rover 420 GSI (high Emissions) - foptics
Can anyone help.

I have a 1995 Rover 420 GSI, using the mems engine management system.

The has just failed it\'s mot due to emission being well over the top like a base idle CO 2 being 9.9%

Now I found a useful site on the web giving sensor values, for this system.

Check Coolant Temp sens, OK 2.5K ohms when hot.

Lambada senors valur 0.8 v and rising, not the usual up and down between 0.2 & 0.8V.

But the odd I found was the throttle postion sensor, supply voltage 5v, at idle it should be 0.5, but it was 4.5v, and at full throttle was only 4.8v.

so I disconnected the sensor wire to the ECU and found I had the same value, checked the device on ohms and the resistance does change.

But I remember some years ago having a MG EFI montego and these used to suffer from blowing the earth pin inside the ECU, normally this was easy to repair, (I use to be a TV & Video Technician so I have all the skills with the soldering iron), I wondered if this ECU suffers from the same problems, I know the Montego one could be done buy using a battery charger.

The montego suffered very similar problems, very high fuel consumption, erratic idle etc and same again the sensor voltage were all floating.

Any help would be welcome.


rover 420 GSI (high Emissions) - David Davies
I'd query your coolant temp. sensor as 2.5KOhms hot is wrong.It should read approx 300 Ohms hot.This will have a drastic effect on the fuelling and cause your high CO reading.Your tests indicate you have a failed throttle position sensor-this is usually checked by reading the output voltage with ignition on.It should be about 0.5v at closed throttle and rise smoothly to 4.5v at WOT.Similarly the temp.sensor should give about 3v cold and 0.5v hot.On this model also make sure that the vacuum pipe is clear(from manifold to ECU,possibly through a vapour trap).I've never heard of the MEMS units failing in the same way as those Lucas types fitted to Montegos etc.They (MEMS) often have problems with the internal vacuum sensor and this again can cause extremely rich fuelling.
David Davies (Tune-Up Raglan)
rover 420 GSI (high Emissions) - foptics
Hi Dave

yes got it wrong 250 ohm's for the coolent temp sens when hot, went back to looking at my notes,

will check the return voltage for the CTS though, that for the info.


rover 420 GSI (high Emissions) - foptics
HI Dave

Thanks for your help.

Turned to be the TPS sensor, check ECU buy putting a Potentiometer in and vary this until I got a 0.5V value for idle, if you do this and then turn it (not connected to the throttle body) you can here the management system change the fuelling and timing.

Stripped down the TPS and found it to be contaminated with water, and this has taken one of the tracks that lead to the carbon film resistive tracks. Remade this with some conductive paint, resealed the unit, refitted and got a 0.6v for idle and 4.6 for full throttle, will now take for MOT.




Value my car