14 Tundra TSS. P0303 misfire, #3 compression issues

Hey Guys first time posting and I have researched but don't see anything quite like my issue completely!

I will run thru this step by step of what happen.

filling up with fuel (truck running) pulled away from pump and left idling (air on for dog) I returned to truck about 20 min. later and it was idling rough and check engine light flashing. I read codes and came up with P0303. not having much time to diagnose I just purchased a coil pack, sparkplug and replaced. reset computer and started, it ran smooth for about 30-45 sec. then the check engine light came back on and started running rough. I now decided to check the injectors, not having a pulse reader I pulled fuel rail and swapped #1 injector with #3. same problem when put back and started. I now thought I better check compression, here is where it gets weird. first time I pulled compression test #3 read 40..... I put it back together and checked compression in #1 and got 168. I decided to retest #3 a few times to make sure of operator error.... next time before I checked compression I reset the computer, and compression was 165! I hit the release on comp. tester to make sure it read it correct and pressure would not rebuild!!! pulled comp. tester and tried again not resetting computer and I get no reading of compression?!?!?! started truck with cylinder open and get what seems like good intake and exhaust pushing and sucking thru spark plug hole BUT that's just a guess with my hand over the hole...

So I have had the truck towed to Toyota and after 1 day they have no answers yet?? I know im impatient but I like to understand everything completely! dealer also says they put a scope in cylinder and it looked good??

truck has 76000 miles on it. I have a lifetime engine warranty but am worried this may be a computer issue that would not be covered!

has anyone encountered anything like this??

 

Following for more info, my 2014 is almost 73k miles trouble free, not an issue but hanging around to see the fix for your problem. I hope you can get it figured out and it’s not too expensive of a fix.

 

Broken ring(s) in #3? Compression in a normal cylinder doesn't vary wildly like that.

If it's the rings, everything may look normal using a borescope through the sparkplug hole. Oil squirted into the cylinder for the compression test could be revealing.

 

So I stopped by and talked with the tech working on it and they think they have narrowed it down to the ECU not providing a pulse to the #3 injector.

he says compression is good SO maybe I didn't get a good reading in the Auto Zone parking lot with rented gauge LOL. At least the ECU is warrantied for 8yrs or 80K

 

I'm having the exact experience with my 2010. A few more miles @ 240000

I'm very curious what they come up with, my next move is the shop. I was leaning towards an ecu issue. the previous owner deleted the egr. I'm assuming to bypass the air injection pump instead of paying for the costly pump replacement. I was wondering if that would have anything to do with it. Idk...?

 

P0303
Replaced coil and plug #3 = issue still in 3

Swapped inj between 1 and 3 = issue still in 3

Compression test value = low

Do I understand correctly?

As @JohnLakeman mentioned,
Some oil in the cylinder + test = compression = rings