Combustion Test ok but still misfiring??

Test doesn't work on hybrids

 

Have you checked the fuel?

 

Bad fuel will cause problems. Where do you get your fuel? 7-11 stores?
Texaco? Sunoco? ???
You can take a glass jar and get a sample of the fuel. Let it sit for 5-10 minutes.
Do you see water in it?

Also, maybe a weak fuel pump? Have you checked the pressure, and volume?

 

Had a bad head gasket but the test didn't work for me, a piston to the side of block was better test

 

I would add an oil catch can

 

Most normal misfire sources don't quickly stop after a coldstart. But owners often fire the parts cannon anyway. At least they know what it isn't.

Yes it could still be a gen3 Prius hg. Early stage hg fails often leak very little, only occasionally overnight fouling a plug which causes the transaxle damper to rattle. After starting, the early stage hg fails tend to seal up quickly. As a result combustion gases are not there long enough to register.

A borescope inspection will usually show a steam cleaned piston or you just wait until it gets worse. Then the coolant may go down a noticeable amount. Late stage fails will blow white smoke and rattle while driving after normal engine off periods like at stop lights.

 

That test checks for combustion gas in coolant, that's all. The 3rd gen head gasket failures tend to be coolant seeping past head gasket, into combustion chamber. Leak-down test and/or boroscope inspection will be more conclusive.

That's getting up there.

Was there any warning lights? If so there should be codes.

 

"fire the parts cannon" and "assume it's the head gasket" are not the only two options in diagnosing a misfiring engine.

There was a good article on some other techniques in the Second Quarter 2009 issue of Toyota Tech (starting on page 15).

 

tests that check for combustion gasses in the coolant are only one direction tests... from the combustion chamber to the coolant.

you want to check for coolant in the combustion chamber.

a bore scope will show you what the inside looks like. pulling the plugs might show a cleaner plug for the cylinder/s that have a leaking head gasket, but not always.

 

I linked to the article (that blue word 'issue'). I don't know if it began life in Japanese, but the version I linked to is English. I haven't seen it in any other language.

 

literally having the same issue. Following..