Back Story: I bought my 02 3.4L V6 a little over a year ago with 128k miles on it. Until recently I have not done any maintenance outside of regular oil changes (had it inspected before I purchased and the dealer didn’t note any issues). It now has 138k’ish miles and I started noting a knock that only seems to take place after braking to a stop. I can’t rule out that it happens when driving at speed but I can only hear it during the last 5 mph of braking to a stop and then it seems to disappear after about a second of acceleration. The sound is between a knock and a tic and the volume of it can vary, but it is a cyclic knock where the frequency changes with the engine RPM. It has not been a constant issue, I can drive for days with no knock then it will do it for a few stops and go away again. In the process of troubleshooting this I replaced the spark plugs, (they were the original, but surprisingly had little carbon buildup and the electrode was in ok shape), and this seemed to lessen the frequency of the knock. I also had an oil change and it seemed to have no affect.

That all being said I don’t have a clue where to look for a solution. I can’t tell if it is a pre-detonation since it seems so quite compared to what I would expect. Anyone with any ideas of where to start looking?

Also Im not 100% on what the service history is or what needs to be done. I would assume its probably not a bad idea to do the timing belt, fuel filter, and clean the MAF, but please chime in with other maintenance related things I should look at doing to keep everything going strong.

Thanks!

 

Knock Knock, who's there,, your Toyota. Sorry couldn't resist.

But on topic, if you plan on keeping your car and serving allot of it yourself you can invest in a good code reader OBD-II that is capable of showing live data (RPM, ignition advance, coolant temp, etc). I got one at Advance auto for $150.00. Or see if you can borrow one from a friend.

By watching the spark advance/retard as you accelerate and decel, you can see if there is too much or no retard/advance. I had a Mitsubishi that had a similar problem it would knock like crazy but wouldn't throw a check engine light. It ended up being a bad knock sensor and I found it by watching the ignition advance.

I could be totally off on the problem (my expertise is in A/C and Refrigeration) but its a good place to maybe start.

 

If it's an auto trans, you should change the ATF and filter or the gear oil if it's a stick. Do the water pump at the same time as the timing belt and inspect (if not just replace) the idler pulleys and the drive belts - since you'll already be draining most of the coolant out of the block, I would flush the radiator too. I would also clean the throttle body and IAC since it's easy. I suggest switching to synthetic fluids too (if you haven't yet).

If it's an automatic: When it's knocking (while you're in gear and stopped), does it go away if you put it in neutral?

 

Thanks for all the good info. Im a bit leery about changing the ATF since I have no clue when, if ever, it was previously changed and don't really want a tranny failure.

UPDATE: I have never been out of the car while it was started but noticed Saturday that when it is first started about 2 seconds after it cranks it makes a signifigant knock/tic/flaping noise. Im gonna drop it off at the shop tomorrow and see what they can come up with.

brian2sun: I thought the same thing about putting it in neutral but when you put it in neutral it still knocks / tics with the RPM's as they increase. It does seem like the knock goes away/lessens at higher RPM's but it may just be that I can only hear it when it is at idle speed.

Thanks

 

I don't think just draining, changing the filter, and re-filling would/could hurt the trans. That's just normal maintenance per Toyota recommendations (service or inspect every 15K). Since you don't know when, if ever, the trans was serviced, you may be taking more of a chance by not doing it. At least look at the fluid if you haven't done so yet and if it's really dark/dirty or smells burnt, it's old fluid that needs to be changed.

I've heard the horror stories about flushing the trans. and then it grenades. That's usually when people take it to a shop and have it machine flushed with detergents. If it's an old tranny that's already on the verge of failing, the machine flush has been known to put them down for good. I personally have never heard of anyone killing their tranny just by servicing it (unless they don't use the right ATF or something). Has anyone else?

Also, if you decide to service the trans, consider the DIY flush that uses the tran's own pump to flush itself. That way you can replace all the fluid, and not leave several quarts of the dirty stuff still in your torque converter. Here's a link to a great write-up:
http://home.centurytel.net/stevenjac...sh/tranny.html

I did this to mine w/ 185K on it and it has never shifted smoother. Good luck, hope you figure out the knock issue. Fogrunner's advice is good - I have a scan tool and it has helped me out a few times when the CEL did not.

 

Well I got my answer! Its pretty funny cause I told the wife Sunday that I thought it was the AC compressor and guess what! Its the compressor imploding. I talked to the Toyota tech at the stealership and he confirmed that the 4runner and taco both had issues with the compressor failing. So by tomorrow I should have a new compressor, clutch, and ?air dryer? (no clue what that is). So $900 later no more tic/knock/flap, wohoo!