Simple 2.7 slow down ECU replacement - only for no cats

So I have been chasing slow down lights for a while on my 2.7 355 which is frustrating due to the fact I have had the cats removed. I do not wish to spring for 2 new CCU's and possibly new thermocouples to fix a problem that doesn't actually exist. I have designed a simple circuit that replaces the cat control unit and sends a constant signal to the motronic unit. Results so far is I have had no pesky slow down lights and bank shutdowns.

I should note - DO NOT USE THIS SETUP if you still have cats. The thermocouples are there for a reason!

The vescovini CCU simply creates a linear 0.5 to 5 volt signal for the main motronic ECU depending on cat temperature. Normal range seems to be between about 0.5 and 3.5v, over 3.5v the light flashes, and nearer 4v it stays on solid and shuts down 1 bank of cylinders. So, a 2.5v signal should do nicely to fool the ECU. There are various threads around that detail the CCU operation in more detail so I'm not going to get into that too much here. Suffice to say 2.5v has been tested on my car and works perfectly.

The circuit is simple - a 2.5v zener diode in series with a 1200 ohm resistor to limit current to a theoretical less than 10mA to protect the circuitry (both motronic and the zener). The motronic has a weak internal pull up to 5v on the signal wire, so this circuit requires no power supply or connection to the 12v wire (pin 1). Pin 4 is unused on motronic 2.7 as far as I can trace with a scope during normal operation. So this circuit only requires 2 wires to connect to the motronic ECU. The 4 way connector is easily sourced on ebay (I got a 5 pack for a few dollars from a seller in China) with a standard crimping tool this creates a perfect waterproof fit to the existing CCU wiring loom.

All up 2 CCU replacement modules can be created for just a few dollars and the slow down light issue is permanently fixed. Win.

I haven't tested this circuit on a 5.2 car, but in theory it should work the same. If motronic has a weak pull up to 5v on the signal line then it will work.
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Circuit soldered up and potted with epoxy in a PVC plumbing end cap. Wires terminated into the correct size connector which fits the ferrari CCU wiring loom perfectly.

I got this connector on ebay "Waterproof Car Auto 4 Pin Way Sealed Electrical Wire Connector Plug NEW" Electrical Wire Connector Plug Car Auto Set 4 Pin Way Sealed Waterproof 2 pcs SE | eBay

You may want to silicone up the unused wiring holes for total waterproofing.
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2 units fitted to the car. I have just cable tied them to the engine side main loom so they don't even need to be disconnected when doing the major service. The weight and size is minimal so I do not expect vibration to be an issue.

Engine running, no slow down lights!

Many dollars saved which can go nicely towards the Christmas beer fund
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Nice!!

 

The type of first hand technical knowledge this site so needs.

Great work.

 

5.2 motronics carry a 5v bias voltage on the signal line as well so this should work identically.

Nice work!

I know someone with a 5.2 who deleted the cats and has a persistent sdl associated with the bypass valve TC. He has been waiting on Goths bypass box to try just this at that location.

 

Very nicely done. And you gotta love a guy who has a Christmas beer fund.

 

Great work!

 

Outstanding!

Thanks for sharing.

 

Wot??? No Cavallino Rampante on the plumbing end cap??? )))

 

You made me think about this thread http://www.ferrarichat.com/forum/348-355-sponsored-bradan/378429-thermocouples-slow-down-lights-related-cel%92s-how-conquer-them.html

 

This is great! This takes what I started years ago with a 1.5V battery to the next level. I never liked the idea of Ferrari trying to idiot proof the car with the SDECU dialing back the motronic when temps got hot. I would rather have and indicator since I still have a brain. I think you can use your method with cats IF there is another way to monitor and alert the driver. For Example, I used EGT when I went manual on the SDECU's. I get more information about car running from EGT too. So EGT with an Oil style idiot light would be fine IMO. Otherwise I have high hopes for Goths SDECU's sold through Ricambi. Good job!



For those electrically challenged can you go through what made you look and how you figured out the 5v pull and what does a zener do? Always want to learn more...

 

That's me !

Should this keep the CE light off for the code 1448 Bypass issue ? Goth did not send his bypass version TCU to ricambi unfortunately. Not sure what's up with that.

Still hoping for the answer. Car loves being "unleashed"!

 

Skipp - I would try this for your bypass location.

 

Thanks. I'll see if I can get one made and report back.

On a brighter note, I own property in a state that doesn't require inspections. Guess where the car is headed to........

 

It might be fun to take the present circuit to fool the SDECU and then attach the thermocouples to a meter so we could just see the temps on a dial in the cabin.

 

That's what I did. I think it is in my original thread. All the parts were from aircraft spruce

 

WBT. Check your PM box please.

 

They are now completed by Gothspeed and scheduled for shipment to Ricambi. We'll get there, neighbor!

 

Thanks Daniel. Please let me know when they arrive.

Skipp

 

I immediately thought of that thread as well. It shows how to build your own cat ecu (dead simple) and also shows how to fix most cat ecu issues by resoldering the connector pins.

 

All the discussion seems to be about SDL. Will the same strategies solve CE lights ?

 

SKipp, the bypass location SDECU activates a CEL (your issue) and not a SDL (cat locations).

IN your case its about sending the Motronics a 'happy" voltage that doesn't trigger the CEL. As we don't know what voltage your BP SDECU is sending out right now, I am unsure what is creating the CEL and why.

In Jevs thread above he used .5V at the BP location and all was fine. That would be where I would start. I can assume that Goth's piece outputs something similar.

 

I'll buy Goths and report back. Thanks to everyone who has helped me.

 

Gents, has anyone tried this on a 5.2 yet? I made a few of these simple plugs and am thinking about fitting them (haven't built up the nerve yet)

I even managed to fit the diode and resistor into the plug (no external wiring).

Cheers
Ian