I've had a sound on my car when ever I punch it and the RPM's get to 3000 I hear a strange sound ( Think a nickel in a coffee can shaking it vigorously ) . If I let up on the gas it will stop . I thought it was a clogged cat . I have replaced my front y-pipe ( no pre-cat style ) and have had my Main cat Gutted ( temporary till I can get my new cat on ) . I took the car out tonight and it is still making this sound . I don't notice it if I'm stopped in neutral and rev the rpm's past 3000 . It does it in both D and OD and seems to be every time I step on the gas and the rpm's hit 3000 .
Any buddy ever have a similar issue ?


Thanks in advance ,
PatsFan

oh yeah I almost forgot my car is a 91 A4 with 68000 miles on it . It isn't throwing any codes

 

Check the heat shields above the converters. When they loosen, they rattle like that.

 

First Id like to say thanks for the help .

I have no Pre-converters now so is the only other heat shield I have on the main cat ? I had a friend do the exhaust work for me so I didn't see / play with the cats @ all. Is the shield hooked to the cats or is it connected to the bottom of the car ? Just wondering if the pre-cat heat shields are still there even though I put on a new y-pipe.

Thanks again , Patsfan

 

It has been years since I had the shieds and converters on my car. But if I remember correctly, there were 2 smaller shields bolted to the plastic floorboards abobe the precats. I had to remove them to clear the collectors on my headers.

 

Detonation?

 

When you gutted your main cat, was all the ceramic in there? My main cat deteriorated, and I later found chunks of it lodged at the crotch in the rear Y-pipe.

 

I almost forgot, the factory style rear y pipe has 2 heat shields on it. They sometimes break and rattle.

 

If it doesn't make this sound while in neutral (and revving to 3K RPM) and does make the sound while in drive or OD (and revving to 3K RPM), then would this still might be the heat shield(s)?

 

Is your knock sensor connected?
-Beppe-

 

Possible Under load.

 

The thing that make think to a detonation problem is the defininiton of the noise: "a nickel in a coffee can shaking it vigorously ..".
Obiouvsly ... if the noise is audible like cow bell .... i'm really out on my diagnosis ...
-Beppe-

 

I would first think the heat shield or loose old cat guts. Check the exhaust system for the shields and make sure there not loose and use a rubber hammer and hit the exhaust pipes and listen for rattling. If nothing then conv90 could be right...

 

Guys thanks for all the help . I'm going to check it out on Thursday . I'm working crazy hours the begining of this week . I'll let you know how I made out and I'm sure I'll have more questions .

Thanks again , PatsFan

 

OK guy's I think I might have found the rattling issue's . It seems after my rear y-pipe y's off ( separates to each muffler ) The pipe on the drivers side is almost touching the rear suspension ( Its only a couple CM's away from it ) . If I push on the pipe even a little bit I can here it Clank off from the part of the suspension its resting on . It's kind of hard to explain so I took some pic's . I have had the rear y-pipe off to have my cat gutted ( soon to be replaced ) and some used lt-1 Mufflers put on . I was told by the guy installing it that the Mufflers were a SOB to get on and straight/ on ( Do to going from a L98 to a LT1 I think ) . I think maybe he adjusted the y-pipe a bit to help get the mufflers straight and maybe that's why the pipe is so closer to the suspension . The only weird part about it is i could have sworn I heard this noise before I had the guy do the work for me . I figured it was a cat rattling . I'm sorry for rambling here's the pic's and does it seem like this is to close and could cause the issues I'm talking about ?

You can really see ho close it is ion this pic

You can really see ho close it is in this pic ( its take from between the mufflers looking out )

Taken from the outside of the car looking in



Oh yeah I almost forgot I couldn't find a single heat shield on the car except for the on around the cat and that seemed tight.

Thanks again for the help guy's ,

PatsFan

 

The round rusty spot on the last pic is where the sield was welded. Someone ripped it off because it is too close to the rear suspension. Looks like you found the rattle anyway.

 

Well I'm glad to hear that I/we found it . I just crawled under the car and it appears that there was a heat shield in that spot on both sides and both are gone. It look's like the guy I had put the mufflers on pulled them off to gain clearence . I gotta think they we're on there for a reason . I wonder if it will cause me future problems with the suspension with out them ?

Thanks again for all the help , Patsfan

 

In my opinion, the main reason for the shields is to deflect heat from the pinion seal area on the rear. The factory uses a viton seal to help also. If you manage to gain some clearance, I would not worry about it. Mt 87 has an aftermarket set of duals that have no shieds. They have been on for 16 years and no problems related to heat.