What is this noise? Any help is appreciated

I had my rear bearing go at Watkins Glen two years ago. All the ball bearings were out of the cage. Man, was that noisy! Fortunately it happened during the last session of the last day.
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Drbob, has your car had any history of a cel for a misfire, in some instances , unburnt fuel will cause a converter to run hotter than normal, the excessive heat can be a cause of the cracked core


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That cat ineffiency code can slso be the result of unburned exhaust gasses, be careful you don't ruin the new cats from some underlying issue, could be something as simple as needing new plugs or wires ,
You could possibly have an issue causing higher than normal exhaust gas temps. Was that rattly cat from the same side of the motor as the discolored header? If so you have a bank running rich . Look for bank specific causes such as a maf sensor. Might not be enough to thow a sdl , but enough long term temp increase to damage the cat
A great tool to help diagnose this can be bouht fairly inexpensive , an infrared thermometer , it has a laser point simply aim it at various points on the exhaust, snd it will give a digital readout of the temp, you could tell if one side is hotter than the other
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Do you mean 0422 and 0432? Causes can be bad down stream O2 sensors, exhaust leaks before cats, bad cats, clogged cats (possible if they are breaking up), bad wiring to O2 sensors, leaking injectors (i.e. running rich as drivedaily said). Were you getting the CELs before or after the headers were replaced?

As for connectors, I thought you car already had "the treatment".

 

If you have a discolored header and a failed cat , i would say that bank is running hot, do what i said with a laser temp gauge. Upstream o2 sensors can effect mixture , downstreams only monitor the efficiency of the cat and have no effect on mixture.if you can verify the bank is hot , limited things can cause a whole bank to be hot , like johnk said , connectors , possibly a weak coil pack , a dirty or miscalibrated maf sensor , few things can effect a whole bank. do you have paper air filters or k &n 's , sometimes oil from the gauze in a k &n can cause a dirty maf sensor. Be careful tho , i've seen some cars , notably some fords , and especially escapes , where a misfire can ruin a cat in as little as 5 or 6 miles. Sounds like that is not your case , but just an example , the effect of a misfire can quickly cause problems. but , because of that discolored header , i would say your cat failure may not just be a fluke , there could be an underlying issue. But , its also possible that the loose care was causing some backpressue , in turn causing your bank to run hot , get that temp gauge, put your new cats in and compare temps side to side.

 

Yup! Funny thing is too many just replace cats calling the oem cat cr@p and replacing headers because the OEM ones are called cr@p. There are better cats and headers but they do not solve the root causes nor will they prevent meltdown if mixture control is left unchecked, for which the 355 is extremely unforgiving being closer to a race engine than a street engine. How many valve guide head rebuilds could be avoided if these cars ran right? One key piece of evidence that convinces me of this pathogenesis is that the death of valve guides etc is random among the fleet and in no relationship to mileage or use. I will go out on a limb and say a factory cat is pretty darn good.

 

If you get the laser temp gauge you can aim it at each cylinder header tube. Its a great little tool . Simply aim the red dot . Your cel is not on yet because downstream o2 sensors are not cinstantly monitored, your ecm reads that value at predetermined intervals , when the dtc is detected a number of times, usually 3 , the ecm will them illuminate the cel, its out now , drive it a little and it will come back on i 'm sure. Just curiuos are you around reading, subject to pa enhanced emmissions?


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Fbb is 100%dead in , there is a reason for header failures other initial build quality. I've seen pictures of severely melted tubes , inducating extreme heat. I also read a tech article years ago concerning header wraps and insulation, and a condition they can cause, they can draw the carbon out of the steel , weakening it and making it more likely to crumble , melt and fail. Probsbly why aftermarket options are not insulated. Ferrari is the only make of car i see with headers insulated , perhaps why the header failure is limted to ferrari. I see other makes with heat cracks , but never a meltdown!
A rich system would cause the converter to run hot due to unburnt exhaust gasses, but a lean system would cause the headers and whole exhaust system to run hot, the possibilities for the cause are endless, simple things like air filters , injectors or more deeplyrooted , a fuel system that can not keep up, possibly even the initial programming of fuel and timimg curves. Could it be the 355's exhaust diverter and y pipe? Whatever it is the 348 doesn't seem to be affected by it. Why did ferrari go back to 4 valve cylinder heads?

" serenity now "

 

Forget tne heat shield - that thing works through it. If the cat is hotter by a bunch then I suspect a lean condition on that bank. Typical causes are thermostat if both banks are high. One side high may be a cracked header in the usual place. There are other reasons for those as well and tne 355 brain trust can better make suggestions. Typical for the model though. 355 cats are better than the POS ceramic versions on our 348s.

 

That makes sense. Just a thought ,just pondering if the heat can be inherent to some design factor right from the drawing table. I put decat pipes in my 348 just to reduce engine bay temps just for safe measure, luckily my situation is unique, i'm an inspection mechanic so my car always passes. Wink . Wink . But to answer the question bob, even though theyre insulated you will stiil be able to pinpoint hot spots, and higher values side to side. That will give you an accurate idea as opposed to relying on the factory thermocouples to trigger a sdl.if they are not working properly you can be running hot and not be aware if it


" serenity now "

 

Bob,

You will have to drive the car a while before all the monitors become ready. Most likely you just have cats that are on the way out. Damaged do to the ceramic breaking up. Not unusual. here is a link to a pretty good write up on OBD II in general. Discussion of the catalyst monitor is on page 32 of the pdf (labeled page 42 in the text). http://www.lbcc.edu/attc/documents/OBD2.pdf. I think all FChatter would benefit by reading it.

 

I would guess chain tensioner, located under front timing chain cover.

 

If this is the case, is this a difficult or expensive fix? My 1997 does the same thing....it comes and goes.
Concerned!!!!!!!!!!!!

Thanks for any input!!!

 

Good feedback...
I even bought the mechanics stethoscope, but have yet to catch it at the right time. Will prob do it at next cold start-up. Your explanation makes a lot of sense. Did you also notice that sometimes it goes away as soon as you start moving in reverse of forward? Then it comes back at idle when the car is in neutral or the clutch pedal is not pressed?