2005 Prius Mystery Misfire

Hey everyone,

I’ve had a heck of a time with a 2005 Prius here. I just thought I’d look for any input before/while I prepare to swap my engine out.

I’ll try to keep my story brief, I revived a Prius that was sitting in a driveway for a little over two years. I brought it home, swapped battery packs and tried firing it up. Immediately it started knocking aggressively and I shut it off. I was kind of upset with myself that I didnt pour a little oil in the fill port and that I didn’t pull the plugs and fog the cylinders. This would have helped lubricate things from sitting so long, I just wasn’t expecting it to start so fast.

To my surprise however, it eventually smoothed out and would idle and run fine. I changed every fluid in the car, put new plugs in and it ran perfectly fine for weeks moving in and out of my shop, and ran fine for probably an hour with throttle pedal down while I was bleeding cooling system.
It never misfired at all during this.
(Mind you that still isn’t a lot of load on it)

When I was finally finished the project, I decided to try taking it out for the first test drive. Almost immediately on road it started misfiring horribly, and barely would run. Now with any load, (such as charging the hv battery), it will misfire and do the normal misfire loud knock fairly badly. When it’s not charging the battery, it’ll misfire only randomly on cylinders 3 and 1.

First thought was to try a compression test with the crank command with my scan tool, but car is knocking so hard the readings just keep jumping and the car stalls out after only a few seconds.
Outside of the crank mode compression looks great of course since it’s being turned over so fast. I’m thinking of trying to put impact on it, but have no idea how I will guarantee or measure 200rpm

Next I started trying all of the most common things:
-swapped plugs with known good car
-swapped all coils with known good car
-changed and cleaned throttle body
-pumped out all fuel in tank-checked for water (really wasn’t much whatsoever) then put new fuel in
-swapped all fuel injectors with known good/tested ones
-checked wiring visually
-swapped Pcv valve
-tried to check for vacuum leaks (don’t have smoke tester though). Tried spraying starter fluid all around intake manifold to see if would improve-not really
-checked fuel pressure-holds it fine and has pressure running but it just jumps all over the place with hard knocking as well


The car seems to repeatedly fail on cylinders 3 and sometimes 1 all the time. When it’s under load, it starts misfiring on all the cylinders.
No other codes other than lean code (which may be just cause of misfiring).

Today I just tried a leak down test on that cylinder three and only seen a 10psi drop
At TDC so 8%. Some air is escaping intake valve and out engine oil fill cap. This is apparently okay I guess according to online sources.

Does anyone have any other suggestions or ideas? I’m preparing to swap out the engine but I’m just terrified that I’ll do all the work and still have a misfire. I’ve heard of those horror stories..

Thanks,
Matt

 

The car was a taxi previously, but in overall the car is in alright condition for its age. It had the whole combination meter issue so who knows how true this is but it reads 252000kms.

I checked the leak down test on two other cylinders and it was about the same result-nothing crazy. Tried the compression test again on number 3 and it pops up to 60 but scan tool for whatever reason won’t read me the rpm fast enough before it stalls out. So no idea if it’s actually getting to 250rpm.
Not sure why it stalls so quick but whatever. Just wish I could rule the engine or computer/controls out for certain.

I’m going to try looking at some schematics tonight. May need to take it somewhere with an oscilloscope to verify the computers acting properly with everything.

 

Hey everyone thanks for the replies.

Just for an update-I finally was able to check compression properly by getting it into that Hv crank mode. I learned that after you remove plug/coil, you need to plug them back in/ground the plug or else the ecu freaks out with a myriad of coil related codes.

Anyways, got all four tested and they were around 85-90 across all cylinders. Just to check accuracy of my gauge, I tried checking on my daily driving car, and also got this reading. Now I’m unsure about the quality of my basically new Canadian tire compression tester. So until I can get my hands on another compression tester this is still unconfirmed I suppose.

I have not checked the timing chain yet, as I feel this thing would be having more issues than it is if it was out of time. If I get time I’ll check it anyways.

The car idles and revs fine with no load. While reading on my scan tool, it still is misfiring on those two cylinders on occasion at no load, but It’s only when charging the battery or physically driving that it starts knocking up a storm on all cylinders.

In the meantime I have also confirmed that all cylinders are getting signal/spark, and are getting injector triggers from ecu.

This whole issue also kind of makes me think to check fuel delivery again. KO fuel pressure was good, and it pumped out an entire like 1/4 tank for me while I was checking for water…however there must be some sort of regulator with the pump. I’m kind of curious if the needle on my fuel pressure gauge shouldn't have been jumping at idle like it was..even with a misfire. Unless the gauge is faulty and reacting to the extra vibration (which I don’t think it is), a misfire really shouldn’t affect fuel pressure..I know some newer vehicles will shut the injector off if it detects a misfire to prevent unburnt fuel going to the catalyst, but not sure yet if Prius’ do that…

I’m going to keep digging and keep you all updated. I’m hoping to get my hands on another compression tester, and that fuel pressure tester again. Once I get a fuel pressure tester again, I’m curious to throw it on my good car and see how it reads there.
Any more thoughts or previous experiences would be very appreciated.

 

Just noticed I never initially added in, I am regularly getting a P0171 code on top of the P0300, P0301, and P0303 codes. Like I mentioned I’ve checked hoses and replaced intake manifold/throttle body manifold completely already, and sprayed starter fluid around…no obvious vacuum leaks.

 

All I’ve done was swap them with another known good car I have. Mind you this car isn’t super low mileage, but it does/did run well. I ordered replacement seal kit for them and installed it as well. I checked resistances on them as well and made sure they were within spec.

Even if the new seal kit is NG, you’d think something would happen by spraying starter fluid around there..

 

I’ve actually completely swapped batteries as well between that same car I got the known good injectors from. The original battery needs the whole battery terminal/frame wire replaced as the battery ecu connector was corroded.

The car the battery came from ran fine..

 

Well I have some hopes here...I was rechecking all of my tests, and found power and ground was present at cylinder 3 injector harness (the cylinder that is worst/nearly always missing) when key is on. There shouldn't be ground here until the ecm triggers it/it's running/open

When key is off I'm still getting a good ground there with my meter.

All the other injectors and my good car never have a clear ground path like that on the ecm side. I checked continuity between the ecm harness disconnected and the injector plug and it's near perfect. I then checked continuity from wire to ground and got nothing. So I don't think it's a wiring short.. Seems like ecm is outputting some form of ground to injector all the time. This would mean injector would always be open when key on.

Hoping that this one miss could cause all of them to fall off like it is?
Thinking of replacing ecm tomorrow to see...

Apparently I’ve heard you don't have to program them as immobilizer and everything are done through hybrid ecu..

I also noticed the one injector seal on cylinder 1 is squished out slightly, so I got a new set of seals coming from fel pro to try out. Might be able to reuse seal as they are basically new, but in all-Kind of doubtful of this being an issue though as I was spraying there with starter fluid while testing while back with no change.

 

Thanks for the message. That day I did check for the presence of the constant ground with the one plug undone from ecu and it disappeared instantly.

You might have hit the nail on the head though, I didn’t think to mention it earlier but back while I was testing the injectors for the very first time, the injector for cylinder 3 barely had any resistance at all. Of course back then I got all excited thinking that was the issue and changed it, but evidently it wasn’t the complete issue anyways. I’ll double check but I think it was only like 1 ohm or something..

That’s a very good point in all, and could make sense...

Hoping to get it tested/swapped this weekend sometime and I’ll let you all know