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Discussion Starter · #1 ·
Had a P0300 multiple misfire code with individual codes on cylinders 1-3-5. I cleared the codes and only P0301 reappeared.

Put new coils on 1-3-5 and new plugs all around. P0301 reappeared.

Rented a compression test gauge from the local parts store. Measured 90psi, 180psi and 195psi on cylinders 1-3-5, respectively. Got #1 to TDC and applied air pressure. Leak was coming out of the exhaust pipe. Nothing out of the intake, nothing out of the crankcase, nothing out of the adjacent cylinder.

Since I was unsure whether I was at TDC on the compression or exhaust stroke, I removed the coil and plug on cylinder 2 and applied air pressure.

To my alarm, air was leaking out of the intake!!! Since cylinder 2 follows cylinder 1 in the firing order, it should be 120 degrees behind on the same stroke. So whether cylinder 1 was TDC on exhaust or compression, cylinder 2 should either not leak or leak out of the exhaust. Unless the intake reopens to improve exhaust scavenging?

Puzzled, I grabbed my new compression test gauge (returned the rental) and proceeded to test all 6 cylinders with the following results:

Cylinder 1 - 150 psi
Cylinder 2 - 80 psi
Cylinder 3 - 220 psi
Cylinder 4 - 150 psi
Cylinder 5 - 220 psi
Cylinder 6 - 215 psi

Repeated 1, 2 & 4 to verify.

#1 is still weak relative to 3 and 5. But why wouldn’t I have misfires on 2 & 4?

I still haven’t solved the intake leak mystery, but I figure getting #1 to TDC on the compression stroke may be easier by getting #4 to TDC on its exhaust stroke. From there, it’s time for a leak down. Is there anything else I should be doing while I’m in this deep?
 

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Discussion Starter · #3 ·
I had suspected a bad fuel injector on cylinder 1 when I did the compression test, so today I decided to swap injectors on cylinders 1 & 2 so the "bad" one might be easier to replace. When I went to disconnect it, the connector came off in my hands. Not only was the blue wire severed, about an inch was missing. Completely baffled as to how this came to be, but $3.69 later at O'Reilly's I had a replacement connector.

Satisfied that the back bank of cylinders was as good as I was willing to make them, I put the whole mess back together to see if the issue moved to cylinder #2. Expectedly, the engine threw several codes trying to start with no fuel in the rail, cylinder 2 misfire among them. I cleared the codes and restarted and, much to my surprise, everything is now running like a top!!!

My hypothesis:. I think the misfire on cylinder 1 resulted in the VVT getting in a position where the weird stuff and low compression on cylinders 1, 2 and 4 resulted. Since 1 & 4 move together and 2 is next in the firing order, it sort of makes sense that the computer would adjust these cylinders to help balance against the misfire. Testing all of this with the cams adjusted in this way resulted, art least in-part, to the readings an odd valve positions. I'll test this by driving for a few days and re-performing a compression test on cylinder #2.

For now, this Sienna's back in action!!
 

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Glad it is up and running good again. I am hearing from some of my friends that aftermarket filters are being a issue with VVT stuff and oil pressure.
 

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Discussion Starter · #5 ·
My hypothesis:. I think the misfire on cylinder 1 resulted in the VVT getting in a position where the weird stuff and low compression on cylinders 1, 2 and 4 resulted. Since 1 & 4 move together and 2 is next in the firing order, it sort of makes sense that the computer would adjust these cylinders to help balance against the misfire. Testing all of this with the cams adjusted in this way resulted, art least in-part, to the readings an odd valve positions. I'll test this by driving for a few days and re-performing a compression test on cylinder #2.
Hypothesis confirmed. Drove 50 miles with no codes and tested cylinder #2 at 210-psi.
 
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