No Cat, No Oxygen sensor.

[mikinoz]

Hey, here is some help.

Your ECU is MK2 Digifant - but there are 2 different Bosch units and a Siemens unit. I had up until recently the same one as you.



You need to run an O2 sensor as the car wants a reading so as I understand the reading will be inifinite currently and reading that it is ultra lean...

1. General Description - 1.4 Digifant II Engine Management System

1.4 Digifant II Engine Management System

The Digifant II engine management system-so called because both fuel injection and ignition are controlled by one integral system-includes fuel injection that is completely electronically controlled. As illustrated in Fig. 1-1, several sensors supply information to the central electronic control unit which then electrically operates the solenoid-type fuel injectors. Fuel is metered to the engine by controlling the amount of time that the injectors are open. All functions, including the amount of fuel injected, are controlled electronically by the control unit.

Fig. 1-1. Main components of electronic Digifant II engine management system.



For more detailed information on the fuel injection functions of the Digifant II system, see 7. Digifant II Fuel Injection. Additional information on the oxygen sensor system and other emission controls is covered in EXHAUST SYSTEM AND EMISSION CONTROLS. The ignition functions of the system, including the knock sensor, are covered in IGNITION.

And this is the critical detail...

=5. Oxygen Sensor System

The oxygen sensor system provides the fuel injection system with information about combustion efficiency by measuring the oxygen content in the exhaust. The exhaust-mounted oxygen sensor is constructed of ceramic material coated with platinum. One surface is exposed to the exhaust gas, while the other is exposed to atmosphere. The difference in oxygen content between the two surfaces causes a chemical reaction which generates a low-voltage signal (100-1000mv). This signal is monitored by the control unit which, in turn, signals for changes in the air/fuel ratio in the fuel injection system.

Since the oxygen sensor system relies on low-voltage signals, it is very sensitive to contamination or poor connections. Making sure that the electrical contacts are clean and dry may cure system problems easily and preclude the need for time-consuming testing.

Because the oxygen sensor system is different for each fuel injection type, the repair information in this section is organized according to fuel injection type. For help in identifying the fuel injection system, see FUEL SYSTEM-GASOLINE.

Replacement of the oxygen sensor is a scheduled maintenance procedure. The specified replacement interval varies depending on model year. On 1985-1987 models, the sensor's replacement interval is signalled by an indicator light on the instrument panel coming on as a service reminder. After the oxygen sensor is replaced, the mileage counter must be reset. On 1988 and later models with oxygen sensors, the service reminder light has been omitted. See LUBRICATION AND MAINTENANCE for more information on the oxygen sensor replacement interval and the mileage counter resetting procedure.

Send this to your mate who has 20 years experience, the knock sensor diagram from the bentley...

1.2 Knock Sensor System

TCI-h ignition with knock sensor differs from the basic TCI-h system with the addition of an engine knock sensor and knock sensor control unit (Fig. 1-2). With this system, the distributor has no vacuum or centrifugal advance mechanisms. All adjustments to ignition timing are done electronically. The knock sensor system detects pre-ignition or detonation (commonly called knock or ping), and adjusts ignition timing electronically to eliminate it. The system also makes the timing advance adjustments which are necessary at higher engine speeds.

[mikinoz]

Here is a picture of the sensor and the connector on my MK1. (behind the headers, no cat)



The sensor is generic and has been spliced in to the connector before the plug (hard to show).

[mikinoz]

Some manifolds have the connection for the O2 in them, not on the pipe.

Finally, here is how you test the O2 on Digifant and it has a pic of where the connector originates.

5. Oxygen Sensor System - 5.3 Testing Oxygen Sensor System (Digifant II and Digifant I) - Testing Oxygen Sensor Function

Testing Oxygen Sensor Function

This is a sensitive measurement. In the interest of accuracy, the engine must be fully warmed up, with idle speed, ignition timing, and CO content adjusted to specifications. The exhaust system between the engine and the catalytic converter must be free of leaks, the engine coolant temperature sensor should be connected normally, the voltage supply to the oxygen sensor heater must be OK, and all other electrical consumers including air conditioning should be switched off. In addition, test measurements should only be made when the radiator cooling fan is not running.

Run the engine and record a baseline CO measurement. With the engine running, raise the engine oil dipstick slightly. This allows extra air into the closed crankcase ventilation system and, therefore, into the intake manifold. If the oxygen sensor is performing correctly, the CO reading should drop for a few seconds, then return to the original value.

NOTE-

For Digifant I electrical tests see FUEL SYSTEM-GASOLINE.

To check oxygen sensor wiring (Digifant II only):
1. Disconnect the harness connector from the Digifant control unit, as shown in Fig. 5-7.
Fig. 5-7. Digifant control unit and oxygen sensor showing mounting and harness connectors.



