Engine run-on.

Once or twice now, in about 1000 miles, the gas engine in my 2005 has produced a bubump bubump sound with sympathetic vibration when automatically
turning off such as at a stop light. Sounds and feels like engine run-on sometimes caused by fuel spilling into the combustion chamber of a very hot engine. Curiously, this has happened when the engine was cold. Anyone else experience this?
Bill
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I've had it happen a handful of times in about 10K miles, but for me the engine has been hot.
--
Mike Rosenberg
<http://www.macconsult.com Macintosh consulting services for NE Florida
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It's very common and apparently normal. See threads at
http://www.priusonline.com/index.php
and
http://priuschat.com/forums/index.php
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wrote:

Hmmm. I get redirected a foreign language site with the first link and find nothing relevant at the second. To me "normal" means this behavior is the rule. In my case it is the exception.
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The site appears to be hijacked.

It's hard to find specific information in threads unless there's a good search engine.

Normal means that it is expected, even if rare, behavior. Sometimes, the Prius has that rough idle just before the engine shuts down. Expect it to happen at random times when the engine shuts down. It's not usual, but it is normal.
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wrote:

Actually, "normal" means "conforming to the standard or the common type; regular, usual, natural, or not abnormal" according to my old American College Dictionary. Like I said, in my case it is the exception or "abnormal" as we define the word here in the United States.
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Perhaps the proper word is "benign."
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Spurious engine run-on is neither normal nor benign. It is a symptom of a fuel injection problem, an overheated engine or both. Of course, we really don't know that it happens to EVERY Prius so we honestly don't know if this problem is unique to you and me or common to every Toyota Prius. In either case, it certainly isn't benign.
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More on run-on:
From here: http://www2.ctcentral.com/ctcars/fullstory.asp?ID 012003NB5546
"Dieseling isn't a problem with fuel-injected vehicles, as the electrically operated injectors stop fuel delivery upon engine shut-off. Dieseling can be harmful as it places severe stress on the crankshaft."
But the author thinks this problem doesn't happen to fuel injected cars. He is wrong. To wit:
http://www.connact.com/~kgross/FAQ/tb/tb.10.7703.html
Where we find a technical bulletin to fix a fuel injected engine exhibiting run-on.
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Interesting. That appears to be a bulletin for a Porsche 924, and the modification is to prevent an electrical sneak path through the alternator indicator light.
Mike
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Sure it is; it does no harm.
Keep in mind that the Prius uses an Atkinson/Miller cycle engine, not the Otto cycle used by other ICE-driven cars; symptoms do not necessarily mean the same things for it that then do for the others.
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That's assuming, of course, that it really is "Spurious engine run-on". You have no evidence that it really is doing that. Having experienced it, I don't think it is run on.
Don't forget that the engine is actually connected to two electric motors that control what it's doing. There is no "neutral" and the engine's output is always conencted to the drive wheels via gears inthe power splitter. The "run on" might very well be the very last power stroke of the ICE as the power splitter stops the engine from spinning.
The "neutral" in the CVT is effected by the motor/generator spinning one of the CVT gears in exact sync with the engine, canceling it out. If the motor/generator stops before the engine does you might get a bumping sound/feeling as the engine comes to an abrupt halt. The atkinson cycle engine has almost no torque at very low engine speeds so it would stall easily.
If it bothers you, take it in to the dealer and explain what you have experienced. The computer stores a lot of information and my actually have recorded the condition.
Daniel
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It sounds and feels like engine run-on but yes, it could be an unfired engine being cranked by a clutch mechanism that doesn't always operate properly. In either case, the symptom appears spuriously. I suppose the human parallel to this condition would be vomiting. We all do it at one time or another but it certainly isn't normal. I'll ask the dealer in a few weeks when I get back to that town.
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Please let us know what he says. Thanks.
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I think the more correct bodily analogue would be burping. A quick, momentary rumble. As someone said, it feels more like a 1/2 second of rough idle just before the engine stops. No mess, no apparent impact and no cleanup. It's not the bang, knock and lurch of engine run-one, right?
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Yup; it is not abnormal, so it is normal. If the engine on a non-hybrid car shut off at a stop light, that would be abnormal.

Well, we here in the United States don't redefine words to suit our meanings as you apparently do.
Oh, and since you are so anal about words, learn the difference between "like" and "as."
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Ah, that's the description of what I've occasionally seen.
--
Mike Rosenberg
<http://www.macconsult.com Macintosh consulting services for NE Florida
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wrote:

Yes, that would describe it as well, and may explain why it occurs when the engine is cold.
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I've had that experience two or three times in the last 30,000 miles. I don't remember what the cause was supposed to be. It only happened in summer when the outside temperature was pretty hot.
Daniel
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