Nobody

Im quite stumped....Ive changed the plugs/MAF/PCV/cleaned the air filter/had a injector flush/- but I cant seem to pin down what is causing a rapid short knocking only between 2400-2700 rpm on load. In passing gear- no knocking - Ramping up to 2400-no knocking - in overdrive on the freeway no knocking at those rpm's. I dont have a EGR system,

I can hear what sounds like an unusuall valve train sound when parked and revving the engine around 2500....Im leaning tward a valve adjustment but why is the knocking so isolated?? only at the rpm's specified?? I would think that if the valves need adjustment I would get heavy rattling at idle-nope.

96K on Runner
new timing belt
new plugs - the old ones looked 'texbook' - so im not leaning twards combustion chamber anomilies ie. head gasket leak or bad rings/valves etc.

no codes have been thrown -
acceleration and overall engine performance is great- no loss of power

got ya scrachin yur head yet????? welcome to the club.

if you are please guess! - any help appriciated

Nobody

Stopped by the stealer today and the rep said he believes that it is 'sympthetic harmonic' in other words - outside the engine - I hope he is right! - gonna try a poor man's Dyno (jack stand the rear and power brake) and see if I can dupicate and hopefully pin down.

"IM GOIN IN"

ilocan

Is the knocking sound fairly loud or only noticable to someone with a keen ear? Does it knock only when the weather is hot? Or does it knock regardless of the outside temperature? The 3.4 does produce a secondary harmonic vibration at 2500 rpm which is normal for this engine. The reason I ask is because what you described as a knocking sound under load ONLY between 2400-2700 rpm under load sounds very familiar to what I hear under the same conditions with my 99. I did have an Oil analysis done and everything checked out normal (I use Mobil 1 5w30).

Nobody

Not loud..you almost have to listen for it-going over highway lane bumps or the stereo at a comfortable level drowns it out..started a few months ago-it was still warm here-hasen't gotten any worse or better since. I have experienced the secondary vibration-seems to be independent of that. It definitely is a knocking- rapid and relatively quiet

ilocan

Hmmmm. Well, I don't know if this is going to help you any but my knocking noise almost sounds like a very faint jar of marbles rattling around at times. I had traced mine down to an exhaust leak on the #1 O2 sensor. The gasket had corroded and caused a knocking noise when accelerating under hot climates. I had a friend hold the brakes while reving the engine under load at 2300 rpms while I traced the knocking noise. Sure enough, when the climate started to get cold the noise had change to a loud ticking noise characteristic to an exhaust leak right at the 02 sensor. Since you already cleaned or change just about everything, you could probably inspect your exhaust system for any corrosion or signs of any leaks around the exhaust flanges near the cat. Hope that helps

Nobody

Good idea....I'll check it out.

humanoid

I just had the same problem lately. It could be where you get your gas. I dropped by a Costco gas because it was cheap. Well, the next day I started to hear a minor knocking/pinging when I was passing at highway speeds 60-70 mph at around 2500 RPM. I used this tankful until the red light came on and went back to my stand-by of Unocal and the knocking subsided. If the problem isn't an exhaust leak then try a different gas station, but not a higher grade of gas becuase your rig won't need it.

Nobody

Well I tried the Poor man's dyno - wasen't consistant enough..coulden't keep it at 2500rpm. I have also tried different gas- no dice...I'm trying to find a real dyno-they seem to be hard to get to use around here.

Thanks for the replys - keep em commin!
Wild guesses wanted also!

goretro77

Hi Mark,

Just a side question...is this your first timing belt change at 96k?

Thanks, just curious.
El.

Nobody

I actually changed the belt at 80K

Pauljp15

I own a 99 tacoma 4x4 with a 3.4 liter V6. I cut a hole in the airbox to draw in more air to the engine. Well ever since i did that my engine had a slight knock kinda like you described. I tried every thing. It ran strong as ever, but at low rpms the engine tapped. well i know it got worse and finally my timingbelt broke. After replacing it the knock was less noticable but there. Well let me tell you this. I replaced just about every thing on the engine, as far as tune up stuff. no change. I told the toyota shop about this and the first thing he asked was what octane fule are you running , well comming from a middle class pay bracket i said 87.
He suggested a higher octane becouse of the extra air being sucked in. well i filled up with 89 and just like night and day the knocking stoped. Completly stoped. and to this day i can put 87 in it and it starts knocking. I believe the hole in the airbox was couseing the truck to run lean. so the higher octane made up for this . I run 89 now and never hear that nose again. Bottem line i suggest you try running 89 or even 93 but 93 is kinda a waste becouse i cant tell a diffrence between the two. 89 will prob solve your problem if you havent already tried this.

Nobody

I usually run a higher octane but I did try all grades over the last couple of months and there has been no change at any octane in reference to the knocking... hopefully after the first of the year I can pin down some Dyno time and get this solved

Just had a emissions test today - passed with no probs and the engine is running great..leads me to believe that the knocking is outside the engine.

CUBERA

Could be a rattle if you removed the air box elbow.

The plastic piece that runs up the fender maybe.

Nobody

Ive had that out for some time....the knocking started a well after..still havent been able to get to a dyno..the knocking is exactly the same- and i have put almost 5K on it since i noticed it- hopefully the dyno will give me answer..

CUBERA

If you think it's that plastic piece in the fender, it can be removed by pulling back the fender plastic lining that give you access to the antenna and that piece of plastic you can remove.

I think it was member 96runner that had the same knocking noise and he removed it.

I left my elbow hooked up and just did the deckplate which is sufficient air any way. Good luck!

Nobody

Well I got the dyno done (148hp 187fpt@4600rpm) the power curve is very smooth..no drop at 2500rpm. I did get to hear the rattling and it is definatly not in the engine, although I still coulden't pin it down. It sounds like its near the power steering pump..i'll tear into the timing belt cover and such the next time I change belts and check to see if the timing belt tentioner is suspect. Needless to say that im not as worried about it as I was (watch- now something is going to fall off the engine goin down the highway!) quite a relief to know that its not enternal.