Engine noise - need help!

[bosco659]

I have developed an engine noise that I can't seem to get rid of (permanently) and am looking for suggestions. Here's what I have: '00 Runner Limited, 3.4L, S/C, Walbro fuel pump, 305cc injectors, 2 heat ranges colder plugs, 170 degree thermostat, SAFCII, automatic, 145,000 KM (90,000 miles). The supercharger has been on the truck for over half of its life already so I am not a newbie to the world of boost on this truck and its associated problems.

Here's the problem: It is an intermittent noise that seems to be coming from the passenger side of the engine. Sometimes it can be heard under minimal acceleration from 2000 to 2200 rpm and again at 3000 to 3200 rpm. Sometimes it will disappear completely and other times I will only hear it under boost (high or low).

This one has me stumped. It does not sound like pinging or pre ignition. I know what that sounds like. It sounds more like a chattering or clattering sound that almost sounds like lifter noise. But again, sometimes it will disappear for days.

Here's what I have done so far: no codes, Seafoam treatment, new plugs, new thermostat, always run 94 octane and octane booster doesn't help, all vacuum lines in good condition, cleaned MAF sensor.

Any ideas out there? Some suggest a knock sensor or a O2 sensor on their way out (not far enough to throw a code). Do the 3.4L have any history of lifter problems? Even if it was a lifter problem, whay would it be intermittent? I have trie pulling the EFI fuse to see if the noise comes or goes but it doesn't seem to make difference. I will install my wideband tomorrow to see how my AFR's are doing.

Any input would be appreciated.

Thanks

Vic

[Good Times]

Is there any way to isolate the sound from a specific location? i.e. using an extension and pressing up against sections of the block to hear where the chatter is coming from? Not sure but knowing where the sound is being generated from may help others with some other suggestions.

good luck

[bosco659]

Thanks for your message. Unfortunately I can only reproduce the noise when driving. It is very quiet when idling or even when revved up in neutral. I even tried to put the truck in drive, step on the gas while holding the brakes but could not get the noise to appear. Scared some guys watching me do this as the supercharger develops a lot of torque at low rpm and some guys said they were scared that the engine was going to jump out of the engine bay LOL.
Although inconsistent, it seems to be engine load related. I just had a look at the factory manual and it confirms that the lifters in this engine are like my supra - valve clearance needs to be adjusted with shims and they are not hydraulic like some cars so I will rule out the bad lifter theory.

[bosco659]

Update, AFR's are fine so it leads me to believe that the o2 sensor is doing its job. Any ideas?

[MTL_4runner]

Did you happen to see what the AFR was when this noise was going on? Have you ever replaced the O2 sensor?
The load related part would tell me that the issue is along the driveline (engine, tranny, U-joints, etc).

It can ber VERY difficult to diagnose things that are intermittent like that and even worse when they only occur while driving. There are chassis microphone setups that can be installed to locate the problem but with a problem that comes and goes like what you're describing, it wouldn't do much good. The other issue is that often noises bounce around when produced so like a good ventriloquist, they can often be coming from a different part of the truck altogether than where you perceive they are coming from.

[bosco659]

The noise is heard at specific rpm ranges regardless of boost or throttle position. It is however a bit louder when you step on it and you get into boost. Since the rpm ranges are still within the closed loop mode of the ECU, AFR's remain around 14.5 to 14.7 (have always been there :(), under full throttle and boost the AFR's will run from 11.2 to 11.6.

I will try to hook up a high tech scanner this weekend to try to isolate the problem. I will be able to watch each injector, knock sensors etc.

If all else fails, I will book some time on a dyno and will hopefully be able to reproduce the noise while the truck is stationary, running under load and someone can stand beside the engine and listen.

It definitely sounds like the right hand side of the engine but I agree that sound does travel quite efficiently under the hood. I am almost certain that it is not the other drive train components. I am hoping that it is an electronic component problem and not an internal engine part.

O2 sensor is still the original. I figured it was ok since the AFR's are what I was accustomed to seeing and the fact that no codes were stored on the ECU - could I be wrong?

[MTL_4runner]

O2 sensor is still the original. I figured it was ok since the AFR's are what I was accustomed to seeing and the fact that no codes were stored on the ECU - could I be wrong?


No, I have a feeling you're on the right track.
Booking some time on a dyno to isolate the problem is an excellent idea! :thumbup: