[Diy_efi] fuel injection problem, cont'd (2)

[David Cooley]

 All you need to do is block off the return and take a WOT run to see what
the pressure does... No need to buy a new one till you know it's bad

 
-------Original Message-------
 
From: charlesmorris at direcway.com
Date: 01/18/05 10:31:23
To: diy_efi at diy-efi.org
Subject: [Diy_efi] fuel injection problem, cont'd (2)
 
Adam Wade <espresso_doppio at yahoo.com> wrote:
>A big clue is the rust and varnish throughout the
>system. The one thing I didn't see you say you'd
>checked was the fuel pressure regulator. If there's
>crap in the regulator, it may well be bleeding fuel
>back through the return.
 
Good idea. In one of my posts, though, it says I measured the return line
flow with the injectors/engine off and the pump running at 43 psi. This
represents the total amount of fuel available to run the engine at that
pressure... and it is way too small. It should be about 4 liters per minute
or so (255 lph rating at that pressure) and it's not anywhere near that. Don
t remember
the exact figure but it wasn't even 100% injector duty cycle (less than 2
liters per minute).
 
So I said to myself, what happens if the regulator is partially obstructed
and not allowing fuel to return? The pressure would get higher as the fuel
demand drops. It doesn't do this - it is never *higher* than 43 psi with 0
vacuum at the regulator hose, but it is often lower. Pulling off and
reconnecting the hose at idle changes the pressure repeatably from 36 to 43
and back, as it should.
 
What if the regulator is stuck completely closed, allowing no fuel to return
at all? Then with the injectors off, I would expect the rail pressure to
rise to the relief valve opening in the pump, typically 100 psi or more.
 
Lastly, what if the regulator can't close down enough to maintain pressure
with the engine pulling fuel, as you speculate above? Then the pressure
would be normal at idle and low load, and drop at higher loads, which is
what it does. BUT - then there should be lots of return flow when it's not
going into the injectors, and there is not.
 
Based on that logic I didn't replace the regulator ($70+ since it's a
Eurospec part) but I may "shotgun" it anyway - nothing else is left!
 
>You should also clean the injectors in an ultrasonic
>tank, as they are likely all running lean from
>varnish, if not from crud plugging their intake screens.
 
Unfortunately that is already done, they were actually pretty clean
according to the shop.
Thanks for the ideas though.
:(
-Charles
 
 
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