How to test a fuel pump - petrol DJ

[Jabes]

Hi there. I have been having problems with my van cutting out. Someone suggested checking the fuel pump pressure. Does anybody have info on how to check a fuel pump, and what the pressure should be? Thanks.

Info: van is a 1990 German import Bluestar 7 seater, with a 2007 vege DJ engine and digifant. I have had it 3 1/2 years and it is was a daily runner till I had this problem!

Jon

[AdrianC]

Hi there. I have been having problems with my van cutting out. Someone suggested checking the fuel pump pressure. Does anybody have info on how to check a fuel pump, and what the pressure should be?

First things first - when did you last change the fuel filter?

Basic theory of the injection - the whole section of pipework from pump, through the plastic section on the bulkhead, the T-piece, the injector rails, to the fuel pressure regulator (FPR) valve should all be pressurised. Somewhere around 2-3 bar. All the injectors do is open four little finely calibrated taps to allow some of that pressurised fuel out.

So - the pump generates pressure, the FPR holds it in. Either failing will cause a lack of pressure in the pipework. Whatever your problem is, it's intermittent, so you're going to have to test immediately after it cuts out. Turn the key off immediately it cuts out. Then - quick and dirty roadside diagnosis - IIRC there's an 8mm head blanking bolt on the t-piece going to the rails. Have a rag handy. You _should_ have a spray of fuel, briefly. Don't worry, it's incredibly unlikely to catch fire... (But not smoking might be a good plan)...

Can you hear the pump running? It's underneath a LHD sliding door. It's the buzz you'll hear briefly when you first turn the key to on, but don't start the van, as it pressurises the rail. It then cuts out unless it "knows" the engine's running - controlled by the pump relay, controlled by the ECU.

So - even if the pump isn't running, it might not be the pump that's dead. It might be an ECU, relay, or wiring problem. If the pump's running, but the FPR's failed, then there'll be fuel circulating, but no pressure in the rail.

If you really want to get technical on it, you can measure the pressure with a fuel pressure gauge, but you can get a damn good idea what's going on just with a little light dismantling and a multimeter.

E D I T: Just noticed you're talking Digifant, hence SS/MV, whilst I'm thinking Digijet, hence DJ. The plumbing may differ between the two, but the basic theory's the same.

[Jabes]

Hi there Adrian,

Thanks for your time responding! I have never changed the filter but the garage has blown it through. The problem I have is that, after I had a breakdown at Christmas (which is the subject of another of my posts), I took it to my VW specialist and they couldn't find a problem. I have subsequently used the van and ended up getting towed home. So I have a very intermittent problem and I intend to sort it myself.

Your pointers are really helpful and give me the confidence to have a go. I will let you know how it goes and probably ask you more questions too! Thanks again.

Jon

[AdrianC]

I have never changed the filter but the garage has blown it through.

The _fuel_ filter...? Change it. Change the garage, too, if they think that "blowing it through" is either effective or decent value.
Can't find it on BW, for some odd reason, but...
http://www.amazon.co.uk/dp/B005JDM85I" onclick="window.open(this.href);return false;

[Jabes]

Thanks. Have already ordered the filter - If that's it and £5.53 fixes it, I will find you and give you beer. Cheers

[slowcoach]

Thanks. Have already ordered the filter - If that's it and £5.53 fixes it, I will find you and give you beer. Cheers

Fixed a lot of wobbly power and cutting out on mine, think i had some back fires too. I got a simple pressure gauge from ebay too, which can screw onto the fuel t piece next to the oil breather tower. With that you can watch the pressure hold, or drain away. .

[Jabes]

OK chaps...

The fuel filter is here but I haven't put it on yet.

I took out the bolt from the supply tee and fitted a pressure gauge. As soon as I turned the ignition on and the pump started, it got up to about 1.5 Bar. When I started the engine it ran at about 2.2 Bar constant. I let it warm up a bit and ran the gauge on a long length of pipe so I could see it from inside the van. I took the van out and as soon as I got off the drive - no power. Fuel pressure still steady at 2.2 Bar though.

Just about managed to get it back on the drive. Turned engine off and, 10 mins after it still shows 2.2 Bar.

So, I think that fuel pump, filter and relief valve seem to be ok.

Does anybody know how to check the voltage output to the injectors? I have had some dodgy wires in the digifant loom and I have got an idea that the signal to the injectors might not be getting through.

Cheers!

[slowcoach]

Yes your pump and pressure regulator sound fine.

You can detach the fuel rails from the heads (one bolt), while still hooked up to the fuel lines and injector wiring. They can then be sprayed into a container, to see if they're delivering fuel. Its outlined in Haynes or the bentley books. I expect that could be messy, I've never done it but maybe someone here has?

[Aidan]

ecu flashes the injectors to earth (ie they are permenatly live fed), so observing them spraying is a good idea, make sure that the lead from the coil is disconeected at the distributor and earth it to the chassis to prevent any spark being generated whilst cranking
have you got a copy of Bentley or Digifant manual ?

[Jabes]

Thanks guys. I have a digifant manual. I still think that the problem is wiring. I am going to check the resistance of the injectors and maybe bypass the cable to pin 12. I will let you know.

Cheers.