Fuel Pump not working

[imoto]

My car has been sitting for 6 weeks and had a flat battery I charged it and did not hear the fuel pump start up when the ignition was turned on . The starter is cranking OK.I checked the fuse it is Ok and has power on both in and out sides when the ignition is turned on. I removed the relay and put a replacement in and still no power to pump ( assuming pump is OK ). Looking at the current flow diagram which i confess is not one of my strong points , it looks like the relay is wired differently to say a head light relay. Terminal # 30 is the output to the pump and hot battery source 12V. I thought it would be hot but does not have power to it when I put my test light to the terminal with relay removed. The rubber relay holder looks like the wires behind it will be hidden inside the plug. Relay plug has power to # 86 and 87a when ignition is on and relay removed. I thought # 87a of 87 would go to the pump # 86 switched which it is the igniton switch is the switch.
I would hope this all makes sense to someone here.

[rsscotty]

What year car are you working on?

[timmy2]

Assuming your car is post 1974, Pull the relay and insert an in-line fused jumper between 30 and 87a of the relay socket and turn the ignition to the run position. The pump should run.

[imoto]

Originally Posted by rsscotty

What year car are you working on?

Its a 1981

[imoto]

Originally Posted by timmy2

Assuming your car is post 1974, Pull the relay and insert an in-line fused jumper between 30 and 87a of the relay socket and turn the ignition to the run position. The pump should run.

Timmy as the 87a socket has power when ignition is on it is switching then and you suggest jumping across to terminal to the 30 socket which the flow diagram which goes to the pump. What size fuse, I can use an inline fuse holder with the ends stripped. Timmy is the terminal 30 supposed to be hot from a 12v source?

[kodioneill]

The fuel pump will only run while cranking on a 81. You can pull the plug off the rear of the cis sensor plate and it will run with the ignition on.

[pete3799]

If he bypasses the relay (30 and 87a) it will run with the key on.

[boyt911sc]

Originally Posted by imoto

Its a 1981

Search for DKLever's post about FP relay. I had posted the detail tests for each terminals of the FP relay socket. This should give you a good idea where the problem could be. Keep us posted.

Tony

[ossiblue]

You've been given plenty of information on how to diagnose the problem--if you truly have one.

Your electrical tests show power to the relay socket is correct--it should show power at 86 and 87a. As soon as you insert the relay, however, 86 powers the relay coil and it will switch internally so 30 (to the pump) connects to 87, the starter--that's why you don't hear the pump when the key is "on." Once the engine starts, the relay loses its ground connection (from the intake switch), the relay coil loses power, and the relay switches the pump (30) to 87a for continued running.

Your car has been sitting for six weeks. It's quite possible you have a minor leak in the fuel supply somewhere and you may simply need to prime the injectors. Remove the air cleaner, turn on the ignition, and gently lift the plunger inside the intake. You should hear the fuel pump come on, feel resistance, and in a second or two, hear the injectors squeal. If all that happens, go back and try to start the car. If that fixes your situation, your next step will be to test the system with a fuel gauge set to see if you have a residual pressure problem.

[imoto]

Originally Posted by ossiblue

You've been given plenty of information on how to diagnose the problem--if you truly have one.

Your electrical tests show power to the relay socket is correct--it should show power at 86 and 87a. As soon as you insert the relay, however, 86 powers the relay coil and it will switch internally so 30 (to the pump) connects to 87, the starter--that's why you don't hear the pump when the key is "on." Once the engine starts, the relay loses its ground connection (from the intake switch), the relay coil loses power, and the relay switches the pump (30) to 87a for continued running.

Your car has been sitting for six weeks. It's quite possible you have a minor leak in the fuel supply somewhere and you may simply need to prime the injectors. Remove the air cleaner, turn on the ignition, and gently lift the plunger inside the intake. You should hear the fuel pump come on, feel resistance, and in a second or two, hear the injectors squeal. If all that happens, go back and try to start the car. If that fixes your situation, your next step will be to test the system with a fuel gauge set to see if you have a residual pressure problem.

Yesterday I went to start the tests on the car but the battery was too flat ( I had to also charge up my ute) I put charger back on the 911 all night and today bypassed the relay with inline fused 25A jumper, car started immediately like it usually does. I also noticed the sound when ignition key turned to ACC position before engine cranks over. This is the sound I had assumed was the fuel pump ? I put the relay back in and the car started again straight away . Would it be that there was not enough charge in the battery when I first tried to start it therefore the circuit you guys describe that the fuel pump only runs when air flow sensor lifts ??? Not sure
but its running OK like it always does.

[ossiblue]

Glad to hear it's running. It is possible that a very low battery was your problem. As mentioned, at start up, the pump only works when the key is turned to "start" then it switches over once the engine is running. The initial start up takes two large draws from the battery at the same time--the starter and the fuel pump. A low/weak battery may not have enough power to feed both or, if it does, both will turn over at less than full revolutions. The fuel pump may not have been providing enough pressure.