Loud engine knock under load

tanner23456

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!

Mr_Shiftright

It's hard to define "knocking sound" from this distance.

Do you mean like the click of valve lifters--a loud tapping?

Or do you mean a KNOCK, which is a sharp RAP you could easily hear from outside the car?

Does the noise increase and decrease with engine RPM?

What happens if you put it in gear and race the engine a bit (not too much) while your foot is on the brake (that is, putting the engine under load)?

tanner23456

I'm not terribly experienced determining engine noises, but to me it sounds a whole lot more significant than valve tapping. It's very audible when driving uphill when there's a lot of torque on the engine. To the point that it echos off of people's houses.

When you say increase, I assume you mean volume. I don't think there is any change in volume with speed. The frequency of the noise definitely increases with engine speed. The sound only gets louder when I'm at low rpms going uphill. When the engine is under load.

I haven't tried racing the engine in gear with the brake on but I suspect a similar thing will happen that happens going uphill.

thecardoc3

How many miles are on this since the oil change? This would be a time if you have enough miles on the oil, that an oil analysis might reveal specific wear materials that have collected in the oil. Otherwise you need an experienced technician to actually hear and investigate the symptom to have an idea where it is coming from.  

tanner23456

That's fair. I changed the oil pretty recently and there really wasn't anything alarming. It was about average for my car. That's good advice though. I think I'm gonna try and take it to someone today and see what they think.

Mr_Shiftright

You need an experienced ear because this symptom can be so many things. I have been fooled a few times in my life, when I swore I had a bad engine and found, in one case, a loose keyway holding the front crankshaft pulley on! (or a loose bolt for that matter). I suppose with this high mileage you have, there are lots of possibilities here.

tanner23456

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?

tanner23456