348 Slow down lights, final truth

Okay here is the deal.

Since you are runnning Tubi test pipes it is one of two things.

1) Your exhaust ecu is bad.
2) You have a bad thermocouple

In either case it is an easy fix. The simple test is to swap the exhaust ecu's from one side to the other. By doing this you will find out what is actually the problem. If after you swap sides you now get the slow down light on bank 1-4, then you know it is the exhaust ecu. However, if after you swap sides and you still get the slow down light on bank 5-8, then you know it is the thermocouple. You can also do the same test by swaping the thermocouples, but it is easier to just swap the exhaust ecu's.

The exhaust ecu is mainly for monitoring the temperature of the catalytic converters via the thermocouples. The quick fix is to unplug the exhaust ecu/s. The thermocouple plugs into the exhaust ecu, then the signal from the exhaust ecu goes to the Motronic ecu. You will NOT mess up the Motronic ecu's by unplugging the exhaust ecu's and running the car. I know this because I have had my exhaust ecu's unplugged for over 2 years. What you will get is a silent code stored in the Motronic ecu's memory, but you will be able to run the car without any ill effects to the Mortonic ecu.

"If" you were running catalytic converters and you unplugged the exhaust ecu's, there is a chance that cats can get damaged from over heating (the insides get burned out), and possibley a fire started from the cats over heating. This is why the Motronic ecu shuts down the bank of cylinders that it gets the over heating signal from. It is also why you need a properly functioning exhaust ecu if you are running cats.

However, as has been the case with most "slow down" lights, it is usually a bad exhaust ecu that is the problem, and sometimes a bad thermocouple.

So, since you are running Tubi test pipes you can unplug the exhaust ecu's without fear of causing a fire or messing up the Motronic ecu. But this will not properly address to faulty part (ecu/thermo). Just for kicks I would swap sides to see if it is the ecu or the thermocouple. Then in the future if you decide to sell the car, or run cats, you can replace whatever part is bad.

 

own of our costumers had a 348 and his car caught fire due to cat overheating
on a diferent stoy
we removed the cats on an F40 and we put the sensor on the new muffler just to be on the safe side we didn't want to mess with the ECU's (we tought if we disconected them we were gonna have problems

 

What "silent" code means is, that the "Check Engine" lights will not come on. No it won't adjust the parameters, at least as far as I am aware of. The only way I am aware that it will adjust the parameters is when they are plugged in and get an "over heating" signal. Then they shut down the bank of cylinders for the signal.

 

True earnie, oh so true.

 

Thanks Rob.

Say since you ran a 348 challenge car, I heard that the challenge guys unplugged the exhaust ecu's. True/false?

 

Oh we did all sorts of things when time was short, like electrical tape over the slow down lights...

We had to run the catalysts, so we kept the thermocouple/exhaust ecu system functional. Many updates to the thermo ecu in '94-'96. Had to stay on top of inspecting the catalysts as the 348 design was much weaker than later designs and the core would shift into the shape of a cone, then break apart.

Best,
Rob

 

So then what did you guys do to prevent the ecu from shutting down a bank?

 

now i don't have an ECU since it's a 1982 2v, however i have testpipes and the thermocouple probes are not hooked up. no lights for the cylinder slow down when running. also i did clean the engine and did get some water into the front banks sparkplug wells, when i started the motor the light for bank 1-4 illuminated. so for me i don't think the probes were sending the signal, not sure what sensor is really. just thought i'd share.

