Fuel Pressure Problem

OK - any advice welcome

Problem - my secondary high pressure pump is very noisy and fuel pressure is fluctuating from 20 PSI to 60 PSI.

I removed the non return valve on the outet for the bosch pump, mistake ?? -

I’ve changed the regulator but still no difference.

Set up is as below


I would have thought that the regulator would go in a bypass line which would be between the fuel pump outlet and the return from the swirl pot, shown going back up to your ‘T’ piece.
The existing set up will cause pressure fluctuations due to air from the swirl pot.



Sorry Andy,
Have just looked at this again and the outlet to the fuel rail is top left, so the set up is correct.

1)Is the fuel pump flow and pressure regulator matched.

2)Is air being drawn into the fuel pump inlet?

3)Are you using the correct connections on the swirl pot?

4)Are these pressure fluctuations with the engine stationary or running?



Thanks for the questions

1.Pressure regulator is an adjustable one so you can get whatever pressure you like at idle - pump is a Bosch FSE0580254044 - 22104

  1. I dont think so as I’ve bled the swirl pot and there are no leaks etc

  2. Bottom connection is outlet to pump, There are three connections on the body and one bleed at the top - The bleed has a blank fitting on it ( so no vent …mmmm ) and the return from the regulator is the oppositite side to the
    inlet and return from the tank

like this


4. Well theres the point - there is a vacuum connection which is connected and I adjusted the pressure to give 43 psi ( recommended by the injector suppliers ) at idle.
Now, when under load teh pressure was rising to 60 psi or so, when your off the gas it dropped back to 30 psi or so.

Now after 60 miles or so the idle pressure is down at 30psi.

I cant help thinking its a pluming problem… but the pump has been very noisy from day one

Ooops … that pump is rated

Max psi - 180

Somewhat overkill maybe

To select the flow rate required use the info below:-

As a rule of thumb, at wide open throttle an engine requires 0.5lbs fuel/hp/hour
A US gallon of petrol weighs 6lb

Therefore for an engine rated at say 300hp it will require 150lbs of fuel per hour OR 25US gal/hour.

A US gal is 3.8litres

Fuel flow rate required will be 25 x 3.8 = 95l/h

In terms of pump pressure requirement 3 to 3.5 bar (43 to 50psi) is adequate.

Another point is that some fuel system layouts have an inlet and outlet on the fuel rail with the pressure regulator fitted on the outlet line back to the swirl pot. This ensures a constant flow of fuel through the fuel rail rather than a dead end.

Your existing fuel pump rated at 400l/h @ 180psi is too big!!!

400l/h would equate to 1200hp, surely you are not trying to get that out of a Honda engine?
We will have to call you King H otherwise!!!




Yup 300 HP is where all the SC Honda’s end up or there abouts.

Yes, I asked for a specific pump that was actually rated at 180L/H and I got this one ( it will do the job ok Sir …) and didnt look until this morning at the specification …

This may explain why my first pressure regulator started to leak …

Thanks for the help ! I will get the correct flow pump thsi time and start again …


Andy, I will call you later. I don’t think it is because the pump is overkill, however I have a few you could borrow to try. Do you know if the pump sucks as well as blows?? I know that if it only blows (as most of them do) it will have problems getting a nice gravity feed through a fuel filter.

Cheers Sean