Eric Vaas

Hi guys,
I have a weird problem with the Central Warning Unit on my '83 5-speed. I get a flashing warning light on the dash and console, but there are no indicators lit. Pressing the reset button does no good. Also this does not occur until the motor has warmed up! The lights are off when the motor is cold. When it does flash, its only when the revs are below 1500! Is this a possible behaviour? I know the bulbs are good, because all the indicators light up when the ignition is first switched on. I've disconnected the battery several times to reset the unit. I know I need a new O2 sensor, because its giving a low voltage reading, about .4 to .6 volts. Does the CWU monitor the O2 sensor, outside of controlling the OXS indicator?
Its really annoying.
Thanks,

Rick

GlenL

Have your re-built the pod? If not then it could be there's a bulb that is trying to light but can't.

I'd look in the owners manual for some hints.

SeanR

Glen, my first thought also, 2nd thought was bad ignition switch.

U-928

Have you done a CE box clean up? Just did it on my '82 and it fixed my crazy malfunction light issue. Just a thought, can't hurt.

Eric Vaas

Have not had the pod apart. The car, is in fact, missing the ignition key, and luckily, the red gas cap key fits the ignition, with a little twisting and pressure. I dont think the car has the factory alarm, which would require the longer key. Have always suspected the ignition switch. For a long time I had have a flashing Brake Pr. indicator warning, and traced it down to a faulty sensor on the MC. For now I have just pulled off one of the sensors, and this has eliminated that warning. Could this be related? I plan on taking the ignition tumbler out this winter, and getting the proper key make for it.
Rick

Landseer

Go to the CD set.

There is a 928 electrical training doc that does a pretty good job of outlining how the 83 vs 84 central warning system works.

WallyP

Up thru 1983, the brake lights are operated by twin pressure switches on the bottom of the brake master cylinder. From 1984 - up, the brake lights are operated by a simple plunger switch mounted on the brake pedal under the dash.

The earlier brake light switches do double-duty, operating both the brake lights and the brake pressure warning signal. These switches can cause some problems.

The switches are identical - one in each hydraulic circuit. They are single-pole, double-throw switches. This means that you have only one circuit (single pole) thru each switch, and that the switch chooses one of two outputs (double throw).

Each switch has three connections: power, central warning computer, and brake light.

Not Activated
There is a power feed into each switch. When the switch is not activated (no pressure in the brake circuit) the power isn't hooked to anything.

When the switch is not activated, the central warning computer and the brake lights are connected inside the switch. Nothing happens, since there is no power applied on either circuit.

Activated
When the switch is activated by brake hydraulic pressure in one of the circuits, the central warning computer connection is broken, and the brake lights are hooked to the power feed. This removes the central warning computer from the circuit, and puts power on the brake lights.

(This might be easier to visualize if you think of three wires: one for 12 vdc, one to the brake lights and one to the warning computer. The lead that goes to the brake lights is connected to the one to the warning computer until brake pressure pushes it off of that wire and over to the one going to power.)

All three leads go to both switches.

When you apply the brakes, both switches should activate. Both switches disconnect the warning computer and connect the power to the brake lights. The brake lights come on, and no signal is sent to the warning computer, so it is happy.

If only one switch activates (either no pressure on one side of the brakes, or a bad switch), then things change.

On the switch that is not activated, the brake light circuit is still hooked to the warning computer.

On the switch that activates, the brake light circuit is hooked to 12 vdc.

The brake lights come on.

In addition, power flows on the brake light circuit back to the non-activated switch. Since in this switch the brake light circuit and warning computer are hooked together, 12 vdc is applied to the warning computer circuit. This set the Brake Pressure Warning light.

If you have a bad brake light switch, I strongly suggest that you replace both switches.
(P/N 113 945 515 G)

dimi5928

I have the same problem with my 83s euro,the problem was the oil pressure sender unit...
When the oil was cold was ok,when come,s hot,sent low presure signall...!!

(maybe helps...)
Sorry for my English...(I leave in Quebec...)...

Eric Vaas

dimi5928 -
Wow, that sounds exactly like what it is doing. High oil pressure signal whan cold, and lower when it warms up. I even see the warning light start to ficker just as it starts happening. I'll check the oil pressure sender.
Thanks,
Rick

86'928S MeteorGrey

I think the only flashing warning is low oil pressure... Does your low oil pressure light come on when you flip the key to on before starting? I'd check the connections on the oil sender first. A good cleaning and make sure the terminals are tight. If the oil ressure sender does not cure it, you might try some 20-50W oil depending on your outside temperature range.

I just had this problem a month ago. I bought a used pressure sender from 928Intl, and all is fine now. I did notice that my terminals were rather loose when I went to R&R it, so my original sender might have been good...

Landseer

Oil pressure, oil level, brake circuit, brake fluid level

86'928S MeteorGrey

I suppose low revs could effect vacuum, and therefore brake components that are vacuum controlled. It still sounds like an oil viscoscity or sender problem, unless the engine is very tired... What kind of mileage does she have?

Eric Vaas

The yard that I got it from claimed in only had ~60k miles on it. I have no reason to doubt it, it looks pretty good, no tool marks on any bolts from working on it. Put a new water pump, timing belt, RMS, and pan gasket (now leaking!) Timing gears were not worn. It runs pretty strong. I could believe the oil pressure sender problem because I had to use my old one, and the connections were kind of mangled.
Rick