Mysterious misfire ONLY when low HV battery, but No DTC’s

Go to the Engine and ECT Live tab then at the top click on Monitors. Then once loaded. If it says completed click on EGR FLOW INSUFFICIENCY. This will show your result for the EGR Flow.
The MAP readings are on the live data tab.

 

The test on the EGR valve / MAP sensor is slightly more complex.
First you must start the car in maintenance mode. “The pedal dance” then let the coolant temp rise to at least 75°C.
Once this is done enter the engine ECT tab. Then click the active tests tab.
In the new list that appears you’ll see something like “test egr stepper motor”. Select this then if all criteria are met you’ll be able to test the EGR stepper motor inside the valve.

Make sure to have the MAP sensor readings displayed in the live view then monitor the MAP value. Whatever it is reading during idle with the stepper motor on 0 steps, this will be your base figure, then open the stepper motor (no more than 30 steps & for no longer than 10 seconds)
when the stepper is opened the engine should go into a rough idle and the MAP value should increase by at least 10kpa. (You can change the unit value for air pressure in the Techstream settings from psi to kpa)
If it doesnt rise by at least 10kpa then apparently this would indicate a problem with the egr valve/motor. Or the MAP sensor?

When I do this test it is only rising by 1kpa.

 

Am currently looking into the fact that the fuel injector for this cylinder may be faulty, I’m assuming the oily buildup would have been in all of them if the injectors were all faulty. After all, the gunk that used to get thrown into the intake via the PCV valve wouldn’t only go into plenum number 2. So I’ve switched injector number 2 for injector number 1 and am planning on checking the condition of the intake plenums next time I remove the intake to clean it again in I reckon no more than 1000 miles...

 

Strangely there is no oil consumption which is why I think the buildup in plenum 2 is from the PCV valve. (I now use a catch can so hopefully the buildup should stop in there now)

I only wipe the external cage of the MAP sensor. Doesn’t look like you could even wipe anything else if you wanted to?

I’m also very weary of touching expensive sensors!

The only thing I’m concerned about with the readings on Techstream are the MAP sensor readings when I run the EGR stepper motor test. Apparently it should increase the reading by at least 10kpa. Mine goes up by 2kpa. Yet the readings for testing the MAP sensor seem within the normal range of between 80 & 110kpa when engine switched off and below 80kpa with engine running.
With the engine in an idle state it reads 30kpa. Then when the EGR stepper is opened to 29 steps it only goes up to 32kpa. ?

 

Ok so following advice from here I’ve proceeded to do a block test and a compression test.

Block test results... Conclusive, c02 is in the expansion tank...

Compression test results slightly strange.
According to Toyota repair manual. Normal compression should be 199psi or above.

Cylinder 1 was 139psi.
Cylinder 2 was 130psi.
Cylinder 3 was 130psi.
Cylinder 4 was 130psi.

So armed with that information I decided to go ahead with removing the head.

Results of Cylinder head pressure test will follow when I get it back from the machine shop.

Head gasket looked like it could have been leaking a very slight amount of water from the water jacket around cylinder 2 directly into the cylinder.

 

It took me 8 hours to get it to this stage but I wasn’t rushing by any means. I had one problem with one of the exhaust manifold nuts rounding and refusing to come off so had to remove the head with the exhaust manifold still attached! This added to the time.

Cylinder #1 is the one nearest the timing chain.

I plan on cleaning mine well, luckily the gasket leak was only very small so not really any oil/water gunk mixture anywhere other than inside plenum #2...

 

The MYSTERIOUS MISFIRE has gone!

Turned out that the head gasket was leaking a very small amount of water into cylinder 2, it was such a small amount that when the engine was running it was just being burned off and not noticed, but when the ignition was on but the engine wasn’t running (water pump still works at this time) then the small amount of water leaking into cylinder 2 had the chance to build up therefore causing the misfire whenever the engine restarted (normally when the hybrid battery got low enough).

The valve stem oil seals for cylinder 2 were shot! That explained the oily sludgy buildup in the intake plenum for cylinder 2 and also the blocking up of number 2 fuel injector adding to the misfire.

Before taking the plunge and stripping my engine down I put a borescope into each cylinder. Piston 2 looked steam cleaned compared to the other 3, This confirmed my suspicion of a head gasket leak.
I also did a block test and compression test, all resulted in further proof of head gasket failure. (Likely caused by a blocked up EGR system for at least 100,000 miles causing the engine to run hotter than specification for too long a periods).

I’ve attached some pictures of the findings and rebuild.

Currently sitting on 199,150 miles. Hopefully I’ll get another couple of 100,000 miles now.

Thanks for all the suggestions.