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Discussion Starter #1
Anybody have any experience diagnosing a false "Slow Down" light? I'm quite sure the cats are not overheating. On my '96 USA F355, there are three thermocouple probes in the exhaust, one in each main converter and one in the muffler. Any idea whether I can just disconnect them to narrow down the problem, or will th ECU not take kindly to that. Will it set a check engine light? Or how about disconnecting the buffers that the TCs plug into? Anyone know how the software is written? Thanks.
 

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This is a common problem and I've had it a couple of times. The fault is with the oxygen sensor. The sensor unit is in sealed in a black rectangular plastic unit and the seal tend to shrink and allow moisture into it. That's the cause of your trouble.

It sends the wrong message to the ECU, but unfortunately the ECU will act according to the transmitted info. The alarm will light up and one engine bank will shut down if you keep on ignoring the warning. Sadly you have to change it, that's the only solution, in my case at least.
 

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Discussion Starter #3
Thanks for the reply, but I am a little confused. The black plastic sealed unit is the buffer for the thermocouple, not the oxygen sensor. It certainly could be a faulty buffer, but I'm not quite ready to go out and buy one yet. The one on the right side has inputs for two thermocouples, and one on the left for one TC only. Which did you replace, and what was the approximate cost for the unit, please?

Steve
 

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As Stradale says this is a common problem.. I had it on my old 95' 355B. I took the car to Ferrari and (I believe) they swapped the sensors over (Without replacing them) and I had no further problems.

Dermot
 

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absolutely confused

Please excuse me, but now i am completele confused.
Maybe my english is to bad.
Since i have my 355 there is the same problem, when the engine gets slowly warm.
What is now the problem. The black box from the temperaturemeter, the sensor of temperature or the oxigensensor.
Did you now change sensors or not.
Please help me to understand
Rainer
 

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Discussion Starter #6
Kein problem, mein freund. Ich spreche Deutsch! But not that well. Here's what I now know. The oxygen sensor has nothing to do with the problem. It must be either one of the thermocouples, or one of the "black boxes", which are thermocouple amplifiers, also known as buffers. I have tried a few things: Disconnecting any one thermocouple (TC) gives a continuous flashing "slow down" light, so we can't do that. Disconnecting either buffer does the same thing. I disconnected one TC and substituted a K type thermocouple, and got the same result, so that won't work either. However, in the process of disconnecting and connecting all the TCs and buffers, the problem has gone away! At least temporarily. Now, as I understand it, a flashing light means slow down because the cat is getting hot. When it DOES get real hot, the light goes to a solid light, no longer flashing. The failure mode I have seen is that the light never flashes, just goes from off straight to solid, and almost immediately, half the engine cuts out ( bad news in traffic). I must assume that one of the TCs goes from OK to instantly very hot (unlikely), making the light go solid. If I see the problem again, I will buy one TC (about $150 - $200), and try it in each of the three places, until I hit the right one. Does this make sense?
 

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I think a bit more "science" would help here, as in how are these things wired and what is the software looking for to trigger an alert (high voltage / low voltage / grounded / comparison with ambient temp / ???) :-?
 

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Discussion Starter #8
I agree, 4kids3fish. That's what I asked for in my first post. I worked for General Motors engineering for many years, and we kept software algorithms pretty secret. I suspect Ferrari is the same way. I'll keep you all posted as I continue to dig further and further in. Hopefully, we'll get an answer to this common problem. In the meantime, nothing sounds like an F355, so it's all worth it :) ---Steve
 

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nice to see, that there are good discussions in usa. Here in germany every forum looses very fast sencefull words.
In my(it is only half mine) 355 there is the light always only on one side. So i will change the sensor from left to right side.
Only for information: I can modify the ecu from the 355 first serie and have almost all dates. But the exausttemperature is modified by the black box and gives only a information like on/off to the ecu.
Anyhow I think the exhaust gets really too hot and we have to find the reason why.
Rainer
 

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That's interesting. Bring on the boffins, I say!

BTW, this site isn't US-based. It is actively supported in Japan / SEAsia / North America / Europe-UK / Australia-NZ and even Russia (Hi Olga!). I've forgotten lots of others too. :oops: Welcome!
 

