Simple 2.7 slow down ECU replacement - only for no cats

Just buy Goth's box. It works.

 

Thanks, Skipp, but I only need a temporary solution, around 8~12 months, until I fit cats at my next major (along with my recently purchased Goth bypass valve ).

Cheers

 

I'd still do Goths box just to be done with the whole issue. Small price to pay to not have to think about it ever again !

 

I'll put it on my very long "to do" list, Skipp ))) The Goth cat and no cat TCUs seem to be an ideal solution (better materials... very close to original... and cheaper)

Cheers,

 

Quick question to the original poster "WBT"...

Does the "X" in your diagram correspond to an unused slot in the plug? The 5.2 diagrams show an unused slot (confirmed on the real car), but the wiring diagrams for the 2.7 show all slots being used (4 wires).

Thanks,

 

Here's a "wireless" version of wbt's simple non-cat TCU simulator. Not yet tested, but should work as described by wbt.

Sorry for the blurry photos...

Requirements:

As above.... a couple of 4-way automotive male connector kits, 1200 ohm/500mW resistors, small type 2.5volt/500mW zeners (see photo), crimpers, soldering iron, resin cored solder, pin crimpers, wire cutters and needle nose pliers (or Leatherman tool). A wedge type tip on the soldering iron may offer better heat transfer to wires during soldering. Also, if required, black sealant for waterproofing. My local electronics store didn't have any 4-way connector kits or diodes, so I ordered them online. I bought half a dozen kits, just in case I didn't get my first versions correct.

Diode:
Position the diode so that the cathode (black ring) is not on the pointy end of the connector pin. Fold over the wire lead on the anode side and trim, so that
1) the centre crimp area will crimp two bits of wire.
2) the diode sits in the rear crimping area.
(See "1" in the photo and graphic in next post).
Slip the yellow rubber grommet over the diode. Crimp the wires firmly and gently crimp the diode/grommet so as not to damage the diode.
(see "2" in the photo). Don't put the diode too close to the wire crimping area (it might damage the diode and make fitting the yellow grommet difficult).

Resistor
Repeat the procedure for the resistor (it has no polarity, so it doesn't matter which end goes towards the pointy end of the pin).

Figure out which slots in the 4-way connector the resistor and diode go into. The resistor and diode go into the middle slots. The female plug (harness side) has only 3 wires on it (at least on the 5.2 car). i.e. one of the outer slots of the 4-way connector is missing a wire. Figure out which slot this corresponds to on the male plug (ie. the TCU simulator plug we are constructing). The resistor is closest to this no wire slot.
Figure out which way to bend the wire ends to form a bridge between the resistor and the diode (the diagram in the next message may help). You will have to Pre-tin/Solder the area of the wires to be soldered to make it easier to solder the two ends together. Before inserting the pins, melt an indentation in the plastic between the two middle slots in the connector so that the wire bridge will lie inside the confines of the connector (and perhaps even allow some sealant to cover the wire). Trim the ends off the wires (see "3" in photo). If you leave the ends of the wires on during soldering, it will help you to position the soldered surfaces together. Trim the wires after soldering.

Insert the pins into the connector, double checking you have the right holes. You may need to use some needlenose pliers or a Leatherman to carefully assist pulling the pins into position (It's difficult to push the pins into position. Pull until you feel a click. See "4" in the photo for the desired result. Fit the 4-way connector kit's red plastic insert into the connector (it helps keep the pins in the correct position).


Regarding which way up the pins go in the connector... The trapezoidal hump on the pin does not go on the (external) clip side of the connector.

If required, apply sealant to the rear of the connector for waterproofing. If your connector kits include female plugs, you could seal the ends of those and fit them to your old TCUs to protect the exposed pins.

The job is a bit fiddly.... Practice makes perfect

Cheers
Ian
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Here's a graphic to help with construction...

Downloadable gif


Note that the colour bands on the resistor may vary according to what colour code is used.
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BRILLIANT Ian!!!

Thanks for taking the time to do, and share this!

 

Can't take any credit for this one... You're the brains... I just added the "beauty" )))

 

Hi Ian. Would you be able to sell me two of these to fool the TCUs? And send to Norway? I have a friend with a de-catted 550 who has the SLOW DOWN continiously on... quite annoying.

Erik

 

Erik... I sent a PM

 

Hi,
I’m just putting the final touches to my P4 replica with F355 Motronic 2.7 ecus.
On checking the Ecu flash codes I keep getting those associated with the CCU’s.
The exhaust has no cat’s so I looked to replace the CCUs with a fixed voltage input to the ecu’s via a simple potential divider.
Searching to see if this had occurred to anybody else I came across your better solution using a Zener diode.
Looking at your diagram and the workshop manual wiring diagrams I’m a bit confused I hope you may be good enough to help me.

