Subject: Oil Pump Question...




A couple of things;

First - to test a sender
A) electric sender - remove from engine and ground with jumper wire to 
engine block, battery neg, etc. Turn on power so that sender is powered. 
Apply air pressure from a source of compressed air with a known pressure. 
Read gauge, pressure reading on gauge should match the air pressure being 
put to the sender. The way to put air pressure to the sender is easy, get 
a blow gun with a soft rubber tip and hook it up to either a compressor 
or a compressed air tank (like you use to fill you tires at an autocross) 
the air pressure should be set with the regulator to about 50psi (not 
higher than the gauge will read or you will defeat your purpose). You 
then hold the blow gun's rubber tip up to the opening in the sender 
(tightly so as to prevent any air pressure escaping) and open the blow 
gun's trigger so as to apply the 50 psi (or whatever you set the 
regulator at) to the sender. The sender will think its getting 50psi of 
oil pressure and the gauge will read  accordingly. If the gauge/sender 
both work right you will get a 50 psi (or whatever you set...). If you 
get some other reading check to make sure the air pressure is being 
applied to the sender properly, if it is and the gauge consistantly reads 
low or high you know how far off your gauge/sender combo is and will at 
least know about what your oil pressure is (ie when you put 50 psi to 
sender gauge reads 30 psi, when you rev engine with sender hooked up oil 
pressure gauge reads 35 psi, you have between 50-55 psi oil pressure).

B) Mechanical sender -
follow the preceeding directions except that you don't need to ground or 
power the sender.
If this test shows your gauge/sender combo to be reading out incorrectly,
you can play with changing the sender and see if the gauge reads right, if
there is no change then the gauge is off, if that fixes the problem then
the sender was bad. 


On pumps and mods, if you have an old engine which won't get the oil
pressure up, simply increasing the relief valve spring tension may not
affect oil pressure at all. If the pump is pumping for all its worth and
the clearances in the engine are so great that it still can't get up a
very high pressure, the relief valve will not even be opening. At this
point a stiffer relief valve spring will have no effect. The proper fix of
course is to rebuild the motor at that point. What will help (as a temp
fix only) is to increase the oil pump's output (volume not pressure) so as
to supply more oil to the bearings and be able to pump up some pressure
(pressure comes from supplying more oil to the bearings than can pass
through them, the greater the cfm of oil supplied the higher the pressure)
If 50 cfm of oil can pass through the bearings and you supply 30 cfm you
will get no pressure, if you supply 75 cfm you will get X psi and if you
supply 100cfm you will get Y psi. If the problem comes froma worn engine
more oil will be the only help. If the problem comes from a worn pump
(excess clearance at the gerotor) the pump must be replaced. If the
problem comes from a worn relief valve (sagged spring, excess clearance at
valve body) a stiffer spring may help. 

I am not trying to say where the problem comes from or what might fix it, 
just trying to relate actions to reactions. I would (as has already been 
suggested check the gauge/sender combo first and then if they are working 
right I would pull the pump and look at the gerotor. If it looks OK (it 
will be scored some but it shouldn't look like its been pumping sand) 
then I would try stiffening the spring. If that doesn't help I would try 
putting a turbo pump in instead of the stock one. If that still doen't do 
it I would stiffen the spring in the turbo pump. If that doesn't do it 
rebuild the damn motor. :-)

Hope this helps, Merry/Happy whatever

Marc Sayer
Performance Engineering
1070 W. 2nd Ave. 
Eugene OR 97402
(503) 484-0904  Fax 746-0863
msayer@efn.org