[Tigers] Fuel Pressure Too Low?

[Ron Fraser]

Jim
	Stock SU Fuel Pump AUF.301
>From the Shop Manual

Flow rate = 15 gallons per hour	Fuel = 6 lbs/ gal 	15 gal/ hour = 90
lbs/ hour
Pressure or delivery head = 48 in	48 in H2O = 1.73 psi

The convention is that at wide open throttle an engine uses about .5 lbs/ hr
/ hp	90 / .5 =180hp

As you can see the SU is a low pressure pump working in the 2 psi range and
will support up to around 200 hp, exactly within the range for the stock 260
and 289 engines.

	As you see the stock fuel pump is low pressure so your readings are
correct and proper.   I would look for debris in the fuel system.  I see
flakes from the tank now and then; I have a fuel filter before the pump on
my Tiger.  I would check all the rubber hoses, the lines after the fuel pump
and the filter before the carb.  If they all check OK then its into the carb
for a clean up and rebuild.

Ron Fraser

-----Original Message-----
From: tigers-bounces at autox.team.net [mailto:tigers-bounces at autox.team.net]
On Behalf Of James Lindner
Sent: Monday, July 23, 2012 9:35 PM
To: Tiger List
Subject: [Tigers] Fuel Pressure Too Low?


Hi Listers,

Recently, I have been experiencing some engine stumbling/hesitation after I
have driven for 30-40 minutes. It felt as if the engine was starved for
fuel. I checked the accelerator pump and power valve, ruled them out and
then figured it might be the fuel pump.



I installed a mechanical (not the liquid filled type) in-line fuel pressure
gauge just before the carburetor. The fuel pressure read about 2.3 with the
ignition in the on position. It remained at that number once I started the
engine and at 1500 rpms. I took a drive and the stumbling started and I had
to stop to let everything rest. At that point the pressure gauge was reading
zero. After resting an hour I barely made it home and the pressure was still
about zero. Now convinced it was a fuel pump problem I changed out the fuel
pump. I installed a NEW stock fuel pump from Sunbeam Specialties in the
factory location. I also correctly vented the vent tube into the trunk
compartment. Previously, I shielded the muffler with heat wrap. I also
inspected the old pump and found no evidence of foreign debris.



Once I installed the NEW pump, I checked the pressure. With the ignition ON
the pump sounded strong and the pressure again read 2.3. I got the same
reading at idle and 1500 rpmsb&all which seemed low. I did the following
none of which changed the readings.



B7        Opened the filler cap to make sure it was not a venting problem

B7        Jumped the fuel pump power tab directly to the battery

B7        Grounded the fuel pump directly to the negative terminal on the
battery

B7        Switched out fuel gauges just to be sure it was not a faulty gauge



Yesterday I took it for a test drive. Fuel pressure was 2.3 upon starting
the car. Car ran great for 30-40 minutesb&then it started to stumble badly
at speed and nearly stalling when starting from a stop. I headed home and
checked the fuel pressure as soon as I arrived. It continued to read 2.0-2.3
(needle bounces around a bit.)



I am getting ready to move back to the carb (itbs an older Holley 1848 that
has been rebuilt once) as the source of the problem since the fuel pressure
is being maintained, but I still have a nagging feeling that the fuel
pressure is too low.



I intend to check pressure one more time using a combo vacuum/fuel pressure
gauge tapped in where the current gauge is located. In the meantimeb&My
question isb&



Is the fuel pressure too low? If so, why would a brand new pump have such
low pressure? I am interested in what others with stock fuel pumps might
have for pressure and any other thoughts.



I know an after market pump mounted in the MkII location in the trunk is an
option but for now intend to keep things stock.



Thanks, Jim
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