need input on tapping sound ! (Page 1/1)
Rilak SEP 28, 10:47 AM
hey guys ! please help ! any ideas ! thoughts !
Im back in the fiero business !
Owned 2 Gts years ago so im familiar with the breed and just recently purchased a 3rd and got it running. 85 GT stock v6 4 speed manual.
im getting a very loud tapping sound on throttle under load only. off throttle its quite. its barely noticeable at lower rpm like 25 mph in 3rd gear bogging the engine it still accelerates but the tapping is very subdued. around 2500-4500 its loud and followed RPM with the speed. but the second u let off the throttle it stops. soon as the car carries a load it returns, i can hold the rpm steady at 2500 down hill quite, level and up hill tap tap tap tap....

so is it engine detonation ?

exhaust leak? sounds too metal to metal to me i owned a v6 with a bad exhaust gasket before and it didnt sound like this.

or just some metal banging around vibration related ? (not sure why under load only though, the motor mount seems pretty soft maybe a slight shift in the engine)

if i rev the engine hard with clutch in its barely there.

i thought valve train but that should be noisy at idle correct and load should not matter ?

chipped tooth in trans ?

[This message has been edited by Rilak (edited 09-28-2020).]

Rilak SEP 28, 11:43 AM
quick update, only rattles after warm up, i drove it cold and was pretty quite.

after warm up i can replicate the noise for a second by blimping the throttle from idle.

rattle as the motor spins up but if you hold it at say 3k rpm pretty much gone. does not stay constant.
IMSA GT SEP 28, 11:55 AM
Hopefully not a rod knock due to a bad bearing.
fierosound SEP 28, 11:56 AM

quote
Originally posted by Rilak:

so is it engine detonation ?



Detonation can destroy an engine.
Don't keep "testing" to see if noise is still there.

Check the timing and fill up with premium gas. Give that a try first.
If still noisy, then you'll know it's not that and it's something else.




------------------
My World of Wheels Winners (Click on links below)

3.4L Supercharged 87 GT and Super Duty 4 Indy #163

[This message has been edited by fierosound (edited 10-01-2020).]

Rilak SEP 28, 12:18 PM
i did put the timing pin in the OBD. still rattles gonna double check the timing with the gun latter.
fierofool SEP 28, 01:43 PM
A cracked front exhaust manifold can be quiet when cold and open up when it gets warm. It's usually at the #6 port. It often sounds like a loud tick. Fuel injectors can tick, too, but generally aren't heard within the passenger cabin. Use a length of heater hose as a stethoscope with one end to the ear and listen around the engine when it's ticking. It will narrow down the area of the noise.
cvxjet SEP 28, 02:11 PM
Outside chance but I had horrible rattling one year after hitting a piece of wood on 299......Stopped to ask a GM service rep in Redding....Listens, then asks, "Have you had anything hit the bottom of your car lately?" Turns out that the Catalytic is made like a honeycomb and can be shattered by impact, then the pieces rattle around until either they all get blown out or......They CLOG your exhaust!

I know you said it was only after warm-up, but just wanted to cover the bases..........

Also, check all of your exhaust mounts/springs/connections/heat shields!
Rilak SEP 28, 07:48 PM
actually the cat has been removed but i cut open half my muffler and it had several large chunks of the honey comb in it ! the entire system is welded so there could be more in the pipe along the way.

had car up on stands did the oil. and zero noise on the stands.... big heat shield by gas tank was missing 2 bolts and 1 kinda half loose. i put in 2 solid bolts and test drove it the sound was greatly reduced but after 10 minutes came back some...

can a loose timing chain bang around ? im hoping its just more cat honeycomb in the system. loose heat shields.

the engine shifting under acceleration might be touching something... or the torque in the tranny ? putting pressure on a bad bearing ?
Rilak SEP 28, 11:38 PM
A cracked front exhaust manifold can be quiet when cold and open up when it gets warm. It's usually at the #6 port. It often sounds like a loud tick. Fuel injectors can tick, too, but generally aren't heard within the passenger cabin. Use a length of heater hose as a stethoscope with one end to the ear and listen around the engine when it's ticking. It will narrow down the area of the noise.

well i do get some weird smoke from the firewall side on occasion when starting. ill try to get in there and peak around. if all it is that ill be super happy. i just didnt want to damage it more by driving it (detonation) when cold it sounds fine just regular engine noises clicking etc...

i also dont have a thermostat in it so the car stays below half on the temp gauge. (need an o ring is all)