Valve Cover Leak Causing Misfire?

T

thrice1825

New member
Hey Everyone - I purchased my 2000 4runner (6 cylinder) about 4 months ago. When I purchased it, all seemed to be fine with the exception of a rear axel seal and a leaky valve cover gasket. After about a month of driving I started to get a "random misfire" code. The car is misfiring pretty bad.

As I read on here, the valve cover bolts were hand tight. I tightened them down (but not too tight) and am still having a really bad random misfire.

Is it possible that the valve cover gasket is so torn that it's leaking oil into the spark plugs causing the random misfire? Does anyone have any other ideas as to the cause of a random misfire on these cars?

Thanks
-Matt
 
Register to hide this ad
Thanks for the response! Yes it is in fact. It would previously go off then back on but it's now been on for a couple hundred miles. When I would run the OBD2 scan it came back as "random misfire".

On other cars I would get a "misfire on cylinder 4" which made it much easier to trouble shoot (swap over coilpacks, etc.) but this one seems more tricky.:shrug:
 
What brand of spark plugs do you have in it? could be a bad plug wire. Maybe a fuel injector. I'm leaning toward a bad spark plug or faulty coil pack.
 
DrCoffee - It looks like I have "Autolite" plugs. I've never heard of them so that's probably not a good thing. They don't look to be too corroded however. I plan on replacing them anyway with some NGK plugs.

Also, one other thing I should mention. When the car is in nuetral, it doesn't appear to be shaking or misfiring. When I put in in drive however it starts shaking all over again.
 
Last edited:
nice name love the band thrice, i had a misfire recently on cylinder 6 and it turned out to be a bad injector, have your injectors checked out, now it runs like a champ. So far I've changed 2 injectors that have gone bad, bound to happen on a 15 year old truck.
 
oil on the plug is a possible way to cause a miss fire just a couple drops of water doing some water splashing can do it. pull the plug wires if there is any oil on them besides a possible light film then that should answer the original question. But if thats not the problem check the plugs they might be gapped wrong and look at the burn color and deposits.
 
It's actually the gasket on the spark plug tube that is more likely to cause your issue. Yes it is possible the oil leak would cause this, especially if it's random. The plug gets wet, misfires, as it runs you burn the oil up and then the misfire goes away. The other possible issue is your wires. Wires that go down in the valve cover like these can actually arc on the spark plug tube causing the misfire.

Next time you get the misfire, pull the plugs and look for oil on them. If they're wet, change the spark plug tube gaskets and valve cover gaskets. If they're dry, probably plugs and wires. If that doesn't do it, most likely an injector.
 
Thanks all for the many responses! The truck has nearly 180K on it so I think I'm going to cover all my bases and replace the spark plugs, spark plug gaskets, and the valve cover gaskets. Depending on the cost, I may even throw some new injectors in there. I'll try and provide the best write ups on these as possible.

Is there a general consences on the best companies to get parts from? I know in the bimmer world there are several companies that stand out above the rest in prices and service.

-Matt
 
I'm not sure it's an injector but since you will be that far into the engine, consider buying 6 injectors and just replace them now. Rockauto.com has GB Remanufactured OEM injectors for $29 ea. I just replaced my left bank (wish I did all 6) but they all run great now. You've got a lot of miles on the clock, if they aren't bad now, they soon will be. The right side is easier to do.

All injectors are exact OEM replacement injectors, not similar or aftermarket substitutes. This guarantees form, fit and function. All injectors are 100% tested to meet or exceed OEM specifications.
 
Drcoffee said:
I'm not sure it's an injector but since you will be that far into the engine, consider buying 6 injectors and just replace them now. Rockauto.com has GB Remanufactured OEM injectors for $29 ea. I just replaced my left bank (wish I did all 6) but they all run great now. You've got a lot of miles on the clock, if they aren't bad now, they soon will be. The right side is easier to do.

All injectors are exact OEM replacement injectors, not similar or aftermarket substitutes. This guarantees form, fit and function. All injectors are 100% tested to meet or exceed OEM specifications.
Click to expand...

I wish I knew about this lol I dropped $130 on one OEM toyota injector. :cry2:
 
Same thing happened today

Same thing happened today to me... 96 runner 180k miles. Idle off's and missfire in 3 and 4. Pull spark plug out to see it covered in oil... So new valve covor gasket, tube seals, spark plugs, plug wires and ignition coils :( im broke now...
 
You must log in or register to reply here.

Members online

No members online now.
Total: 350 (members: 0, guests: 350)

Forum statistics

Threads
278,310
Messages
3,554,080
Members
248,016
Latest member
Advally Service

Share this page

Trending content

Back
Top