Looking at the 4-pin connector I think the 12v supply is ‘A’ or ‘1’ with the Violet or Orange wire.
The earth is pin ‘B’ or ‘2’ with the Black wire.
The signal is pin ‘C’ to engine ecu pin 44 with the Violet/White wire. 0.5v

My confusion is with the pin ‘D’ with the Pink/Black wire that seems to go to the engine ecu pin 11.
Do you know the purpose of this wire?

Other use of Motronic 2.7 shows pin 11 to be a knock sensor input and I’m at a loss to find any further information.

Another query is around the diagnostic plug with K G L markings where I think the ‘G’ black wire is earth.
The ‘L’ grey/red wire goes to engine ecu pin 13, this when earthed initiates the flash codes on the CEl.
The ‘K’ blue/violet wire that connects to engine ecu pin 55 presumably carries a data stream to a scanner.
Is it possible to retrieve data from this wire without having to own a Ferrari franchise?
If so, is there a diy solution?
Thank you for your time,
Steve Bradford.

 

There is another message thread on the forum discussing this 4th wire. I can't find it at the moment. Since wbt (the designer of the zener solution) has tried the plug successfully on his 2.7, you probably won't need to worry about that fourth wire. By the way, wbt is associated with the "Technistrada" (New Zealand) company which now produces aftermarket thermocouples, thermocouple ECUs and these no-cat dummy plugs at relatively low costs.

If you have the 355 workshop manual, it has the procedure for checking for codes using the pushbuttons near the Motronic ECUs on USA cars. If you don't have the button, it looks like it simply shorts out the G and L lines when pushed. Perhaps you can add your own pushbutton. The USA cars also have an earth on ECU pin 39. I'm not sure if this is associated with the self-diagnostics.

The parts manual shows the pushbutton (in the inset). Items 49 and 48

https://www.ricambiamerica.com/car-diagrams/ferrari/v6-v8/355-group/f355-m2-7-1995/injection-device-ignition.html

Here's an extract from the manual:

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Wow... Sounds like a very cool project.

 

Hi Qavion,
Thank you for your reply and earlier posts very interesting.

I came across Technistrada via google and had I kept the cats I see this would have been a good solution.
Years ago on FerrariChat I remember seeing a circuit that was a pair of resistors as a potential divider with the load resistance set by a Zener diode and smoothing capacitors, I liked it but as I had no codes at the time I just saved it on an iPad but at some time must have inadvertently deleted it.

Looking again I found the simpler solution by bwt and liked it. Stupidly I didn’t realise there was a second page to the thread where today I found your elegant packaging. My resistors and Zener arrived today but I’ll wait now for connectors to copy your solution. So thank you.

I had to make my own loom for the car by studying the workshop manual diagrams and placed push buttons close to the ecu’s. Initially I had codes and progressively cleared them but missed the convenience of scanners like Snap-On’s souls. Seeing the K wire made me think there may be a data stream available, easier than back pinning with a scope to get the values.

I’ve attached photos of the car as it is now after six years of work, I keep on finding more things to do, recently air-con, fire extinguisher system and reversing/dash cameras.
Hope you like them and thank you again,
Steve.

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Now that's what I call a Ferrari !.. and by the looks of things, road registered, too.

Technistrada also make the resistor/diode (no-cat) solution based on my "elegant packaging" as you call it.

https://technistrada.com/355-360-456-550-575-f50-enzo/5-dummy-load-sdl-bypass.html

... but it looks like you have more than enough abilities to make your own.

Thanks for the pics! Quite spectacular.

 

Hi Ian,
My connectors arrived today so I followed your example, built them and plugged them into the car so very pleased, thanks again.
But I was interested to see what was actually happening voltage wise.

Disappointingly I measured 2.02volts going back to the ecu, this is short of the 2.5volt that was aimed for initially.
It was 50 years plus ago I learnt ohms law so I hope it still applies.
I measured the open circuit voltage output from the ecu at 5volts.
Then measured the voltage at the junction between the 1.2k resistor and the 2.4 volt Zener diode at 1.67volts connected back up.
So the current 2.02-1.67volts divided by 1.2kohms was 0.29mA.
The internal resistance ‘R’ of the 5volt source is 5-2.02volts divided by 0.29mA is 10276ohms or 10kohms rounded down.

With the 10kohms calculated and aiming for 0.25mA current draw and knowing the Zener is holding around 1.67v at close to this current I calculated
a resistance needed to hold 2.5volts at 2.5-1.67 divided by 0.00025A at 3.3kohms, by luck a preferred value of resistance.

So for my car a resistor of 3.3kohms is required to keep the input to pin 44 at 2.5v.

2.02 volts is probably ok so long as the ecu doesn’t think the exhaust temp to low, I don’t know if this is the case.
I think this simplified two component thermocouple signal simulator just uses the reverse biased Zener diode low current impedance as a resistance in a potential divider In series with the resistor and not using its Zener property to hold a voltage, nor is the resistor being used as a current limiter as the high 10kohms internal resistance of the 5v source limits the short circuit current to ( 5v divided by 10kohms ) 0.5mA safe enough.

