Alright, so I just get in my car and take off down the street. Get to the first stop sign and I hear this odd, hollow gurgling type sound from either my downpipe or engine area. Lasts for about half a minute, not too loud, but I get **** when I hear anything. Turn around, pull in the driveway, and look for an issue. Nadda, no leaks, or other strange noises.Take off again, listening and waiting. Going through town and hear it one more time, and then about 4 minutes later, there is a noticable KNOCK! Like a hammer dropped on concrete or something. Drive around, parked at store to shop, went back homeand nothing else.

Next day, heard the same hollow sound from center of car when first start driving. Drove around for awhile going down the highway, and then that knock sound happened again. Nothing else after that. Today I drove it and there was no noise.

Still runs and shifts fine, no smell, no noticeable leaks, no drop in gas mileage,but I'm no mechanic. Gonna get it checked next week, but if anybody can relate or has an opinion it would be great. I'm used to the sound of my K&N intake and ZZP throttle body, but it's that knock I'm worried about and that hollow sound didn't come from the driver side.First dayI did turn on my A/C right asI got in, which I neverdoand rarely use, if that might have anything to do with it.

03 3800 N/A

 

Your cat could be clogged or bad. Does your temperature climb real high? Your cat could have finally died and the pieces clogged it up. If that happens and the exhaust gases cant flow, it will heat up the combustion chamber. It may be heating it up enough to cause the gas to detonate before it is supposed to, thus causing a knock. Just my theory, wouldnt hurt to check it out.

 

I don't think it's my cat, just got a high flow one and downpipe put on about a month ago. The thermostat doesn't go above 195, but maybe there is a clog in the exhaust manifolds? My car is giving off the P0420 cat O2 sensor code. Just wish I could find some seafoam in my area to try it, but I was wondering if it was KR. Just got new plugs and wires too, my A/F ratio couldn't be that bad off could it? I'm only N/A.I know no KR is good (especially if its that frickin' loud), but I hope it's that rather than an expensive internal problem, maybe I'll have an excuse to get that powerlog or HPTuner I've been looking at Thanks for the idea

 

Well if your temp doesnt rise above normal, it rules out a clog. Every time I have seen a clogg in the exhaust system, the engine temp is always above normal because the exhaust gases are being trapped in the cyliners. The code is from your high flow cat. The high flow cat will not heat to the same temperature as the stock cat, which throws off the rear O2 sensor. People usually have that code deleted by comeone with an OBDII code reader. Try running some premium through it to see if the knock goes away. The higher octane will keep it from combusting from the heat in the cylinder and only by the spark. If that helps your problem then it is definately KR. You will have to have it checked out.

 

Thanks again for the info, I searched through the forums for what others use for gas, and I Im definitely gonna try something other than the local Caseys low grade that I always get.

 

Ifbetter gasdoes end up fixing your problem, try replacing the thermostat with a lower temp one like you can get off of ZZP. It will help cool down your engine a bit and help with the KR.

 

Put in some 89 octane, and after driving and listening the car seems quieter. If there is any noise I can't hear it over the intake. Would of been smart of me to have gotten that Tstat when I bought my spark plugs and wires, atleast theyre cheap.Still gonna get it checked this week by a local mechanic, just to be safe.

 

You will get this no matter what if you have a high flow cat. I had a Random Tech and currently have an SLP and they both go off from time to time once I clear the code.

I would stick with the 89 Octane and shop around for different 87 octane gas. I use Shell and BP's mostly and avoid Kwik Trips.

What do you fill it with?

 

I've been using 87 octane from Casey's but i just found a BP on my way to work that a fellow monte owner uses, so I plan on filling up there whenever I can and staying with 89