normal mpg than I would expect is if I did not let off the gas pedal long enough to drop the rpm's down all the way, thereby getting the CVT into effectively an overdrive gear ratio. I have gotten into situations where I was running at a higher rpm than I really needed to for that situation. Is it possible that you are not fully letting off the gas and allowing regen to kick in before applying the gas again to get into the lowest mpg range? Watching the RPM gauge seems to me to be the best way to verify what the mpg should be reading if you are not bogging the engine down.

Re: Occasional Fuel Economy Problem with my HCHII
 

This problem happened to me again last night. The car had already been driven several time during the day so it was mostly warmed up. It happened on the way to the store and the way back. The temp was about 70. This morning, the temp was also about 70 and everything was working perfectly after 1 mile of driving. I ended up averaging 65mpg over 50 miles of driving today.

I really do not believe that my problem is forced regeneration. As I stated in a previous post, this strange behavior happened to me when I had 7 bars on my SOC. With an SOC of 7 bars, you do not get forced regeneration cruising as speeds no greater than 35mph. Under these conditions, my SOC has to drop to 4 bars before I get the forced regeneration. Also, the green bars make it pretty obvious when forced regeneration is occuring. There have not been any when I have experienced my problems.

Re: Occasional Fuel Economy Problem with my HCHII
 

What about the rpm situation? Again, depending on when and how I let off the accelerator and re-apply (timing) I get different results and can end up at a differnt rpm/CVT gear ratio. From what I can tell, this is the biggest factor on getting the mpg meter up, as it will not go above 50 mpg with the rpms above some level above 1500rpms. The rpms have to be extremely low to get into the very high mpg range.

Re: Occasional Fuel Economy Problem with my HCHII
 

Are you suggesting that what I am calling an occasional problem with my car is just me occasionally forgetting how to get good gas mileage? I travel this particular route probably 10 times a week and am quite familiar with it. Also, I have logged most of the 5300 miles that are on the car in my nearly 4 months of ownership. I have driven the route with the car enough to know when it is not acting properly.

I will try to explain this problem again.

During normal operation: I am cruising at 50mpg. By slowly letting pressure off of the accelerator, I can get the FE to increase to a variety of levels between 50 and 100mpg. If I keep letting off of the accelerator, the ICE will eventually shut off.

During the abnormal operation: I am cruising at 50mpg. By slowly letting pressure off of the accelerator, I cannot get the FE to increase above 50mpg. If I keep letting off of the accelerator, the ICE will eventually shut off.