matthart

Disclaimer: I'm not a mechanic or a professional automotive engineer. I've done a lot of reading, especially the articles by STU @ MSD that are in Fast Ford.
I'm also sort of Stu approved about this topic: https://passionford.com/forum/5480334-post17.html
But of course, anything you do to your own car is your own fault, I'm just trying to be helpful.

STU's Tech articles: http://www.motorsport-developments.co.uk/stus.html

Relevant fuel pressure article: http://www.motorsport-developments.c...AF242.tech.pdf

EFI fuel systems like the XR2i, Fiesta RS Turbo etc rely on the fuel system being able to maintain the pressure DIFFERENCE between each end of the injector.

Most injectors (certainly the Ford ones I've used) expect a 3 BAR DIFFERENCE. Therefore, when you hit 1 BAR of boost, the fuel pressure regulator will try to hold the fuel pressure at 4 BAR.
An example:
Inlet side of injector is at 1 BAR (you're in boost)
The expected pressure DIFFERENCE across the injector is 3 BAR
Fuel rail side of the injector needs to be at 4 BAR

In an N/A engine, the inlet side is always a vacuum and never goes positive, so an example when you stamp on the throttle:
Inlet side of the injector is at -1BAR (yes MINUS)
The expected pressure DIFFERENCE across the injector is 3 BAR
Fuel rail side of the injector needs to be at 2 BAR.

This is where people (including me) get into trouble when they turbo their car, it's been running fine as an N/A but you're suddenly demanding a lot of a 20 year old pump/wiring/pipework.

Lesson over, onto the testing. This was all done on an EFI Turbo (Fiesta RST engine). It should work the same on other cars but the connectors might be different.

Step 1: Take off that Rising-Rate/Power-Boost-Valve/FSE Fuel pressure regulator, bin it, and put a standard one back on. Then don't touch the adjuster screw, it should be sealed shut.

Step 2: Order an in-line fuel pressure gauge, some couplings and pipes, and make up something like this:

Mine has ends like this

And this in the middle

Basically you need some way of fitting a pressure gauge between the fuel filter and the fuel rail. I cut up an old line and inside the formed plastic, there were push fittings I could clamp on. I admit it actually leaked a tiny bit, but this is NOT FOR USE ON THE ROAD.

Step 3: Locate the fuel pressure regulator and pop the vacuum line off


This is where I stopped taking pictures

Step 4: Find a foot pump or bike pump that has a pressure gauge on it and fit it to the vacuum inlet on the fuel pressure regulator.
My bike pump had a screw clamp that just worked, you might need to find some way to make a good fit, it doesnt need to be perfect.
I used a bike pump with a fitting like this

which made a half-decent seal on this


Step 5: Make sure your battery is strong and fully charged.
Now find a way to run your fuel pump continuously WITHOUT starting the car.
As I have OFAM (megasquirt) I just told the ECU to turn on the fuel pump. For standard cars, you can remove the fuel pump relay and bridge the pins. You might need the ignition on.
Don't put wires to the pump itself, you are trying to test the wiring the car will use so don't bypass it, use the car loom as much as possible.

Step 6: With the fuel pump whirring away, it should sound healthy, no growling and a continuous tone. The in-line gauge should be showing near the pressure you want, in my case 3 BAR.
Leave the fuel pump going.

Step 7: Use the bike pump to put some extra pressure into the fuel pressure regulator, BUT DONT GO MAD, YOU COULD BURST A PIPE OR JOINT
I run 1 BAR of boost, so I tried to match that using the bike pump gauge as a guide. Then make sure the fuel line gauge reads base pressure (3 BAR) plus the added bike pump pressure (1 BAR) so in my case 4 BAR.
Your pump might change tone a little but it shouldn't really drop much in the speed it sounds like it's running. It is hard to describe the noise but you will know when it sounds wrong.

With no pressure on the fuel regulator, my fuel pump sounded absolutely fine. With 1 BAR on from the bike pump, my fuel pump sounded like it had halved its speed and was making a noticable growl. When I checked my inline fuel pressure gauge, it was flapping around 3.8 BAR, so my fuel system wasn't actually capable of reaching the 4 BAR it should have been.
My car was going lean on boost at 1 BAR, and it was because the wiring to the fuel pump wasnt able to carry the current my cossie pump needed

Karl @ FPT

Great write up Matt!