i have a 99 4runner that i bought about a year ago, absolutely love the thing. it's got about 190k on the chassis and had a jdm motor with "less than 50k" swapped in before i purchased it (receipt verified). a few weeks ago i was driving it on the highway when it suddenly lost power, then threw a check engine light. it felt like it was running on 5 cylinders, which i confirmed the cause of the next day (more on that in a second).

i limped it back home and was almost home when suddenly at a stop light it started knocking really badly, almost sounding like rod knock from inside the car. i immediately shut it off and had it towed home, where it's been sitting. i finally tore into it those weekend and found the cylinder 5 spark plug missing the ground and one of the straps and some significant black carbon buildup on it. replaced all plugs, as well as the coil pack on 5 and what i figure was the leaking injector on 5 that caused this mess. while i had everything off i boroscoped cylinder 5 and did not see any visible damage. i also drained the oil and replaced the filter. the oil did not smell like gas, so i don't think any gas made it past the rings into the oil and spun a bearing.

after putting everything back together, i cranked it and the noise continued, but less. its really random and does not sound like rod knock. it almost sounds like something smacking the passenger side valve cover from underneath. obviously i haven't wanted to run the motor while it's doing this, so it's been tough to pinpoint the location of the exact noise. it definitely sounds like its coming from the top half off the engine, though, and not down in the block. check out the attached video and let me know what y'all think i should do. anyone ever deal with this? should i try some mechanic in a bottle and hope its just carbon buildup on the valves that's getting something stuck? should i just torch the f$%@ing thing? thanks in advance!

https://www.youtube.com/watch?v=LsOh...ature=youtu.be

 

Do you ‘feel’ the sound if you touch the passenger side valve cover in various places? If so, I’d pull the valve cover and take a good look.



Andreas

 

i did pull the valve cover actually. nothing seemed out of order. i even turned the motor over by hand to make sure the tappets were free on cylinder 5 and not stuck. anything else i should be checking? i could pull that valve cover again this weekend if necessary since it's the easy one to get to.

 

All I can say from that video is that it's def. NOT a rod knock/piston slap.

Maybe get a mechanic's stethoscope and try to narrow down the source of the sound.

 

will definitely try that this weekend. thanks for the input

 

Cracked flex plate?




Andreas

 

5 speed, unfortunately (but also not unfortunately)

 

5 spd 3rd gens: UNITE!

It's def. an unusual noise. A rod knock wouldn't come and go, and (it's hard to tell from a video) they usually sound a bit deeper sounding. Clunk clunk clunk, not tap tap tap.

Another thing to try, a modest PITA but not as much as taking the valve covers off - remove all the drive belts and start it and see if that changes anything. Just to rule out the alt/a/c compressor/ps pump/fan bearing. It still could be something weird going on with the water pump or belt tensioner under the cover. But just based on a hunch, of taking them off doesn't change anything, I'd proceed to the valve covers.

 

great suggestion. may pull the timing cover as well, just to check the pulleys and timing.

i also ordered a mechanics stethoscope to try and pinpoint the source a bit more accurately, so i'll give that a shot and see if i can get y'all some better information. big thanks to everyone that's weighed in. so far, you've saved me from just lighting the thing on fire in my parking lot and roasting marshmallows over it.