Loud engine knock when under load.

[Tanner Nelson]

I’ve tried just about everything at this point. I have a 2005 mitsubishi outlander that’s at about 165,000. At the beginning of the year, it started developing a small knocking sound and it’s gotten progressively worse to the point I don’t feel comfortable driving it. It only happens when the engine is under load, usually going uphill. I used to think it was affected by the rpm’s but I’ve since decided speed of the engine does not affect it. It’s really quite loud and rhythmic. The only time it seems random is when I let off the gas a little going up hill. It sounds great at idle and I can rev it up to 3500 rpms in neutral without any problem whatsoever. The weirdest thing to me is that I don’t feel like there’s any loss of power. If I was completely deaf, I wouldn’t suspect any sort of issue.

Here’s what I’ve tried so far:

-Replaced timing belt, balancer belt, and pulleys
-Replaced VVT solenoid
-Cleaned out the EGR valve
-Replaced the fuel filter (though not sure if this would actually affect anything)
-readjusted the valve clearance
– changed oil

There was no change after each of these things

Other possibilities I suspect could be the issue:

-Bad knock sensor
-carbon build-up (Plan to try the seafoam cleaner)
-bad rod bearing
-blown head gasket
– Vacuum Leak

I’d appreciate any input as to what to attack next. Thanks!

Topic

[Richard Kirshy]

Other possibilities I suspect could be the issue:

-Bad knock sensor Check for any codes that may be stored
-carbon build-up (Plan to try the seafoam cleaner) You could remove the spark plugs and using a borescope have a look int each cylinder for buildup deposits.
-bad rod bearing Possible, though usually they make noise with or without the engine placed under load.
-blown head gasket Compression and leak down test could provide an answer
– Vacuum Leak A scan tool can help determine a possible lean condition

I’d appreciate any input as to what to attack next. Thanks!
I’m assuming you have checked for codes
[color=orange]Discounting the possibility of bad fuel for over 5 months.
You may have a faulty lifter or push rod[/color]

[Tanner Nelson]

I appreciate the reply. Those are excellent suggestions. I have checked the codes pretty religiously throughout the time the engine has been knocking. The only code I’ve received was a misfire code but that went away relatively quickly.

It should also be noted that when I bought the car used, the previous owners tried to glue a cracked radiator together which caused a pretty bad overheat. That’s what made me suspect a bearing or head gasket. I’ve been thinking about doing a compression test to hopefully eliminate the head gasket scenario. I’ll look into the faulty lifter or push rod.

[Steve Klein]

Assuming it may be a mechanical issue, you can try disconnecting 1 spark plug at a time and see if it goes away. That would at least identify a cylinder to look at. Have you pulled the plugs and looked closely at them?

[Tanner Nelson]

That’s a good thought. I did replace the spark plugs back in July so it doesn’t seem all that likely that there’s an issue there. I took them out a few months back to check the gap and nothing seems out of the ordinary.

I’ll try your suggestion with taking one of the plugs out. There isn’t any problem present when the car is idling so I’ll need to drive it around. Can it cause any issues to drive the car with one plug removed?

[Steve Klein]

No, you wont cause any damage. But, unless you also unplug the associated fuel injector, you will have fuel going into the cylinder. So, make the drive short.

[Billy]

Hard to make a meaningful guess without video, but what you’re describing sure sounds like rod knock. If that’s the case, then (a) don’t take it far from home, and (b) sorry to hear you invested all those hours and parts in it.

[Tanner Nelson]

Thanks for your help. After some research, I found that it was a blown head gasket between two cylinders. I’ve spent the day getting to the head gasket and it confirmed my analysis. Unfortunately, when I got the cylinder head off, I noticed damage to the piston. There was nos debris left behind, so I’m assuming this has been the case for the previous owners as well. Judging from this picture, will the piston need to be replaced?

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