Topic

Trying to get my 1998 MGF through the emissions test is driving me nuts - The dreaded High CO.Initially I fitted a new Cat (Bought from the MG owners club) and a new O2 sensor from fleabay.CO level was still high so I invested in a PSCAN to see what was goin on - turns out the O2 sensor just wasn't working (stuck in open loop) so I purchased another from a more 'reputable' source. PSCAN now tells me that the O2 sensor is working and the car now operating in closed loop.however the O2 readings are still too high (around 0.8 where before they were even higher).Guy at the garage says the other readings don't indicate an exhaust leak, just the car is running too rich.I've attached 2 screen shots of the PSCAN data (at idle and 2200 rpm).Help - why is the car running rich?!

It must be too rich because there is insufficient air to burn the amount of fuel injected so either the air is restricted, which is kind of unlikely or there is too much fuel going in. The amount of fuel injected is dependent on throttle position, so check the TPS voltage at idle. It is also dependent on temperature. Check the operation of the temperature sensors. The state of the injectors themselves can make a big difference. You would not believe the effect of a thousand spirited miles of driving on a car that did fifty miles a year. The idle is quiet and smooth without lumps and roughness. Run a bottle of injector cleaner through it and give it a proper run. Use all the revs, and put a hundred quick miles on it. That will probably sort it out. The garage queens suffer emissions issues far more than cars that are regularly enjoyed.

Just to echo Minimax's comments re using the car. My TF had only done a thousand miles or so in the two years before I bought it. A 500 mile round trip to Southampton and an oil change completely transformed the tick over and performance generally. It's called an Italian tune up....

I have standard readings at Idle hot for my MGF using PScan that I have taken over the last 2 years so I can judge when my car is running out of the norm and attempt to identfy the problem.

Your screenshots are a little difficult to read but the throttle position sensor is at 0.5v, mine is 0.7V at idle - at 5K rpm, my voltage is 2.2v, at 2200rpm yours is 0.7V. Stepper looks fine. Idle fine as is the throttle opening position (although the 5 degrees at idle is relative to closed position) and the other readings do not look out of normal.

Coil charge time at 3.7ms compares to mine at 2.4ms at idle and at high revs.

I did an ECU reset once using Pscan which clears the engine adaptions which allowed the ecu to relearn from zero. The ECU should be adapting constantly to the age of the engine et al but the reset appeared to clear a glitch for me.

I hope the above helps in some form.

From the above, it looks like the throttle position may have been " adjusted" to compensate for a throttle position sensor fault. If the voltage at idle, which should be 800 rpm warm, and that at 2200 rpm are the same, then I would ensure that the plug on the back of the TPS is fully clicked home and if it is, check its lead for chafing before double checking the voltages and finally ordering a new sensor.

An update from today in the garage.
I removed the fuel injectors and tested them with a jury-rig. One of them was passing fluid before it was energised so could have been causing the excess fuel. Gave them all a good clean through and they all now function correctly .
Noticed the HT lead from the coil to the distributor was a bit fretted so will get a new one and stick the injectors back in when I get new seals.
Will also look at how to reset the ECU back to factory.

Your fault is too much fuel and you have a leaky injector. Don't over think this. Get some injector cleaner through them and give the car a good long run at high power and using fresh fuel. The problem is very likely to fix itself if you do this.

TPS is fine. 0.5V at idle, 0.7V at 2000rpm. With throttle fully open it reads 5V. Don't even see anyway of 'adjusting' it.
Injectors now all cleaned and back in with new seals, New HT lead fitted to replace the fretted one and a bottle of petrol cleaner ready to put in and give a good thrash tomorrow.
Only noticeable differences in Pscan readings are "Long Term Trim" was 24µs now reads 0µs and "Purge Duty Cycle" was zero and now around 4% at 2500rpm.