P0304 & p0306 psa

[kcdehart]

PSA: If you're running into issues like the misfires during startup that nothing seems to change, it might not be a headgasket. REPLACE YOUR INJECTOR ON THE MISFIRING CYLINDER.

I was on the Tacoma forums and happened across a thread where someone mentioned that apparently the coolant jacket is a bit thin near cylinders 4 and 6 in the older models, and that this (when coolant temps run hot once or twice due to other cooling system issues) causes the injector(s) on 4 or 6 to fail and then leak into the cylinder(s) when the vehicle is turned off for an extended period of time. This then floods the car when it starts up and makes that cylinder misfire.

I had been getting a P0304 code *every* time I started my 4Runner after it sat for more than an hour for at least the last month. Maybe 2 months. I tried everything short of replacing the injectors (swapped plugs, coils, cleaned everything in the intake tract). Finally took it to a shop and they looked it over and told me everything seemed fine with no signs of a headgasket failure. Yet it continued to misfire (they claimed it didn't miss for them - I think they just didn't want to mess with it any more, as it missed as soon as I started it the next morning).

I came across the Tacoma forum thread (which I haven't been able to find a second time...but will keep searching for) and he mentioned that the failed injector will also cause gas to leak past the piston rings into the oil. So, I checked my oil and sure enough, it smelled like a gas pump. Changed the oil and dove into changing the injectors (which was a hassle, those boogers enjoy making vacuum leaks if they're not seated perfectly with zero dirt. Also, don't buy eBay remanufactured injectors. They suck, and I ended up putting all of my originals back in except for cylinder #4. It got one of the eBay ones that I confirmed worked properly).

I changed the #4 injector last Thursday and after 400 miles and probably 10 cold starts, haven't had a single startup (or otherwise) misfire. I'll update if I get another CEL from them, but so far so good! Check those injectors people! They're not as bulletproof as some claim.

Edit: Found the Tacomaworld thread! 1GR-FE's, Fuel Injectors... Discoveries... | Tacoma World

 

[4RunnerMexico]

i'm replying to back you up on this.

Have an 05 Tacoma at 248k truck started and misfired and poured white out of the exhaust. It did this about once a week for 10,00 miles.
Local dealer diagnosed it as a Head Gasket. I replaced cylinder #4 injector on a whim and its been happy, no more issues, truck runs great at 317k.

Also have an 03 4Runner, same symptoms, same diagnosis, replaced #6 injector and its running great with 237k.

Both trucks got little warm at some point, the 4Runner needed a thermostat and the Taco needed a fan clutch...

 

[kcdehart]

i'm replying to back you up on this.

Have an 05 Tacoma at 248k truck started and misfired and poured white out of the exhaust. It did this about once a week for 10,00 miles.
Local dealer diagnosed it as a Head Gasket. I replaced cylinder #4 injector on a whim and its been happy, no more issues, truck runs great at 317k.

Also have an 03 4Runner, same symptoms, same diagnosis, replaced #6 injector and its running great with 237k.

Both trucks got little warm at some point, the 4Runner needed a thermostat and the Taco needed a fan clutch...

I'm curious how many dealers saw gas pooled in the cylinder and misdiagnosed it as coolant. I'm sure there have been cases of actual headgasket failures, but I get the feeling they've been misdiagnosed fairly often, as happened with yours.

 

[earthrealm]

yeah, am leaning towards that too..have a persistent p0174 and a p0304 sometimes, and a lil stumbling if the trucks been sitting for a couple of days. my LTFT bank 2 is quite high 38%, while bank 1 is 18%
did you have a lean code?.. did you check your LTFT?, before and after the injector swap?
LTFT ....long term fuel trims.

bought ebay remanns- yet to receive them, a pals misfire resolved after swapping out all his injectors with same ebay denso remanns.
the remanns you bought, were they 12hole densos?

 

[kcdehart]

yeah, am leaning towards that too..have a persistent p0174 and a p0304 sometimes, and a lil stumbling if the trucks been sitting for a couple of days. my LTFT bank 2 is quite high 38%, while bank 1 is 18%
did you have a lean code?.. did you check your LTFT?, before and after the injector swap?
LTFT ....long term fuel trims.

bought ebay remanns- yet to receive them, a pals misfire resolved after swapping out all his injectors with same ebay denso remanns.
the remanns you bought, were they 12hole densos?

My only code was a P0304 pretty much whenever I started the vehicle. I didn't monitor LTFTs :/

The injectors I got weren't Denso, but did happen to be the same brand as the OEM fuel rail. I'm guessing the reman just sucked, as they were pretty cheap. Several visibly leaked while the fuel rail was pressurized and I'm fairly certain they may have fouled my cat because I've been getting a catalyst code every so often since install - even though only one of the remans is still in there...

 

[GarrisonMcD]

P0304 and p0306

I have a 2003 and mine is popping up with P0306, P0304, and P0300 all at once. It starts up rough and idles rough for a few minutes and then smoothes out until I let it sit. I replaced the spark plugs and moved the coils, but would you think that both injectors went out at the same time? Really hoping it's not the head gasket.

 

[djpope09]

I have a 2003 and mine is popping up with P0306, P0304, and P0300 all at once. It starts up rough and idles rough for a few minutes and then smoothes out until I let it sit. I replaced the spark plugs and moved the coils, but would you think that both injectors went out at the same time? Really hoping it's not the head gasket.

Does it only start rough after sitting for extended periods of time? If you restart it after running, does it start rough?

Start by checking your coolant level in the radiator and overflow tank. If either is low, fill them up and see over the next few days if the level goes down. If the level goes down and you don't have any visible coolant leaks then it's likely coolant causing your rough idle at startup.

You could also do what the guy above did and smell your oil to see if it smells like gasoline.

 

[GarrisonMcD]

Does it only start rough after sitting for extended periods of time? If you restart it after running, does it start rough?

Start by checking your coolant level in the radiator and overflow tank. If either is low, fill them up and see over the next few days if the level goes down. If the level goes down and you don't have any visible coolant leaks then it's likely coolant causing your rough idle at startup.

You could also do what the guy above did and smell your oil to see if it smells like gasoline.

I checked my oil and it reeked of gasoline. I went ahead and did a compression test and it all checked out fine. I replaced the fuel injectors and threw 2 new spark plugs in there and it cleared out the P0304 and P0306, but now it's showing up a p0303 and it is stalling when it idles. Could this be from a bad seal when replacing the fuel injectors over on cylinder 3?

Also appreciation to OP, everyone was screaming head gasket and this saved me a few thousand dollars.

 

[djpope09]

I checked my oil and it reeked of gasoline. I went ahead and did a compression test and it all checked out fine. I replaced the fuel injectors and threw 2 new spark plugs in there and it cleared out the P0304 and P0306, but now it's showing up a p0303 and it is stalling when it idles. Could this be from a bad seal when replacing the fuel injectors over on cylinder 3?

Also appreciation to OP, everyone was screaming head gasket and this saved me a few thousand dollars.

When you replaced the injectors, did you get the all the old seals out? There should have been an o-ring where the injector is pushed into the fuel rail and then another seal where it sits in the intake. I replaced my injectors recently and most of the o-rings didn't come out with the injectors. If you have 2 o-rings on top of each other that could cause issues I guess.

Where did you get your injectors? On one of my threads someone mentioned that Chinese knockoffs are common and don't work well.

I hate to suggest it, but you could move that injector to another cylinder to see if it's the problem.