FP vs boost - ASH ?

[CalTe]

How well can I aspect the fuelpressure to follow the boost.
I use a original FPR altered to a adjustable one and the EDS Phase 3,5+.

If the basic pressure is 4.5 Bar (whithout vacuum) and the boost is 1,5 Bar should then the fuelpressure be 6,0 bar ? its sounds quite logic but is it allways a fact.

When my boost is -0- the FP is 4.6 Bar.

When I have a Oboost of 2 bar the FP is 6,24 bar, 0,26 Bar is missing.

When I have a Vacuum of 0,4 the FP is 4,9 !!!! ???

Ive checked if there is any leak but no.

 

[Joe]

Yes, the formula :
vacuum fuel pressure + boost pressure = fuel pressure
works in general quiet good.

But its naturally only possible under perfect conditions:

Your fuel pump has to be able to deliver a fuel pressure more or equal to the max. calculated fuel pressure whilst at the same time the maximum of fuel volume stream needed by the engine, can be pushed through the pump and pipes .

Your fuel pipes diameter have to be big enough, so that the pipes pressure reduction under high flow is not signifcant.

You shouldn't have a hole or leakage in your pipes

When I have a Oboost of 2 bar the FP is 6,24 bar, 0,26 Bar is missing.

When I have a Vacuum of 0,4 the FP is 4,9 !!!! ???

4.5 bar vacuum fuel pressure + 2 bar boost pressure = 6,5 bar FP
0,26 bar lost !! This is possible due to problems with the conditions as stated above . But as the overboost lasts not very long, I think it should be ok.

Your vaccum value should be 4,2 bar ! 4,9 bar is by far too high ! But I don't understand why the fuel pressure is higher than at 0 bar ! Are you pretty sure that you havn' misread the gauge ?

How have you checked your pipes ? A visible check is not(!) enough! It might be possible that you will encounter a little hole or a leakage in one of the small pipes, which can't be detected if not under pressure !

I personally think that a vaccum fuel pressure of more than 4 bar with the stock injectors is a little bit huge. But I know that EDS sells its Phase 3.x kits with such an high FP adjustment.

 

[CalTe]

Hi Joe - my fuelflow at the rail is ~ [email protected]. I think thats OK ?

Yes it sounds like I have a leak somewhere, I have to make a new line leaktest. I will now take the whole line from the trottlehousing to the original "dump"valve at test it.

I have bypassed the hotstartvalve and I have clamps on the hoses.
There is NO leak from the FPR.

 

[rds]

Fuel breather system is not working properly! Try taking the fuel tank filler cap off and then redo the test, should have the fuel pressure you require. This happened to mine :wink: