bodace5

Hi. Fuel pressure at idle was 2.5bar so ive adjusted it to 3bar but once i remove the vacuum/pressure pipe it shoots up to 4bar not 3.5bar? Should i change the pressure regulator? Its an aftermarket regulator thats bolted to the map sensor bracket with an adjuster on the top

oldford

Looks like you have a non-linear regulator. If your mapping is not for this regulator, but rather for the standard linear regulator, then Yes, change it.
I would change it anyway, and when necessary adjust the mapping to a linear regulator.

bodace5

Ive only just bought the car. Its running 803 greens, t34.63 turbo, wasted spark, 3 bar map sensor and an MSD chip but reading through the receipts, the aftermarket fuel regulator wasn't mentioned when the chip was ordered and i don't think its had a proper set up on a dyno?

stevieturbo

You never set fuel pressure with the vac pipe attached.

bodace5

Why? It should still drop to 3bar not 2.5bar anyway

stevieturbo

Because you never set fuel pressure with it connected.

Manifold vacuum is a variable, trying to set fuel pressure tp a specific value with a variable applied is stupid.

And how much it drops depends on how much intake vacuum there was.

There is no generic it "should" drop a set amount, because the governing factor is a variable.

If you want to test the setup properly, get a Mityvac or similar and test it properly by applying known amounts of vac/pressure to the regulator and noting fuel pressure, and ensure any gauges you're using are known to be working correctly.

Guinnless

You need a standard Weber Marelli fuel pressure regulator set to 3 bar with the vacuum pipe disconnected. Once set, you reconnect the vac pipe.

This vac/boost pipe provides the signal to the FPR to regulate the fuel pressure according to the inlet manifold pressure. At idle the fuel pressure will drop by the same amount of vacuum in the inlet manifold so as to maintain the correct differential pressure. At 1 bar of boost you'd should have 4 bar of fuel pressure.

Because you now have 4 bar at idle you are asking the fuel pump to deliver 1 bar more pressure for the same boost level (5 bar for 1 bar boost), if your pump and wiring are not able to cope you'll run lean and blow the engine.

2Litre

I disagree but fuel pressure depends on what the chip is written to run. Saying that most run a fuel pressure of 3.5 bar with vacuum pipe disconnected, the pressure tends to drop to just under 3 bar at idle. Yet this is neither here nor there.

Best.

Tim.

oldford

Standard fuel pressure for the standard Weber Marelli fuel pressure regulator is 3.5 bar with the vacuum pipe disconnected.
But that's for a standard chip. Ask MSD what fuel pressure regulator you should use and at what pressure this must be.

Guinnless

Yes, you're right it is 3.5 bar. My error.
MSD normally use standard fuel pressure
but no harm in asking.

gcfcos

This exactly. Checking and settling fuel pressure should be done with vac pipe unattached

bodace5

Im going to get it set up properly at MSD next year anyway. Im trying to get everything working as it should the best i can before i take it. Everything ive read says it should be 3bar attached and 3.5bar disconnected so im going to invest in a new regulator probably from MSD just to make sure. Whats the advantages of running a non-linear regulator?

oldford

In my opinion, none whatsoever, there are only disadvantages.
If a car like this one is presented to me for (chip) tuning and has a non-linear fuel pressure regulator, I refuse the job until a normal linear fuel pressure regulator is used.

bodace5

Its got one of these on it. What do you think should i change it?

stevieturbo

That looks more like an old carb type regulator.

cozzy jeff

iTrader: (4)

I would remove it if I was you, nothing wrong with the standard regulator