Slapping sound when WOT from stop

[Spydaz]

i started hearing this noise when i blew away a chevy tahoe from a merging lane at a red light. I put the pedal to the metal and heard slap, slap,l slap, slap, slap repeditively throughout first gear WOT. ???

So i parked the truck and let it idle no noise at all when ideling, then i opened the hood and hit the throttle by hand and it made the noise only if i push the throttle past 2500-3k.

Sounds like a slapping noise (valve tap)??? Again, there is no noise at idle just when at very high rpms WOT from dead stop. I have my oil changed religiously and the truck now only has 51k on the clock. I purchased with 35k 8 months ago.

I did have only one problem with the truck. She had bad cats and on a 100 mile trip they decided to die on me and blow up my Vaccum pressure regulator (flying saucer looking thing) and started to make the exhaust manifold burn cherry red (only for about 5 mins). But i drove the truck back home and had it fixed promptly but had both cats cut out and replaced with one magnaflow high flow cat. Now the truck sounds better but i feel mabey this is new sound is related to the cat problem and repair??

can someone help me out here. I just want to make sure nothing is wrong with my engine and i do not want to bring my baby to the local toyota dealer.

 

[Spydaz]

Can anyone help me here??

 

[speyrod]

sorry I'm just shocked that you blew away a Tahoe or anything with an 80.

Reading your sig line surprising the cats would go before 50K.

 

[Spydaz]

well we were not racing. The cats went becuase the truck has been sitting for a long time in a garage. I have no idea they went until that whole thing happened with the Vaccum modulator exploding.

Do you know if that sound sounds like a valve slap??

 

[OZCAL]

What is WOT?

 

[MoGas]

Wide
Open
Throttle

 

[lovetoski]

I'm taking a flyer on this, but here goes...

Valve tap doesn't sound anything like what you describe, so I'd rule that out.

If the engine's been maintained well, it should be good.

Since the exhaust has been worked on, I'd look there. Vibration maybe is causing the problem? There is a known problem with the heat shields vibrating. Mostly this is at idle, or just above. But, you have a different muffler, and somebody's been working in that area, so I'd check there to see if you can find anything that's loose.

Cool on dusting the Tahoe...

 

[alaskacruiser]

lovetoski- I *seriously* doubt he "dusted" any Tahoe with an unblown FZJ80 unless the Tahoe was running on 4 cylinders.

 

[chip7238]

My 1FZ dusted a guy pushing a shopping cart once...that was right after I installed that powerful Tornado air intake thingy

j/k

Seriously, I would check the vibration suggestion. Do you also hear this noise when the truck is under load at low RPMs (like going up a steep hill)?

 

[Spydaz]

Hey guys, i really was not racing the tahoe just trying to get ahead of her.. LOL Her. Anywho it is most definately not a vibration thing. I know what valve tapping sounds like and it sounds just like it. The previous owner i bought it from took good care of it but it only had 35k on the clock when i bought it. I did not hear any valve tapping at all then.

The wierd part is, i only hear it when under heavy load putting the peddal to the metal driving (which i rarely do).

I do not hear anything at idle or a low rpm, only at 3k or over i hear the slapping tapping noise and it gets louder if i go higher rpm.

I am going to have to have the engine checked out i guess. It runs so damn smooth and i brought it to a mech right after i purchased it and at the time he said the thing is like new.

Do you think i need a valve adjustment??

I can tell you one thing, when i hit it when i was trying to beat the tahoe, that friggin noise was real loud i mean it was slapping, kinda sounded like my old 2 door tahoe that i had all done up with striaght pipes at WOT that exhaust slapping sound except its comming from my engine compartment this time on my LC.

HELP??????

 

[MoGas]

Chain tensioner?

 

[Spydaz]

What is a chain tensioner??

 

[Spydaz]

Can someone help with this problem. I was told it may be timing related, Rod tap, Valve Adjustment, Bearing Spin????? Help, this does not sound right for a well taled care of LC with 51k on the clock!!!!!!

 

[Spydaz]

Anyone??

 

[photogod]

Rod bearing? Previously discussed here a while ago. Is it a loud valve tap sound comming from deeper in the engine?

 

[Spydaz]

No it sounds like its on top of engine, but why at only higher RPMs??

 

[Spydaz]

Ok it sounds like a Knock but more of a tap. Its making me crazy becuase i feel now i have to dump a ton of cash into this engine if i think it is something bad.

 

[IdahoDoug]

At high rpm you're not going to hear any individual valve tap like sounds. I'd look elsewhere - non engine internals. External parts - pumps, exhaust man leaks, exhaust pulse sounds, etc.

DougM

 

[Spydaz]

Idaho: Thats what i thought it could be, i can tell you this, i now confirmed it only happens when the motor is hot, like driving for 10 mins hot.

I am starting to think it is an exhuast manifold leak and the crack is probably very small and when the metal heats up and expands the crack opens and then thus the noise.

And i also found out that the noise is on the passenger side of the motor, where the manifold is.

What do you think?? It only happens when the motor is hot and has been running for at least 10m mins.

 

[IdahoDoug]

Fortunately, the 95+ don't have the PAIR valve in the way so you need only remove the heat shield and can see the entire exhaust manifolds easily. I'd also be suspicious of a broken exhaust flange stud and/or a non-replaced or missing exhaust pipe O-ring where the mans and pipes join courtesy of your exhaust folks. They come with a compressible alloy(?) O ring on each pipe.

DougM