What's up, I just bought a 2004 Discovery SE, I'm hearing loud knocking at first when I start up the car, the noise quiets down after sitting idle for a little, My car is throwing P1170 and P0430, it looks like a aftermarket cat was installed on the passenger side of the rover but not the driver. I think the headers were done a few years ago, the car is at 185k in mileage, would it be time to change the gaskets out?

 

Wow, You mean to say it didn't do that when you test drove it or it wasn't noticed in the pre purchase inspection process?

Does this happen every time you start the truck, or specifically at a cold start?

Does the oil light illuminate when the knocking happens when you first start it up?

Exhaust leaks are common and make that noise on cold start especially if recent exhaust work was done, I'd suspect that first. Could be gaskets but also inspect the bolts on the manifolds and the nuts on the downpipes underside the gasket for proper torque.

Even if the bolts are tight, the Y pipe itself is a common fail point in the areas where the upper flanges are welded on. The metal becomes weak and porous near the welds. You look for that by either looking closely after a cold start or pumping air up the exhaust pipe and applying soapy water to the area, while the engine is off and cold of course. The remedy is new Y pipe which includes new cats.

 

I test drove it no code, disco sounded good.
It was for 1800 with a thick service history
The Guy I bought it from was a mechanic and friendly enough, I tend to be gullible...
Anyways I kinda rushed the process and should've done more due diligence before buying the truck, like getting a pre-purchase inspection done.

Example of what the it sounds like (neither are mine):


The noise might quite down but it doesn't go away. and I want to say it's been happening every time.

There is no oil light, the SRS light is on though.

Also when I am going around 2k rpm or when i lightly put my foot on the gas while in motion, I hear a metallic clacking which I'm thinking is the transmission, and I've only changed one clutch on a smaller standard car, so I still don't know what to hear for when it comes to that.

Like I said, one part of the Y is OEM and the other part is aftermarket.
I'm going to give it a leak test tomorrow to see what's up, then Decided if I should go to the scrap yard or not.

Thank you for your time with helping me by the way.

 

Also, The valve gaskets were replaced 30k ago, 3 years

 

Pretty gnarly noise... Ouch... Lots of threads and info on here about that noise, none of it good.

Otherwise, the metallic clacking noise while in motion is most likely the front drive shaft. If it is the source of the noise it is beyond a simple service. U-joints or complete new aftermarket drive shaft are your only two options... Cheap compared to the engine noise. But then again, first things first.

 

To update this old post, I recently had similar codes, P0441 and 1171... With a not so loud noise on cold start up. Turns out I had both a leaking purge valve and leaking fuel injector O rings. The codes and noise are now gone along with a good chunk of money.