So what have I learnt?
Well I think if I had just put a 10kohms resister in between the signal to pin44 and earth this would have split the 5volts in half holding the signal at the desired 2.5volts and the current at 0.25mA. Very simple: just one resistor.
More importantly the 8p ( 10cents ) I paid for the Zener could have gone towards the fund for the next Ferrari, I am being facetious.
l hope I’ve not bored you to much.
Steve.

p.s.
I saw on e-bay exhaust temperature gauges and thermocouples for less then £20 ( $25 ), see below, the electronics for mV to volt conditioning must be inside.
Perhaps removing it would provide a cheap basis for a replacement CCU for those who need to retain their cats.

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Steve, you'd have to ask wbt for the logic behind the zener. It's been quite a few decades since I studied this stuff. I recall resistor heat is a factor in some applications (albeit at higher currents).

Anyway, if wbt is now selling these, I'm sure he's tested them throroughly.

 

You were unnecessarily disappointed. Zener diodes do not hold their exact Zener voltage (Vz) in all conditions, as you can see from the Zener diode (2.7 volt Zener example) typical characteristic curve shown below. The diode in this example holds 2.7 volt at 5 mA current flowing through it but, if this current is smaller, the Zener voltage will be lower (and higher if the current is higher). In the case of the ECU pin 44, the 5 V bias voltage on it (generated internally by the ECU) has probably well limited current (1-2 mA, I guess) which causes the Zener voltage to be below declared 2.5 volts. And there is nothing to worry about exhaust temp signal simulation - you don't need to have exactly 2.5 volts. You just need to have it somewhere below the SDL "flashing voltage" which is 3.75 volt so 1.5, 2, 2.5, 3, 3.5 simulated volts will be fine. I don't think the ECU bothers about the exhaust being "too cold", as long as the simulated voltage is more than 0.5 V which is the base voltage of the SDECU (the exhaust black box) at ignition switch "on" and remains at this value even when the engine has fully warmed up while kept at idle all the time from the cold engine start (the exhaust does not heat-up significantly at idle). To get the SDECU voltage start rising above 0.5 V (more than 5 mV Thermocouple output), you have to seriously rev the engine to heat the exhaust up higher. Only when driving and pushing the engine harder, when the exhaust gets seriously hot, will the Thermocouple voltage go to the ranges of some 15-25 mV (1.5 - 2.5 volts SDECU output).
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I don't see much point in having a Zener diode in the SDECU simulated voltage device. The 5V bias on pin 44, having high internal resistance (small mA available), is easily brought down by a simple load on it. I think just a suitable resistor, of value as determined by some trials, instead of Resistor-Zener would achieve the same thing. After all, the Zener here acts just like another load (another resistor).
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In the case when the SDECU output is brought to pin 44, its voltage will "override" the 5V bias (since the SDECU output has much more milliamps available) so, whatever is the SDECU output voltage, it will also be on the pin 44 (perhaps a minute amount higher because it "fights" the weak 5V bias).

 

Hi,
Thank you for all the replies, many interesting points of interest raised.
I’m happy that my ecus, with the signal simulation, will not now signal slowdown or shut down the engine down.

I think what concerns me now is the loss of the important warning system that the slowdown system presents.
I believe the rationale for the system was that high exhaust temperatures may manifest as the result an engine malfunction.
So the system not only protects the cats from melting / burning but warns of an underlying problem.
Likely problems I believe may be coil packs, injectors, loose connections, ht leads etc., anything that promotes mis-fire.
The net result being combustion in the exhaust system of unburnt mixture and resultant high temperature.
Given that each bank is independent it is possible that anything that causes a mis-fire may be not be immediately detected while driving.
And even if it is detected, it may not be immediately apparent even which bank is troubled if no check engine light shows.

I’m fortunate in not having to run with cats so happy with the simulated signal for exhaust gas temperatures.
Ideally working CCUs would retain the warning system but unfortunately my pension in 20 odd years old now and I’m always attracted to work-around solutions.
So what I have done is install two narrow band air / fuel ratio meters.
They were cheap, less the £25 the pair, and occupy a formerly blank area of dashboard. They are digital and only illuminate when running showing matt black like the dashboard while at rest so don’t look out of place.
They switch rich / lean quickly while the ecu fuel control is in closed loop mode and everything is ok.
If in the event of a mis-function the offending bank will lose the closed loop control mode and will display fully rich or lean on the meter before any lasting damage is done.
When I fabricated the two bunches of bananas for my exhaust system I added two extra O2 sensor collars with blank bungs so if I need to investigate any
on-going fueling problems I can use an Innovate wide-band oxygen measuring system on the move.
Thank you again for responding,
Steve.