Adding O2 to an early Euro Mondial t/348 with Motronic 2.5-application to stoogeness!

This document can be used to:
1) Add closed loop to stock non cat Motronic 2.5 cars (Euro 1989-1993)
2) Properly tune CO screws to your car's particulars
3) Add CELs to Motronic 2.5
I have all the schematics for the F119 engine in 348 and Mondial t's, and will be happy to share them with anyone (best to PM me)

So I did it. I see a lot of people de-catting on the US side of the border. We in Europe had about 2-3 years of production cars going to market without catalysts. In this process there is a whole circuit being deleted from the cars, the O2 sensors and the Vescovini manufactured thermocouples.

The mixture at idle and partial throttle is controlled by the MAF CO screw, and the setting is somewhat elusive. 383 Ohms has been pitched as a factury standard, but I can confirm after a LOT of research, including speaking to a few Ferrari techs from Maranello, that the CO screw is set according to the CO and hydrocarbon (HC) in the exhaust, and that this varies over th life-cycle of the car.

Thinking of this, I concluded that moving to closed loop would ensure the car can self adjust during its life-cycle. Clearly, this is valid otherwise why bother with the ECU reset etc?.

I started with a well running car, with some exhaust burbling and popping at idle and some inbalance and vibrations from 1000 to 3000 RPMs. The MAFs were set to 340 ohms to deliver the CO and HC numbers according to the user's manual.

After closing the loop on the system, the CO screws were set to 430 ohm on the 1-4 bank, and 520 on the 5-8 bank, and the idle is HUMMING with no popping and burbling at idle and smooth revs throughout the RPM range. Now if I put it in 4th at 20 mph and floored it, it just slowly and smoothrly rolls through the RPMs instead of juddering and almost stalling before.

If you care, this is what I did...

I had O2 bolts (17mm) welded on my straight pipes and bought universal thimble/Zirconia 3 Wire O2 sensors. Use shrink wrap tubing on all solder joints. Use solder and not bullet/spade connectors. Have a good soldering iron and a good multimeter at hand.
--- Disconnect battery and ECU's
1) (Picture 1/2) wired the following pins in the ECU socket, using Bosch connectors (can be ordered by numerous suppliers, and simply click in the empty slots in the ECU connector)
Pin 31 and 10 to Earth (cutting the earth at Pin 1 of the ECU and mering them with shrink tubing as insulation
-Pin 31 tells the ECU this car has O2 sensors and tells it to look for it when the coolant temperature hits 60 deg. C
-Pin 10 is the reference earth for the O2 sensor
Pin 28 to the signal wire (black) on the universal 3-wire O2 sensor (you could use universal 4 wire O2's and wire the earth wire to pin 19 on the ECU) - leaving the O2 sensor signal wire disconnected at the O2 sensor side - will be connected after the CO screw is tuned.
2) wired a spade fuse connector socket to the switched side of the fuel pump power supply relay, so that the O2 sensor heaters are turned on only when the fuel pump is running
wired on of the heater wires into the spade fuse connector and used a 7.5 amp fuse. The other heater wire (white) was connected to a convenient earth position
3) tidied everything up reconnected battery, started engine up and waited till full warm-up (cooling fans kicked in)
4) As the O2 sensors are like mini gas analysers, I "Tuned" the open loop mode CO screws, starting at 340 ohm (set to this after a dyno test showed 383 was too high in the CO output) ending at 520 ohm for 5-8 and 430 for 1-4:
-- Some background: O2 sensors generate around 465 mV at lambda 1 (AFR 14.7) but the curve is very steep between 800 (rich side) and 100 (lean side). This means you can put your multimeter on a 1V scale on the signal wire and find that you can turn the CO screw quite a lot (either on the rich or lean side depending on where you are) with very little impact on the O2 sensor voltage, but there comes a point where a tiny change will cause a massive jump or drop (from rich to lean or the opposite depending on where you start from). This point is where you are on the stoichiometry line. Go to where it drops to lean (less than 100 mV) then move towards rich just after it pops up to 8-900 mV. Repeat for each bank - This will ensure you will not lean out if your O2 sensors fail -- This IS the ideal MAF setting for your engine's particular condition!. Turn the engine off, pull the MAF connectors and measure your CO setting across pin 1 and 6 and record it for later reference.
5) connected the O2 sensors to the signal wire wired into pin 28 on the ECU.
6) connecting pin 22 of the ECU to a bulb earthed on the ECU effectively gives you the "Check engine Light" that is disabled on ALL Motronic 2.5 based vehicles.

The car is now enabled for closed loop!

You'll notice a reduction in the pungency of the exhaust smell, a much smoother idle, a much smoother engine operation at lower RPMs and as I have noticed about 10-15% reduction of fuel usage. You can also stick on some metallic core cats if you want to really take out the exhaust smell and know that your engine is managed as efficiently as the CAT version of the car. I had a pair of magnaflow 2.25x4x8 in cores welded onto my strainght pipes. These are designed for 6 liter engines and have no overheating problems in the F119 engine application.

Changed the character of the car completely!

Marco
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http://www.autoelectricsupplies.co.uk/product/680

Very quick service and have a lot of other goodies.

The pins I bought were for 1.5 to 2.5 sq mm as I originally intended them for use as the heater plugs. if you want pins for the main Motronic ECU plug, I suggest you use the 0.5-1.0 sq mm female terminals (pn. 051601) instead. These will click into place in the blank terminal holes, either as a replacement for damaged ones (imagine for 20 UK pence / 40 US Cents you can fix an individual pin, saving you several hundreds instead of replacing the whole loom as would normally happen)

The 3 way housing kit, replaces crank position sensors, the 2 way females replace all injector plugs and cam sensors, the 6 way female replaces all MAFs and so on...

Marco