engine stumbling

Hey, my '05 is a week old today too. Anyway, mine does it too from time to time, I noted it when it is really cold out (below 35 degrees). No problems with it going after either. I am chalking it up to breaking in, temp, or something benign.

 

Perfectly normal, PriusChatters. It's the ICE shutting down. It seems to happen at both cold and hot temperatures, particulary if the ICE hasn't warmed up completely yet. Nothing to worry about.

 

Ditto in Florida Too

My Prius TRAC car is a month old and it does the same thing when it first starts in the morning. The problem goes away when the engine warms up (which will take longer up north). It also seems to happen less often than it did a few weeks ago,

 

I just wanted to chime in on this thread after having read similar posts in the archives. While I too have noticed the occassional rough engine stop at a red light (normal, if still a little disconcerting), I have also noticed it a few times when the ICE kicks back in (normal?).

Has this happened to anyone else, or is it just me and my leadfoot?

shaun

P.S. Slightly off topic, but I was curious if anyone knew if there is some type of mechanism to help keep the oil pressure up in the ICE (e.g., for when you're at a long stop light/train crossing/ or are incredibly lucky and can drive the car solely with the Electric motor for an exorbatant amount of time). My assumption is an electric oil pump that is always running, or something similar that starts back up just before the ICE does to help prevent unecessary wear on the cylinders et. al.

Hopefully I've explained myself well enough :blink:

(thanks in advance)

 

It has a mechanical oil pump. Self-lubrication is one reason why the engine is spun briefly before compression, fuel, and spark are applied.

 

The oil pump in the Prius is non-drain-back trocoid design (vs impeller designs) and provides pretty much instantaneous oil pressure as soon as the drive shaft is turning, so there's no risk of being without lubrication.

 

Yep, normal.

 

I experience this sometimes...EVEN after the car is fully warmed up and the HV battery is on green bars.

The shaking is excessive and the ICE seems to keep changing its mind from staying on or off. Sometimes it feels that the ICE will be shutting off, but it shakes a bit and remains on, and eventually goes off.

It's quite strange, but it does not bother me yet.

 

When your Prius decides it's time to start the ICE, it mechanically, using the electric motor, spins up the engine, without supplying fuel or spark, to about 1000 RPM. Oil pressure goes up then and oil is flowing when spark and fuel are supplied, so no worries about an un-oiled engine when load is applied. I think this is one reason why transition from EV to ICE is so smooth - everything is moving, electirc spinning the ICE until fuel and spark, then ICE spinning the electric generator/motor. The marvel of the Power Split Device.

The smart Prius needs its HV battery and protects it, not letting it get too high a charge, and turning on the ICE when the charge gets too low. If you have a full green battery (about 80% battery saturation), usually by going down hills with regenerative braking, and then stop, a little too much charge might have been put in the battery. To drain off this excess charge, the Prius uses the electric motor to spin the ICE. The ICE isn't supplying power, it's draining power. Excess electric energy is being used to compress air and blow it out the exhaust. The ICE sounds like it's running, and it cycles on and off, but look at the screen and you'll see a full battery. When the charge is right, the ICE stops cycling.

Yes, it's very disconcerting the first few times it happens. But normal, don't worry.

 

Try this for an additional explanation it will help with your understanding of how the HSD works:
http://priuschat.com/forums/kb.php?mode=article&k=14

 

My theory as to why it shudders at stops is because of the miller/atkinson ICE design. Some fuel mixture is pushed back out of the cylinder througth the intake valve into the intake manifold. Some of this fuel vapor may get captured by the charcoal pack in the air cleaner case. So, I believe the engine has its fuel supply cut off, but still provides spark to burn up the residual fuel vapors. In such a situation, it could easily shudder as if it were running out of gas, because it is, on purpose.

 

Thanks for the info on the engine shudder. I have it happen with my Prius and had worried something was wrong. THe salesman told me this was normal. Hearing it from you folks is reassuring.

 

Thanks (as well) to all who informed me about the rough engine start-up as well as the oil pressure pump. I figured they would've designed something to prevent uneeded engine wear, so it's nice to learn how it all works

Cheers!
shaun

 

I've had mine for nearly two years. It only happens within the first five minutes of driving. Perfectly normal.

 

I too, just want to say thanks for the information. I have had this problem with my '05 (3 mos new) and was slightly concerned. Thanks for putting my mind at rest!