Cat Control Unit

More than just monitoring cat temperature, these cars have the TWC (three way cat) system with considerable inputs to the CCU to keep HC, CO, and NOx reduced and air-fuel ratio near stoichiometric ideal.

I've seen many threads pertaining to the protective diode going bad and on the 328 it's plugin replaceable. You may be jumping in the deep end for a simple problem. What makes you know that your CCU is bad?

And you don't need to reverse engineer the CCU, it's open source, in most OMs (page 73 of 535-88). The ONLY chip is the thermocouple temp IC. Everything else are relays.

 

The cat control unit ONLY OPERATES THE SLOW DOWN LIGHT........period.....exclamation point.


A three way cat is a stand alone unit. It has no monitoring or communication with any other part or system.

I am unsure where that info comes from but it cannot be more wrong.

 

There are reliability reasons for epoxy coating in a harsh environment.

 

Thing to remember is that it's not a "cat CONTROL unit".

It's a Catalyst temperature MONITORING unit.

It's entire function is to measure/quantify the temperature of the catalyst and it's exhaust
gases and warn the user if they are too high.

Jim

 

It may be a signal to the injection ECU that "confirms" that the cat (and, therefore, the O2 sensor) is up to some minimum temperature before trying to operate in a closed-loop fashion. It only seems to be used on the US K-Jet with Lambda models (i.e., that wire is not connected to anything on the US carb, US K-Jet without Lambda, and US KE-Jet with Lambda models that have cats -- so on those models, the CCU, for sure, only runs the warning light and can't have any effect on the engine's operation).

Since you indicate that your CCU is already having some weird behavior, it may not be working anyway , but things you could try IMO:

1. Measure the voltage (VDC) on this wire (while still plugged in) relative to ground, at idle: A) immediately after cold start-up, and B) at warm idle -- if different, that would be a clue, and

2. Measure the voltage on the O2 sensor single wire (while still plugged in) at warm idle relative to ground -- if all is working correctly (and it's really running closed-loop), the voltage should be wandering slowly between 0.1 VDC and 0.9 VDC. Then unplug the CCU and see if this voltage from the O2 sensor just goes to a relatively fixed value (i.e., running open loop). If you unplug the O2 sensor single wire from the injection ECU (while still measuring the voltage coming from it), this will also force the system into open-loop operation so it would give you an open-loop comparison value for when operating with the O2 sensor plugged in and the CCU unplugged.

Just some thoughts (and, if someone else with a US K-Jet with Lambda system could also make these measurements, I would be grateful)...

 

The CCU has a thermocouple from the cat. This is it's input to let it knowhow hot the cat. is.
Its only output is the light on the dash.

The oxygen sensor is one of the inputs to the Lambda ECU to control the fuel mixture.

The two systems, have no connections whatsoever. You can remove the CCU from the car and it will have no effect on the way the car runs.

Brian Brown
Patrick Ottis Co.

 

Except on the US K-Jet with Lambda models -- have you confirmed that the connection between the CCU and the injection ECU on those models is superfulous and do you have measurements?

 

Steve,
I'm away from home at the moment but can get to it in the latter part of next week unless someone measures it first. My system seems to be working properly - no warnings since I replaced O2 sensor last year.

 

Boy am I disappointed - opened this thread in eager anticipation and what a sudden letdown. I was really hoping for some reviews before shelling out for one of these:
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Don't waste your money. Everyone knows you cannot control a cat. They might let you think so once in a while but it just ain't so.

 

Thanks. I figured it was too good to be true when I read the fine print about working through the power of positive thinking. Oh well - back to the tried and true method - the spray bottle!

 

Mea culpa, sorry to confuse you Futureman. I was mixing references to CCU (catalytic converter unit) and ECU (everything on the plate)...the ECU is well documented, not the CCU.

The CCU not only goes to the slow down lights(1,2) the other connections (3,4) are ground and +12v although they appear going to fuel injection ecu circuitry.
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There are 6 terminals on the Cat Control Unit:
2 for the thermocouple (basically a variable resistor);
2 for power to the detector circuit (probably for biasing an op amp or something that interrogates the thermocouple resistance).
2 for the SLOW DOWN light circuit.

