Fuel Pressure and Pump?

[Shannen Durphey]

In this case, it sounds like the factory pump may be insufficient.  Is the
factory LT1 regulator still on the fuel rails?  If it is not damaged, then it
should be regulating pressure to factory levels, provided there is sufficient
fuel volume.  

One quick test to check the pump's ability to provide pressure would be to pinch
the return line and watch the pressure rise on a gauge.  If it does not rise
considerably, the pump is not going to work.

You should also check volume.  You can do this indirectly by driving with the
gauge installed and watching pressure changes.  Accelerate, power brake, drive
up a large hill.  If the pressure is consistently at 35 psi, and the above
"pinch off" test indicates that the pump can build pressure, then you may have a
bad regulator.  But if fuel pressure drops way off, then insufficient fuel is
being delivered to the engine.  Providing the fuel filter is not plugged, the
pump would be the most likely suspect.

If the diagnosis pointed to the tank, I would first try to replace the in-tank
pump with something able to provide enough fuel.  I've had to troubleshoot a few
draw-through, two pump systems, and the in tank pump can sometimes present
considerable restriction.  If the in tank pump can provide a large volume of
fuel at low pressure, then a two pump system is a reasonable option.  But using
an in-line pump to draw fuel out of the tank can cause problems, imhe.

Shannen

Manuel Desantos wrote:
> 
> You can run a second in-inline pump with the stock pump.
> I'd get an adjustable Fuel Pressure Regulator.
> You can also try and run the in-line and turn off the in-tank pump and
> see if there is enough flow through the in-tank pump.  If there isn't
> enough flow then I'd remove the in-tank pump and just run an in-line.
> 
> -----Original Message-----
> From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org] On
> Behalf Of Whit
> Sent: Friday, January 18, 2002 11:37 AM
> To: diy_efi at diy-efi.org
> Subject: Fuel Pressure and Pump?
> 
> I'm running an LT1 in my 89 Jeep cherokee and am having fuel pressure
> problems.  I am wondering if the stock fuel pump will do the trick.  The
> stock pump was meant to run FI on the Jeep at about 35 lbs.  After
> intalling
> the motor it is still running about 35 lbs and I understand the LT1 is
> supposed to run in the mid 40s. I bought a new regulator but my gut feel
> is
> that the stock pump is either inadequate or it needs to be replaced.
> Any
> have exprerience here?  What are options here?  Can I run a second
> inline
> pump?  If so, do I need the stock pump at all?
> 
> Thanks,
> Whit
> 
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