Thermocouples, slow down lights, related CEL’s, and how to conquer them...

Grant, how do you think the box is wired up? Thermocouple - bypass box - ECU? If the box was working for the first 100 miles, then it simply sounds to me like it's now sending the wrong signals to the ECU. If the CEL was simply a result of the old thermocouple ECU not being plugged in, wouldn't you think the CEL would have come on sooner?

 

I think the tc ecu is not even plugged in and his box is not plugged in either so this is why he is gettng the cel.
Perhaps this magical box is the tc ecu. The op does not inderstand the system enough to give us the correct info.

I suggest the op get a manual and study how the tc ecus work, or read about them.
Also the op needs to study where the tc ecu are located.
We also need to know the year of the car and weather its a 5.2 which we are all assuming.

We need good info guessing will not work.
If it is a 5.2 as I said Bobs post describes what the computer needs

I am still thinking he has nothng in there so this is why the cel comes on.
He needs a tc ecu and a working thermocouple

 

in order to help could you please do the following
Describe which systems have been taken off car
What year is car
Describe exhaust in detail
Headers, main cats, bypass cats, bypass valve(open initially, closed once warmed up or opposite)
Tc ecus for bank 1,2, and bypass
O2 sensors front , rear each bank
Any other mods or removals of original systems

 

In my work on this and in my car specifically, I had an identical issue. It wasn’t until I tapped the output of the BP sdecu that I watched the voltage spikes up to 3.6 volts intermittently. It was an issue with the TC that when checked on the bench was fine but in the car with whatever vibrations etc it would manifest itself.

We don’t know exactly what the motronics is looking for at the BP location. One can assume it will warn on spikes/ truly hot conditions but at that location, diverted from the direct manifold output I think heat is not really what it’s checkkng for.

I think it wants to see a delta from .8v at warm/idling to as I described of about 1.8 v when valve is open. Its looking for BP operation and that would imply some changes. It is for this reason I question the fixed voltage boxes here. If it is looking for delta over a period of cycles a fixed 1.5v signal may in time prove to cause the CEL again. Not for heat or high voltage output but because it isn’t telling the motronics the valve is operational.

All of this is conjecture because we don’t know what the logic of the motronics is looking for but this is my best guess.

With that said, as I said earlier. I would check the output of the tc/sdecu at that location real time while driving and you will have your answers.

 

Watch this video and you’ll see what a properly functioning BP valve TC/SDECU output looks oks like.

This is what you need to see as well. First swap/install properly functioning components as checked this way. Installing and then hoping without doing this will just lead to more frustration unless you happen to get it right.

 

Will someone please explain to me how the cats running cool would cause a CEL referring to the by pass valve? The split in the exhaust leading to the by pass valve occurs before the cats and lower cat temperature should not effect the bypass TC/TCU. However, it could be that the by pass valve is not closing correctly. It has been mentioned here before that when the bypass valve is wired open exhaust can recirculate backwards through the bypass valve at idle. If this were that case, then hot exhaust from the cats could be feeding back through the bypass and the bypass TC is sensing a higher that expected temperature, thus thinking the bypass is opened when it should be closed, triggering the CEL. When the car is running at RPM there is then sufficient back pressure on the up stream side of the by pass to prevent this recirculation. Could be that this actually is a problem with the bypass valve.

 

I might be mistaken, but I always thought besides the 3 ECUs and TCs (on 5.2 cars), the pre and post cat O2 sensors play a role in this, CELs and SDLs.

 

Phil the 02 sensors have no relationship with the SDL system. They do not trigger SDL or respond to them directly. The SDL system is just a heat sensing system using Thermocouples and a voltage amplifier and some logic in the Motronics to respond to those voltages.

The confusion with the 02 sensors involvement in the above might arise in that a rich condition in the operation of the engine might manifest itself with a CEL of this condition sensed by the 02 sensors AND a concomitant SDL triggered because the rich condition created a hot cat. These are two independent events though, just related by cause and effect.

The current posters issue is with a BP valve error CEL which doesn't have any relationship to his 02 sensors. Something is either wrong with his TC/SDECU complex or his BP valve IMO. I don't think its his hiflow cats.

