What controls fuel at WOT?

[Jonas_R]

Thanks prosty will do that.

[EspenW]

Yeh take a variable resistor and play with VAGCOM logging air temp with engine running - adjust for say 0 10 and 20 degrees even if real temp is 20... you may get some knock at very low fake temp so be careful... This is not an ideal test but should something.

Hmm, feeding the ECu with a fake cold signal is an old trick for enrichening the mixture, so that would rather decrease the risk of knock?

[S2central.net]

Tis indeed Espen - but I am trying to see if the fuel compensation in 20 degree ambient is significantly more than 10 degrees... Not that its my chips you understand - just trying to help. In times like these there is something to be said for a variable FPR - but you already know about that !

[EspenW]

Yep, adjustable FPR really is handy. A must for a "flexi fuel" car, but nice on a "fixed fuel" one as well.

[Jonas_R]

Tested with the resistor but no difference at all, still running rich.

And nothing stock in the air filter, but going to Sweden next sunday to see if we can remap the fuel.

Plan is to check the fuel pressure next week to see if it is ok.

Does it matter where I take the fuel pressure on the fuel rail?

[Jonas_R]

Yep, adjustable FPR really is handy. A must for a "flexi fuel" car, but nice on a "fixed fuel" one as well.

What is the advantage with the adjustable FPR?

[Jonas_R]

So I got to test the fuel pressure today:

It shows 5.3 bar at WOT and 3.5-3.6bar at idle.

Now this seems to be way to high, I think the FPR is fooked

[Jonas_R]

Does the coolant water readings from MFTS have anything to do with how much fuel is put through the engine at WOT?

There is also compensation for air temperature so that might explain the extra fuel you are seeing - that is quite a jump though. Could be a mistake in the mapping maybe if this is first hot weather running you have done... You could prove that by faking a colder air temp signal into ECU of course - if that alone makes for better mixture then your map needs another tickle.

[S2central.net]

So I got to test the fuel pressure today:

It shows 5.3 bar at WOT and 3.5-3.6bar at idle.

Now this seems to be way to high, I think the FPR is fooked

Hold on... what FPR do you think you have ?

If its a nominal 4bar FPR then subtract roughly 0.5bar vacuum at idle to give 3.5bar
and then add manifold boost pressure to nominal 4bar to derive fuel pressure.

The fuel RAIL pressure is set to be 4bar above manifold pressure... Unless you have a 3bar FPR - then these numbers you have are terrible and will cause rich running.

You can measure fuel pressure anywhere on the way INTO the fuel rail. The regulator is located at the EXIT of the fuel rail - you don't want to measure pressure in the return pipe that exits the FPR and back to the tank.

[S2central.net]

Does the coolant water readings from MFTS have anything to do with how much fuel is put through the engine at WOT?

Nope - water temp is derived from coolant temp sensor at rear of the head - not the MFTS - it is worth checking this as permanent cold water temp will give rich running.

[S2central.net]

What is the advantage with the adjustable FPR?

Simple really - gives you a good degree of mechanical adjustment for fuel pressure. Its not something to **** about with of course - but lets you have car beautifully mapped on some setup then over time the MAF (or whatever) starts to degrade / become less accurate over time - with lambda control at part load the mixture will be OK, but it could skew off rich or lean at WOT as there is no lambda feeback...

Being able to tweak FPR little high or little low would correct mixture at WOT. Its just another tool... also useful if running a mixture of fuels and you have a switchable ECU which needs different FPR to work properly. Running between petrol and E85 for example.

[Jonas_R]

Hold on... what FPR do you think you have ?

If its a nominal 4bar FPR then subtract roughly 0.5bar vacuum at idle to give 3.5bar
and then add manifold boost pressure to nominal 4bar to derive fuel pressure.

The fuel RAIL pressure is set to be 4bar above manifold pressure... Unless you have a 3bar FPR - then these numbers you have are terrible and will cause rich running.

You can measure fuel pressure anywhere on the way INTO the fuel rail. The regulator is located at the EXIT of the fuel rail - you don't want to measure pressure in the return pipe that exits the FPR and back to the tank.

I have a 7A FPR and this is 4bar, so I should meassure 3.5 bar as you say and I'm seeing 3.6 bar at idle. So I guess that is ok?

I'm measuring the pressure just when it enters the fuel rail.

But here is where I get confused because you mention 4bar above manifold, then I suppose I should see nominel pressure (4bar) + relative boost pressure (1.7bar) on the fuel pressure gauge?