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MG MGF Technical - FAQ Rob Bell.

Hi Rob,
Hope you dont mind me picking your brains on this one!!

I apologise to anyone else for the non F content but as an ex F owner I value certain peoples opinions on this BBS!(at least the engine is the same!)

I recently had my S2 serviced, also while they were at it they cleaned the Carbon airbox,re-set up the large TB 55mm-60mm.(All ex tuning mods carried from my MGF) and connected an aluminium pipe from the airbox to the TB for better airflow.I also had a sports exhaust fitted at the same time.(Which i am not too happy with at the mo as it does resonate and boom a lot although it does sound good at low revs)Anyway went to the Ring yesterday and the car felt sluggish.Asked around and a few comments were it could be running a little lien..... iE too much air!I always thought you could never get enough air.The car has backfired once since then. Anway I normally use 95 octane but on the way back from the Ring I tried the shell V max 100 octane and she felt a little better and more rev happier,or was it just my imagination? Still any feedback you might have Rob or anyone else would be much apreciated.


Hi Stu,

FWIW I don't think that your problem is going to be one of too much air - but since the problem started at the time of the service, it seems logical to re-examine what was done at that time.

Just so as to have a clearer idea of the extent of the problem, just how sluggish was sluggish?

I'd start looking at three areas that you've highlighted as being a part of the service:

1. the throttle body adjustment
2. the air filter
3. the exhaust

In reverse order then:

Not all exhaust systems are created equal. Just because it is loud doesn't mean that it is any better than the standard system that was fitted to the car from new. When we did the exhausts tests with MG World, we found that a couple of the systems actually made the torque curve WORSE.
What system is currently on the car? Might be worth reverting to the standard system to see what happens.

The air filter you have fitted is an oil-penetrated foam filter inside an airbox. Cleaning is obviously essential - but if too much oil is added, the airflow through the filter can be seriously impeded. Might be worth taking a look to check the filter is clean, and not too laden with oil...

What adjustments were performed on the throttle body? Have all the hoses been reconnected properly? Is the throttle body sealing properly against the inlet manifold plenum?

There are other areas to look into - but these are the first ones to tackle IMO.

Keep us posted!
Rob Bell

RE running lean, the MEMS uses a MAP sensor to test the pressure of the air in the manifold, it uses this knowlage to set the fueling requirements, all the mods you state are upwind of this, so you shouldn't have any leaning off problems. This is assuming MEMS.

The TPS setting should only have effect at idle and to detect when to richen on acceleration, but try resetting the TPS with the normal routine, also check that the throttle opens fully (cam has no more movenemt with pedal on floor).

It is possible the MEMS is in a failsafe mode:

The lamda sensor is not used on full throttle, but a lamda failure may cause a 'limp home' effect.

There may be a fault with the temp sensor - does the fan run when hot and not run all the time? this will cause the MEMS to over richen and rob you of power. Clean the contacts of the brown sensor and plug.
Will Munns

Thanks Rob, Its not THAT sluggish its just that I was expecting more prehaps from the adjustments.The car definately feels a "little" slower.I will check everything as you advise.

The exhaust came from
CNC machined and a claim of an extra 6BHP!

TB apears to be connected correctly.
How about spark plugs?

Cheers for your input Will,i will take a look at the temp sensor.


O2 sensor... where is it on the S2? Could the exhaust fitting have caused a problem here?

Temp sensor: Quite possible if not probably.

TPS: Not been connected properly or damaged? How's the idle and the rev drop off? If off, both will indicate a problem wit hthe TPS.

Hmm... not saying much new am I? :-)

I guess all of this is nothing that testbook wouldn't pick up.

Good luck and let us all know what happens... :-)

Paul Nothard

Hmm - the TPS: this could cause problems especially on your GM throttle body. How is yours attached to the TB - and has it been moved since before the service? You could try the MEMS/TPS reset procedure (pressing the throttle pedal 5 times with the ignition on, then switch off) to see what difference that makes.

Plugs, leads and distributor parts are all possible candidates for causing problems, although in this case I think unlikely in view of the age of the car and the nature of the problems - although there is certainly no harm in inspecting the condition of the spark plugs and replacing if necessary.
Rob Bell

This thread was discussed on 06/07/2004

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