Help! What is causing my misfire/engine shake?

Background: Slow valve cover leak on my 2005 V6 4x4 with 300k miles that I finally decided to remedy. I installed the new Fel Pro gasket on the passenger side, cleaned the mating ends and bolted everything back up. No silicon. While I was there, I put new Denso plugs in the 2, 4, and 6 cylinders. Two days later…Check engine light on and a read indicates a 306 code, misfiring in the 6 cylinder. Since the spark plugs were new, I swapped the coil pack from the 6 to the 4 and vice versa. Cleared the codes and two days later check engine light comes back and the read says 304, the 4 cylinder. So I installed a new coil pack on the 4. Cleared the code and it ran great for a couple days. While the check engine light hasn’t yet come back on and there are no pending codes, now the truck, on cold (California) starts, almost shakes. After you put some gas through and start driving, it doesn’t misfire as hard and isn’t noticeable to many. It starts fine when it’s warm. It’s clearly not the spark plugs. The coil pack is new. What else could this be? Is this an issue?
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Another fun issue is that it jusssssst started overheating. Fine when driving on highways, but when the truck is idling the temps skyrocket. Reservoir in the tank was full, after the near overheating, the reservoir is empty. This has happened twice in less than a week: full reservoir, almost overheats, nearly empty reservoir. No apparent leaks. I bought a fan clutch for it, though that might actually still be in good shape. If you have thoughts on this one too, I’d love your input!

Thanks all!

 

Magneto?

 

Head gasket?

 

Hate to say it but you might have a slow leak in the head gasket. The coolant dribbles into the cylinder when it's sitting and then when you start it in the morning it "chokes" on the liquid for a minute until it burns out of there.

You need a compression/leakdown test

 

With coolant loss and cylinder #6 involved on a 2005, I would suspect head gasket.

 

(Shrug) What is magneto?

 

No oil in the coolant and the oil on the dipstick looks so fresh and so clean. Could it still be a head gasket issue?

 

Hmmm... Ok. That sounds like a feasible situation. When I pulled the coil packs and plugs, everything was clean and dry. No residual crusties or anything. But I have not done a compression test. I'll research how to do that on the forum. Thank you!

 

Edited:

The mis-fire could be a bad new coil pack or bad wire or loose plug wire ...make sure you have a good connection between the plug and wire & wire to coil pack


For the over heating...
With the engine warmed up (drive until NORMAL TEMP is reached) check the top cooling hose and then the bottom cooling hose. BE CARFUL; the hoses will be hot.
If one is hotter than the other; chances are you have a frozen / sticking thermostat.

Good luck!

 

not just compression though, leakdown testing will pressurize that cylinder with air and then you look for air bubbles coming out of the rad cap

 

Why not replace the other plugs?

 

Sounds like you thermostat is going out

 

But the coolant level is dropping consistently in the reservoir so its going somewhere

 

Smell the smoke coming out of the exhaust right after you start it cold. If it smells sweet, you're burning coolant. Bubbles in the coolant reservoir just after starting is another common sign of a head gasket issue.

No matter what happens, 300k miles on a 2005 V6 is a great run.

 

I will. I only had time for one half. This weekend I've got open to see what I can manage.

 

Agreed! This truck has been great! Legit no issues until I "fixed" something that wasn't really broken. And I sort of think they'll be manageable problems anyway (with the help of this forum - thank you all!).

 

how many miles do you drive before the coolant level drops?check your exhaust, white smoke is coolant blueish smoke is oil

 

In my opinion the slow coolant loss syncs up with the cold start stumbling

That year (05-06) is when toyota had trouble with the headgaskets. And it was usually the back 2 cyls

It probably did have a coil pack issue too, she said she moved the coil and the misfire/code followed so that's legit.

She's getting the one-two punch.. it sucks but the truck is kinda getting up there in miles, thats the way these things go sometimes..

 

UPDATE: I used the two hose feeling technique suggested by rmac010 and tried the thermostat. Those who thought it was that were right! The truck is nice and cool now! Thank you guys!

In diagnosing I watched the temps rise a few times. No coolant drops. No air in the coolant. So that’s cool.

As far as the misfire goes, a pending code for the 4 cylinder with a pending code for an O2 sensor down from the cat showed up yesterday. I switched the coil back from the 4 to the 6 and reset the codes again. Shortly thereafter the check engine light came on with the 4 misfiring and the O2 is still pending.

At this point, I’m going to pull spark plug from the 4 and replace with one of the new ones I bought for the other side and haven’t installed yet, clear the codes and go for another drive. Crossing my fingers$
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Changed the spark plug and cleared. Pending 304. So it’s not the plug or the coil.