The AUSubaru.com.au Forums

what do these actully do....something with the vaccume on my ea82t
not sure what? it goes on the drivers side strut tower

They are pressure switches - one tells the ECU that boost is present and lights the boost light on the instrument cluster; it closes at just over atmospheric pressure. The other is the boost cut sensor - when there's too much boost, the ECU will stop firing the injectors. You can run the system without them, at least with the older 3 plug ECU.

and where do they hook up to?

They plug into the 2 cannon plugs on the DS strut tower and into the manifold engine side of throttle butterfly

Here:

You can just see them in this pic:

sure can.....

OK, I dont seem to have these switches. Seeing that the factory manual decribes the function of the pressure signal to the ECU is to ignore at boost the O2 value due to being high.
Now I find that the O2 is busted and not connected.

Where am I at without either device? Will it run in protective mode and run retarded or run rich?
Sorry I havent had time to run it up to get fault codes, as the charging system is shot and hasnt been mobile.

Only the 84-86 turbos had a boost switch to change the ecu into closed loop mode. so if your car is 87+, the only boost switch you should have is to light up the turbo light on the dash.

With no o2 sensor, the o2 sensor input will be ignored, so a/f ratios will not be optimum, but car will still run

Suparoo, is that difference related to the 3 plug ECU to the later 4 plug also?

Another question arises, O2 sensor, what type or equivalent do I need and approx pricing? I think from posts I have seen generally a new one is better. Can any type of shielded cable be suitable, as I dont think mine exits? I think these are separate to the loom, correct me if I am wrong.

EDIT: I have had a better look today and found that I have a 4 plug ECU.
Also there is no O2 sensor and pressure switches, so it would be safe to assume it is not Aust spec, but Jap import version. Seems only Aussie models had those other bits for emission control.
Also no "knock sensor" connected. Doesnt appear to a plug for it, but sensor is fitted (one behind intake manifold - white plug base, 2 pin)

The 3 pin ecu's are the 84-86, 4 pin is 87-94... so the only pressure switch you should have is the one for the turbo light on the dash (not ecu related)

I priced an o2 sensor today,.. $61.00 8O and thats non genuine.
The o2 sensor is plugged into a connector that is located with the electrical connectors that go to the tranny, and all mpfi and turbo cars had em.


Quote "Also no "knock sensor" connected. Doesnt appear to a plug for it, but sensor is fitted (one behind intake manifold - white plug base, 2 pin)"

By this do you mean that the ecu is throwing a code for the knock sensor. The connector should be on the intake manifold loom.

Thanks Suparoo for the info.
Ok I see the harness connectors x2 in the tranny tunnel. There is nothing connected to the device thats down stream of the cat at the base of the dump pipe - is that correct position? Temp sensor is at the top at the Turbo - correct?
I think I will need one then. Whats the pin out for the O2 sensor for the 4 pin ECU? I didnt see any shielded looking cables at the ECU plugs.

I have no dash light for boost, as its a conversion in a TW.

I will be going through the fault codes soon, car not running at present. Just noticed the knock sensor not connected, will look a bit further for a plug.

Suparoo wrote:I priced an o2 sensor today,.. $61.00 8O and thats non genuine.

That is a damn good price. Do you know the Brand name and Part No by any chance. I was quoted $100 approx.

Looked through the Part 2 of the download manual for an '89. It shows the position of the O2 after the turbo before the cat. Is it before or afterwards of the cat? The thing I found near the turbo has a green single wire out of it. the busted thing at the base of the dump pipe had some sort of wire in it.
Roger.

So you mean that there are two sensors on the turbo downpipe?
Some downpipes have 2 o2 sensors, one before the cat, and one after the cat.

Use the one before the cat

Gannon