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Sorry I am new to the Forum. This is going to be a long post. But I do need help.I live in Taiwan and I recently bought an used '97 550 US spec. As there are no official importer here I have to rely on the internet and a shop here that works with Hong Kong for help.
Recently driving it I got a slow down light turning on and the engine lost power. As posted in the thread It must have been the engine shutting down one of the banks when either the Cats got too hot or the oxygen sensor got mositure in it!
I was just wondering is there any way to find out which problem is it?
I was driving and the engine temp was normal.
Also as Taiwan is a very very hot country in the summer months (lows in the 30 F and high's close to 40F) With heay traffic at times. Is there any way to keep the operating temp low in the 550?
Sorry for the long post.
 

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Tim,

Welcome to the site. I don't know the answer of telling if it is A or B for the problem. The problem of heating you mention is impossible to cure if your in stop/go traffic. Also with the high heat it will only make it worse. If it is dead stop traffic I suggest turning the car off while you sit.

Welcome to the site, keep the long post coming, we don't mind and always want to try and help! 8)
 

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Andrew,

New so alot of questions.
What is a normal operating temperature for the 550?
Are there any difference between the Euro and US spec cars?
Also I went on line and found a company Imola Racing from Germany - they proposed a solution of using the A/C to cool the fuel lines and thus increasing horse power and lowering the temp. does this sound normal/workable? Also they mention that using a sports cat wuld lower the operating temp also. What do you think?
 

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tim550 said:
What is a normal operating temperature for the 550?
Sorry I can't help on that one, but I will look for you and post if I find it
Are there any difference between the Euro and US spec cars?
Very minor, the US version has to burn cleaner and I think has a cat on it (will also confirm this).
Also I went on line and found a company Imola Racing from Germany - they proposed a solution of using the A/C to cool the fuel lines and thus increasing horse power and lowering the temp. does this sound normal/workable? Also they mention that using a sports cat wuld lower the operating temp also. What do you think?
Imola has been discussed on here before. Those guys know what they are talking about and have probably done the above. You could use the A/C to cool the lines but you'll get hot inside your car if your using it. Not sure how the application works and would be interested in seeing how that works.

The sports catalytic(sp?) converter allows for better air-flow than your factory cat. Better airflow, cooler system. I don't know about Taiwan's emission laws. If you aren't green for earth remove it and put a strait pipe to get even more airflow (basiclly, remove the part). Of course pollution will go up.
 

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That was a fast reply!

When I bought the car it had a Tubi cat back on it already.
It is a bit loud though.....
Taiwan we are not really green! So ......... that is not a real problem.
If I were to look for a sports cat what would be the best choice?
 

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tim550 said:
That was a fast reply!

When I bought the car it had a Tubi cat back on it already.
It is a bit loud though.....
Taiwan we are not really green! So ......... that is not a real problem.
If I were to look for a sports cat what would be the best choice?
Strait pipe. Remove the cat all together.
 

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whiteNSX,

I experienced the same problem with my 355. Slow Down light came on. I'd left the car in hotel carpark in pouring rain and I guess moisture had got into the sensor (usually garaged). As the car dryed off the next day the light went out.

Never had a problem since. Never had a 'dirty weekend' since either though !!! :lol:
 

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Discussion Starter #19
Thanks 355GTS. Your experience convinces me even more that it as an electrical glitch, not a real malfunction. Unfortunately, I had to give the car back to the owner. Since my last post, he said the light has come on twice for about a half second, and the engine continues to run well. We may have to wait years to try your rain theory here - I live in Phoenix.

Steve
 

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Enzo250GTO said:
tim550 said:
That was a fast reply!

When I bought the car it had a Tubi cat back on it already.
It is a bit loud though.....
Taiwan we are not really green! So ......... that is not a real problem.
If I were to look for a sports cat what would be the best choice?
Strait pipe. Remove the cat all together.
Okay So my cats are shot and i need to replace them. Did some research. I have decided to go with straight pipes :lol: !
Also during my research I found out there is a company caleed Stebero that does and X cross over pipe. Are they any good?
And where can I find a supplier for a straight pipe?
 
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