S10forever

HI,Does anyone know the location of the fuel pump relay in 1994 S10 z-engine,dealer told me by the windshield washer bottle but did not see
anything that looked like it also no relay bOk what you have in simplicity is two switches in parallel with one power source. Now how the oil pressure switch becomes a single switch that can conduct B+ to the fuel pump and how it can under one and only one condition shut the fuel pump.

As an electronic technician I have ascertained from the posts that MT and Califokie are both correct although MT is only incorrect in thinking that the oil pressure switch can not shut fuel pump, he is correct in all his other statements.
The way the system is set up is very intelligent and I take my hat off to GM's design tech's.
The oil pressure switch is a variable resistor driven by pressure. When enough pressure exists the switch closes and in that state can pass B+ to the fuel pump.
This is only pertinent if the main switch in the parallel circuit that drives B+ to the fuel pump fails (fuel pump relay) while under driving conditions (high enough rpm's to keep ops as a closed circuit).
One switch in parallel with another switch both closed has no effect on the circuit.
But if the main source of B+ to the fuel pump (fuel pump relay) should open under that condition the ops would maintain B+ allowing veh to remain running.
Now comes the part about how the ops can and will shut fuel pump.
Under the above condition the ops is a closed switch conducting and maintaining fuel pump power,but if and when RPM's slow and oil pressure lowers the resistance will then increase until the resistance is to high to maintain fuel pumps requirements and pump shuts down.
So one can see that the oil pressure switch under that condition takes over as MT stated for safety but will when pressure is low enough shut pump.
I am not taking sides just clarifying how a simple circuit is used in a very intelligent way.
So it is a safety circuit (but not as shut off of fuel pump in the way Califokie thinks)and one that without your debate may not have ever been noticed since symptom would be == I was driving home or to store etc parked veh shut down came back and now only turns over but will not start. Changed fuel pump relay and all is good. The driver would never know that while on highway doing 65 mph fuel pump relay failed and oil pressure switch allowed to safely park. It's nice to know GM'S got our backs. Thanks for the informative debate. Ron
ox like I have seen on other vehicles,thanks

S10forever

HI,Heres food for thought that fuel relay problem I have been having may turn out to be
the inertia switch under the dash after all and we bought a relay to see what it looked like and it is really small compared to the other ones like about 1/3 the size of them.
Time will only tell if we found the problem.

S10forever

HI,Well heres what I have found out about the so-called inertial switch in GM vehicles they do not have one like FORD vehicles do,we found a switch under the dash that if turned would reset fuel pump to work.
It appears from what I found GM uses a combination of OIL PRESSURE,COMPUTER and
redundant wiring to shut off fuel pump you have read it understand it.
I will see if I can do a copy any paste on how they came up their way of doing it.