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'04 4200 Coupe Cat problem - suggestions please!

15620 Views 53 Replies 11 Participants Last post by  TravisJ
Hi Everyone........ just run into my first potential problem with my '04 4200GT Coupe CC with only 20,000 miles on it.
I had the check engine light come on. I had it checked out at the Maserati dealer in San Antonio and the fault appears to be that I have an overheating cat on the right hand side. The car seems fine and is drive-able right now, however, It seems quite likely that I will have a problem in the not too distant future. There is no way in hell that I'm going to replace crap with crap (ie stock Maserati parts) so what do you guys recommend? I would like to keep the exhaust similar to stock; maybe just a tad louder as the wife still has to drive it too!
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Thanks for the great info guys............. it's always a pleasure to deal with you all. The knowledge and experience is priceless.

Unfortunately Maserati in SA are really not much help; all they really want to do is unbolt stuff, bolt on factory replacements and then charge an arm and a leg for it. I'm still searching for a good indi here in San Antonio. They couldn't even tell me if it was the primary or secondary that was causing the problem. Although I'm guessing it has to be the primary as isn't that where the sensor is located?

So..... gutting the primaries and re-welding them, replacing the secondary cats with Larini (from FD) and re-locating the O2 sensor to the rear of the new Larini cats seems like the way to go.

A couple of dumb questions though: If I live in TX where emissions are not an issue, do I need the cats anyway? Would the car run without them or does it need the back-pressure? Why does the O2 sensor need to be relocated?

Again, thanks for all the great help and info on this site!
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Thanks for all the great info.................. now I just have to find someone who can do the work!
Once again, some great info. The guys at FD are awesome. I would certainly not want to run cat-less. I still have to drive the car. How much will gutting the pre-cats alter the volume of the car's exhaust? Anyone got any personal experience? I'm also interested in what ESCofVirginia said in the following quote:

I would want to make sure the engine is running properly as well. With a cat over temp problem this early on, I suspect you have very slight misfires causing raw fuel to run through the exhaust and cause the overheating cat.

The usual suspects in that scenario are worn spark plugs, faulty ignition coils and an ailing camshaft timing variator solenoid.

Anything is possible, but it is unusual for a catalyst to completely fail on it's own this early.

The car only has 20K on it and the exhaust has never been bottomed so I'm curious. Wouldn't some of the issues mentioned about also give a CEL?
Well ..... The problem seems to have sorted itself out. I reset the power switch in the trunk, turned on the key to let the system re calibrate itself. On the suggestion of a friend, I replaced the batteries in the key, started the car and no CEL even after some 80 miles of driving at various speeds and loads on a hot Texas afternoon. What gives?
Could it have just been the batteries in the key? My buddy has a Jag and apparently the key seems to be the root of a few problems in his car.
I'll have to put a few more miles on my car to see if this really has "cured" the cat problem but I prefer the sound of a few dollars for new key batteries than a few thousand to replace the cats!
I did a quick temp check on both primary cats on got a considerably different reading on each side; 250 degrees on the left and 470 degrees on the right. The OBD code also indicated a high right cat temp. Next step should be a visual inspection of the cats plus an exhaust gas analysis?
Well the CEL did come back on so it's time for the next step - scoping the cats.

If I end up having to gut the primary cats and replace the secondaries with those from FD will the car still run leaving the O2 sensor where it is or do I have to relocate it to the secondary? What about the engine management mod that seems popular? How does this work? Where is it and how do I remove it if I need to send it away for a re-map?

Thanks again guys for all the great info.......... it truly is a goldmine in here!
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