2005 P0304 code questions

2005 Tacoma, V6, automatic, 117,000 miles, oil changed last week, plugs changed at 100,000 miles, usually gets around 17-18mpg.


Engine light came on, coded P0304 MisFire on Cylinder 4. The truck was running fine until yesterday when it had a rough idle at startup, but then smoothed out. Check engine light came on this morning.


I'm going to switch the coil pack, boot, and plug to a different cylinder and have the code checked again. If the misfire moves I'll know it's one of those things. This also gives me a chance to check the plug for oil or some indication of something else.


Questions;
1 - Assuming it's a coil pack is there a certain brand to buy that is best, or a brand to avoid?
2 - If one coil is going out are the rest likely to be on limited time also? Should I just replace all of them?
3 - I had a Ford once that coded misfire and needed new coils, but it was just the boots that needed replaced. Is this a possibility with my Tacoma?
4 - Should I be looking for something else?

 

It's not common for the coils to fail so I wouldn't worry about doing them all (yes Ford Triton engines and various others have a high coil failure rate but it doesn't seem to be that common on Toyota trucks).

If it ends up being that I would say stick with OEM or if you go aftermarket go with Standard Motor Products.

Misfire on startup and then smoothing out could be early signs of coolant getting in the cylinder from a head gasket leak, you could verify by leaving the plug out and pressure testing the cooling system while looking for signs of coolant leaking into the cylinder.

Do you get a puff of white smoke at startup?

 

Thanks for the reply.

I don't know if I get white smoke on start up, haven't had anyone back there to check yet. To clarify on the rough idle that smoothed out yesterday; I had already made an 1hr drive, then a 30 minute stop, then the rough start. It hadn't happened after an overnight sit. This morning it started smoothly (before the light came on).

The truck is white. There are some exhaust stains right above the tailpipe that are darker in color. I imaged that would indicate a rich mixture, but to be honest I just figured that since I never wash the truck the white paint would pick up some discoloration from exhaust in general.

 

It was just a thought, the 05s had a higher head gasket failure rate and coils generally cause misfires under load or miss all the time but if your not losing any coolant or having overheating problems it's unlikely a head gasket..
You could put the coil in a different cylinder and the plug in another cylinder and see if it follows either.
There's always going to be some discoloration by the exhaust pipe even on a perfect running truck.

 

If it ends up being this, for the coil, go with Denso 673-1308, they are the OEM manufacturer

 

Update;

I just pulled #3 and 4 plugs for comparisons. The plug with the code is a little more white and chalky than #3. They don't look a lot different but there is a difference. Also, the black stripes on the coded plug's ceramic are gone while the other one still has them. Is this cylinder getting hot? Could I have a bad injector causing a lean condition? I don't see any plug coloration that indicates water, but I can't claim to be great at reading plugs.

 

Did you use OE copper plugs? The 4.0 doesn't seem to like platinum or iridium ones.
A bad injector is a possibility but you need specialized equipment to test injector balance.

 

Plugs for comparison. The left is the coded #4 cylinder, the right is #3.

I went ahead and switched everything from one hole to the other. Hooked the battery back up and started her up. No engine light. So now I'm not sure what to do. I'm guessing a little test drive might get the light back on? Then I can take it back to the shop to run a code test on it to see if the code changed cylinders?

 

Yes go take it for a drive and try to replicate the issue. Have the codes pulled if it starts acting up again and report back

 

Could you explain? What kind of issues do the non-copper plugs generate in the 4.0's? I would love for this to be as simple as a plug change. I'm really stretching here hoping to find something other than a head gasket...

 

Not everyone has issues but I have ran across some threads where people had various driveability issues from poor fuel economy to surging and misfiring after changing plugs and the fix ended up being putting the correct copper plugs back in, just something to think about.

 

Just drove down the highway and back a good 15-20 minutes. Stopped and shut the truck off a couple times. Can't get the CEL to pop back on. It's a waiting game now. I wonder if it was a connection starting to corrode or something that was remedied just by taking apart and putting back together? I'm guessing that's just wishful thinking but I'm going with it until the light comes back on.

 

I'll put some research into it. This would be the best case scenario possible in my opinion.

 

I'd get a compression check by a mechanic or do it yourself using one of the post on the forum. I have seen 3 pre 2010 tacos do this, all of which were from a head gasket leak. Pre 2010 they had a flaw with the design of the head gasket and caused it to fail. Not saying this is the cause but 100 bucks or an hour of your time with a free rented tool from advanced auto or orileys could give you piece of mind and save from a possible failure while your driving. Lmk the results

 

The electrode one the left looks “odd”. Not as centered as the one on the right.
I like stick with OE plugs on Japanese vehicles.


Autolite makes good plugs, I just find they work “better” on American engines.
You can’t beat them for 70’-80’ vintage push rod engines. I’ve even used them in our lawn tractors with good results. (This only my opinion)

 

I'll be damned... that one is wonky! Good eye!

I took several pics when they were out. Went back and enlarged another one that shows that plug looking pretty bad. Hope it is bad due to the plugs failure and not due to a mechanical problem. Looks like I'm going spark plug shopping this weekend.

 

Maybe I'm OCD but on mine I went back with the original configuration of NGK on one side and Denso on the other

 

A whole slew of 2007+ 4.0L owners are gonna try to tar & feather you, for condemning their head gaskets by proxy.

The original head gasket design, the one that everyone is so concerned with was on the 2003-2006 1GR-FE (4.0L) only. Tacoma, 4Runner, FJ, Tundra...doesn't matter what it came in. Midway through the 2006 model year, the new gaskets were phased into production. If you saw failures on newer model years, it wasn't because they were the original "flawed" design.

 

Not me. I went Denso. No real reason other than most on this forum recommend them. .

If it had not been for this forum, I would have went NGK. Because they are great in all our 2 stroke stuff.

 

Well, considering his is a 2005, it still applies. Also, I prefer honey over tar