Hi.

My 4Runner has been misfiring for a while now. It runs rough at idle, and at 1400 RPMs it shakes the car. I'm able to drive it fine, but I have a decrease in mpg and it lacks power. I can hear a dead cylinder in the exhaust, and by pulling off ignition wires at idle I've determined that it is the #6 cylinder. My check engine light has also been coming on and showing codes 14, 25, and 26. I replaced the 02 sensor a year ago (although with a generic one), so I don't think that it's that. I've also replaced the cap, rotor, and plugs. The wires tested good, and switching the wires didn't make the misfire change cylinders. Any ideas?

 

First step would be a compression test.

Do that, then report back.

 

X2 on that. Sounds like a case of the 3.0 burnt exhaust valve blues

 

Well, bad news. I checked the compression on #1 and #6 cylinders. #1 was about 155. #6 was about 30! So I've got a burned exhaust valve? How much would that cost to fix or how involved would it be to attempt this myself? I'm guessing you have to take the head off.

I've been driving the 4runner like this for about two months. The only real driveability problem is a loss of gas mileage (from about 18-19 mpg to about 15). Of course it idles rough and has a loss of power, but it still drives. Would it be bad to disconnect the fuel injector so it isn't wasting gas and then just run it on five cylinders?

I guess the good news is that I won't waste time and money chasing after gremlins like fuel injectors, etc.

 

Next step is to determine valves, or rings.

pour a small amount of ATF into the cylinder, and do the test again. If the compression comes up, its the rings. If not, its the valves.

 

If it were the rings, wouldn't the cylinder still fire at least nominally? The engine doesn't smoke, but the exhuast does have an unburnt fuel smell.

This problem didn't come up until I had my catalytic converter stolen a few months ago. There's no way that a missing cat would cause a valve to get burned is there?

 

check coils.