I have an 04 MCS that I’ve owned about a year and a half. It currently has an airbox, pulley, eBay header and exhaust. 154k miles.

I recently got a CEL and pulled the codes. One was for the camshaft pos. sensor and the other for downstream O2 sensor showing lean. I replaced the camshaft position sensor and cleaned the O2 sensor. I also seemed to have a small exhaust leak at the flange between the stock car and the exhaust pipe. I believe I closed that up.

I got the CEL to go away for a day and then it came back. The car now gets really hot when I slow down for traffic.

The cat was removed from my stock exhaust manifold after the manifold broke and mated to the eBay header. This header sucks, it sounds like crap.

What issues could I be dealing with, or where do I start? Please help!

 

Does your header sound like abunch of air just rushing through it ? I think I too have this header but pace setter exhaust behind it and the header sounds like an exhaust leak although it for sure is not a leak .it just sounds that raspy before it exists and then sounds great.
How are you verifying it's running hot and what temps does it get up to or does it get do hot it actually overheats

 

The header does sound like one big leak, it’s terrible and killed the awesome whine of the supercharger.

As far as heat, when I slow down or stop in traffic now, the needle heads to it’s hottest point quickly. When moving again, it goes back down to just below the halfway point

 

Also, I replaced the plugs with cooler ones per recommendations with the upgraded sc pulley (about a year ago)

 

The header should have nothing to do with your overheating issue. Given your description, I would bet on either a bad thermostat and/or water pump. The thermo is the easiest/cheapest fix. I'd start there.

 

Look into the Electric Fan Relay. There is a resistor on it that has a tendency to die. The Cooling Fan has two speeds, so sometimes one of the speeds fails to work, causing increased temps when slow in traffic. There are a few ways to check, I'm sure there is a Thread on it so I won't go in to much detail here. Some people choose to replace the whole fan assembly, some choose to replace the resister pack if the fans check out functional.

If you are blowing Coolant, more than likely it is coming from the Overflow Tank, they are not very expensive and can be swapped out in about five minutes.

Best of luck.

Motor On!

 

Thanks for the replies. I don’t think the header is the culprit for everything, but my thought was that it can be leading to O2 sensor issues that may be associated with the lean code and heat?

I thought about replacing the thermostat too, but doubt that would fix the lean code. Because it is cheap and easy, I may just do it regardless.

I’m just struggling with if I should try and find a stock header and put that on and see if that helps, or maybe new 02 sensors?

I neglected to mention that I replaced the coolant expansion tank some time ago with an aluminum one, just to avoid the common issues with the OEM one.

 

I forgot to ask about the CAT, was it put back on or are you CAT-less at the moment?

Remember there are TWO O2 sensors a Pre-CAT and a Post-CAT, and if the CAT is missing your Post O2 may be sending codes because the data the sensor reads is not within spec in the ECM.

But check your fans about the cooling issue.

 

Great question...the cat is the stock one. I removed it from the OEM manifold and had a flange welded on to mate up to the aftermarket header. The cat seems to be normal inside. I haven’t see any damage or anything that looks like clogging.

Both o2 sensors are intact and the code I have is for the rear that is lean. I suppose that the sensor or cat could be failing? I can put in the test pipe, but I hate the smell and drone that comes with it. I ordered a new rear o2 sensor to see if that may be the culprit. Also going to just replace the water pump and thermo.

 

Even with aftermarket headers and stock cat it CAN throw codes . I've read people using a rear o2 spacer which sometimes turns off the cel because it detects the extra flow from the aftermarket so the spacer eliminates it detecting the extra flow.

 

That’s a good idea. I do have some spacers

 

Update... installed new thermostat and housing. The car seems to be staying normal and cool after a short test drive on city streets. I also pulled the cat and put the test pipe on with a new rear O2 sensor with a 90* extension. Man it stinks! The cat seems to be intact, but about a spoonful of gold flakes fell out of it when setting it on the ground once removed. The CEL has not gone off yet. Hoping with a couple more laps that it will.