Random Multiple Cylinder Misfire?

The problem is that in this case we don't know quite what the definition of "slight" is. What is the OP's definition of "slight", is it 1/4", 1/2" 1" ...? We also don't know how much oil has already been sucked through the intake if the oil has been high enough to get frothed up. My understanding is that initial oil consumption can be a lot higher than normal when there's an overfill involved. Perhaps this has been enough to tip the balance on some already poor condition plugs.

 

You're right-- but logically there must be a margin of error.

 

I am currently having this same exact problem with my 05, with 183,500 miles on it. I took it to the dealer - it is undrivable as it is, with much misfiring and very little power. The dealer says that 2 cylinders are mis-firing (according to the CEL codes) and they are changing 2 fuel injectors. They say they've seen this problem before. I'm supposed to get the vehicle back this evening - I'll post on what they tell me and on whether or not the problem has been fixed. This is the first problem I've had with this vehicle in 183,500 miles, so I'm not really complaining. By the way, my oil level is definitely not too high - I change my oil myself and fill it only 3/4 of the way between LOW and HIGH.

 

One additional comment: If two of the fuel injectors are bad (and I really can't see how two would fail simultaneously), and they are replaced, does that cause a problem with the computer trying to control the fuel mixture. With 2 worn (but working) injectors and 2 new (not worn) injectors trying to control mixture, I can see how the computer might be confused. Presumably, each time the worn injectors fires, a little more fuel would be injected than when one of the new injectors fires. I was trying to decide whether or not to replace all four, but decided against it.

 

I have a 2007 prius with 395,000 miles. I am having similar issues. At first I was getting a p0300 p0301 and p0420. I changed spark plugs but still get p0300 and p0301. Cleared codes. I drove the car 100 miles at 65 and when I got to destination I had p0300 and p0301 pending but no mil. When I drive over 70 mil comes on with p0420 code. Im suspecting water in the fuel and Im going to try heet but I'd like to know if it's my fuel injectors

 

A misfire (P0301, cylinder 1) is going to be caused by lack of spark, lack of fuel, or a bad cylinder.

Considering your car has logged so many miles, I would start by doing a cylinder compression check on all four cylinders - use Mini VCI and a compression gauge that screws into the spark plug hole. If cylinder 1 has a compression problem, then it would be pointless to worry about fuel or spark. Just replace the engine with a used engine or get rid of the car.

If the cylinder compression check is good, then my next question is whether you installed the correct NGK or Denso iridium spark plugs.

If the correct spark plugs were installed, then the next step would be to swap the spark igniters for cylinders 1 and 3, to see whether the misfire moves. If it moves, then replace the faulty spark igniter. If the misfire does not move, then I would suspect the fuel injector for cylinder 1. Considering the odometer reading, if you get to that point you'd might as well replace all four fuel injectors while you have the fuel rail off.

Regarding P0420, you can try replacing the air/fuel ratio sensor first, but you probably will need to replace the catalytic converter.

 

Using a scan tool, what's your long-term fuel trim?

-Chap

 

Ok this is what I KNOW to be true, no second guessers necessary. My first prius was purchase on a warm day. Ran great for about a week until my wife drove to the bank on a very cold day. I had to tow it home from the bank. Small battery dead, hybrid battery dead. So I charged both up and got a bunch of codes with techstream. The most interesting code was engine failed to start. I fought this for about a month! Apparently the owners manual says to check the oil when the engine oil is at operating temperature. I had checked it while cold, and it was jus a little over filled. So, I drained it just below full line, changed the plugs and cranked it up. I checked it when hot, and it was way over the full line. The design of this engine has the pcv valve at the lower back part of the valve cover. Any overfilling will cause oil to be sucked into the pcv valve and straight into the intake, where it gets sucked straight into your engine, oil fouling the spark plugs. To prove this is happening, take you air filter box off and open the throttle by hand. Use a flashlight and look down into the intake. You will see a large puddle of oil. There should be no oil at all. This oil has to be removed, the spark plugs either cleaned, or changed. The oil level cold should be drained to about 1/2 way between bottom and full mark. Then crank up vehicle and drive it until engine is hot, then rechecked and filled about an eighth of an inch below full. The problem with the whole thing is that your car takes 3.7 quarts of oil, not 4. Most oil change places have an automatic oil dispenser. You dial in the number of quarts. They don't have fractions of quarts, they either have 3, or four quarts. Ok this being said, if you drain the oil, it is physically impossible to drain all of the oil out of an engine, there is always oil in the pump and oil galleys and lifters, etc. Sooo, if it has a maximum oil fill of 3.7 quarts when the engine is completely dry at the factory, and you put in 4 plus the residual oil, you have this exact problem every time. I am not debating this! This is very common in these cars, even the dealers do this a lot of times. Peace, love and hippie flowers. I hope this helps out a lot of people!