Question about the engine during deceleration

You'll get better responses with more real information, but I'll try to be the first to jump in.

It appears you already know why this is happening more with the car in the first 15 minutes -- the ICE needs to warm up and it will not shut down (and stay down, as it were) until it has reached that prime operating temperature. You'll still see 99.9 mpg, because you are traveling a decent distance with exceptionally little gas being burned. You have no load in the ICE and no real drag on the engine. Sometimes you'll see the mpg show 99.2 or 96.4 or some such numbers. This again let's you know the ICE is running but you are not making any demands upon it.

Why does it happen when you've been running for a long time? It could be that you continue to have other draws on power that require the ICE to run. Does it happen when your SOC is showing green bars and you have no electronics or climate control running? That would be a bit odd, I think. Still, I'll be coming back to this thread to read the better technical responses.

 

Pearl often takes 5 or so seconds to shut down when she could do so immediately. It appears this delay is built into the software. Other times she shuts down the ICE as soon as I start slowing for a red light. Neither time is the delay for "ICE temp/cat initial warmup", though without a cat temp meter it's possible it was cooling off, though unlikely as the engine was running for some time before (it appears to take only about a minute to warm up a completely cold cat converter).

So it looks to me there are two situations where shutdown works differently. I'd like a button to tell the car we'll be stopped for the first one. It's embarrassing sitting there for the 5 seconds with the engine running.

 

My ScanGuage shows that I can be getting up to 240 mpg with the ICE still running. So yours is likely running in the situation you describe when it is showing 99.9 mpg.

I too am perplexed at times when the battery shows a decent charge and the water temperature is 180°+ and I can't get the ICE to shut down by backing off and "feathering" the gas pedal.

PA P

 

Bryan5,

Toyota technical data says that the ICE must be running when the ECU does a
purge cycle of the HC vapor retaining cannister in the fuel system. As the
canister holds HC vapors generated during startup and shortly there after, I
suspect that some of the ICE run-time during and shortly after warmup is to
accomodate this purge.

The technical data also says that the ECU periodically -- period, frequency and
duration, not specified -- initiates pulling a vacuum on the space between the
hard-case fuel tank and enclosed bladder to see if there is a leak in the
bladder. Again, the ICE must be running. It is possible then that some of the
apparently unnecessary ICE running after warmup may be from this test.

 

Bryan5,

I am only-just-out-of-Newbie-dom, just went past 5K mi. I too am still learning
what makes my Amapola tick. Believe me, I'm trying to be helpful.

My earlier post is the dumbed down version!

To see obfuscation at its finest -- the full Toyota Tech version -- go here:

http://www.autoshop101.com/forms/Hybrid13.pdf

Oops, this might be helpful too:
HC = Hydro Carbon; petroleum, gasoline
ICE = "Infernal" Combustion Engine
ECU = Engine Control Unit (?), one of 6, or 8, or 13 computers in the Prius

Cheers!

 

You were in S3 idling check mode.
http://priuschat.com/forums/knowled...perating-mode-availability-reference-aid.html

Ken@Japan

 

My prius was delivered with a cracked fuel tank. The first trip to the dealer they reset the check engine light at about 150 miles. At 300 miles the light came back on and I brought it in for smoke tests to find the source of the leak. I scheduled the repair for a week later... in that week I drove several hundred more miles and the check engine light came on around 450 miles.

This leads me to believe that the frequency is every 100-150 miles that it does the leak-checking procedure you mentioned.

 

Thank you for that tidbit of information, the tech data is silent on this point.