 

Thank you Dr. B.

Without making the original question more complicated, does the secondary air injection system play a role in this? And do the O2 sensors effect the secondary air injection system?

 

The air pump operates at cold start up to provide oxygen at that time. The 02 sensors do react to the air/fuel ratios but they dont affect the operation of the pump. It just comes on at start up for a few seconds.

You will get a CEL if it isn't functioning though. I believe that level of function is determined by the 02 sensors.

 

I follow your logic but do not think this is the reason

 

Thanks for the comments. I have some additional information. The mechanic measured the voltage from the bypass sensor. He states the voltage runs from 0.8 to 4.8 depending on the temp and other factors. He is quite sure the sensor is functioning normally. THe "box" is actually a replacement for the bypass sensor as was mentioned above by someone. Once the box shorted out, the original sensor was replaced. Finally, European cars read the voltage readings from the sensors differently. Changes were made to the motronic system in the US due to emission issues, at least that is what I have now been told by several "Ferrari" mechanics. Apparently the US system is easily switched with the European version which fixes this problem. Unfortunately, getting the part or parts is not easy and Ferrari is not currently making either version.

To again reiterate, this problem began occurring after the OEM headers and cats were changed out for FAB Speed replacements in 2016. I am uncertain whether the "bypass" cats were altered but will attempt to find out. When the light first started going on, the feeling was the OEM bypass valve was to blame, which is very possible. THe valve was replaced with FAB Motorsports valve but this did not fix the problems and the valve has now been checked several times and is working. The current theory causing the problem is that the exhaust system temperature is altered somewhat when you change the exhaust system (even I get that). The sensors from the cats measure the information which is then somehow compared to the information coming from the bypass exhaust sensor. The motronic system then analyses the data and if the data aint right, CEL light comes on. And the light stays on after that till I have the code read and the light resets. THe car is again fine for a while until, while idling, the CEL goes off again.

The suggestion that somehow changing the "bypass" cats seems intriguing to me if in fact the sensors are reading exhaust measurements there rather than the main cats. That is something new not mentioned before. And probably expensive. All of the sensors, thermocouples etc. have now been vetted multiple times. I think the person who said the issue is with the motronic system has it right.

My final but least favorite option is to buy the code reader. That way the light goes off, I check the code, if its the bypass I reset and keep driving. Not ideal but these cars kind of make you stand on your head.

Again, thanks for the input. Clearly there are a lot of owners who know an awful lot about how these cars run.

 

Sorry. Should have mentioned that the American ECU is different from the European ECU and that they can be swapped for one another. Apparently, the European ECU allows alterations of the exhaust system to be much less problematic.

 

Ok
So guessing a bit he ause you still did not answer
Your car is an american car with american ecus and tc ecus
Your bypass cats are still there
You have fabspeed headers and fabspeed cats
You have cleared all codes and swapped the tcecu from the bypass to bank 1 or 2 and driven enough to get a Sdl or if what yor sayng is true you should get same error as before
Do the same thing but now switch the thermocouple from bypass t bank that has the old bypass tcecu

Bypass error with a cel at idle but not when driving on bypass should be result both times.

This is what. Should happen and proves everything is working as you describe.

You need to do all this or more simply follow Bobs lead and tap the tcecu for bypass and see if its the same as Bobs.
Then tap at the main ecu and see if it's the same
Something will show up and we can go from there.

 

My bypass cats have been removed for some time (no CEL generated). I have standard sensors and a USA Motronics ECU. That's why I'm puzzled at why people are getting temperature-related CELs with exhaust configuration changes. Did your technician say if these problems are usually caused by specific exhaust system manufacturer configurations? By the way, what brand of silencer/muffler do you have?

This magic box is a mystery. As far as we know, the Motronics ECU is looking for a temperature change when the bypass valve opens. If the original thermocouple sensor is not attached, the box would have to generate two false temperature signals. How would the box know when the valve is open (or commanded open)? It would have to be somehow hooked up to the vacuum line coming from the exhaust bypass solenoid valve ... or electrically hooked up with the open command signal from the ECU (going to the solenoid valve).

