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'04 4200 Coupe Cat problem - suggestions please!

15621 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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I agree - don't drive it until it is fixed. There are lots of informative threads on the subject but don't be afraid to ask if your have specific questions.

Dude, are you serious?
I'm sorry, but if you're suggesting gutting your pre-cats and getting an getting an ECU remap from Evolution as an "inexpensive" alternative, then I suggest that you think again.
What is a less expensive solution to correct a failed pre-cat condition?

Dude??? Im not sure of the tone of your text but Im not gonna get into anything with you here. But JLOBO, a member here, who i have also talked on the phone in depth about this issue had gutted his cats for a few hundred bucs, then sent out his ECU to EVOMS and had it remapped for 1,600 bucs. I would gladly pay two grand to fix a pre cat issue. If you have a cheaper solution to this please tell us.
I personally feel like the ECU remap is pointless just for the cat issue. I believe this is the most cost effective work around for bad precats...

1) Gut the existing precats (possibly illegal)
2) Replace the main cats with FD aftermarket units (main cats are typically contaminated when precats fail)
3) Extend rear O2 sensors downstream from the main cats (this has some challenges but is MUCH cheaper than an ECU remap)

Yea but Travis, if you remember, JLOBO not only remaped the ECU so that the 02 sensors wouldnt go off, but he also had something done to give him a much better throttle response similiar to the DBW. so to me he did two things with one shot....
I thought we were talking only about catalytic converter issues. If we are talking about multiple modifications, then that changes the picture.

And also FD aftermarket cats are not cheap ether. Out of curiosity how much are FD aftermarket cats? Never mind i just looked. Their $850, then you have the labor to install and then you have to move the sensors, and the sensors have to be mounted in the correct spot for the proper reading so they dont throw a code.. Seems like quite a bit of work. ID rather go the other way,,seems much easier to me, especially if your gonna gut the pre cats anyway
I think you are missing the point of the FD aftermarket cats. Those are needed to replace contaminated main cats. An ECU remap isn't going to uncontaminate main cats. Moving the O2 sensors has nothing to do with the main cats. It is just a more cost effective method of avoiding a CEL. Much cheaper than an ECU remap.

Pre-cats are in the headers and main cats are downstream. When pre-cats fail, the catalytic converter material either gets sucked back into the engine or blown downstream contaminating the main cats. The least expensive fix for the cats themselves is to gut the pre-cats (in the headers) and then either replace or remove the [now-contaminated] main cats downstream. Welding in aftermarket main cats, like the FD units, is generally least expensive as they are cheaper than factory replacements and also cheaper than the Larini options.

When pre-cats are gutted, there will be a CEL unless someone relocates O2 sensors (presuming they have main cats), uses spacers on the downstream sensors (reportedly hit or miss), or does an ECU reflash. Of those options, relocating the downstream sensors is least expensive. Someone could relocate the sensors and install a FD DBWEM for less than an ECU reflash.

I could never figure out why we call the downstream cats the main cats....seems to me that the header cats with the 02 sensors would be the main cats.......the downstream cats secondarys.
It could be partly due to size (the main cats are much bigger) but it is probably because ROW cars only have the main cats. Pre-cats are unique to NA cars. Since all 4200s in the world have the cats downstream from the headers, it is natural to consider them the "main" cats.

I think Jlobo paid 1600 for his reflash and im not sure what all he had done, but when i called EVOMS, i told them i wanted more throttle response and that i wanted to stop the 02 cell from coming on if i gutted my cats and he quoted me a price of $1250. I thought that was a pretty good price to get one issue resolved and a mod done at the same time. If i have an issue with my cats,,,(knock on wood) ill be going in this direction to kill to birds with one stone. As stated above, relocating the sensors could be a hit and miss and i wouldnt want to have to keep messing around with that. Id rather go for the sure thing Jlobo said scince he got his done his throttle response is razor sharp. Soon as he hits the pedal hes off and running.
I'm not saying the EVOMS deal is bad. Just a very expensive fix for an O2 sensor issue alone. For multiple mods it may be great. If you are looking for throttle improvement now, I think the DWBEM is the best bet. Do you really want to wait for a pre-cat failure to get that mod done?

No, waiting for a failure would be silly so if i wanted a DBW id call FD and buy it. But in this case with a cat failure id go the other way.
Got it. I agree. If someone has a cat failure, guts their precats, doesn't own a DBWEM, and would purchase one anyway, the EVOMS solution would kill two birds with one stone.

