MK3 7MGE Emissions Problem
 

Hi, wondering if anyone could help me here.. I`ve got a 1990 7MGE supra and has just failed it`s mot on emissions as the CO is too high, was coming up on the machine at 4.10% and it has to be under 3.50%. So far i have changed the plugs, put a bit of injector cleaner through it (only had it running outside the house for 20 mins and a short drive to mot station though), and i have ordered a coolant temp sensor.
Tried diagnostics on it but had no fault codes, does anyone have any more ideas? Do these have a mixture screw anywhere?
The mot tester said usually there is a screw around the throttle body and if we can find it then we can adjust it while it`s on the machine but i can`t seem to find anything.
Any help would be much appreciated as i am stumped here.
Cheers

Test the Oxygen sensor with a needle style volt meter. You can also check the Vf fuel trim voltage for a rich or lean condition. There is no manual adjustment as this is a fuel injected computer controlled engine. The procedure is detailed in the repair manual or online. High CO would indicate not enough Oxygen remaining to make CO2. Could be running hot also. The cat converters could be past it if euro spec cars have them. Then there are the "Pass the MOT" in a bottle concoctions out there made to lower emissions for one tank of gas. You are not far from passing. Check the timing, spark plugs, and air filter. A tune up may get you under the limit.

Cheers.

Thanks for the reply. I have changed the spark plugs and the air filter is in good condition aswell, i have just put in a new coolant temp sensor and now engine management light has came on.
Before i put the new one in there were no fault codes but now it`s coming up with fault code 22 which is for the coolant temp sensor, tried clearing it but it`s staying on. Bit confused at that one.
Think i will need to get myself a volt meter and start checking some things, only have until tomorrow afternoon to get the car retested so looks like i will be forking out for another full mot.

Check the coolant sensor plug to make sure the prongs inside are not corroded or pushed back in. Clearing engine codes is accomplished by removing the EFI fuse for 30 seconds.

Here is a helpful engine code link:
http://www.toyota-supra.info/forums/...c-codes-2.html

I have attached a photo of a typical coolant sensor area on the engine. Yours may be similar.
The coolant temperature sensor is the square plug on the side on the engine just to confirm.

Yeh i tried clearing the code by taking out the fuse but just came back on after a couple of seconds, also tried disconnecting the battery but came back again after that too.
It`s a brand new sensor that i have put in so don`t understand why it would throw a code up, the old one`s prongs were rusty inside the plastic housing and snapped very easily when i took it out.

It could be a bad plug connection. They get corroded too. Also they get pushed back in the plastic holder where they don't make contact. They are supposed to pinch against the prongs on the sensor. You could rig up a test harness with connectors that grip the prongs on the sensor (without touching each other and shorting) to bridge to the plug to see if the code goes away after clearing it first. There is also a test procedure using a Volt meter to probe the back of the plug at the ECU which is located behind the glove box.

Here is a link to the test procedure.
http://www.cygnusx1.net/Supra/Librar...aspx?S=FI&P=41

The plug back layout.
http://www.cygnusx1.net/Supra/Librar...aspx?S=FI&P=31

The voltage between THW and E2 should be O.1 to 1.0 Volts with the engine warmed up and the ignition switch in the on position (not running).

Here is a test of the sensor itself.
http://www.cygnusx1.net/Supra/Librar...spx?S=FI&P=113

Getting those square plugs with the spring clips off with out damaging them is always a chore.
I use a pointy tip to pull the clip away on each side and carefully wiggle it loose. They snap on a lot easier with the clip back in its groove.

Thanks for the help, tested resistance and there wasn`t any so bought a sensor from toyota and passed it`s mot with emissions going down to 2.3.
Now i`m going to treat it to a nice fresh paint job.
Cheers