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Fuel pump problems

T

tref

PCGB Member
Member
OK... I don't think petrol should look like this:



How-ever, I don't think that is related to my problem.

The fuel pump wasn't pumping, so I have replaced it. The new supposedly good pump doesn't pump either. I now have it wired direct to a battery, with the loom disconnected, and can feel it "kick" when power is first applied, but that is it. Thinking this suggested blocked fuel lines, I have disconnected and blown through both the fuel lines and non-return valve on the end of the pump... (hence the contents of the jam-jar), so these are free. When I clamped the hose from the tank to the pump I initially didn't clamp it hard enough and fuel widdled out until I clamped it harder, so I believe fuel is getting to the pump, even if not that much. So... why does the pump only "kick" not pump? I thought that if the in-tank pump had failed it would allow sufficient fuel to pass that the main pump should pump something, even if not the full volume?

Any-one any ideas?

For reference, it was all working before it went into the body-shop for two years!

D6B8659781A44F5BA7FCDC264C23508C.jpg
 
Tref, that is what we, in the trade, call gunge. If I was you I would unscrew the internal pump, and empty the complete contents of the tank, if you haven't done so already. For what ever reason, that looks like seriously stale petrol, possibly with some nice pump jamming rust in suspension. For the benefit of others, the fuel is the lubricant for the pump and if any of that has got into the moving parts, any pump is not going to be happy.
  • is the second pump new?
  • have you checked to make sure the outlet from the pump(into the check-valve) is not still blocked.
  • are the connections to the pump capable of passing 10A continuous?
  • is the battery capable of delvering 10 A continuous?
The mesh over the end of the inlet to the internal pump is quite fine and could be blocked, but even the little widdle should allow the pump to spin. Perhaps you need to blip the motor with the +&- reversed, and wash it through with clean parafin. I would recommend against washing it with clean petrol and then blowing it through because of the fire risk from vapourised petrol
 
Thanks,

To answer your questions:

No, the second pump isn't new... and I didn't want to "test" it without it being in fuel for lubrication reasons... It is clean fuel in the tank... at least I thought it was... I wonder now if that has gone the same way as that in the fuel lines. Probably is the answer I guess. Time to take the in-tank pump out anyway.

Outlet from pump to check-valve I haven't checked... other than visually - anything else I can do? It looks clean.

Connections are now nice and new, ring connectors, on new cable, all nice and shiny... directly onto a new Bosch Silver Battery... which is capable of cranking the engine over nicely, so I would think it should be able to spin a fuel pump when it is not!

I hadn't thought of trying the pump backwards, and wouldn't have known it to be acceptable to do so... sounds like a good way of proving the pump without pumping crap through the system...

Eitherway, time to take the pump out I guess. What I would like to do is to some-how test away from the car, and get working properly to give it the best chance when I put it back on (for two reasons - one because it saves grovelling under the car more than necessary, and two, I can take the pump components to work on and test whilst I am away from the car at work).

Afraid my thought process has just come up with connecting the outlet of the high pressure pump to the inlet of the in-tank pump, and testing it like that... Hmmm... thoughts please... other than the usual perpetual motion infinite pressure drive system suggestions!
 
In diagramatic form the pump, is a roller/chamber pump which looks as if it will suffer few ill effects if momentarily, i.e.one second or less, it is reversed. This is to enable any small particles of rust to become unwedged from the rollers. After that, I would try flushing out the pump. Put some paraffin in a washing up liquid bottle, and bodge up some kind of connection into the inlet. Perhaps you could use an old screen wash pump and reservoir. Give it a flush, See if any crap comes out of it.

If you have removed the check-valve from the end of the pump and it loooks clear then it is probably as clear as it needs to be to get fuel flowing.

When all said and done, if you have a working pump, a 10 A supply, and fuel, it must work; you have fuel, and a 10 A supply, ergo the issue must be with the pump.
 
Yep, I have a feeling you could be right.

