Fuel Mixture Adjustment

[hengti 2]

Picked up a few interesting ideas from the forum this week - will have a go at lowering my seat and re-stuffing my seat bolsters this weekend (although Pug quoted me £140 +vat for new foam earlier - !? - trip to the scrappies first thing Sat!).

 

Something else I've been meaning to do since having HG changed is fiddle with the fuel mixture. The engine comes up to temp v quickly (although doesn't 'overheat'); I've noticed the plugs are pale and think this is the last possible cause of the heat problem on my list.

 

I can't afford a RR tune for a month or so, so wondered if there's anything I can do to cheer the plugs up a bit (and hopefully bring the heat issues down).

 

I've searched but can't really make much sense of all the info out there. And the Haynes manual is useless.

 

What's adjustable? I'm guessing I can tinker with the mixture adjustment and AFM - although I've really no idea of how they work ...

The car's also fitted with a FSE (which I'd pref not to muck about with). It's had a head skim as well - I'm wondering if thats thrown the fuel mixture out - ?

 

 

Basically - can anyone offer me a brief idea of how to set up the mixture at home? Is it possible? or am I opening a can of worms?!

 

Thanks all

[Rob_the_Sparky 9]

Officially you can only adjust idle mixture and speed and the ignition timing (worth getting this right first). However, it is also possible to adjust the AFM spring tension and that will alter fuelling across the range. However, this was set acurately at the factory and you don't know quite what the result will be without at least an accurate way of checking the mixture and ideally you want a rolling road to make sure it isn't too lean anywhere.

 

Adjusting the AFM spring is only to be done very cautiously. Commonly adjusted to lean the mixture at idle (to stop them hunting) but without considering the effect on all other rev/load conditions.

 

It could be the FSE that is the problem of course. The amount of fuel injected by the ECU is controlled by opening the injectors for an appropriate amount of time. This works because the flow rate of the injectors and the fuel pressure is known. The FSE adjusts the fuel pressure so it is possible that this is what is the problem. I haven't had a GTi that ran anything other than a pretty muh perfect mixture apart from at idle (where it is generally rich).

 

Rob

[hengti 2]

Thanks Rob

 

I've had another look in Haynes and have spotted reference to an allen key adjuster on the AFM body which is described as being for mixture adjustment - does this only adjust idle mixture as you've inferred though? Tbh, don't much fancy fiddling with the AFM dial as not confident I'll be able to get things back to where they might have been beforehand if things go wrong (I'm only assuming this though, as many people seem to have afm bother ... am I right to be wary of fiddling? If it's do-able, how do I adjust?)

 

Also, do you know which way to turn the nut on the FSE to increase pressure?

 

I'm thinking that if I take a note of original positions, I can put things back if I'm not happy

 

Cheers

Henry

[Rob_the_Sparky 9]

Making notes of initials is extremely wise.

 

Yep, the mixture adjust on the AFM is only idle (well pretty much only anyway). AFM measures the amount of air passing over the flap and meters the right amount of fuel. The screw is a small air bypass over teh flap, the more air that passes through the bypass, the less is measured by the flap so less fuel is injected so leaner running. As it is only a small drilling it is insignificant at pretty much anything but idle. To weaken the mixture turn anti-clockwise and clock to richen.

 

Fiddling with the AFM spring is not really advisable unless you are confident you know what you are upto. As a general rule it is bad to fiddle with this but under the right conditions it has potential.

 

On the FSE I have no idea but the general feeling from the people on here who have tried them isn't good. Try a search on the subject, I'm sure there are some first hand experience posts on here.

 

Ignition is a potential source of much improvement, it is not uncommon for 1.9s to be run on unleaded. This requires quite a lot of ignition retard which makes them feel "flat" and looses power and economy. If yours has ever been tuned like this then some additional ignition advance could work wonders.

 

Rob

 

P.S. I forgot, you can also clean the AFM internally, but that generally only helps idle issues, and re-track it. Pretty sure there is a guide on the main site for re-tracking the AFM (they tend to wear grooves where they have been running for years) but I've not tried this myself.

Edited February 10, 2006 by Rob_the_Sparky

[Rally Slag 0]

ok call me stupid but after just reading that where u said its not common for 1.9s to be run on unleaded, where they designed to be run on leaded petrol? just a quick (probably dumb) question, i allways run mine on super unleaded anyway, probably have to adjust my ignition timing, advance it a bit, but aint got a timing light at work at the minute and snap on dealer is being a pain trying to get one

[Ahl 4]

They are designed to be run on super unleaded. (or any high octane petrol, thought the CAT models don't want leaded!)

 

I find it works out cheaper to run on super anyway. You don't need to set the timing with a timing light. For optimum economy and performance you want to advance it until it begins to pink, then retard it a small amount.

This has been described loads of times before, a search should find the topics.

[Rally Slag 0]

lol cheers m8, i allways run mine on the tesco super stuff cause it says its 99 ron, just out of curisity what you other guys running yours on, bp ultimate? shell optimax? The tesco stuff is just as cheap as normal shell petrol, duno if its any good but says 99 ron so fuk it

[hengti 2]

lol cheers m8, i allways run mine on the tesco super stuff cause it says its 99 ron, just out of curisity what you other guys running yours on, bp ultimate? shell optimax? The tesco stuff is just as cheap as normal shell petrol, duno if its any good but says 99 ron so fuk it

 

 

My personal order of preference is Ultimate - Optimax - Tesco99

 

Ultimate is expensive and can be difficult to find

although I think it's the best of the lot

try it with some Millers Octane Booster ...

 

 

 

Haven't had chance to fiddle with my fueling yet; ta to Rob for the guidance though

Edited February 11, 2006 by hengti

[jonD6B 0]

My personal order of preference is Ultimate - Optimax - Tesco99

 

Ultimate is expensive and can be difficult to find

although I think it's the best of the lot

try it with some Millers Octane Booster ...

Haven't had chance to fiddle with my fueling yet; ta to Rob for the guidance though

 

 

Does Octane Booster actually work then?

[hengti 2]

Does Octane Booster actually work then?

 

Definately

in my experience anyway

 

it helps alot in reducing pinking (allowing you to run more ign adv) - I've certainly noticed it running a bit 'crisper' in the mid range

 

my car's set up to run on it though (or it was anyway - above refers!)

You could try it and see what difference it makes to a car that hasn't been specifically tuned to run it. Mates have tried (with non Pugs) and have noticed a difference

Edited February 11, 2006 by hengti

[Rally Slag 0]

yeah a m8 of mine uses it, think it gives like 7 more ron so using tesc 99 would give u like 106 ron fuel which should deffanatly be noticable compared to say normal 95 ron unleaded

[Rob_the_Sparky 9]

Check the bottle, from what I've read on octane boosters additional octane is measured in points. e.g. 7 = 0.7 octane boost. However, I've never used it but they guys were discussing all sorts of additives and seemed to know what they were on about.

 

Rob

 

(Oh to be able to type it right first time!)

Edited February 13, 2006 by Rob_the_Sparky