Hey everyone,

New to the forum and am trying to diagnose what I think is likely rod knock. I've attached a quick video of the engine at idle. The knocking noise is especially loud when the engine is cold. Once it heats up a bit it quiets down but still seems louder than the "Toyota Tick" I've seen people post about.

I've taken it to a transmission place and determined that is not a cracked flexplate. Another mechanic said the noise is coming from the engine and a rebuild/engine swap will be needed.

I just purchased the 4runner and had it inspected by a mechanic before purchasing....but here we are. I'm thinking its somewhat of a lost cause, but am hoping it might the lifter ticking.

Im located in the Bay Area and have received a quote from Yodaman in Santa Rosa for a rebuilt engine and it was $8,500 which is more than id be able to afford.

Engine: 3.4 V6

You Tube

Thanks!

 

Hey everyone,

New to the forum and am trying to diagnose what I think is likely rod knock. I've attached a quick video of the engine at idle. The knocking noise is especially loud when the engine is cold. Once it heats up a bit it quiets down but still seems louder than the "Toyota Tick" I've seen people post about.

I've taken it to a transmission place and determined that is not a cracked flexplate. Another mechanic said the noise is coming from the engine and a rebuild/engine swap will be needed.

I just purchased the 4runner and had it inspected by a mechanic before purchasing....but here we are. I'm thinking its somewhat of a lost cause, but am hoping it might the lifter ticking.

Im located in the Bay Area and have received a quote from Yodaman in Santa Rosa for a rebuilt engine and it was $8,500 which is more than id be able to afford.

Engine: 3.4 V6

 

Joe,
Remove each plug wire one by one (the passenger side are coil packs) and check that each spark plug is tight.

Let us know what you find.


Andreas

 

I had early stage rod knock on a 5vze and this does not match my symptoms. Besides what Andreas suggested (difficult to test all cyl because of shared coils) the definitive symptoms for my early stage rod knock was-

1. Run truck at 2500 rpms (set gear to maintain this regardless of load) and feather the throttle so you are just between load and coast. probably easier with a manual but engine in this state will sound exactly like a diesel. You did not really say if it goes away with load but that would be the case for early stage.
2. On startup after engine sitting for at least 8 hrs you will hear a rapid knock for 1 sec or less. This is not due to temp but rather that the oil has leaked out of bearing surfaces.

I did not have any noise at idle. Normally I thought by the time knock at idle occurs engine will shortly self destruct.

I would try to rule out the timing belt tensioner. See if you can get the steth on it from below or use a screwdriver in ear. If it seems it might be bad, perhaps you can run with upper timing cover off. What happens is that the belt slaps the tensioner making a knocking sound - because oil leaked out of tensioner.

Other culprits can be the fan bearing or water pump but rod knock sound is unique, sort of deep in the engine.

You could also pull a small amount of oil from the pan and run into a glass jar or through a coffee filter. You can do this w/o draining all oil, just remove plug and put back quickly. I did not see any metal though, I think particles were small and oil filter caught them. Those pictures you see with metal in the pan are post destruct. I have heard even an oil analysis often does not report any metal on early stage bearing failures.

Hopefully your engine is OK. Its odd because I have run about 6 previous cars into the ground and have had lots of various drive train failures but never a bearing failure even when I neglected oil changes. This truck I bought new and ran synth exclusively, never overheated it. I think it was related to a head gasket repair. When I removed the HG half of it was stuck to the block and when I scraped it off a lot went down the oil returns. I knew this was a risk so I poured lots oil on heads when installed to flush those returns then dumped the crankcase oil before first start and again after running 1 min. About 2k miles later knock started.

Obviously Toyota is highest quality but if they have a stain its HG's. I had a 91 Supra - blew HG, friends with 3.0 that blew HG's, 5vze with composite HG and even the early 4.0's have it. Knew one guy with a 4.0 and had it fixed professionally and blew again. Cant really complain though, nearly 300k miles on mine.

 

So after replacing all rod bearings on my 98 Tacoma 3.4 with manual trans, I still hear the knock so I'm starting to question whether this is really a rod or main bearing knock. Its been doing this since shortly after my HG replacement which was 2000 miles ago. I did have a valve job done on the heads. From everything I have read, there is no way my engine would survive this long with a rod or main engine bearing issue. I have run it full throttle to redline quite a few times and it seems normal. I also put an oil pressure gauge on it, it is a bit low with 5w-30, never really goes above 20 psi or so but I suppose not surprising for a 300k mile motor.

The rod bearings were scratched pretty good but did not go through the aluminum layer. I did some random checks with the std replacement bearings and plastigauge showed about 0.0025 or so, a little loose but still within spec.

I saw one post where a guy had a similar knock and he reported that he found out it was actually loose cam journals! Never heard of that one.

As I said above, I hear a rattle on cold start for about 1 sec. I don't think I get the cold start rattle if I run starter with EFI fuse pulled first so it is oil pressure related.
I also get it at 2500 rpm in gear driving when I modulate the throttle right between load/no load. I think I can hear it in neutral also at about 2500 rpm, again modulating the throttle so its not likely a drivetrain issue. I have heard this is how rod knock starts out, that's why I honed in on my rod bearings.

I'll check the cam journals for damage and clearance with plastigauge since this is fairly easy but has anyone heard of this or encountered this?
Unfortunately my understanding is that this cannot be repaired so have to replace the head. But if its not an impending failure situation I'll probably just live with it. I just don't understand how the cam could "feel" the engine load - perhaps some valve train harmonics.

Need to check compression also.

Thanks

 

Did you ever figure this out? My truck is making the same noise and stumped on what it is. Thanks