328 slow down light comes on

Review owner's manual.

It is either an overheating catalytic converter (very dangerous, thus the warning light) or, it can be a failure of the warning system itself. It is very common for the system to malfunction, giving a warning when the cat is not overheating. BUT, since the risk is there, you should investigate further, before continuing to drive the car.

Is the car running well, otherwise, or do you notice a power loss?

 

Oh, yes...that idiot light. Mine has been doing that intermittently...the last 7.5 years! Been checked by a dealer - no problem. The car runs fine. I've tracked mine a few times. No loss of power. Cat is not flaming red. I just don't pay attention anymore.

 

Hmm. If I recall the wiring diagram correctly, the CCU doesn't just run the slow down light. It also enables closed loop operation on the lambda computer, when the cat (exhaust) warms up to operating temp.

But it's been six or seven years since I looked at that circuit.

I suppose somebody ought to scope out a working one and start producing aftermarket reverse-engineered CCUs. The originals are getting old.

 

^^ and they're getting quite expensive, from what little research I've done.

Makes straight/test pipes look better every day.

 

I've been wanting to reverse-engineer the CCU and ECU; there are a couple of recent threads from Futureman on this. If anyone has an 'old-beater' CCU and/or ECU, I would be interested in cutting open so as to generate proper diagrams and be able to rebuild with basic Digi-Key parts.

The CCU is basically an op-amp network with a VR so as to turn on the light if thermocouple reads too high, and causes the light to blink at 900C and be steady at 940C. There is one wire from the CCU to the ECU which we have delegated the "mystery" wire. I like the idea from DGS that the wire is an input to the ECU to tell it the cat has warmed up and is ready for closed loop; but, still no diagrams to prove it.

My circuit was like most, light on without warm engine and all cylinders firing properly; thus I simply removed the light bulb. Basically, if you have a hot engine and you are over-revving it, you should stop that. If you lose engine power because of a misfiring cylinder, then you should stop and troubleshoot before the fire starts!!! I have a Halotron fire extinguisher ready for action...always!

Since emissions requirements are up for me in 2012, I will replace the cat then with the test pipe then.

 

On cars with microswitches to indicate throttle position, the "mystery" wire simply tells the ECU that the throttle is shut down which the ECU treats accordingly. "Mysteries" aren't mysterious when you know the answer.

 

I don't believe you.
I know that terminal 4 of the CCU is indirectly linked to the TMS via a diode, but my guess is the diode is there to dis-associate the TMS ckt from the CCU terminal 4 signal, while both supply a signal to the ECU at the same terminal (see fig 65 in Owner's Manual). Why would the CCU tell the ECU that the throttle is off when the CCU is associated with TWC temperature? From my earlier reading, I belive the TMS tells the ECU when the throttle is fully open (WOT) so that the ECU will enter open loop mode during high acceleration. This idea does lead to the possibility that the CCU line to the ECU sets the ECU into open loop when the TWC is too hot.
You will need to provide an adequate reference for this one, Paul.
Thanks though.
Rob H

 

Way cool if someone can reverse engineer one of the "slow down" light ECU's, as they are very spendy, and seem to give false readings after awhile. My understanding is that my 89 328 is the same one ( 62347000 CONTROL/CAT) used in the Mondial & TR ( they have 2) , and earlier models use a different on that's even more expensive. On the rare occasion that mine comes on, I keep thinking of ordering a new one. Might try cleaning the sensor, but I am afraid I might damage it!!

So, if some one builds one for my car, put me down as a buyer!!!

Bob

 

I've still got plans to tackle this, if only my life would "slow down". Unfortunately, my boss and family can't see my personal "slow down" light.

 

More than likely its a bad O2 sensor-

 

Ditto that. My light would come on or flicker after 15 minutes of driving. I let it go for a year or so then replaced the O2 sensor. After about 1/2 hour of driving the light has never flickered or come on except when car is first started - as it should.

 

Pardon my ignorance, but which O2 sensor did you change?

Thanks,
Bob

 

Mine only has one sensor.

 

OK,
So my car has one O2 sensor, and the thermo sensor in the cat. I thought that the thermo sensor is connected to the ECU in the rear via the two wires. How does the O2 sensor feed info to the ECU that turns on and off the light?

I can understand if the cat was getting hot from bad mixture due to the O2 sensor, but that would be a more constant issue, that would cause the light to come on more frequently.

What am I missing here?
Thanks in advance for clearing this up for me
Bob

 

Change the O2 sensor--The thermo probe sends temp back to the idiot light to let you know the converter is overheating--

 

My '86 328 w 26k miles gets used very infrequently. Starts great, runs well until 20 or so minutes out. Then throttle become intermittently unresponsive - no stalling just involuntary slowdown with Slow Down light. This comes and goes for the rest of a 45-60 minute trip. Happens repeatedly. Any advice about possible causes much appreciated.
Thanks

 

Your symptom goes well with (intermittently) losing one bank of ignition (and the slowdown light system actually working correctly ). The architecture of the 328 ignition system gives a few places (both mechanical and electrical) where a fault can disable one bank's ignition (and leave the other bank unharmed). Try searching on something like "328 power module", or maybe "328 MicroPlex", for prior threads about some simple tests to investigate (as other faults, besides a power module fault, can cause the identical symptom).

 

Many thanks for this advice.