Flusteds DIY Giro valve (check valve)

[flusted 0]

So we believe the ecu can bleed boost out of the ISV once its reached 1bar.

Companys sell a one way valve which allows the ISV to breath air,but not to blow boost out.

I decided to make 1 today as i was breaking a golf mk2 gti,and found some usefull bits to do it.

I used a reducing pipe from the isv on the golf mk2 gti and the 1 way valve that runs to the brake servo.

Heres the pic of the hose on the golf gti and then you can see the finsished item on mine.

All i need to do is add a breather on the end.

Took me 10mins max and cost me sod all 8)

[steveo29 0]

i thought it was a bad move?? stops the isv bleeding boost when its suposed to

[flusted 0]

depends how you look at it. Sometimes isv's leak anyway under low boost,this way garauntees it wont.

[peteTDI 0]

but if it needs to vent over boost ie a boost spike then it can't, then your rods bend then pistons fly out the block ect ect

[catch_twotwo 0]

Hmm... starting to think maybe a K&N filter might be better for me than the re-route I was planning.

 

@Pete: Is this fact, or just pure conjecture on your part... i.e. has to ever happened to you, or a just a friend of a friend who once had a Corrado ???

[flusted 0]

Jabba have sold loads of em ( i know that doesnt say much though) and ive not heard of anyone having a problem.

Most chips run a tad rich higher up anyway so that should compensate

[flusted 0]

Ive just done loads of searching on the vortex and found that 1 of the chaps from sns is addiment that only some ecu's STANDARD chips have the function to vent,so as soon as you re-chip your car,you wont have this feature anyway.

People have run 1.5bar of boost with no sign of the isv leaking

[catch_twotwo 0]

Surely if it's such a rare occurance to vent... there is no point in re-routing at all.

[Polo Classic 0]

The thing is, that if the ECU does not sense less boost when it has told the ISV to bleed, it retards igniton. This hurts performance more than the loss of a little boost

 

The ISV normally bleed when the MAP-senor voltage is around 3,7V

[flusted 0]

Surely if it's such a rare occurance to vent... there is no point in re-routing at all.

 

"The isv only vents when it leaks" is what the american chaps are saying and they do occasionally leak.

 

I presume it doesnt retard ignition either,only if there is pinking

[Edition 1 0]

This is a quote from Beavis over on the Dubforce forum, hope it sheds some light on the subject ! -

 

The beloved MAP sensor issue. Good old Mr Bosch was far too through with his fail safes when he designed the Digifant system. The failsafe are all well and good on a standard car but unfortunately bite back when we tune the cars by throwing a spanner in the works.

The original 200kpa map sensor found in most Digifant ECU's is a 200kpa absolute sensor which means it has a 2 bar pressure scale, 1 bar of the scale is atmospheric pressure, so a 2 bar absolute sensor will only be capable of effectively measuring 1 bar of positive pressure and 1 bar of vacuum.

Inside the map sensor chamber is a small silicone chip that flexes a given amount when boost/vacuum enters the map sensor chamber. The resistance of the chip changes as the chip flexes which alters the voltage of the output signal which is roughly 1-5V.

The part ECU processor determines which points of the main fuelling map are to be accessed by using signals from the engine senders. The hall sender relays information in the form of a pip signal from which the processor can calculate RPM and the voltage of the map sensor dictates the other axis.

A map sensor at atmospheric pressure will produce a signal of around 2.5V, on vacuum overrun just under a volt and at 1 bar 5 volts.

On various cars I’ve mapped they either play ball and do not bleed off at all and you can successfully map them, others are a pig and bleed off very early. The values of any parts of the map do not alter this bleed point unless the car pinks and then the ecu will detect this and knock the timing back until the pinking stops.

The voltage of the maps sensor e.g. 5 volts kicks the bleed cycle off along with ignition retard.

By swapping the map sensor to a 2.5 bar sensor it allows you to change the threshold of the point where the ECU will bleed. One bar of boost applied to a 250kpa sensor will only hit say 3 volts, hence the bleed cycle is not triggered until later.

Swapping the map sensor for a different pressure does mean you encounter other issues. The Processor is seeing 3volts at 1 bar for arguments sake, this means that is referencing its 3volt value, which would equate to say 0.6 bar, so will only fuel for 0.6 bar of boost from the value of the original map.. 0.6 bars worth of fuel with 1 bar of air will mean the car is running lean.. Then it pinks and the bleed cycle is off again.

Once the maps sensor is fitted I have to change the values of the whole map to compensate for the different scale, so the at the 3volt reference point the value has to be similar to that of the old 5volt reference point.

The moral of the story.. If you only swap the map sensor and you run the original map you will soon have a hole in your piston.

The other way of looking at it is reducing the manifold pressure by changing components of the engine to allow it to flow. Manifold pressure is a measure of the pressure backed up and not the pressure in the cylinders where it is doing its job. Fitting a higher lift/longer duration cam combined with a flowed head will see a drop in manifold pressure. The same priciple applies though regarding the map. You have now got more air in the cylinders for combustion, but the ECU is seeing 3 rather than 5 volts.. But the 5 volt fuel is still required so the index points need to be altered accordingly.

 

Better to know than stabbing in the dark :wink: