Here comes some questions related to improving my Fel 1.3i SPI in rally use. If you have idea at least to some question, please tell me.

1) There is always need to simplify all systems and remove all extra accessories (extra weight and fault risks...). I´m removing carbon filter filtering gases from fuel tank but could it cause some problems if just remove it and plug pipes? This has nothing to do with replacement air feeding to the tank, right?

2) There is several hoses coming into intake manifold. One comes from oil filler cap in valve cover, I think this operates ventilation when idling. This can be plugged, I´m pretty sure. Another one leads from air filter housing to manifold next to hose coming from carbon filter. What this one does and what if I remove/plug it, does it affect to anything?

3) In thread "SPI -> MPI conversion" James told something about fuel pumps capacity (more or less 60 l/h) but what are the pressures, how is pressure before and after regulator?

Edited 14 July, 200916 yr by FelRace
typos

2) Remove the PCB feeds to the inlet manifold and air-cleaner, block the holes in the intake, and redirect the PCB to a catch can.

I found some answers by myself and then more questions came into my mind...

2) Thanks Ken, that´s what I has already planned to do, having already catch can to use. Anyway I´d like to know the function of that another one little hose comin in to the manifold very near to tube from charcoal canister. From Haynes it can be somehow guessed that it has something to do with that charcoal filter function, so if canister will be removed maybe this hose can also be disabled.

3) Haynes gives those pressure after regulator, for SPI it is 0,8-1,2 bar and for MPI 2,5 bar. Still I dont know if there is markable difference between pressures from the pump to regulator. Reason why I´m interested is that I should raise fuel pressure to injector a bit and when in SPI the regulator is integrated to injector, it can´t be changed. And not tuned either, says Haynes.

I was wondering if regulator would be feeded with higher pressure, it could let some more pressure also through. Still I´m not sure, any ideas?

dont plug up the hose that was on the charcoal canister it will cause problems with fuel delivery/pressure... think of it like this, when you use fuel from the tank, the space it takes up needs to be readily replaced by air otherwise you build up a vacuum in the tank which makes the job of the pump more difficult...

if you plug up the hose from the rocker cover (breather) the engine will burn a lot of oil because there is no negative displacement in the crankcase to evacuate the vapour, and the engine will idle very rough

the hose from the canister to the throttle body is to allow fuel tank vapour to be burned in a controlled way, think of the chacoal canister as a kind of tempory storage tank for vapour, under certain operating conditions the cfsv (carbon filter solenoid valve) or (purge) valve allows the vapour to be drawn in to the engine

with regards to fuel pressure, firstly the pressure is measured before the regulator, after the regulator the fuel is fed back to the fuel tank via a second hose, this hose is not pressurised, it is only the flow which forces the fuel down it. i wont go into the benifits of having an excess of fuel in the system.... ok there may be another way of increasing fuel flow that you may not have explored... i'm not overly familar with the bosch or magnetti spi injector units, but i've had a quick look at one and it appears that the injector can be removed seperately from the unit. it's possible you could find an injector from a similar unit in a breakers yard from say a 1600cc engine as this would have a higher static flow rating than the original skoda one.. so in short, the pressure remains the same, but you get more fuel because the injector squirts in more fuel per cycle.

dont plug up the hose that was on the charcoal canister it will cause problems with fuel delivery/pressure... think of it like this, when you use fuel from the tank, the space it takes up needs to be readily replaced by air otherwise you build up a vacuum in the tank which makes the job of the pump more difficult...

if you plug up the hose from the rocker cover (breather) the engine will burn a lot of oil because there is no negative displacement in the crankcase to evacuate the vapour, and the engine will idle very rough

the hose from the canister to the throttle body is to allow fuel tank vapour to be burned in a controlled way, think of the chacoal canister as a kind of tempory storage tank for vapour, under certain operating conditions the cfsv (carbon filter solenoid valve) or (purge) valve allows the vapour to be drawn in to the engine

with regards to fuel pressure, firstly the pressure is measured before the regulator, after the regulator the fuel is fed back to the fuel tank via a second hose, this hose is not pressurised, it is only the flow which forces the fuel down it. i wont go into the benifits of having an excess of fuel in the system.... ok there may be another way of increasing fuel flow that you may not have explored... i'm not overly familar with the bosch or magnetti spi injector units, but i've had a quick look at one and it appears that the injector can be removed seperately from the unit. it's possible you could find an injector from a similar unit in a breakers yard from say a 1600cc engine as this would have a higher static flow rating than the original skoda one.. so in short, the pressure remains the same, but you get more fuel because the injector squirts in more fuel per cycle.

Thanks Tom. I already removed the chaircoal canister and plugged all the pipes (not removed pipe from tank to canister yet) I was only wondering that isn´t there any other air replacement channel to fuel tank than pipe from canister? Haynes says that tank is sealed but how can that pipe to canister act as only replacement air channel when there is suction to manifold when solenoid valve is open and otherwise it is closed -> air can´t flow to tank either..?

Related to breather hose, I was removing only smaller hose from rocker cover to manifold (operates breathing when idling I think). The bigger one will be led to catch can so breath will not be totally removed.

I think that you, Tom, explained me the function of the hose from chaircoal canister to manifold. I know that very well but still there is one hose, aboub 6mm between air filter housing an inlet manifold and in manifold that hose has connector near to the connecion of hose coming from canister. In filter housing this hose is connected in same terminal with hose to "hot/cold air switch" in air inlet channel. Well, that hose is now removed, let´s see what that makes.

Thanks for the advice to try another injector, I haven´t tried to modify fuel pressure regulator yet but if that doesn´t work, I can try to fing injector for example from 1.6 Vento havin Mono-Motronic system. Still about the pressures, when saying after regulator I ment the pressure to injector, not to return pipe that really is unpressurized. If those pressures (0.8-1.2 and 2.5 bar) are pressures for pump, how are pressures to injector in different systems, how much the regulator cuts the pressure?

the other option is to find a fuel filler cap with vent holes in it, iirc some of the favorit ones and vented and will be a direct replacement

the regulator doesn't cut pressure, it keeps it constant, it has a spring loaded diaphragm which also is vacuum regulated via a small hose iirc,