Ferrari F355 2.7 motronic cat ECU amplifier pin out question

The 355 2.7 motronic ECU needs to see a 0-5 volt signal from the Cat ECU (amplifier) to determine the cat over temp condition ,I’m trying to find the signal wire 0-5v that goes to the Motronic ECU but when I probe the 4 pin plug I get on pin one+12 v…..pin two neg ground…(normal supply to cat ecu)but pin 3 & 4 are +5V coming FROM the ECU ? I think pin 3 is the signal wire but I need to put 0-5v up this wire to the ECU from an amplifier but this pin is supplying 5v can someone tell the pin outs for these wires ? I’m beginning to think that pin 3 & 4 Need to have a resistance between them rather than a 0-5v input in which case my amplifiers won’t work with this application any help is much appreciated. Fabio

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Second pin from the left is the signal that goes to the ECU. That needs to be a solid signal between 0 and 5V. Don't worry about whatever voltage level that is from the ECU when the module is not connected. That level is not valid.

 

That’s great thank you for your time & quick reply , so I only need to use 3 pins for power and temp feedback do you know what the first pin on the left in the picture is used for ? Or is it an Auxiliary spare & not used for anything ?

 

It appears to be an earth for the signal (earth inside the ECU). Some sensors have their own earth network.

On the Left Bank, that wire is also hooked up with the left throttle position sensor.

Wiring diagram for left bank here:

https://www.dropbox.com/t/BRSXZVcWMIZnR3TU

Right bank here:

https://www.dropbox.com/t/yMhemTLmzKy4yTOK

Links expire in 6 days.

What are you trying to do?

 

Hi Qavion, thanks for helping me again the wire diags are fantastic thank you . I am fitting my own EGT Amplifiers my car started having some issues in that when up to temp and driving fast ish especially on acceleration the right bank 1-4 would cut in and out like a big miss and the EML 1-4 would flash ( sometimes both EML’s but NO slow down lamp) as the engine missed I thought it was the right hand fuel pump relay or pump however sometimes I can drive the 355 and it runs perfectly anyway I went to start the 355 a few days ago to try and find the intermittent fault (Don’t we all hate intermittent faults!) when I started the car it was only running on one bank 5-8 so I shut it down I got my relay jumper and jumped the cyl bank 1-4 pump relay with IGN on and the pump worked fine so that lead me to thinking that it’s either power being lost to the injections (slow down condition cat ecu) or no spark (coil pack or ign module) the coils are new as I replaced them last time I had the engine out for its major service the original coils were ok but old.Anyway I swapped over the ignition modules started the car no difference put the original coil back on no difference then I read the fault codes and again got 4444 no faults recorded. I then did an ECU rest and started the car which again was running only on bank 5-8 but this time the 1-4 EML was on WITH the slow down lamp which pointed me to the cat ecu Amplifier or thermocouple, the thermocouple tested ok then I removed the bank 1-4 cat ecu amplifier I found that this was the old type with black resin potting the other side is the green potting so I think I’ve found the problem I haven’t swapped the cat ecu,s over yet to see if the problem swaps sides but this is next on my list but I’m 90% sure this is the problem. I know that after market cat ecu amplifiers are available but being an enthusiastic design engineer I like to design and make parts for my vehicles it’s part of the ownership experience I enjoy . I have already designed and made a few parts for my 355 with more in the pipeline ,it is so nice to be a member of this forum with like minded people who have a large knowledge base and have always helped me with problems I also try to help where I can. I have learnt a great deal about the 355 from this forum thanks to all

 

Cool.

I don't know if you're aware, but you can make a dummy CAT ECU to help you faultfind problems (on a temporary basis only).

https://www.ferrarichat.com/forum/threads/simple-2-7-slow-down-ecu-replacement-only-for-no-cats.538719/#post-145063021

 

Great stuff a useful diagnostic tool thanks for the link

 

Your 2 measured 5v pins are due to the Motronic internal pull up resistors to the 5v rail and you're measuring open circuit. Resistance not documented but I calculate it to be about 100k. Be careful, these pins are very sensitive to any out of bounds voltage.

 

very interesting I really liked your article on the cat ECU diagnostic device that you designed and made it was a great help well done to limit the 0-5 volt current going over the 5 volt/current max up the signal wire I was going to use the 1200 ohm resistor in line as you have done in your design other options are a shunt or linear regulator as a over current protection device what do you think ? I’m good with electronics but I’m by no means an expert . I learn form the experts like you and asking questions I hope you don’t mind