 

I think I have thrown in my story on this subject before but for informational purposes here goes. I owned a 348SS for about 7 yrs. after a few months of ownership my exhaust ecu on the right bank started to manfunction shutting down the injectors. The cats were not out of normal temp. operating range. After doing some research at that time I found out that it was a common problem for these exhaust ECUs to malfuction. Since all those sensors due is monitor the cat temp for overheating, they aren't connected to the engine management ECUs I disconnected and removed the ECUs and the probes. the 348 ran fine for the next 7 years I owned the car. I now have a 355C and have removed the exhaust probes and ECUs from this car also (3 yrs. ago) other than needing to remove the dash warning lights, the 348 lights didnt come on, the car runs the same as before. It would be interesting to know why Ferrari puts them there in the firsat place I am not aware of anyone else that has used the exhaust temp. sensor concept. Regards, Vern

 

These Thermosystem is developed from some newbie because its realy crap. The boxes where the temperature gets analysed and if its to high send an signal to the ecu and dash is made very cheap with epoxy 2k sealing onto the circuit. Some time in use it gets cracks and water comes into the circuit then the circuit sends an to high temperature signal even if the temperature is ok. Next failure in the development is that they connect this output not only to the signal light in the dash also to the ecu. Thats not the failure it would be good if it is an data input port of the ecu so that the ecu gets the temperature as an analog value to work with this temperature and raise the ingnition angle or change the fuel mixture to avoid overheating or turn the engine of smooth if that don't work. But no they connect it to the immobiliser input the ecu will shut down rapidly if the signal comes so that this give some brake to the crank and so to the rearwheels thats ok if the second bank still works but if both shut down at the same time the rear wheels maybe lock and the rear comes arround. No good engineer would develope such crap. Next problem the bad cats used ... if they would spend more money in a better cat they dont have any temperature problems and dont need this funny slow down system. You can disconnect the wire to the ecu and change the cats to good ones. Then you have no bank shut down but still have the slow down light activ in the dash. So you see when the systems alerts but can decide if you will slow down yourself or not. With a good cat you dont need to slowdown normaly. . or put in an exhaust temperature display if the temperature is under 1000°C there is no problem. Why has Ferrari put this system in, they don't know how to build cars. But at least they know how to design cars better then anyone else.
__________________________
Samy

 

Most of the electrical problems were bad ground connections. For a while we ran external ground straps to the lambda sensors. We kept up with the thermo ecu updates. Keeping the electrical contacts clean, updating the negative battery cut-off on rear batery cars aided reliability too. The other funky thing was Ferrari uses brass on the high-curent distribution blocks under the dash, changing to copper reduces resistance.

 

Hi Rob, Question for you, have you ever had a problem with at cat over heating (except for cars that had worn out units)? I ask only because in my research(somewhat limited) I couldn't find anything on the cats overheating because of hard use(challenge cars come to mind here). No other manufacturer uses this system that I am aware of. It seems sort of redundant ie; there are other sensors connected to the engine ECUs that could trigger the CELs if the, lets say, engine was running leaner than computer parameters allowed for, which could overheat the cats. The CEL comes on anyway because of the lean mixture telling the driver there is a problem. Anyway, just curious what you know. Sorry if I'm getting off topic. Regards, Vern

 

has anyone had experience with this issue on later model Ferrari's, specifically 550? I had an off track excursion which tore off one of the thermocouple wires. I don't run cats so don't see the reason to replace the broken thermocouple. Currently I have just bridged the thermocouple ECU input. The SLOW DOWN light still flashes, but it hasn't cut an ECU yet....

 

There are 6 electrical connections/wires to each exhaust ECU. 2 connections on each xECU go to the temperature thermocouple. 1 goes to ground. 1 goes to power. 1 goes to your dash Slow Down light. The other goes to the Motronic A/F ECU shutdown pin.

One solution will exist of some combination of first disconnecting, then possibly grounding, or applying +5 or +12 volts to that ECU shutdown pin. You'll want to leave all of the other 5 pins alone.

The exhaust ECU only has the option of disconnecting, grounding, or applying +5v or +12v to that pin. One of those options will signal "all is well" and another option from that list will have to signal "shut down this bank of cylinders."

Obviously you would want to mimick the "all is well" signal from the Exhaust ECU to the Motronic A/F ECU, which means disconnecting the real signal and inserting a permanent signal of your own. I'd suggest using a voltmeter on a working system to detect the correct "all is well" signal.

