Misfire codes 0300, 0302, 0305, 0306

Hi All, I have a 2000 Tacoma 3.4 prerunner.
Above codes are now appearing, they started with 0306, so I did trouble shooting for that cylinder which included checking wire, coil, changing plug and checking injectors.

All of which were good.

brief history, both heads replaced 01/23 and the timing belt.
truck ran perfectly until this point.

Thinking it could be a faulty head gasket I ran a course of bars leaks just to keep it on the road. No effect. I also checked the Crank sensor and it was within specs.

What else can I check to isolate the problem? My compression checker is not able to reach the cylinder's without removing valve covers. so i have not done that.

Any help is much appreciated.
Thank you.

 

Radiator pressure test to check if it's holding pressure in the cooling system and an engine combustion leak detector test to check for combustion gas in the cooling system

 

thanks, also the car does not overheat nor does it smoke or have any oil or water in respective reservoirs. The truck has never been over 80mph and the heads were slowly broken in.
What is the likely hood that the timing belt is at fault?

 

If timing jumped, which I've seen before, you'll get p0300, 01, 02, 03, 04, 05, 06 and the mil light will be flashing.

 

Lots to check… It appears that you have a scan tool, if so, look at the short and long term fuel trims, should be +- 5% ideally, anything over 15% should be investigated. A positive number means that the PCM is having to add more fuel to keep the engine in the 14.7 : 1 air/fuel ratio as read by the front O2 sensor. Check the g/sec mass air flow sensor, at idle should be in the 3.5 to 4 ish range. If your scan tool is in lbs/sec see if you can change it to g/sec. See what the intake air temp is as well as the ambient air temp, if radically different, I would suspect the mass air flow sensor. Verify that the PCM enters closed loop too. Spray some carb cleaner around the intake to check for vacuum leaks, check the brake booster hose too.

 

Check your coolant level

 

I ran an engine combustion leak detector test and it came back negative. The radiator seems to hold pressure quite well as it stays pressurized for at least a half an hour when cooling down.

 

The stft is -2.3%
The ltft is 2.3%

IAC is 98°f outside 76°f

 

Fuel trims are spot on so no vacuum leaks or injector problems. It just might be heads/gaskets. Like mentioned before, monitor coolant reservoir and radiator fluid level.

 

With a negative combustion leak test I don't know if it is a blown head gasket. Or cracked head. Especially since I am throwing codes from both banks of the block.

 

I would try musical chairing the plugs and coils around to see if the issue moves..
Also do you have a squeaky belt or anything by chance. Sometimes a slipping belt or worn belt tensioner will trigger the misfire counter.. is it actually misfiring?

 

Yes it is definitely misfiring. Check engine light on. Flashing on hard load. Shaking with load at low rpm. I will move some coils and wires. But all are new with head job. Tensioner good belts good.

 

Let us know what happens, i've cracked new plugs before and caused similar issues

 

No insult intended… you do know that this is a wasted spark ignition system, one coil fires for 2 cylinders.

 

No insult,
I guess I didn't say I physically replaced heads, and the timing belt and the car ran great for 9+ months? I bought the truck with the whole top end in a box in the back camper. I do have an idea. Though I am not an auto mechanic, so I am not up on diagnostics and tests.

thought it would be fun to teach my teens how cars work.

 

Do not trust that combustion leak test entirely. You can get a false negative. I used that same block test kit and it also came back negative yet I was leaking coolant somewhere. Head gasket job with new heads did the trick.
Again, are you losing coolant or not?

 

Pulled plugs and misfiring cylinders smelled of gas.
Exhaust smells of gas. I must have missed something in the ignition.. white arcing marks at base of #5 cylinder.

 

Mass air flow, cleaned and put back in. Moved coils, cleared codes, drove again, still misfiring. Code 0306 prevails. Going to replace plug.

 

Solved!

The 5 and 3 misfires were combo of finicky and dirty MAS. The 0306 was a bad spark extender shorting out. See photo. Didn't know whT to look for initially.

 

Thanks for everyone who input ideas. It was all helpful!