How much should the pressure increase when you rev the engine, mine is set at 4 bar but only goes up .5 bar when you rev it, im sure it used to go up more but i cant honestly remember!

 

Fuel pressure increases with "boost", not rpm.

So if your pressure is set to 4 bar at "atmospheric", then just add what ever boost you have, and that's what the fuel pressure should be.


Mark.

 

Thanks for the reply Mark, what would standard pressure be then?

 

generally speaking the cars idle at around 2.5-2.6BAR and then dependant on spec you will see around 3.5BAR on boost at 1BAR of turbo pressure..............

alyn

 

3 bar is standard with vacuum hose disconnected.

 

What will it be with it connected?

 

Less - Alyns figures a few posts above

 

Alyns figures are based with the vacuum hose on, so the boost pressure will be negative (in vacuum), and therefore lower than at "atmospheric" (boost hose off).


Mark.

 

I think i get it now, with hose connected 2.5-2.6 bar ( standard car running 1 bar boost approx ) so running 1.4 bar boost should be 3 bar on idle with hose connected ?

What would cause the knockling to get animated at 7k?
The car runs perfectly with no action on the knockling at all until it gets to 7k then goes up to amber and red if you redline it (which for obvious reasons I avoid!)
Would a broken release bearing in the gearbox cause this, or a loose heatshield on the downpipe?
Or is it charge temp related?
It has a bigger topmount from a newage car but there isnt anything to direct the air into the intercooler as such and there is quite a gap between the intercooler and the scoop if you know what i mean!

 

no the fuel pressure at idel on a std car is 2.5-2.6 BAR............at 1.4BAR off turbo pressure add this to the idle pressure so it will be around 4BAR on full boost in that spec

alyn

 

Not entirely correct alyn.
The idea is that the pressure between the fuel and intake manifold always remains equal.
stock this pressure differential is 2 bar.
At idle pressure in intake manifold is about 0.3bar absolute thus fuel pressure is 2.3 Bar
for a NA engine at wot intake manifold is about 1 bar absolute. thus fuel pressure is 3 bar.
For a turbo engine making 1.4 bar boost (or 2.4 bar absolute), fuel pressure is equal to 4.4 bar.

if you disconnect the vacuum connection on the FPR it "sees" 1 bar and thus makes 3 bar.

 

So does this mean fp on idle should be 3.4 bar approx? (with hose connected)

 

This is getting very confusing, and it's much easier to talk about pressure, as seen on a normal boost, & fuel pressure gauge.

Standard fuel pressure is 3 bar, set at "atmospheric" (vacuum hose off), which is "0" on a boost gauge.

However, turbo engines run in "vacuum", until the turbo produces pressure, so when the vacuum hose is fitted to the fuel regulator, the pressure drops below "0", by circa .4-.6 bar, and the fuel pressure will drop by the same amount, so it will be 2.4-2.6bar.

When positive boost is run, the boost pressure is added to the pressure at "atmospheric" (3 bar), not the pressure at idle, or when the car is run in vacuum.

So at idle you will see circa 2.4-2.6bar fuel pressure, rising to 3 bar at atmospheric /"0", and after that, you will see 3 bar + whatever boost you're running.


Mark.

 

This now makes sense (I think) how does the fuel pressure rise then?
If it rises with boost is the ECU supposed to control it?
or is it manual so to speak ?

 

Im still none the wiser chaps!!!!!

1.4 bar boost 4.4 bar fuel pressure on idle (hose connected)

 

take the hose off the regulator, set it to 3 bar. put hose back on. leave it alone.

If you didn't understand Mark (lateral) 's post. leave it alone

 

O.K im officially thick

from what Mark said the fuel pressure needs to be atmospheric pressure + boost so 3 bar + 1.4 bar = 4.4 bar if thats not the case i should probably sell the car and buy a saxo

 

no, you will never see 1.4 bar on idle as the turbo isnt producing the boost.

