oxygen sensor computer wiring 1982 911

[aircooledmiket]

Hello
First post to this forum
1982 911
Chasing a short in lambda system have some ideas based on other threads
Located this wire under seat not connected
Does anyone know what this connects to?
Appears to be white/red and white/green
Manual seems to indicate there is a test wire, seems strange to
be laying loose.

[AndrewCologne]

Located this wire under seat not connected

Seems you forgot adding a picture?

[aircooledmiket]

[aircooledmiket]

[bmwphatpat]

Just spent time tracking down wiring diagrams. My '80 sc is wired a bit different than this with a 6 pin connector, but if you have an '82 this should match exactly

[aircooledmiket]

Thanks Pat
I guess #17 might be the wire on your diagram of test wire.
here is a better oriented photo
Maybe what I should have asked for was a photo
of a complete harness for the dome lights/ox sensor system

[pmax]

I can't find exactly what it is but it's not part of the lambda harness.

[targa80]

In your picture there is a white connector that does not have the oxygen relay connected. Did you disconnect it? Or is it missing? In the 81 schematics there are a lot of rd/wt and gr/wt wires. Have you checked to see if the wires have power? If they have power then you can pull fuses to see what circuit they are tied to. Do you have things that are not working like interior lights, seatbelt light. I did not find a circuit that had both wires being used in the schematics so my guess each wire is for a different function. I also looked under my passenger seat and could not find those wires terminated there on my 80SC.

[aircooledmiket]

I disconnected the relay that is o2
Not sure if there is power at wires shown
Disconnected interior lights and relay for safety
There is also a short at engine compartment light.
Cannot find path from engine light hot side to
Interior dome
With the interior light connected to fuse
Fuse 18 cuts out
I have good continuity at frunk light
Glove box light and dome
Only known short is at engine cpt light
(And these mystery wires)
Thanks

[targa80]

Originally Posted by aircooledmiket

There is also a short at engine compartment light.
Cannot find path from engine light hot side to
Interior dome With the interior light connected to fuse
Fuse 18 cuts out
I have good continuity at frunk light
Glove box light and dome
Only known short is at engine cpt light
(And these mystery wires)
Thanks

I would suggest that you troubleshoot one issue at a time and since you state that the engine compartment light does not work and you do not know where the power is coming from I can provide the following info. The engine light is not connected to the interior lights or frunk light.

The engine compartment light is a gray (gr) wire connected thru connector T1a (near regulator panel left side) to connector T6b-terminal 4 (in engine compartment right side) with Grey/Red (gr/re) to rear left side marker light and rear light. it is also connected to Grey/Black (gr/bk) wire going to fuse 4. Fuse 4 also feeds via Black/Grey (bk/gr) wire through connector T1b (behind left headlight) the left front side marker light and left parking light. Fuse 4 receives power from the light switch or from the parking light contact in the turn signal switch. With the engine off and the light switch off if you select the turn signal to the left the left side marker lights will turn on. This is a European safety feature when parking your car on a narrow street at night. This will not fix your other issues but once resolved you can move on to the next issue and eventually it will lead to the two wires that are not connected if something else is not functioning properly. I do have a pdf of the 1982 schematics, just send me a PM with your email address if you need them.

[Walt Fricke]

The test wire (green/wt from the ECU terminal) goes back to the engine compartment by the engine compartment fuse box structure. It is joined there by a ground and a +12V wire in a plug which is loose (not fixed to the chassis) and ends in a rubber covered 3 pin connector, which has a rubber cap as a cover. The wire from the ECU runs in the main Lambda loom. So your two stray wires are not related to that.

Why don't you trace that pair farther? They are just under some upholstery. That may help identify them.

Those mystery wires don't appear to be causing a short - they are just cut.

Fuse 18 isn't connected to the engine cpt light. That light is controlled by fuse 4, which also controls the left rear brake (or parking?) light. The wiring diagram has an ambiguity - it indicates that the luggage compartment light is controlled by the rear lid switch. What is meant is the rear of the front lid, which is where that switch is located.

With the rear deck closed, if you connect the CIS ECU relay, does that blow Fuse 18? If you start the car, does that blow Fuse 18? Fuse 18 supplies a miscellany of circuits - the clock, interior lights, glove box, front trunk light, and the electronics for much of the CIS. The switches for all the lights are on the ground side of the light bulbs, so turning any of these things on should not blow fuses.

A positive power wire downstream from a relay could blow the fuse on the main power circuit (not the low power circuit which energizes the coil) when the relay closed. If plugging the O2 relay in causes a fuse to blow, you'd want to check the terminal terminal 87 and 87b black red wires from the relay to their loads - the acceleration enrichment unit which is close to the relay, and the frequency valve back on the engine. These wires are not apt to be shorted. The FV is a solenoid, and those don't tend to short. You can see this on the circuit diagram previously posted.

The wire to the interior lights runs through the A pillar and back to the right side interior light. I forget where the left side one runs. It is perhaps the most exposed to rubbing of the wires on this circuit. If a hot wire contacts ground, the fuse blows. It doesn't matter whether the intended load for that wire is on or off.