Lets try break it down with a rough idea for the guys in here to give some an idea. How much do you think it would cost to gut cats, install FD cats, and move sensors
Here are my guesses (probably less if labor hours are reasonable).

Gut pre-cats = $250 labor (cut access hole, remove honeycomb, and weld shut access hole)
Sport cats = $900 with shipping
Main cat install labor = $200 (simple cut and weld)
Relocation of oxygen sensors = $200 (install O2 bungs downstream and lengthen wires)

It has been many years since I went through the ringer with this exact issue. I don't remember exactly what I paid but it was much more than this because I had the car in three different shops due to two different inept service departments. It all ran up lots of money in towing, labor hours, etc. Seems like my car spent the better part of a month being towed from shop to shop.

An important note is that it can be VERY hard to find a shop willing to gut the pre-cats. I ran into multiple shops that didn't want to risk the EPA getting in their business.

If I had to do it again, I still think I would have gone this route. But, that is because I already had a DBWEM. If I didn't and was going to purchase one anyway, I would have gone the EVOMS route. Of course, that bumps the $1,550 operation I estimated above up to $2,600.

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Yea i agree. It would be hard to find a shop but doable. The costs you mentioned add up to almost 1500 and i agree with that estimate. Then you have to hope that the sensors are mounted in the rite spot. The 1500 estimate seems equal to goin the way im suggesting. See what i mean. If you have to spend 1500 why not get more out of it
The way you suggest would be $2,600...

Gut pre-cats = $250 labor (cut access hole, remove honeycomb, and weld shut access hole)
Sport cats = $900 with shipping
Main cat install labor = $200 (simple cut and weld)
EVOMS reflash = $1,250 (disable O2 sensor CEL)

Nope, haha,,,the way im saying is gut pre cats 250 or so, and a reflash 1250,, thats all you need to, 1500, 1600,,,.if u gut precats and reflash, u dont need sport cats
the sport cats are to replace contaminated main cats. Under your scenario, if the main cats were not contaminated (not likely), here would be the two options...

Gut pre-cats = $250 labor (cut access hole, remove honeycomb, and weld shut access hole)
Relocation of oxygen sensors = $200 (install O2 bungs downstream and lengthen wires)
Total: $450

Gut pre-cats = $250 labor (cut access hole, remove honeycomb, and weld shut access hole)
EVOMS reflash = $1,250 (disable O2 sensor CEL)
Total: $1,500

Regardless of the options taken, the reflash is always going to be about $1,000 more than just relocating the rear O2 sensors.

Got it. Someone like myself with the main cats out would have to either go the way im suggesting, or reinstall their old cats and move sensors, or buy FD cats then move sensors
Yes, if someone wanted to run zero catalytic converters, they would need a remap, O2 sensor spacers, or some other solution like non-fouler O2 sensors. They would also need some ear plugs and some understanding neighbors :cool:

If you get a remap, you dont need to worry about 02 sensor spacers or non foulers cuz with a remap, they can eliminate the 02 sensor part of it, thus no cats no cell.....Ear plugs i have to agree haha
Yes. I said someone would need one of the three options. Not all of them. The remap is probably the easiest of the three I listed but by far the most expensive. By the end of my catalytic converter saga, I would have gladly paid any amount just to get my car running again. I chime in on these threads in particular because I don't want anyone else to learn everything the hard way.

Thanks for all the great info.................. now I just have to find someone who can do the work!
When it comes to gutting the pre-cats, your best bet is to find a small muffler shop and just talk to them in person. Asking them if they are willing to remove catalytic converters over the phone smells like a setup to most shops.

As usual, great advice from FD.

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?
It is easy to see if the pre-cats have failed. Your mechanic can do a visual inspection using a borescope through the O2 sensor bungs.

It is best to cut off the OEM pre-cat and fabricate using mandrel bends back to the next pipe and put a high flow cat inline back there with a relocated 2nd o2.
There has been at least one member here that cut out the pre-cats and welded in aftermarket cats in their place. IIRC, they were happy with the result.

You're not out of the woods just yet.
Agreed. IIRC, it takes 3 cold starts with a significant number of miles in between each one before the OBD2 system goes online.

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?
Visual inspection should be your first step after pulling the code.

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?
If you gut the pre-cats, you will either need to live with a perpetual CEL or do one of the other fixes discussed ad nauseum in this thread. the very best thing to do is to call the folks at FD and talk through all your options with them. They won't steer you wrong.

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