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 Andy
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| posted on December 29th, 2002 at 09:54 PM |
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Fuel pump woes
Well, I decided to get the original mechanical fuel pump resurected after it died some time ago on my Kombi ('77 with 2L dual carb motor), and
it's been running an an electric pump since.
Here's a run down of what I've tried over a period of time:
All fuel lines replaced, fuel filter replaced, fuel pump drive push rod replaced (was 5mm shorter than the new one), checked the push rod extension
while turning the engine, gives ~10mm travel, new pump kit installed (the old parts were showing signs of hardening).
After all that I still only get ~2.5psi pressure at idle (should be ~5psi) and that quickly drops off as revs/load increases, which was the same
problem I had to begin with.
Consequently it runs fine at idle and under light loads, but looses power when ever the fuel pressure drops (ie the pump cannot supply enough
fuel).
So where do I go from here????
Any suggestions?
I remember reading somewhere that the diaphram needs to be compressed a certain amount before assembling the pump, but don't have any details. Is
this likely to affect the output of the pump?
Thanks,
Andy.
:alien
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geodon
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| posted on December 30th, 2002 at 05:48 AM |
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Check your ins as well as outs!
I'm not familiar with later Kombis but the earlier ones should be able to gravity feed the pump easily. Disconnect the in line & make sure
the tank or pipes are not clogged.
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Andy
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| posted on December 30th, 2002 at 07:21 AM |
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Tried all that, all seems OK.
Thanks,
Richard
[Edited on 29-12-2002 by Andy]
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geodon
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| posted on December 30th, 2002 at 07:10 PM |
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Can you bypass it?
See if you can beg borrow or steal an electric pump & bypass your pump. It at least will point the way to go ie confirm that your pump is the
problem. I'm thinking your float valve may be the problem but if its restricted, then the pressure should rise! I wonder if the inlet valve on
the pump is leaky? This acts as a non-return valve that stops fuel going back into the tank when the pump blows. That would explain why at low revs it
works OK but under higher loads it fails.
In the older pumps they are accessible. They are just a hexagonal piece of bakelite about 10mm accross with a fine spring to keep it closed except
when the pump is sucking.
[Edited on 30-12-2002 by geodon]
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OvalGlen
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| posted on December 30th, 2002 at 09:58 PM |
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Seems like youve checked things out pretty well. Is it possible you could borrow someones fuel pump to so if it really is a fault in the pump.
Regards,Glenn>
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Andy
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| posted on December 30th, 2002 at 11:34 PM |
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Thanks for the input. I have been running an electric pump on it for a while with no problems (so the carb side of things are OK), I just want to get
the original one working again.
Geodon's point about the valves is a good one. I have looked onto it, the inlet is the small metal flap and appears OK, but the bakelite one on
the out let is difficult to see if the seat is OK.
I've got some time off tomorrow and will be investigating further. I'll let you know if I find anything.
If I have no luck, I can get hold of another working one to try.
I WON'T LET THIS BEAT ME
Andy
[Edited on 30-12-2002 by Andy]
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geodon
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| posted on December 31st, 2002 at 07:37 AM |
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To check your valves
Just blow back either with your mouth ( you should be able to generate 5psi!) or VERY carefully with an air line.
By blowing in the output port you check the outlet valve. It should be completely sealed. If it makes a farting sound it's leaking. But to check
the inlet valve, you have to remove the outlet valve, re-assemble the pump & test again without the outlet valve & the same way. Or you could
try sucking on the inlet port if you're game! JUST HAD A FLASH OF INSPIRATION!
If you can get a 50ml disposable syringe, you can connect it to a piece of fuel line & use it as a vacuum pump! I use them to bleed brakes- they
only cost a coupla bucks.
[Edited on 30-12-2002 by geodon]
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Andy
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| posted on January 1st, 2003 at 10:23 PM |
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Well Geodon,
I think you have it, there appears to be a very slight leak on the outlet check. Not sure if this means it's a bin job though.
I have fitted a new German one for now, and get ~4psi. I havn't taken it for a run yet to see how it goes on the high way, maybe tomorrow.
As for why I only get 4psi, and not 5psi, it could either be a wrong reading on the gauge (new VDO unit), or incorrect assembly of the new pump (I
pulled it appart to compare with the re-built one, hey I know I'm stupid!!!).
At least it holds pressure when I turn it off (I also added a cut off solenoid on the tank outlet). It takes ~20-30min to leak down to zero.
Here's hoping it runs well.
Thanks again for the help.
Just as a side note, does anyone know if these pumps work OK if the tank is below the pump? I've been contemplating adding a second fuel tank
below the floor.
Andy:thumb
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geodon
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| posted on January 2nd, 2003 at 01:57 PM |
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Only electric??
I have only seen this done in very old Jags & they were electric (SU's). The pumps were high on the firewall in the engine compartment &
the tank was below the boot. In SU parlance they had a long suck & short blow! I can't see how the mechanical pump colud prime itself-
you'd be using the starter till the battery went flat. You could use your electric pump on a separate switch (the Queen Mother of reserves!) but
you will need one way valves in both systems otherwise the top tank will drain into the secondary or the electric pump will fill your original! When
faced with a similar problem many years ago, the factory had a simpler solution to increase distance between refills:
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geodon
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| posted on January 2nd, 2003 at 04:27 PM |
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...or REALLY put those flat sides of a Kombi to good use!
Let's see: 10x20litres on each side plus your original tank! Easy to fill, too!
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Andy
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| posted on January 2nd, 2003 at 04:29 PM |
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Looking at that picture, I'd say someone put tha can in upside down!!! I hope it's already empty.
On a serious note, I think I will mount an electric pump level with the bottom of the second tank and use it to transfer the fuel to the main tank.
Cheers.
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