calys968

About a month ago I made a trip to California(about 450 miles each way). On the way back I noticed that my car was making a rattling noise every time you pressed hard on the gas. It sounded like it was coming from underneath the car and wasn't very loud. After a few minutes the noise stopped and my car was fine for the rest of the trip so I didn't think much of it. Yesterday I made another trip to California and it started doing it again after about 200 miles. It was only doing it when I pressed hard on the gas. It stopped doing it after a few miles so again I didn't think much of it. Then I was driving my car around today and it started doing it again off and on
Any ideas on what it may be?

Another_User

That's kind of weird. If it is not something loose, it could be real knock. Have you run engine cleaner through you engine, and/or gotten bad gas lately? It almost sounds like it is detonating until you end up in the low-octane spark table.

calys968

If the engine was knocking would my car be running worse than usual? The reason I ask is because I haven't noticed any drop in performance since it started making that rattling noise.
I bought my car 4 months ago and it has always made a rattling noise off and on while idling. The dealership told me it was my catalytic converters, the muffler shop told me it was my heat shield. My mechanic agreed with the muffler shop and he adjusted the positioning of heat shield. It still rattles occasionally while idling but not nearly as much as before.
I wonder if that could be related to this new problem somehow?
I hope it's nothing big...I've already had to replace the water pump, alternator, headlight, idler pulley, serpentine belt and the bracket that the idler pulley mounts on :-(

Another_User

I trust no mechanic. I don't suppose you could make a WAV file or record it and post it so we could hear it? Are you running a stock exhaust? Exhaust rattles are really common (and sometimes hard to track down)...

Martingale

From your description it sounds like you're having piston slap at idle. As far as the rattle you hear when you hit the gas, does it sound like marbles or nails rattling around in a tin can? If so that's detonation.

luv2spd

iTrader: (1)

Sounds like detonation to me.

NateLS1

iTrader: (4)

I suspect the exhaust is rattling somewhere. Mine does it sometimes. If you drive the car for 200 miles I think the exhaust pipes/heat shields will be slightly larger because of expansion. Maybe surrounding metal expanded ever so slightly as well and its just enough for them to touch. and of course, rattle.

FineWine

iTrader: (1)

What octane are you using? If not 91+, try using that next time you take that trip.

skibo

sound to me like one of your cats has gone bad. same thing happened to me a month ago.

NC98Z

iTrader: (1)

SKIBO did it sound like a rattling under the drivers floorboard when your convertor went bad? I have been trying to figure out out a racket for about a month now. Did you throw any codes? Cause mine hasn't yet

Another_User

Yeah...it would really help to know where the sound was coming from and/or hear a sound file.

calys968

I'll try to get a WAV file of the noise...it's not very loud though, so I'm not sure how well it would record.
I use 91 Octane. Could the switch from AZ gas to California gas possibly have anything to do with it?
My check engine light is on because of the following codes...P0171(System Too Lean Bank 1), P0327(Knock Sensor 1 Circuit Low Input Bank 1), P0420 and P0430(Catalyst System Efficiency Below Threshold). Could the P0420 and P0430 be from my catalytic convertors being bad?

longdaddy

yes the gas switch, bad cat(s) or the combination of both could cause detonation. this sounds exactly like what happened to me moving from east coast 93 to west coast 92. you have 70k mi warranty on your cats, and, if you are covered, the dealer MUST replace them - free of charge - if they are triggering the codes.

calys968

I bought the car in Nov. 2004 with about 77.5k miles on it. When I picked the car up it was making a rattling noise and the dealership told me it was my catalytic converters and they said if I took it to the Pontiac dealership in my town they would replace them for free because they are covered up to 80,000 miles. So I took the car home and made an appointment at the Pontiac dealership. They looked at my car and told me that my 02 sensors were bad and they wouldn't replace my cats until I replaced the 02 sensors. I called the dealership I bought the car from and they told me to take it to another Pontiac dealership in Tucson. That dealership said that my cats were fine and they said that the rattling noise was from my engine misfiring(even though the rattling was coming from underneath the car). Now my car has 85k miles on it so if they are actually bad they are no longer covered :-(

FineWine

iTrader: (1)

Sounds like an excuse to get a set of LT's and a high-flow cats (or ORY!)

FineWine

iTrader: (1)

P0171 is the one I'd be more concerned with. Check your O2 sensors, if they're good I would think you're def. detonating. Lean = Evil

calys968

My 02 sensor voltage ranges from 0.00 to 0.88. Is that normal?
Whoever had the car before me installed a Granatelli MAF sensor. Could that be causing the code?
Thanks for your help.

skibo

yes, it was directly under my driver seat. i did throw a code but it didnt come on for at least a week after the cat went bad. my battery died and it took another week to come back on.

Another_User

Sounds like you need to get your cat(s) replaced and work from there.

B-MAN

I agree, more than likley it's your cats, or a heat shield.