1981 SC 3.0 relay questions please

[Steve F]

I'm trying to get spares together and had questions about the DME and both the round red and the round black relays.

Are they year specific or which range of years would work?

Cannot seem to locate the DME in our host's parts selection, perhaps it is under another description?

Do the red relays interchange with each other?

Same question for the black ones?

Thanks much,Steve

[tirwin]

81 doesn't have a DME relay. That is '84-'89.

All of the black ones are the same and yes, interchangeable.

You need a red fuel pump relay. There is only one.

Avoid the URO brand relays. It has been reported by several users that they have a high failure rate.

While you're at it get yourself an OXS relay (aka lambda relay).

[Steve F]

Thanks Tim, that explains why it's not in the catalog. The locations of the fuel pump relay and lambda relay please?

[timmy2]

Lambda relay is under the seat at the lambda controller.
Fuel pump relay is red and is in the front fuse panel among all the other black relays

[Steve F]

Thanks again!

[KarlM]

Originally Posted by tirwin

81 doesn't have a DME relay. That is '84-'89.

While you're at it get yourself an OXS relay (aka lambda relay).

What does the OXS relay do?

[Bob Kontak]

Originally Posted by KarlM

What does the OXS relay do?

Oxy Relay = Lambda Relay = Frequency valve relay = the black 1" cube hooked to the silver box under the passenger seat for 80-83 US SC's.

It provides power to a part that helps regulate control pressure. If control pressure is high, less overall fuel is delivered. Vice versa for low pressure.

The part is called the frequency valve and does it's regulating based on what the O2 sensor tells the silver (Lambda) box under the seat. If the O2 says it smells rich, control pressure is increased, less fuel. Then it's too lean and the process repeats. Rich, lean, rich, lean all day long if you are just cruising. However, the rich lean swing is very small. The intent is to keep the air fuel ratio in that 14.7:1 happy spot on average.

[scarceller]

The Red top relays are same as the black capacity (AMPS) wise but the red ones have a suppressor diode built in. You can use RED can in place of black but not the other way around.

[boyt911sc]

Originally Posted by KarlM

What does the OXS relay do?

KarlM,

For years people have been referring or calling this relay as OXS (oxygen sensor) relay. I would quess the translation have been carried over the years from German to English. This relay controls the FV (frequency valve) operation and has nothing to do with the OXS. The OXS sends voltage signal to the ECU and in turn activates the FV (ON/OFF) only if FV has power. And where does the power come from? From the S18 or S22 (?) through the relay that is controlled by power from terminal #30 (that supplies power to the FP).

In theory, when the FP is energized at terminal 30 at the FP relay and power is also delivered to the OXS/FV relay's coil to switch the power coming from the fuse. To better understand this logic, please refer to the factory wiring diagrams that would clearly illustrate that the oxygen sensor has nothing to do with the relay. Yet we call this relay as OXS relay instead of FV relay. It is just a name.

Tony

[tirwin]

Originally Posted by Bob Kontak

the black 1" cube hooked to the silver box under the passenger seat for 80-83 US SC's.

My original one was silver and it was some kind of metal housing. The replacement was made of black plastic. Just wanted to point that out in case the OP has a different one. Either way it's the 1in cube sized thing like Bob said. There's only one 1in cube thing under the seat so it's hard to go wrong...

[Bob Kontak]

Originally Posted by tirwin

My original one was silver and it was some kind of metal housing. The replacement was made of black plastic. Just wanted to point that out in case the OP has a different one. Either way it's the 1in cube sized thing like Bob said. There's only one 1in cube thing under the seat so it's hard to go wrong...

Good point.

My original had more of a metal frame or bracket that affixed it to the Lambda box with a screw, if I remember correctly. Kind of remember black cube with the bracket but you may be right. Still easy to find. New one just lays on the floor.

[imoto]

guys is something that only US models have my 81SC does not have anything under the seat.

[boyt911sc]

Originally Posted by imoto

guys is something that only US models have my 81SC does not have anything under the seat.

Imoto,

Your '81SC is probably a Euro or RoW model car and won't have any of this lambda unit we have been discussing. Cars designated for USA, Canada, and Japan markets have the OXS/lambda unit installed and none for the Euro or RoW cars including Australia and New Zealand.

Tony

[imoto]

Thanks tony thought that was possibly the reason