Low compression on bank 1 compared to bank 2

Hello, I been having issues with code P0300 and P0102 on a Tacoma 2015 v6 4.0; multiple cylinder misfires and maf circuit low

I did a compression test and it’s the weirdest thing.

on bank 1 cylinder 1-3-5 have a compression between them around 120-125 psi a bit low I think minimum compression is 145 correct me if I’m wrong.

On bank 2 cylinder 2-4-6 I have around 165-170 psi I did not expect such a difference from one side of the engine to the other.

could this mean that bank 1 timing is not correct? I was expecting maybe 1 cylinder low on compression but that one complete side of the engine is low but has similar compression between them seems weird.

I was also thinking that the head gasket could be bad on bank 1 and is not sealing correctly but again maybe on 1 cylinder not all 3.

 

^Headgasket leak or timing don't explain your MAF circuit low code. I suspect you have rodent damage in the wiring under the intake manifold.

 

Oh yeah, I didn't add it to the post but I was following the factory diagnostic procedure for the MAF code and the third check didn't pass, it supposed to be 10K ohm resistance when checking the connector pin to a chassis ground.

I was more concerned on the compression values since I never seen one whole bank low on compression compared to the other.

 

^Yes "circuit low" code usually means wire shorted to ground. If it's caused by rodents, other wires (like commonly reported with fuel injector wires) could be chewed, causing the misfires.

 

Low compression on one bank vs the other does suggest timing but being you don't have timing codes it would suggest the exhaust cam is off which would be highly unusual unless someone has been in there and didn't time it correctly.


The MAF code is likely secondary and wouldn't cause low compression on one bank.

 

I just did a compression test on my 2006. the 1GR-FE compression should be around 189 psi, minimum is 145 PSI and the difference between each cylinder should be less than 15 PSI.

When you did your compression test, was the engine at operating temps? And did you have the throttle wide open? It wouldnt explain the difference between bank 1 and bank 2, but just wanted to make sure.

 

the engine was sent to be machined and everything changed in 2023 since it was pretty much neglected; it was bored out to 0.50mm and it been working fine ever since this started about last week.

here are the condition of the spark plugs on both banks.

Bank 1

Bank 2

 

It was cold, I didn't touch the throttle.

 

I see, I will continue checking the cables from the maf sensor to the ECU, I didnt check the injector wires but I will now.

 

That could be part of the problem. Here is the method I followed:

 

Well I decided to check timing today on bank 1, I didn't want to do the hot compression test since I didn't want to risk pulling the spark plug threads from what I been reading it can happen; So i removed the valve cover and set it to TDC compression and the timing marks seem to align.

Not sure where I will go from here, my other theory is that there is a sealing problem between the cylinder head and the block; so either a headgasket or rings or valves not sealing correctly; I still find it weird that a whole bank is low on compression compared to the other; I did notice about a finger missing of refrigerant on the reservoir but I don't see any proof that its mixing coolant and oil, the tailpipe doesn't have any coolant residue, the oil cap is clean and so is the radiator cap but maybe it just starting and no residue can be seen yet.