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MG MGF Technical - Over Fueling


One very useful outcome of the G-Force rolling road day was that I found that my F is seriously over fuelling. Not got the figures with me, but typical ration was 12:1 rather than the optimum 13.1:1

I have the FPR as it left the factory. The FPR on the F is not designed to be adjusted, but I am sure I hear of Dave (Andrews?) carrying out some adjustment with a vice.

I am keen to find a solution to this as it must be robbing me of HP (although I was v pleased with 158.7 (adjusted) from my 1.8i, as well as giving crap mpg

The options would appear to be;

a) The obvious solution is as you said to go the emerald route ~ but it gets expensive V quickly. The Emerald M3DK ECU is 654, plus I suspect time at Emerald to set it up. This smells like 1000 to me. :-(

b) FSE Fuel Pressure 'boost' valve say 150 + RR set-up costs

c) can the PFRs get dirty/stick open?
Steve Ratledge

Hi Steve,
why not just change for another Rover stock item? Also dirty/partly not closing injectors could be the problem. As for the stock FPR it can be "tweaked" for slightly higher pressure by gently forcing it into a vice with an appropiate big nut at the airhoose side. For lowering back the pressure it can be slightly more complicated as the main spring inside the housing now needs to be slackend the other way = housing needs to be slightly higher. Probably possible by gently deforming the housing, but hard to get a good grip...And of course it has to be well calibrated in a pressure system,this is probably the toughest part for a DIYr.
Problems like these normally come AFTER change of the fuel-filter when small amounts of dirt has enterd the system...
BR, Carl.
Carl Blom

The fuel-filter was changed last year during the 5yr service. But I have not had the A/F ration measured before, so I don't know how long the issue has been there.

Also dirty/partly not closing injectors would be dificult to detect I suspect with out removing them and then testing. The car does not do a lot of miles, in fact only just 30k in its 5 1/2 year life.

I work as a contrac project manager so if can go months with out much use and then be used every day depending where the contract is.
Steve Ratledge

It might be easier to fit some hotter cams and simply use up the extra fuel. :-) LOL
Steve Ratledge

Problem is that if you have a leaky injector then you are in more trouble as soon as the ECU gets into closed loop running. In this case it will starve 3 cylinders to average against the one leaking.
With a leaky injector I would expect it to run richer at low RPM
Will Munns

Euuuck! Over fuelling - tell me about it.

As Carl rightly says, increasing the rating is easy - that is the vice job. Reducing the rating is harder: would pulling on the vacuum outlet achieve the right result? I suspect that it would be very easy to damage the FPR in attempting to do this :o(

Cheapest option is likely to be an FSE FPR with RR set up. The FSE can be had for under 100 quid if you shop around - I think 150 is expensive. RR time is expensive - but if you can piggy back on a shoot out day like Dave did, then clearly you can save quite a lot of money.

A few of the guys seem very keen to return to a RR in September - which suits me too. Opinion seems to favour the Emerald RR - so you could always have a chat to Dave Walker about your options either before or whilst we're there...
Rob Bell

Rob,
After a long lunch I'm confused with all these acronyms, please be more pedantic.
Regards Mike
Mike (London Office)

RR = Rolling Road
FPR = Fuel Pressure Regulator
FSE Power Boost Valve = A device made by Fuel Systems Enterprises to replace the FPR [see http://www.fuelsystem.co.uk/pbv.htm]
ECU = Engine Control Unit, The brain of your car
A/F Ratio= Air to Fuel Ratio
RPM = revs per miniute
HP or BHP= Horse Power ~ unit of power, work done
Steve Ratledge

Rob, is it possible that the early 1.8i's all do this? I have seen a lot of sooty F tail pipes.

Scarlet what was your A/F ratio like?
Steve Ratledge

Thanks Steve :o)

Perhaps there ought to be a glossary link for all these TLA's? ;o)
Rob Bell

If the injectors are gundged up you could try some Forte injector cleaner, (as sold by garages and MGR) or Redex injector cleaner (as sold by Halfords)
Will Munns

Will, is injector removal a big job? Any instructions?
Steve Ratledge

The injector cleaning is done with a fuel addative (unless you want to pull them out to check leakage) so the jets stay in place.

The injectors are held into the manifold by spring clips... but they are inside the 'snailshell' of the manifold - so an ar*e to get to with the manifold on the car. More obvios on the midget - where you can see everything!
Will Munns

>> Scarlet what was your A/F ratio like? <<

To be honest i don't know - i was looking through my printouts the other day and i'm not sure i have one, or if i do i can't decipher the scale.

I'll scan them in and mail them to Rob, maybe he can shed some light on them.

SF <--- Seriously considering the FSE and an RR 'tune up' :-)
Scarlet Fever

The air/fuel mixture was measured on Scarlet, but unless you specifically asked, Chris would not have printed it off for you. But drop him a line at G-Force, and I'm sure he'll be obliging mate.

Would definitely appreciate a scan of your plots though Andy - will try and get them all together in one place for all to see: a lot of very interesting things learnt on Saturday! :o)
Rob Bell

This thread was discussed on 16/07/2004

MG MGF Technical index

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