As an aside, my first thoughts were to try my old pumps non-return valve... the threads are different - same diameter, but different pitch. Not sure if this is a 924 vs 924 Turbo pump difference or what... but as well to be aware the difference exists!

Regards,

Tref.
 
On my list to replace, but the inline (just behind the bulkhead) passed air ok... I am assuming there is an in-tank one which could indeed be a culprit.
There isn't a diagram of the intank pump/filter arrangement anywhere is there, so I have an idea of what to expect before the pingfukit flys past my right shoulder?
 
The internal pump has a filter mesh cage about 40mm long and about 35mm dia, the same dia as the pump. when you unsecrew the pump the filter comes out with it, the overall length of the assembly is about 160 mm . IIRC the thread is either 3/4 or 1" BSP
 
May i just add that that jamjar full of gunk looks rusty to me which may indicate you have water in your fuel tank, it usually gets in through rusted filler necks and is heavier that petrol so sinks to the bottom of your tank and gets pulled out by the pump in dribs and drabs. If this is the case you need to get rid of it immediatly or it'll completely ruin your metering head, i know i've been there with a Golf GTI and they're not repairable.

To be sure turn the bulkhead mounted filter upside down to see if there's any in that, it'll sink to the bottom of that if it's got that far and may have saved your metering head.
 
I am VERY familiar with the rusty filler neck issues with Mk I Golfs and Sciroccos... but haven't heard of that being a particular problem with 924s. I am pretty sure the fuel is contaminated with rust - the car has been stood in a field for six years, then stood in a body shop for a further two years... the number of heating/cooling cycles over that time with an empty tank will have generated enough condensation to cause a rusty tank issue anyway. My plan was to change the filter regularly for a while, then probably replace the fuel lines... but I would rather leave them in situ and use the old pump/fuel lines until I have removed all the crud that I expect to come loose from in the tank.

Thanks,

Tref.
 
The fuel pump on my 944 was seized and when I connected it directly to the battery all I got was the kick you described. I got fed up with it and opened it up for a peek inside and it turned out that some dirt had formed at the entry seal and had jammed the mechanism. After I separated the plates at the bottom of the spindle it spun freely so I rebuilt it all and connected it to the battery and got a satisfying whir.
 
Thanks,

I am fortunate that I have a couple of other pumps available, just not on nice comfortable ground to crawl under and remove them! I'll let you know what progress I make from the suggestions,

Regards,

Tref.
 
To let you know, have tried the same test regime on my 924T spares car, and teh pumps happily pump fuel! So... I now have them removed ready to go into the cab... which unfortunately now won't be until next weekend dammit. I have wrapped the pumps in clingfilm to keep dirt out/keep them moist, as if anything like the VW golf pump, to which they bare an uncanny resmblance, it will pack up if allowed to dry out - something I fear may have happened to the pump I was given to try.
 
To complete the tale, swapped the two pumps out from the spares car yesterday, and all works fine. As I had the pump wiring disconnected I held the pump wire to the battery whilst Claire cranked the ignition. After time for the fuel to get through, the car started with no additional throttle, and settled down to a smooth idle straight away. Not bad for a car which has spent six years in a field, two years in a body shop, and several months with a shot fuel pump!

The cabrio is running again! yay![:D][:D][:D] Paul will be wanting another article for PP now!

Thanks every-one for your help.

Oh... one thing for reference... I kept the pumps for the past week wrapped in cling-film... from my old VW golf fuel system issue days I can remember hearing that a working pump removed from the car will dry out and stop working, hence, keep it wrapped in cling film to keep it working. I wonder know if car sat in field didn't dry out, yet car sat in body-shop did. Pump supposedly working given to me to test by a club member, didn't work, but wasn't wrapped. Don't know, wouldn't like to say... but so far I have never had a problem with a pump that has been stored wrapped in cling-film, but have with some that haven't.

Regards,

Tref.
 
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