fuel pump running continously

[jpennington]

It's a 2.1l DJ. For the last couple of days, the fuel pump has been running continously when the engine is running. IIRC it used to run intermittently when idling - typically on for 2 seconds every minute or so.
What do other DJ owners experience?
Am I having a senior moment - I never took much notice of pump behaviour before.
I dropped the fuel tank recently to paint some rust and replace some leaky vent pipes, also a split filler pipe.

looking forward to expert advice - currently stuck in a muddy field, aka a campsite in Cornwall.

[CovKid]

Not massively familiar with the 2.1. but if memory serves me right, there is a relay in a box at the back on the left which controls the pump.

[silverbullet]

On any efi engine, if the engine is running, the fuel pump is running.
Sounds as if dropping the tank has stirred up the silt, which the pump is now intermittently picking up and circulating.

[jpennington]

One problem solved, one potential solution.

The muddy field was resolved easily thanks to a tow from a friendly tractor.
The 5 hour drive home, with the pump whining away all the time, gave me an opportunity to consider what might be happening.
I am sure that previously the pump did not make any audible noise when driving.
There are two possibilities - something wrong with the pump, or something wrong with the fuel pressure regulator.

I agree with silverbullet - there is power to the pump whenever the engine is running.
So possibly there is some crud in the pump which is making it noisy. Baxters delivered a new pump today (the pattern part is a much better price than the OEM),
so I'll try that.

However, it might be the regulator stuck open, so the fuel pressure in the pump is low and so it runs faster and sounds noisier?
Seemed worth a look so I checked the regulator as best I can without a pressure guage.
Running a pipe from the tank return side of the regulator into a bucket showed a healthy fuel flow so pump is doing its job.
But checking at the pressure test screw on the input side of the regulator showed no residual pressure as soon as the engine was switched off. It should maintain pressure for at least 10 minutes.
So I suspect that the regulator may be stuck open.

Sourcing a new regulator turns out to be tricky. NLA from VW, last manufactured in 2009, no old stock in any UK VW parts depts.
Not currently available from the usual suspects in UK, although several suppliers in USA. I have found an internet source who claims to have it with me by early next week - we shall see.

Always something interesting with these old girls, isn't there? I was planning a drive to Portugal starting next week, may need to delay a bit.

jp

[jimrat]

Could also be a broken rubber bobbin between the pump and the chassis

I noticed my pump was a bit noisy - when I looked underneath, two of them had sheared - I guess there was metal/metal contact somewhere. worth checking.

Cheers
Jim

[MGP]

If the pressure regulator was stuck open you would not have enough fuel under load or very rich running at tickover depending on where its stuck, its worth changing as its only a spring and may well be tired.

The noisy pump is much more likely to be either pump mounts or the plastic fuel hose touching metal somewhere.

I have only ever known hich pressure fuel pumps to be noisy due to fuel starvation which sounds more like a bearing in the pump breaking up or contact with the body.

[jpennington]

Thought I'd report the end result, in case it's useful to others.

Testing the fuel pressure regulator: I found an old pressure guage (saved from a broken foot pump), so I can properly test the regulator and pump.
Results:
1. old pump and regulator: engine idling - pressure 2.4 bar, blip the throttle and pressure drops to 1.8 bar momentarily. Switch off, pressure lost in 30 seconds.
2. new pump, old regulator: engine idling - pressure 2.7 bar, blip the throttle and pressure drops to 2.4 bar momentarily. Switch off, pressure lost in 40 seconds.

When I fitted the new pump, I also back-flushed the inlet filter (the box-shaped one between tank and pump). I got a couple of teaspooons-full of brown sludge out.
At rest the new pump sounded just the same as the old one, but on the road it was definitely quieter at speed - inaudible above 30 mph.

A genuine Bosch regulator arrived on Wednsday, so I thought I might as well fit it, although the results above suggest the old one was ok.

Result:
3. new pump and regulator: engine idling - pressure 2.3 bar, blip the throttle and pressure drops to 2.0 bar momentarily. Switch off, pressure at 2.0 bar after 10 minutes.


Conclusion: the old pump and regulator were both showing their age (29 years and 2 months). Pump working but noisy and reduced pressure. Regulator leaking slightly.

So, I think I was right to change both, but I shall keep the old ones as emergency spares.

Probably do a couple of long day trips before bookling the ferry.

jp

[boardmonkey]

Well done Sir.

[slowcoach]

Nobody mention the large metal barrel filter by the pump? It'll make the pump squeal if its clogged !

[jpennington]

Fair point, although it is a routine service item. Change every 4 years.
In my case not a likely issue as changed in March 2014.

jp