So am helping a pal diagnose an issue on his 07 runner.
P0300,p0302, p0303 all persistent and refuse to go away.
Swapped coils, changed plugs, swapped injectors, Cel refuses to go away.
Plugs removed were brownish in color.

We are really stumped.
Any clues on what could be the culprit?
Fuel trims are 11% and 19%...car idles ok..but Cel triggers on giving it gas

Could a bad fuel pump be responsible??

0302 refers to cylinder 2, 0303 refers to cylinder 3. I'm thinking it could be fuel pressure related. Maybe the pump, maybe the pressure regulator. Have you tested incoming fuel pressure yet?

Nope he hasnt tested the fuel pressure yet, however he changed the fuel pump about 8 months ago, on the advice of his mechanic.

My question is why the bank 2 and 3 are being highlighted...i thought fuel pressure related issues would affect the whole cylinders

Could be an issue with a specific injector, or an issue with the routing of the fuel rail. Could also be related to the plug or coil on that cylinder (not bank). The code simply refers to a misfire on a particular cylinder.

We swapped injectors, coils and replaced plugs.
No change same codes p0302 , p0303, p0300...

Filled tank with gas.just incase he had contaminated gas...no change either,
So either the fuel pump or leaking head gasket are my suspects now

After everything that you have done, i would check fuel pressure with truck running and off. Don't know the specs but basically pressure must be stable with key off, not dropping. Check pressure at the moment of misfire if it drops. Try swapping
Fuel pump relay also for a known working one. Clean mass air flow sensor, if all good then compression test and leak down test.

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Agreed. Pressure is 42psi minimum, I believe. If it drops below that, you'll misfire. If you have an issue with a leak in pressure, it'll misfire. Could be the pressure regulator or the pump itself. Could also be a plug is not gapped right tbh. Misfire is occuring due to a loss in fuel, air or spark, and your codes refer to specific cylinders. Could be an issue with the coil plug having a bad pin or a boot with a hole in it shorting to ground. Pressure should be consistent across all cylinders, so I find it odd that delivery of fuel would be the issue. Could also be an issue with cylinder compression from a bad ring or a stuck valve. Or if the tank was low on fuel, you could've sucked particulate from the bottom of the tank and it's fouling your new injectors. Not always so cut and dry. The pump could have crap in it that's gotten thru the filter sock and it's floating around and sometimes clogs the pump, the pump could just be getting tired or it's getting hot after a few minutes of running because it's worn out. Start with a baseline, what's the fuel pressure?

owner was unable to test the pressure, swapped the fuel pump with a new unit, issue persisted and got worse... observed coolant level was reducing in reservoir tank. all of which pointed to a HG failure,owner took the vehicle to repair center, all 3 plugs on passenger side, soaked in oil.
HG failure confirmed, 07 v6 bought used at 206k miles, now 215k miles... any other part to replace while doing the head gasket job

If the plugs were soaked in oil, then the spark plug tube gaskets are leaking and should be replaced. Common issue. You should start with replacing all 6 tube gaskets before doing the HG and go from their.

Agreed. The tube gaskets are under the valve covers. Replace the valve cover gaskets and tube gaskets. Head gasket would leave oil in the coolant. If the level is dropping, could be from pump pressure and he's running low. What color is the exhaust? Water in the tail pipe usually results in white exhaust. If the issue is related to a head gasket that would be a good sign. If it is blown, my guess is it was getting hot

So what would have caused the tube gaskets to go bad?.
The oil was worse on bank 1.
Could the shorter plugs be the culprit?.
2ndly, attached is pic from the bank 1 cylinder.wonder what would have made the mark there.
Car was stopping intermittently and unable to move meaningfully.
Owner has instructed mechanic to commence the repairs

Attached Images

 

Did the mechanic clean that cylinder portion of the head or is that the way it looked when they pulled the head?

Blueish smoke from exhaust at start up.
Didnt see oil in coolant.
Removed the radiator cover , started the car and checked for gas bubbles.....none either.

He didnt have coolant in the reservoir tank initially, got him to fill up to full mark and it gradually reduced by about an inch per week. Intercity driving, say about 100 miles weekly

Thats the way the cylinder was.scuffed/pitted.
Recall he had persistent p0300, p0303 and p0302.
Which failed to go away when we swapped plugs, coils, injectors

Blue smoke at startup is from deteriorated valve seals, oil leaks passed the valves seals when the engine is not running and then burns at startup.

Not sure what could cause the pitting but the clean metal is most likely from when the coolant was turned to steam when the cylinder fired.