When I said using the code reader to erase messages, I meant erasing old messages relating to problems which may no longer exist, but allowing new ones to appear. I didn't mean you to use it to hide CEL's. With your magic box attached, it sounds like you are hiding potentially serious faults.

Excellent. Thanks for this information.

 

Sorry but I’ll be frank. If your sdecu is outputting 4.8 v from the BP location your problem is the TC or the SDECU. There is no way in the world that you get 4.8 v from that location for any other reason that what I said.

There is no Euro vs US SDECU. There is one made by Viscovini. It is just a voltage amplifier. It doesn’t have any logic.

I have never heard of a euro version motronics vs NA. In the case if the SDECU, it has nothing to do with emissions, just temp sensing for safety on the cats and temp sensing to determine if the BP is opening.



There is no feedback between the cat TC and the BP TC.

OBD code reader is cheap. Go to an auto parts store and get one. $50 or so.

It is possible they have crossed the cat sdecu output with the BP output. Easy check and it should be checked.

If you’re getting 4.8 v then I bet that’s a spike exactly like I had. Bad thermocouple that tested fine on the bench.

Finally, shoot me an email if you’d like and I’d be happy to discuss this with you on the phone.

Bob

 

Here is a graph of what the outputs look like and the sdl triggers from the Cat locations, not the BP. 3.7 volts and it shuts down a bank.

4.8v and your car is toast. That’s an aberrant spike creating your issue if it indeed does measure that.
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To add with what Bob has explained:
Swapping the Cat TC plug with the BP TC plug accidentally will yield a SDL not a CEL......been there done that

I went through all this with Tubi headers, no cats, and Capristo BP valve.
In my case, the Capristo tech told me that I would get a CEL when using a Capristo BP valve WITHOUT CATS.
I believe this is all temperature related. No cats equals lower temperatures, which makes the BP TC unhappy.

In the end I got Goth's BP box and started enjoying the car !
5 more years until all this S&*$# is irrelevant for inspections.

 

I may be wrong, but I don't think Ehrst is saying that his car was producing these actual values, but that his technician is saying that the range of possible values is around this. Tolerances may vary depending on the point of measurement and the meter's calibration. Does the SD1 tool give SDECU voltages?

There are most definitely variations between USA Motronics ECUs and other country's ECUs. Just look at the 5.2 parts catalogue. There are about 10 different part numbers. The USA has stricter pollution laws (or rather, California). The workshop manual even mentions differences between USA and others in regards to bypass valve operation.

Same here. It does seem odd, though, that a CEL does not also appear. Why does it throw a (flashing, in my case) SDL? Is it because it detects a large disparity in temperature between the L & R cats?

I didn't realise Goth made a bypass valve box. Do you know how it simulates temperatures (or does it modify detected temperatures?)? By no cats, do you mean main and bypass cats? I have no bypass cats but no CEL. I have a Mille Miglia system with Larini main cats.

 

Goth made a set of TCU boxes a couple years ago that were available at Ricambi, but both the boxes and Goth seem to have disappeared.
I purchased the BP version after exhausting all avenues short of putting the cats back on. The box simulates the correct temperature signal and sends it to the ECU, thus fooling the system and keeping the CEL in check. It’s the greatest invention of the past 20 years !

My car has no main cats, but retains bypass cats.

 

No. But, it does provide the temps as seem by the TC (assuming the SDECU is outputting the proper values). It's my understanding that Ferrari (well, Digitek) made a tool to test the SDECU. I forgot the name of it. Someone here once posted a pic - I forget who the user is.

 

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Here are the Goth boxes. If he’s not going to produce these anymore, I wish he would share the plans with somebody who will

 

I believe JohnK already figured out a circuit design several years ago and posted it here.

 

If it's used in the bypass position, how does it simulate different temperatures (for bypass valve open and closed)?

Wasn't the two types for cats (main ones) and no (main) cats? Did you purchase 3 no cat types?

If your car has no main cats, you can fool the ECU with a zener diode and a resistor.

https://www.ferrarichat.com/forum/threads/simple-2-7-slow-down-ecu-replacement-only-for-no-cats.538719/

 

Just a comment since I only know this for my car which is a 2.7. Running w/o the main cats on a 2.7 does not generate either a SDL or a CEL