Please Help - Everyone is stumped

Sorry if this has been covered already, but I couldn't find any info. I have a 2001 Tacoma 3.4 liter. 280,000 miles. Engine purrs like a kitten, no power lose, no smoke, no overheating. Compression on all cylinders is 120.

Every morning I start it up I get a misfire on cylinder 3. It lasts for 10 seconds and then runs like a champ. I have replaced the spark plug wires, the spark plugs, the ignition coils and the fuel injector on #3.

It feels like it is burning out excess fuel by the way it lasts only 10 seconds and then runs great. Here is my question. Based on everything I just wrote, does this sound like a possible valve issue or maybe a timing belt issue? With the compression being ok, I don't think it is the rings. Any advice would be very appreciated!

 

Does the #3 spark plug look any different than the others

 

Sounds like a leaking injector or a headgasket.

Next time you park it for the night remove the plug and inspect the cylinder for liquid

 

I have checked the #3 plug in the morning and it looks fine (and looks like all the rest.) The injector is brand new, so I don't think that is the problem. If I had a leaky head gasket, wouldn't the truck be overheating? And if it was a leaky head gasket, wouldn't it take longer than 10 seconds to heat the block up? And I have also tested the coolant for any leaks and the test kit showed none.

 

I had a cracked cylinder head that leaked coolant. It never overheated, coolant test kit showed negative, but it blew white smoke on cold mornings.
And it had visible coolant buildup in the cylinder after sitting for a day.

After the truck was warm there was no smoke, normal coolant temps and ran great. It took more than 10 seconds though, talking a few minutes until the coolant temp was actually fully warm.

Interestingly it was cylinder 3, and cylinder 3 is the most common location for a head crack for whatever reason.

Symptoms to me sound like a leaky fuel injector, though it sounds like that has been ruled out.
I'd stick a borescope down the plug and check for any fluid. Let the truck sit a day before doing it too.

 

If you move the plug/inj to another cylinder, does the problem move to?

 

Try this first as it is free and takes no time or $

As soon as it is safe when you park her for the night loosen the radiator cap and take the pressure off the system. If there is a crack in the head the pressure from the cooling system will weep coolant into the cylinder over night. If the cold morning start is normal, congrats, you have a small crack/weeping head gasket.

 

No, not necessarily. Not until the coolant gets so low that it can no longer cool the engine.

No.

That's not always the case. Coolant can leak into the cylinder, but no into the cooling system.


I'd try a compression test, followed by a leak down test if needed.

 

Is coolant being lost?

 

Thanks for all the replies!! I'll answer as many questions as I can. Wilcam57 - My coolant level has never dropped at all. Time623 - That is crazy. Never new that about cylinder #3. But, I get zero smoke, even in the morning. Lastcall 190 - I'm not going to go through all the work to try and swap out the injector (yet) as it has a brand new injector. All the plugs are brand new OEM and have been gapped properly. Glamisman - I will give that a try. Tnshooter - Just did a compression check. 120 at all cylinders and I'm at 6500 feet above sea level.

This has really become a serious pain in my rear...

 

Maybe a partially sticking valve? I'd check valve clearances.

You said new injector, coils, and plugs on #3. I would've suggested swapping those to another cylinder to see if the misfire followed the parts

 

I know you’ve mentioned new injector, but I didn’t read OEM injector. Can you confirm it’s OEM. I have read many threads like this where people put in an aftermarket injector that was still leaking.

 

Still sounds like a headgasket leak

 

So I put another injector on cylinder 3 and it started doing the same thing after 2 days. Broke down and took it to a shop nearby with good reviews. They said they can't figure out what is going on with #3. They tell me now that it is either the computer, the ignition or maybe even the catalytic converter. Anyone hear of these things causing only a 20-30 second misfire when cold??

 

OEM injector or another aftermarket? Like I said above, people have done the same thing you have with the same results. OEM injector fixed it.

 

It's probably the head gasket. The coolant leaks into the cylinder overnight while sitting and them it chokes on the liquid for a few seconds when it's started in the morning. After the liquid is burned out it goes back to running smooth

Use a cylinder leakdown tester to put air pressure into the cylinder with the valves closed, then look for bubbles coming out the radiator fill neck

 

I had this same exact issue about a year ago. Coolant was leaking into the cylinder, giving me a misfire for about 20 seconds and then ran fine after. But for me I could obviously see that I was losing coolant. But you’ve already said that you are not.

 

Pressure test the cooling system overnight in the morning pull the spark plug before starting in and use a boroscope to check to see if there's any coolant. If that's good I'd check injectors as they are prone to leaking. Valve stem seals could leak and wet the plug on cold start.