2. Using an ohmmeter or a multimeter set to the 20k scale, check continuity between terminals 2 and 13 of the Digifant control unit harness connector. See Fig. 5-8. There should be no continuity. If there is, there is a short to ground in the oxygen sensor wiring.
Fig. 5-8. Digifant control unit harness connector terminal identification.



3. Disconnect the oxygen sensor harness connector. Connect a jumper wire between ground and the green wire (terminal 1) on the harness side of the connector. There should be continuity. If not, there is a break in the oxygen sensor wiring between the harness connectors.

Hope that helps!

[ryana89]

That does help

3. Disconnect the oxygen sensor harness connector. Connect a jumper wire between ground and the green wire (terminal 1) on the harness side of the connector. There should be continuity. If not, there is a break in the oxygen sensor wiring between the harness connectors.

I think that may be the most helpful part.

Is that above piccy stating that terminal 1, 13, 14 and 25 are all individual wires that go to the oxygen sensor?
Because that is what my entire problem is, I have a 4 wire plug that I have no idea which wires are doing what (Ground, signal, heating).

What I still don't understand is that I thought Digifant 2 only ran a 3 wire o2 sensor?

I wouldnt do a kjet conversion as you would be going back a step from efi. Have u scanned the car for any codes btw, that would be a good idea and should bring up any fault codes.

Currently this "EFI" is using 15L+/100k
Unfortunatly Digifant 2 isn't capable of storing fault codes

[mikinoz]

What I still don't understand is that I thought Digifant 2 only ran a 3 wire o2 sensor?

Head to the ECU and follow the cable that should go to the O2 sensor and see if that is what you get to. I am of the opinion digi2 is 3 wire (2 white for heating and a green signal) But you don't know what has been going on. If you trace it and find a 3 pin connector you will be more happy I'd say the 4th pin if there is would be a ground?

KJET is not viable as you need to replace heaps more stuff and this is going to be hard initially, but it will get sorted.

*please remember I am as much a mechanic as a brain surgeon, so take my advice accordingly.

Paging JMAC!!

[ryana89]

Your advice/help is MORE than welcome, its the members on forums like these that have more knowledge and experience than 95% of local automotive techs.

Also I (we) need to keep in mind this car has had the 2E thrown into it and perhaps some wire mods along with it.
If there is another 3wire plug somwhere, then what is the 4 wire plug meant for in the engine bay!

Going to strip everything out and confirm if I've found the right plug or not tomorrow.

[ryana89]

So I was starting to get optomistic towards finding an explanation when I found this in the Bentley manaul... (Note it mentions the 4 pin/wire connector for cars after 1990)



Then I removed the ECU and looked at the connection.....






I thought Digifant was 25pin?.........Ok


I checked the continunuity of the 4 wire plug in my engine bay, to see if they matched to any of the ECU connector pins.

Remember
#1 - Green/Red
#2 - Yellow
#3 - Brown
#4 - White/blue

And here's what I found

#1 Came out on that massive ECU connection (marked green)
#2 came out on the ECU connection too (marked yellow)

Now the fun bit, wires #3 and #4 did not go to the ECU, instead they had continunuity with this plug, that is connected to nothing in my scuttle tray.....
(#3 marked brown, #4 marked white)



The 2 wire plug that is not connected to anything.....



Just when you thought it couldn't get more confusing

[peedman]

LOL yours is digi1 not digi2. I miscounted the pins, #1 is actually the bottom left and 38 is the top right. So the two highlighted pins are #10 and #27 and looking at the chart, it definately corresponds with those wire colours.

So that plug is for CO Potentiometer, and Knock Sensor!

CO Potentiometer:

A Potentiometer is used to adjust the CO mixture. The Potentiometer is located on the intake air duct before the throttle housing. A tamper-proof plug is used to prevent adjustments by non-service personnel.

An air temperature sensor is located within the potentiometer housing. The air temperature sensor is used to calculate air density.

Digifant I Pinout

As for the plug in the scuttle tray i think its for the ambient temperature sender which is why there is continuity there.

[ryana89]

LOL yours is digi1 not digi2.

Can describe how stupid I feel.......But now I can figure this out!!!!

I miscounted the pins

I was hoping so, reading what you said before you edited was a little confusing

This is making sense now!!!

EDIT: That must also mean that it IS capable of storing fault codes if its Digi 1 (correct me if I'm wrong), thing is the plug for figuring out faults is is meant to be under the gearstick boot cover, which it is not there.

[mikinoz]

How do they have the same numbers as mine but not be digi2? I'm sorry if I added confusion.