1999 Tacoma 2.4L loud knocking sound only when warmed up 222K miles

Took it to a good, honest mechanic. First listened to front of engine with stethoscope. He believed it was coming from bottom of engine. He disabled #1 injector, sound went away. Reconnected, came back. Dropped oil pan to replace rod bearings. Could see no issue. Checked thrust bearings, could find no issue. Replaced all rod bearings. After engine warmed up, knocking returned. I told him I thought it could be timing chain or guides. He checked front of engine and said he could feel vibration coming from oil pump. He disassembled the oil pump and could find no problem. He replaced oil pump and just to take no chances replaced the timing chain assembly (everything). He even replaced the harmonic balancer. The sound was still there! He told me he does not have anymore ideas at this time. $3800 in parts and labor, and he didn't charge me because he couldn't find the problem!

Any ideas?

 

Welcome aboard new member

 

This seems too obvious to me so maybe I’m missing something. After disconnecting injector #1 and the knock going away, I would have dug further into #1 cylinder. If the rod bearing didn’t do it I’d be checking wrist pin and piston next. Of course not hearing the sound it made makes it difficult to second guess.

 

I asked him about the wrist pin being loose. He said they tighen up as they get hotter.

 

True.......pistons being aluminum warm up and expand so piston slap and wrist pin noise usually get better.

That’s all I had.......so I’ll get out of the way now and follow this.

 

Hey did you ever get this figured out? I’m having the same issue! Thanks

 

What about the balance shafts? How much did the engine slow down with the injector unplugged.

 

this is a difficult situation on multiple levels... how much time and money are you going to spend on a 20+ year old truck. Chasing a ghost noise is problem enough and that brings up another issue. If you choose to put a new piston in her where do you stop... do you do a valve job at the same time? If you could do the work yourself I wouldn't hesitate to put in a new piston/new rings and lightly hone that cylinder and drive her. You didnt mention if the truck is a beater or your baby, I would factor that into the decision making process too. At 200k she has another 200k minimum of life left.

 

Any chance its the AC pulley bearing? Sometimes on my 99 2.4L I get a knocking that stops when I turn off the AC or defogger for a while. Did some digging and it turned out to be the AC pulley bearing that gets loose after a while.
https://youtu.be/VjRtLLd0vE4
https://youtu.be/8ehoRUcGsV4

 

That mechanic is a keeper do not let him get away!!

 

No kidding! OP care to share your mechanic??

 

they haven't been on since February and only made those two posts. PM might be the way to go but that depends on if they check email

 

I hate when this happens!!

Such is life!

 

Sorry I went to sleep on this post. I now have 228000 miles and still have the noise. The day after I got the truck back my mechanic called and told me another Tacoma (same year) came into his shop for some work. It had the same knocking sound! I'm going to drive it until one of us (me or the truck) dies. My mechanic is very honest and fair. His name is Mike Holden of Holden Automotive in Snellville GA. 770-982-5546.