2004 Tacoma Prerunner 2.7 (3rz) with 240K miles on it.

Never had major work done on it. Just usual wear items/maintenance.


Went to do spark plugs on my dad's truck today and found that the plugs in cylinders 2 & 3 are blistery white (These plugs have about 100K on them.) on the ground strap, more so on 2 than 3.

Cylinder 2's coil on plug unit is also very discolored when compared to the rest. I thought it was from oil, but all of the coils were wet, but only one was discolored.

So I pulled the valve cover and broke out the feeler gauges to check the valve adjustment.


Findings: Cylinder 2 and 3 had the tightest exhaust valves, but were still within spec: 0.3mm and 0.29mm (I rotated the engine around a few times to double check)

I pulled the heat shield off the exhaust manifold but I don't see any white runners or cracks. I replaced the valve cover and tube seal gaskets and put in new denso plugs.

UPDATE: Compression test results:

1 - 180 psi
2 - 161 psi
3 - 170 psi
4 - 190psi

But I'm worried about burning up the exhaust valves?

Here are some pics I took.

http://imgur.com/a/dbaiT#0




Any thoughts?

 

White means a lean condition from a little research. Might want to take a infrared gun to each exhaust runner and see how much hotter those cylinders are operating at.

 

IIRC the manifold on that engine does bias the airflow to the middle cylinders but odd it would make that much of a difference.

Could be a dirty injector causing it to lean out, I would try doping up the gas tank with injector cleaner and see what happens. Might also try a seafoam treatment (see my other threads for more info).

 

Update: Did a little more diagnostic work today.

Compression test results:

1 - 180 psi
2 - 161 psi
3 - 170 psi
4 - 190psi

So the suspicious cylinder has a 29 psi difference from the highest value.

Guess I need to perform a leakdown next...?

 

Good idea with the infrared gun. I'll try that.

Interesting, didn't know it had bias. Thanks for the info! Yeah, I talked to him about sea-foaming it. I always seafoam my own vehicles.

 

Before that, do the compression test again with a squirt of oil in each cylinder. If the compression comes up, the rings may be suspect. If not, then valves. I don't see anything to make me think heat is a problem, just a discolored coil boot.

The spark plug coloring looks normal to me. EFI vehicles will just about always have plugs that look too lean. The method of gauging mixture by color was made largely obsolete with the advent of EFI and reformulated gasoline.

 

Yeah, had someone else today tell me to ignore the coloring.

Anyway, put a few ounces of oil in the chamber and the compression was still in the low to mid 160s.

Gonna do a leakdown next to see if I can hear hissing from the tail pipe.

 

Leakdown test is a good idea, Then might as well do a seafoam treatment. After repeated treatments and MMO in the oil I was able to raise my compression from a varied 130psi-180psi to and even 205psi across the board. All documented in the thread.