2002 misfire after warm start

I am hoping someone has an answer to my issue. I have searched this site and many others for 3 weeks and although I am sure that my Prius is in better condition than when I started, the following condition remains a mystery.

When I start my Prius after it has been setting overnight or for a few hours after driving it runs without issue. If I drive it long enough for it to warm up, when I try to start it within the first few minutes to an hour it starts knocking and at times the check engine light comes on. I can drive it and after about 5 minutes of running rough it smooths out and runs normal.

I have checked the engine codes and I get P0300 (random misfire), along with misfire codes on cylinders 1,2,and3. Never cylinder 4 for some reason.

Here is what I have tried.
Cleaned the mass air flow sensor.
Cleaned the trottle body
Swapped coil pack 2 and 3 (after several cylinder 3 codes without other misfires)
Ran the tank empty and filled with a fresh tank
Took the car to the dealer where they had it for 3 days and checked all systems including cylinder pressure, fuel pressure and diagnostics.
Dealer found a leaking o-ring on cylinder 1 and replaced all of the o-rings.
Got it back and can still reproduce the problem.
I took the 12v battery out and had the dealer test it and they said it was fine.
I had changed the oil using 5w-20 full synthetic and filled it to the specified level. After reading a post on this site I took a little oil from the engine and cleaned out some oil from the intake manifold.
Reall thought I had it only to find that I could still reproduce the issue. This is my 16 year od daughters car and I really don't want to have her stranded at any time.

BTW, outside temp has been in the 90's although I had it happen today and it is only 80 outside.

Hopefully you are still reading. . I know this is a long first post but I am hoping the detail will help.

Thanks in advance

 

Thanks for the questions and suggestions, here are my answers

1. 140,000 miles,
2. Changed them last summer at 130,000 miles using plugs from Toyota dealer.
3. Good idea, funny I read post to my wife and she said the same thing. I will swap 1 and 4 igniters to see if it changes the pattern.
4. No visible cracks or burn marks, and i have not noticed any bad wires but i will inspect closely tomorrow.
5. O-rings that seal the injectors.
6. Has not rained in Indy all summer
It does appear to be heat related. My daughter just got home and stopped eat, then to a friends before coming home. No more than 1.5 hour stops and she said everything worked fine. It is about 70 degrees.
7. I do not know the pressure. What should it be? I will ask the dealer. They only said it was OK.
8. dealer assumed the o-ring replacement would fix the issue.

Many thanks,

 

Patrick,
Thanks for the advise. It looks like I can get a salvage ECU on eBay or amazon for around $200. Does that seem correct? Also, I have seen posts talking about having to replace the keys by swapping the computer. Is this correct?

Your logic seems sound given that the A/C is not working in the car and the ECU is located behind the glove box making it hotter in the car.

Of course it is only reaching a high of 70 degrees now so I may not see this happen again until next year.

Thanks again

 

Ok, Spring is here in Indiana so the heat is starting to rise. I just changed the oil and the misfire kicked in right away. It would do it some over the winter but the cold weather seams to help so I thought I would put it off. I just looked at my old post and found a few comments. I did not swap the ECU since it was an expensive guess. I am going to look at the post after yours closer to see if the crank shaft sensor could be the issue.

Any luck with yours?

 

Thanks! I will look into it. I got a fancy ohm meter for Christmas and thought that may help me find a failing sensor. I will check the crank shaft wiring.

Did your issue occur more in warm weather and on a restart after stopping for 10-15 minutes?

Thanks again

 

Update, I replaced the crank position sensor this evening. Took the car for a test drive, stopped for about 15 minutes. When I restated the issue was still there. So, at least I can take crank shaft position sensor off of the list. I looked at the replacement for the knock sensor and my auto manual said something about removing the intake. Seems like more than an evening job. The only codes I ever get are random misfires and misfires on cylinder 1, 2 or 3. Still seems odd that I have never seen a misfire on cylinder 4. Maybe I look into the ECU. Seems like not much money and easy to swap.

If anyone has ideas I am all ears.....I will keep you updated on my progress.

 

OK. Replaced the Crankshaft position sensor and it did not change anything. Today the new ECU came in. Very easy to replace and at $195 it was almost the same price as a knock sensor. That was the good news.....bad news..it did not fix a thing. Same issue as it knocks and runs very poor after a warm start. It is always fine on a cool start and runs fine even after it is running warm. I unhooked the knock sensor and tried to start warm, same issue, I unhooked the MAF sensor and tried to warm start, same issue. I pulled a vacuum line (thinking old school vacuum lock), same issue. At a loss. Next item would be Camshaft position but I am not sure if it has anything to do with things. I have never seen a engine code other than "random misfire" and misfires on cylinders 1,2 and 3. Never 4... Swap of coil pack between 3 and 4 did not change this fact so I feel the coil packs are good.
If anyone has an idea I would appreciate the help. So far I am only into the fix for $255 so I am willing to keep going.

 

usnavystgc,

Thanks for the detailed post. I wish I would have checked it a couple of days ago as I just replaced the cam sensor which is about 2 inches way from the thermal sensor.. . I have now swapped the ECU, crank sensor, knock sensor, MAF sensor, and cam sensor. The car still does the exact same thing. major fail on my part at this point.

I will look into the thermal sensor next. I will bet that is it since it looks like a $20 part and so far I have spent about $400 on parts.

Any tricks to removing the inverter coolant tank? I replace the cam sensor by moving the wiring harness to the side since that was easier than taking out the bottom rear bolt on the tank. Looks like the thermal sensor will require the removal of the tank. My hands are just too big.

I also saw the other post on the coil pack. I may try that although my issue never happens while the engine is running normally. Only after sitting for 15-20 minutes and restarting. If I let it cool all of the way down it runs fine which would point more to your theory. I may try both as I am just about to loose my mind at this point.

Again, may thanks for all of the posts and assistance.

Will keep everyone posted.

 

So, it appears that the Gen I and Gen II ECU wiring is different. I believe I have found a wiring diagram for a 2003 that should match. I will dig through the book to find the thermo wiring so I can test from the ECU side. It is impossible to get to the thermo without getting to the point that I could just replace it.

One other thing, If I understand correctly your theory is that the data being provided to the ECU is that the engine is not warm when in fact it is and that is what is causing the issue. If that is correct. How is it that the Hack posted fools the ECU into thinking the opposite i.e. warm when not but there is no issue with rough running?

I long for the day's of distributer caps and setting points....

 

Thanks for the clarification. That makes perfect since. As for the inverter tank. The engineers at Toyota obviously will never have to work on one of their designs. The gas engine thermistor is directly below the inverter coolant tank on the 2002 Prius. There is no way to get to the thermistor without removing it and it appears nearly impossible to remove the lower rear bolt on the tank without removing one of the two motors.

I will do some metering prior to replacing.

Thanks again and I will keep posting my results.