Basically when not on boost ie negative boost <0 fuel pressure will be as Mark mentioned.

When you are no longer producing negative boost nor postive boost ie 0 bar then fuel pressure will be at the 3 bar.

any positive boost > 0 means that your fuel pressure will be 3 bar at the 0 boost point, so for instance 1.4 bar means your producing positive boost you add this 1.4 bar to the 3 bar which is neutral boost

Hopes this makes it clearer for you

 

i dont have the fuel gauage in the car so i cant see whats its doing on boost so to speak!
I figure set it to 4.4 bar with hose connected if im running 1.4 bar boost peak!

 

no because then you will be running 5.8 bar fuel pressure when running 1.4 bar of boost, you will also be massively overfuelling, economy will be worse, the car will run like a pig, your plugs will foul up possibility of bore wash

 

Pressure

Boost gauge....-0.5/-0.6/-0.7/-0.8/-0.9/0/0.1/0.2/0.3
Fuel gauge.....2.5 /2.6 / 2.7 /. 2.8 / 2.9/3/3.1/ 3.2/3.3

 

are we getting there yet???

 

I wont tell you I have a degree because you will take the P*** no doubt, the last diagram was very very simple

Thanks for all your help guys

 

What controls the rise in fuel pressure?

 

the vacuum hose, is connected to the manifold so add the turbo pressure to the fuel regulator, this is why you see the low pressure when stationary and when on boost it will automatically rise to the required setting

DO NOT set the fuel reg to the max. you want at idle

alyn

 

The vacuum pipe going from the regulator I presume, therefore remove the vacuum pipe set the pressure at 3 bar, re connect the vacuum pipe and then the pressure will control its self according to boost...

The pressure will go down at Idle and up when on boost.

Gaz

 

Offcourse Mark is right
I (also) made a small error in the first post

Think of the FPR as a device which always maintains a pressure difference between the fuel and the intake manifold pressure.
stock this pressure difference is set at 3 bar. with an aftermarket FPR it can be adjusted.
it does this job automatically without any interference of ECU or whatever.
it consists of a membrane with manifold pressure on one side and fuelpressure on the other. A spring is used to assist the membrane on the manifold side of the membrane (adjustable for the aftermarket one). the force of the spring creates the constant pressure difference between the fuel and manifold pressure.

hope this makes any sense

 

Thanks guys I think i finally understand it!

standard boost pressure on most cars is circa 1 bar im guessing so i should be running enough of an increase to compensate for .4 bar increase, the car has different injectors as well.

The reason for all the questions is im getting a red led on the knocklink at 7.5k revs and im not sure what the cause is, if i keep it under 7k no knock activity at all, it's a bit strange really, i changed the spark plugs to 6b's from 7b's im not sure if this cause this or not, tired fuel pump could be another I guess or maybe tired regulator, upping the fuel has helped but from the advice i have had on here it's probably a bit too high, it's set at 3.2 bar with vacuum pipe off.Thanks again

 

ah With what fuel pressure was the car mapped?
its best to set the pressure before mapping and then leave it alone.
by increasing it, the car will run richer at all loads and rpms.

but it does sound the car might be running lean up top.
still on standard fuel pump? which power are you making?

 

It's a 2.2L build engine with hybrid IHI Turbo running 1.4 bar ran somewhere near 340hp 320Lbft but that was a 18 months ago. There is also a flash on the knocklink in the higher gears when it comes on to full boost, seems it could be a pause while the Fuel pressure catches up (lazy fuel pump maybe)
Would a MAF give these symptoms?

It feels like the car can produce a lot more power if it had a bigger turbo, the IHI is quite small but does spool quickly boost starts at about 2300-2500 revs and is maxed out at under 4000k but it runs out of puff at 6k and starts to drops back to 1.1 bar (from 1.4 bar) got me baffled ( I hear you cry "that's not difficult")