Engine runs too much and shudders before turning off

What is the air pressure in your tires? 42/40 front/rear helps fuel economy.

How fast is your highway drive? Fuel economy plummets much above 65 MPH.

Unless the shaking feels like the engine might tear loose from it's mounts, it's normal (but of course this is hard to assess from a distance).

 

Short trips also drop your MPGs, you didn't specify how far you drive to commute. The car's computers know best when to turn the ICE on and off, so don't fret too much about it running a lot. It could be because you have the AC or defroster on and are making a higher energy demand of the vehicle. Unfortunately there are a million little circumstances that could be causing all these things to happen. Sometimes my engine slips quietly on and off, sometimes it is a little rough. Maybe that also depends on the situation.

If you do bring it to a dealer, let us know what they tell you. Good luck

 

Mine occasionally shakes while turning off the ICE, but not often enough to bother me.

If you use the Auto setting for the A/C, make sure you set the temp to barely give cold air. When I forget and the car decides heat is appropriate, the engine runs longer...

 

I also live in LA and have the exact same condition. early moring a littlrough on the start-up and sht-down cycles and an average MPG of 45 over the life of the car. So far 4 months and 11,000 miles. At About 9,000, and after an oil change to Amsoil xl 2000 I noticed a slight 2-3 MPG increase.

Part of it is the driving style out here. If you are in the "Flow" of traffic 45 MPG is about average. If you want to practice you can feather the accelerator a bit more,(takes some practice) and get better MPG, but you'll probably get shot in the process!

So, let her break in, nothing out of the ordinary. (for this car, a big change from any other)

 

My Prius will do that sometimes, especially if the weather is cold.

I have been getting 50 MPG since the weather has turned warmer here in MD. Before when it was cold just over 45 MPG. I also have to go over 2 mountains to work & back and I can watch the MPG drop when compared to driving on flat roads.

I have noticed that I get better milage towards the end of the tank, less weight?

 

The Prius has all sorts of odd behaviour, particularly when warming up. What you're describing sounds like its behaviour in "stage 3", which you might typically find it in 5-10 minutes into a journey.

If your journeys are short, you might spend most of your time in stages 1-3, and never reach the full hybrid operation stage 4, where it does continuously switch back and forth between electric motor and engine.

For full details see The Five Stages of Prius Hybrid Operation.

 

I really wish Coastal had a device to display the current stage, so I'd know what was up. Toyota didn't care, or else it'd be somewhere...

 

I'm sorry, but I agree this sounds wrong... Try this, drive out to some empty, relatively level parking lot a few miles away, turn off the AC/fan, make sure the battery is reasonablly charged, and while feathering the gas pedal, drive around. You SHOULD be able to drive around the lot in "stealth mode" for a while. Maybe not 5 minutes, but most certainly for 30sec. to 1min. without the ICE kicking in...

 

A few miles may not be enough. It usually takes at least 5 minutes drive time to get full fuel efficiency.

As stated, really hot days seem to give similar (but not quite as bad) behavior as on cold days, mainly because of electrical demand on high voltage battery. When I left my girl friend (separate words intentional, someday I may be able to make them one word ) in my car with AC on while I got milk at Walgreens. Sounded like the ICE was running, but it may have been the AC compressor. The compressor can be quite loud when running at high speed, and it was a hot day with a very hot cabin.

 

Based on my experience with crappy Detroit cars early in the emission control era, I believe we're seeing just a bit of "deiseling" shortly after startup, when the engine is choking. This gives a characteristic "shudder" when an ICE is shut off. (Deiseling is the tendancy of the cylinders to fire on residual gas even when the spark is absent.) I observe it in my new '05 Prius, and it disappears when the engine has warmed up.

OBW, I note that the first 5 minute interval after start-up always shows a low (~23) mpg, then in the next intervals of similar suburban driving the mpg jumps to 50 or 60. Is this typical and does it reflect rich mixture during warm-up?

 

Hi Genalex,
Actually, I believe the ICE has spark, but no fuel, so as to clear up the intake manifold and whatever is caught in the carcoal pack in the aircleaner. The ICE uses an atkinson/miller system where fuel enriched air is pushed back out the intake valve during early part of compression. In order to reduce hydrocarbon emissions, they would have to burn that up!

Yes, you will get lower mileage for first 5 minutes. This is probably true with any car, but more noticable with the Prius. The mixture has to be rich until the O2 sensors are properly warmed, and probably left rich until the cat and ICE are warm.

 

Thanks, DanMan. Would you say, then, that the shudder which I notice only during early warm-up is because the purging of air/fuel mix out thru the intake valve is a bit less effective when the mix is very rich? It does indeed feel like the "run-on" effect after turning off ignition that I described as dieseling.

 

The reason for the shudder is an educated guess, I'll admit. Yes, I suppose more shudder when cold could probably be because the mixture is rich until the O2 is warmed up. Hadn't thought of that.

 

I too thought the engine shudder was a problem, so I took my Prius to the dealer. They ran all the diagnostics and everything came back fine, so I called another dealer and asked them about it. Both reported the same thing. The engine shudder is a normal characteristic of the vehicle and is not a defect of any sort. I have noticed that when my engine is cold, I feel a stronger shudder upon engine shutdown. After the engine warms up, it is less of a shudder. In addition, I notice I can achieve 'Stealth' mode more when the engine is warmer. I just got my Prius on June 10th and have filled up the tank twice. I filled the first tank at 330 trip miles, and the second at 380 trip miles. So far I am seeing MPG in the mid-40's and a variance of about 1.3% from what shows on the computer. I also discussed this with the dealer and was told that mileage in the mid-40's is normal in here in Florida. Since we have to run the AC a lot here, even in winter (humidity sucks), I may never see more than 45 MPG. When compared to a non-hybrid, that is still better mileage no matter how you look at it. I would love to see my MPG hit the 50's, but it would likely require a move to a different part of the country. I'll take 45 MPG for now, I guess. I also recently inflated my tires to 42/40 so we'll see how that goes. The dealer had under-inflated them at 35/32 for whatever reason. All in all, I can't complain too much about the car.

 

Well, as you can see from my profile, I live in Florida, and I do get 50's MPG. Short trips and highway speeds are the killer, AC is third killer, but not nearly as much as short trips and high speed.

 

[font=Comic Sans MS:867cfdb4ee]Dan, you can only experience the fourth MPG killer, and that not much, when going over the Tampa Bay bridge. Hills really pull down the MPGs. I think the bridge is the highest "hill" down there.[/font:867cfdb4ee]

 

<div class='quotetop'>QUOTE(pettusta\";p=\"102782)</div>

Toyota's recommended tire pressure for the Prius is 35 front and 33 rear. Last time I had my tires rotated at the dealership, I ended up with 32 psi all around (that I consider under-inflated)

 

<div class='quotetop'>QUOTE(Bill Merchant\";p=\"103881)</div>

i believe you are referring to the skyway bridge going from St Pete to Sarasota. I have never driven over that bridge.
I do have some steep hills a little north of where I actually live, but steep can be a relative thing.

I have experienced all the killers I mentioned, but I will also add cold weather as an experienced killer. I have seen the snowflake come on some days.