Once successful, that would still leave your exhaust ECU functioning so that it could still light up your Slow Down light on your dash if a real problem was detected (wouldn't it be nice to know), but the Motronic wouldn't know to shut down one bank of cylinders (say, just as you were entering a turn where reducing power would throw your car into the wall).

If the driver soon reduced speed but the problem persisted, you'd probably want to give the driver the option of manually signaling the Motronic A/F ECU to go ahead with shutting down one bank (giving the driver a "limp home mode"), just to be safe.

 

Not having seen the 550 exhaust ECU schematic, I would merely hazard a guess that your exhaust ECU wants some resistance measurement from your exhaust temperature thermocouple.

If you "bridge" the two wires together (read: short circuit), then your exhaust ECU is probably seeing a "0" zero resistance value. If you disconnect one or both of those wires, then your xECU probably sees an infinite resistance value.

I'd wager that some value in between 0 and infinite is what your xECU would want to see so that it gave its "all is well" signal to your dash light and A/F ECU.

One way to experiment along this line of thought would be to connect a potentiometer in place of your "bridge." By varying the pots' resistance value (done by simply turning a screw on the pot), you will probably find a level that turns off your dashboard Slow Down light. At that point you can either mount your pot or else replace the pot with a resistor of that value.

NOTE: this entire process would only be safe on a car that does not have cats.

 

Excellent advice, even easier would be to read the resistance across the one good thermocouple.
Thanks

Stephen

 

Even more clever! Good show!

 

Catalyst overheat? Yes, but caused by ignition issues and unburned fuel, not due to a catalyst no longer reducing and oxidizing exhaust gas efficiently.

I've not seen this on other marques either.

Yes, lambda sensor issues will set the CEL, though the causes do not necessarily result in an overheated catalyst, and the car is likely to remain drivable, especially on OBDII vehicles. An extremely rich or lean mixture may not cause a lambda error, especially on OBDI.

I had a catalyst meltdown on a Honda years ago when the igniter failed and the car was in gear slowing, so the injectors were still firing, no spark, no power, and fuel burned in the catalytic converter and vaporized the guts... though no fire.

Ferrari uses this system as a fail safe, directly measuring the catalyst temperature (and yes, one can intercept the signal and monitor temperature with a gauge). The ECU does not monitor spark plugs firing in OBDI (I have an brand new F50 meltdown story to tell from '96), and I've got to find my Bosch information to see how OBDII monitors misfires, so other sensors will not yield the same information.

Typical genuine catalyst overheat will be caused by rich conditions or no spark, sending raw fuel into the catalyst. Running a Ferrari flat out, in gear, when an ignition failure occurs is enough time for the meltdown to occur. Unfortunately the number of failures of the monitoring system itself far outweighs the number of actual catalyst overheats.... So it does provide a benefit, and if the system was more robust, we'd not have this thread, and be tempted to retrofit to other cars, rather than disable it on our Ferraris.

Best regards,

Rob

 

I agree there is a better way to implement this system. Unfortunately everything comes down to cost/benefit, and at the time Bosch/Marelli/Ferrari thought it was good enough. I bet in hindsight after paying out warranty claims they may feel differently now. Plus for older cars out of warranty, there's little motivation to correct the issue.

Best,

Rob

 

But why go through all that when Ernie and Vern say you can just disconnect the Exhaust ECU altogether if you aren't using catalytic converters. If the exhaust gets too hot without a cat installed then a regular engine management system should kick in. If you have catalytic converters installed I can see why you might want to go the route to disable the engine shut down but keep the warning light / sensor.
BT

 

The system does work for cars with cats, providing a very real safety margin. 348's with cats should leave this system intact.

I agree that maybe, maybe a few experts might consider self-controlling the ECU signal that shuts down a bank of cylinders (it's just one wire), but the Slow Down warning light should be left on for all cars with cats, experts or not.

 

Let me know if you get a resistance value or a voltage. Thermocouples can actually generate voltage under high heat, so that would be another way for Ferrari engineers to monitor temperature.

Those two wires should either vary resistance with heat or vary voltage with heat...that's all that a thermocouple can realistically do (change resistance or voltage).