[urq] Fuel Pump surge - still having problems

[Ben Swann]

Steve,

Let’s just say, I have enough evidence that this is basically cavitation going into the
pump.  You can visually see what is going on.  I have no doubt that basically the pump
is drawing faster than can be supplied from the tank.  I have been over this and ruled
in and out many things.  There are times when I have been able to temporarily eliminate
the problem too – basically allowing an open feed into the pump – similare to your
suggestion of using a test tank.

As you mention below, CIS keeps a constant system pressure, and that is higher than the
system pressure I’m using.  The difference is EFI tends to be more of a higher flow,
lower pressure as CIS tends to keep the system pressure high and flow not that great.
This is one reason I think raising my system pressure may help.  But I still think I
need some sort of buffer – eg. Surge tank or really big pressure accumulator.

I was doing some research and this appears to be a pretty common problem – more with
converting from carburetor to EFI, but also got a lot of hits from CIS to EFI – a lot
more of this going on with the older rabbits and such.  There is a reason all the later
cars went to an in-tank and or/ two pump system. 

I am 90% certain that the problem is pre-pump sucking/cavitation.  Now I need to find
the best solution.

Ben

[Date: Wed, 16 Apr 2008 07:20:30 -0700
From: "urq" <urq at pacbell.net>
Subject: Re: [urq] Fuel Pump surge - still having problems
To: <urq at audifans.com>
Message-ID: <02ea01c89fcd$07218b10$1564a130$@net>
Content-Type: text/plain;	charset="iso-8859-1"

Man, it sucks to hear that your problem remains ... (pun intended)

A couple things come to mind ... 

 * A low pressure system should be less prone to cavitate.

 * It seems to me in the CIS situation that the pump supplies the same amount of fuel at
all times, if you don't need as much as the pump provides the rest goes back to the
tank.  This would tend to speak against demand-based cavitation.

 * I think many of the in tank pumps were added because the tank sits low ... a full
tank in an urq should have plenty of gravity behind it.  I am assuming that there's at
least a half a tank of fuel during the testing ...

 * Have you let the pump run without impediment into an empty fuel container?  It seems
to me you would hear the most cavitation with the pump running open loop.  

You might want to try using a fuel container to feed the system for a test ... maybe
even better to get a fuel cell that you can sit in the trunk for a test.  

Steve B
San Jos?, CA (USA)]