REV 3 3SGE SW20 - Running rich but runs great

[rick_mr2]

Visually inspect your ECU for leaking and/or corrosion around the 8 electrolytic capacitors while you are at any remediatory work, only going to take you around 15 mins to inspect. I had an overfueling issue recently (amongst other issues mainly rough idle) which was solved by replacing these and reparing the damage caused to the ECU PCB. There are guides out there on other sites if you do a search of the web but I am hoping to create one for here as soon as I can pull mine again to take some photos. Basically, there should not be any discoloration, white (or sometimes green or any other color deposits) below or around the legs of these or on the board itself. Also the tops of the caps should be flat and not domed/bulging.

[JRD93]

Visually inspect your ECU for leaking and/or corrosion around the 8 electrolytic capacitors while you are at any remediatory work, only going to take you around 15 mins to inspect. I had an overfueling issue recently (amongst other issues mainly rough idle) which was solved by replacing these and reparing the damage caused to the ECU PCB. There are guides out there on other sites if you do a search of the web but I am hoping to create one for here as soon as I can pull mine again to take some photos. Basically, there should not be any discoloration, white (or sometimes green or any other color deposits) below or around the legs of these or on the board itself. Also the tops of the caps should be flat and not domed/bulging.

Will be interested in seeing this when you've done it. It was the next thing on my list to check. Currently I'm trying out a coolant temp sensor which I believe may be the problem. My emissions get better the higher the revs go, once it hits around 2.5-3k the CO is within spec. I believe this is when the ECU stops looking at sensors and goes into open loop.

[big long stroke]

Hello everyone, If any of you are still following this post!

Sorry that I have such a gap between posts, I have a weird kind of work schedule and with other projects on the go, the MR2 just got shoved to the side.

Thanks @rick_mr2 for the ECU suggestion, I will look into this as part of my next diagnosis.

Today I decided to have a go at changing the lambda sensor, I have changed it before about two years ago but that was before I did any work on the exhaust or really anything at all to the car so theres a good chance that its possibly been fouled.

Ofcourse, with everything on my car, its been bodged in the past. The connector for the lambda sensor is non existent and instead is just four wires which are hard soldered into the wiring loom of the car.

When I replaced the lambda sensor last time, I just followed what someone else had already chosen before (Denso sensor so Black, Black, White and Blue wires) - Today, I decided not to "trust" that the previous mechanic knew what they were doing, so instead I checked the wires from the loom side.

My car is a Rev 3 Jap import with the 3SGE, its got a 4 wire lambda sensor. The wire colours on the loom side are as follows:

Red with white stripe
Yellow with white stripe
Black
Brown

From what I have been able to research, those wires correspond to:

Red with white stripe - ECU to lambda heater
Black with yellow stripe - 12v
Black - Signal wire for lambda sensor
Brown - ground

My lambda sensor has the wires marked as follows:

Blue - Lambda Signal +
White - Lambda Signal -
Black - Lambda heater
Black - Lambda heater

Mine was previously wired as follows:

Red with white stripe - Black
Black with yellow stripe - Blue
Black - Black
Brown - White

Which in labelled terms corresponds to this:

ECU to lambda heater - Lambda heater
12v - Lambda Signal +
Signal wire for lambda sensor - Lambda heater
ground - Lambda Signal -

Im unsure if this is correct as according to the loom wires - my signal wire is connected to the lambda heater?

If anyone out there has a loom intact for a Rev 3 3SGE and possibly knows where the wires are supposed to go - @JRD93 perhaps?

Please let me know as I would prefer to know what wire goes where, rather than just guess!

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Also, big development in the exhaust situation, while I was underneath messing with the lambda I decided to check all the joins for leaks. Started the engine... and sure enough there was a nice leak coming from the manifold to downpipe/flexi join. I took this off and installed two new gaskets, seems to no longer be leaking.

[jimi]

According to the Toyota BGB diagrams I have the sensor is wired like this
Heater + = yellow/black (B+)
Heater - = red/white (ecu)
Sensor + = black (ecu)
Sensor - = brown (ground)
Which would indicate your original sensor was incorrectly connected IF the colour coding on it is the same as your new one, the sensor heaters are normally two wires with the same colours (usually black or white)

[big long stroke]

According to the Toyota BGB diagrams I have the sensor is wired like this
Heater + = yellow/black (B+)
Heater - = red/white (ecu)
Sensor + = black (ecu)
Sensor - = brown (ground)
Which would indicate your original sensor was incorrectly connected IF the colour coding on it is the same as your new one, the sensor heaters are normally two wires with the same colours (usually black or white)

Thats interesting, Id almost have to hope that my sensor is wired incorrectly as it would explain a lot of the issues ive been having.

Ive message a guy who breaks these cars for a living to see if he might be able to send me a picture or give me some knowledge towards the wiring of the lambda.

Thanks for the info, I assume that Toyota wouldn't change the wiring too much so hopefully the wire colours correspond to my cars wiring as well.

[jimi]

The colours are from the 1993 Electrical Diagrams, I've checked the 1991 & 1995 diagrams and they show the same colours, you can download the BGB's here https://mr2oc.co.uk/downloads/technical-stuff/mk2.html