[Walt Fricke]

Oh, and take Pat Henry up on his offer of a PDF of the schematic. I'd be lost without one. I have the factory manual, but its wiring diagram for the 80-83 SCs is for the Euro SC, which doesn't have the Lambda/FV/ECU system, so I rely on copies of the US 81-83 system I have stuffed into the pages for the '77 (which is what my car started out as). Can't really troubleshoot electrical gremlins without the wiring diagram.

[aircooledmiket]

Thanks Pat for diagram
I have all interior lights
It was a trunk and globe box switch short

Main issue is poor idol warm up
I have 12v at no 30 at ox relay
And 4 v at 86 terminal

When I jump 30 to 87 and 87b
FV does not react

Am I chasing bad ecu
And short at fuel pump relay?

[targa80]

Originally Posted by aircooledmiket

Thanks Pat for diagram
I have all interior lights
It was a trunk and globe box switch short

Main issue is poor idol warm up
I have 12v at no 30 at ox relay
And 4 v at 86 terminal

When I jump 30 to 87 and 87b
FV does not react

Am I chasing bad ecu
And short at fuel pump relay?

Just sent you an email look at 1988081s_klambda.pdf first.

You should not see 12 volts at pin 30 of the oxy relay unless you have lost the ground connection. Remove the relay and test for continuity between pin 30 of connector and chassis ground with an ohmmeter. I would expect a reading very close to 0.0 ohms. If you are reading a high resistance or infinity then you have a bad ground connection on pin 30 red (re) wire to ground.

Also with oxy relay removed and if the fuel pump is energized (running) you should see 12 volts at pin 86 and pin 85 brown (be) wire (chassis ground).

If my memory serves me right the signal supplied to the frequency valve from the oxy control unit (OCU) is not a constant voltage. It is more like a switch being turned on and off rapidly based on the engine fuel demand. In essence the frequency valve sees a pulsing signal from the OCU and rapidly opens and closes the valve that releases some fuel pressure in the lower chamber of the fuel distributor. This action either enriches or leans the fuel to air based on engine demand.

[aircooledmiket]

0 resistance 30 to ground
Car not running

13v at 86
0 volts at 85
Car running

[targa80]

Originally Posted by aircooledmiket

0 resistance 30 to ground
Car not running

13v at 86
0 volts at 85
Car running

Well I don’t know what I was thinking while I was looking at the schematic. Oxy relay Connector pin 30 does not go to ground it actually is connected to 12volts at fuse 18. When the relay coil is energized at pin 86 to ground on pin85 the contacts close and 12 volts is supplied from pin 30 to oxygen control unit via pin 87 and the frequency valve via 87b.

Pin 30 should not have a reading of 0 ohms to ground.
13 volts at pin 86 is normal and pin 85 provides the ground for the relay coil.

Previously you said you had 4 volts at pin 86 but you should have 12 volts coming from fuel pump relay pin 30 on pin 86.

[aircooledmiket]

I wanted to confirm fv is working.
Looks like I only get volts to 86
At ox relay with car running.
I thought it was to give volts with
Key on but not engine running.
Is that correct?

[targa80]

Originally Posted by aircooledmiket

I wanted to confirm fv is working.
Looks like I only get volts to 86
At ox relay with car running.
I thought it was to give volts with
Key on but not engine running.
Is that correct?

Pin 86 gets 12 volts from fuel pump relay pin 30. Pin 30 is supplied 12 volts from ignition switch while on and starting.

Under normal operation the fuel pump relay should get 12volts with ignition on and only run the fuel pump while engine is starting and running. If the engine does not start and you leave the ignition on the fuel pump will shutoff. I believe this would be a safety feature. When the ignition is on and car is not running you lift the air flow sensor to close the air flow sensor switch in fuel distributor and the fuel pump relay will energize and the fuel pump will run, release the air flow sensor and the air flow sensor switch opens and fuel pump relay de-energizes and fuel pump shuts off.

[aircooledmiket]

Thanks again
Tried the lambda test in lorenfb’s post
Created a blown fuse a 18
Looks like a short to FRequency valve circuit
I would like to bench test the FV
But appears removal comes awfully close
To fuel lines. Can barely see it.
Think It’s off to the pros to hunt that down
I did manage to narrow down a lot of power issues
Regards Mike

[Walt Fricke]

The only part of the frequency valve that is at all easy to remove with the engine in the car is the plug which supplies it with its power.

The test I have used with the engine running is to place my hand on the FV. You should be able to feel it vibrate.

The Lambda relay provides the 12 volts of power to the FV, but it also powers the ECU. The ECU controls the pulse width modulation to the FV by closing and opening a path to ground for the FV solenoid. I think a short in either of these is kind of remote unless there has been some sort of quite extraordinary electronic disaster at some point - the kind of thing you couldn't miss, like maybe hooking up a jumper battery backward and trying to start the car maybe.

A wire whose insulation got cut and hits the chassis would be a more likely cause of a short blowing a fuse.