The thermocouple attaches with small screws. The remaining are within the connector. The wiring is such that disconnecting the connector will prevent the SLOW DOWN light from turning on while still allowing operating voltage to be present throughout the entire fuel control plate, including the diode and the relays. Thus no interaction occurs between the CCU and the fuel injection system.

BTW, if you disable the CCU circuit and keep your cat installed, stop your car and turn the engine off if you sense a power loss (loss of spark) or smell rotten eggs (fuel burning in the cat)! This will start a fire.

 

Can't agree with your description of the 6 terminal connections:
2 for the thermocouple = OK
2 for the power to the detector circuit = OK
2 for the SLOW DOWN light = not OK. Only one terminal is connected to the slowdown bulb filament (the other side of the slowdown bulb filament has +12V always supplied to it, and when the CCU "thinks" it needs to turn the light "on", it puts this line to ground).

The remaining terminal is the "mystery" terminal. On the US carb, US K-Jet without Lambda, and US KE-Jet with Lambda models, this terminal is not used at all. On the US K-Jet with Lambda, this terminal is connected to the same relay that disables the cold start injector when the thottle idle microswitch is closed, and it continues on to the injection ECU. It may be only doing some minor "tweak" to the injection ECU's behavior (so removing it has no significant effect, like on the other models), but would sure like to have some real facts.

 

The circuit looks like a multi op-amp network with biasing circuits: the 14 pin chip should be the op-amps and the 8-pin chip a voltage reference (6.8-7Vdc? seems right for 80's technology)...nice pic BTW.

 

Steve, I'll review again. One terminal goes to the diode and the other to the thermo-time switch and electrovalve. I know the diode is there to protect the O2 sensor. I will reply later (off to a business trip). Rob

 

Yes, I believe you are describing the US 328 connections; whereas, I (wrongly) only described the US '84-'85 US 308QV connections. So the two system are soewhat different, but, in both cases (both being K-Jet with Lambda), there is an eventual connection to the injection ECU -- so that's what I'd like to know about (i.e., does the "mystery" terminal cause a change on the terminal at the injection ECU, and what does the injection ECU do in response to that signal, if anything).

 

I have reviewed enough to make a call here. I still need to review the K-Jetronic manual. The F-car manuals SUCK!!!!!

Here's what I have for the CCU connections:

1) CCU terminal 1 provides 12Vdc via F21 (7.5Amps for aux ckts) and relay U;

2) CCU terminal 2 activates the SLOW DOWN light (121);

3) CCU terminal 3 is GND;

4) CCU terminal 4 is the "mystery" terminal and is connected to the anode of diode 166 and to the ECU (Steve was correct);

5) Thermocouple (160) is attached to the CCU with screws.

Terminals 1-4 are part of the connector to the CCU. The diode itself operates in series with the throttle switch (148) which also sends a GND signal to the ECU when triggered.

The SLOW DOWN light has 2 modes, flashing for first high temp condition at 900C and steady at 940C. I believe both of these functionalities are evaluated by the circuitry in the CCU and are related to the accuracy of the thermocouple alone; thus no other inputs are made for determining cat temperature.

Thus the only remaining concern is why terminal 4 connects to the diode and ECU. I will need to review the K-Jetrinic manual to find out (later...I have a job, you know)

For now, if the cat is to be removed, I would only disconnect the thermocouple (since it generates a voltage when temp is high, then disconnecting should equate to a low temp, and thus not a false positive; this can be verified by disconnecting the thermocouple and checking that the SLOW DOWN light remains off...check on this though..I could be wrong; if I am wrong, then you will have to remove the bulb or be annoyed by the light; let us know when you do this please).

I would keep the CCU connector connected until we better understand if the terminal 4 connection means anything. My initial guess is that the connection is not used. From my recollection (i.e., couldn't find in the manuals...must have been an F-chat comment), the diode is present to minimize transiants applied to the O2 sensor. The only way I can see that the diode is forward biased is if the throttle switch is on and the ECU or CCU has a positive signal on the anode. I see no functionality for the CCU to send or receive a voltage from terminal 4 (yet). The ECU, of course associates with the O2 sensor.

Rob