Fuel pump (go figure)

[CK88]

Hey guys, just finished putting a new fuel pump in my 72 gt wagon. About a week ago I noticed (after it wouldn't start) that there was no fuel entering the carb, even when manually pushing throttle. It would puff air, but no fuel. I figured the fuel pump was bad, as these things tend to go out semi quickly, so I replaced that tonight, put the tank back in, and went to start it... Nothing... I sprayed starter fluid into the carb and she fired right up for a few seconds then died. I then disconnected the fuel line from the pressure regulator, and hooked it straight into the carb fuel line... Nothing... I disconnected the fuel line from both the carb and the pressure regulator, sprayed starter fluid into the carb, and down the fuel line that's connected to the carb (not attached to the line to the tank), again, she fired right up and then quickly died. In doing the last test, I noticed that there was no fuel coming from the line attached to the pump/tank while the motor was running. THUS, the pump was not running, even with the engine running. My faulty pump problem, I believe, has now turned in to some sort of electrical/fuse problem.

I ALSO blew air down the fuel line into the tank, and air flowed freely down the line (I could hear bubbles in the tank), and same into the carb. There are no restrictions in the fuel lines that would restrict fuel flow.

I want to know if anyone thinks I should check anything else fuel related, or if it sounds like what I am thinking now (electrical issue). IF it is electrical, then I'd appreciate some input. For instance, is the pump running off of its own power, or is it connected to another source ie starter, etc? And, where is the fuse located for the pump? I tried to trace the wiring from the sending unit back up into the "trunk" area, but I lost it in the sidewalls.

Also, I know that the fuel pump will only run IF the oil pressure sending unit is reading sufficient oil pressure. My red "oil" light on the dash is NOT on at startup, and the plug is securely connected to the sending unit. I would just go ahead and change the oil sending unit, but no parts stores carry them, and I don't want to order one until I've tried everything else at my disposal. I don't think that oil pressure is the problem, but I suppose it could be if I've missed something else. I'd appreciate some help on this, I'm really stumped right now...

Thanks in advance!

[cosvega76]

An easy way to check the fuel pump wiring is to make a jumper wire out of a 2 - 3 inch length of wire and two male spade connectors. Jumper between the parallel slots in the oil pressure switch plug and turn the key on. Also check the FUEL PUMP and START fuses in the fuse box.


Chuck

[CK88]

I don't know if I mentioned this, but it's the stock 140ci engine in this old girl.

Thanks for the info Chuck, I'll check that out when I get home from work today. Now for my NOOB question of the day, where's the fuse box on these things? I would assume it's somewhere under the dash, near the firewall, but I haven't found it yet in digging around under there. It sounds to me exactly like a fuse and/or oil pressure unit failure BECAUSE it was running fine till I parked it in my driveway. Came out the next morning to start it up and go to work and she wouldn't stay running. Something happened overnight that it didn't like. It would make sense that I maybe popped a fuse at startup that morning and it started up just long enough to drain all the fuel out of the line. HOWEVER, I would also assume that, if I didn't have power going to my oil pressure unit (and in turn no power to the pump), that the red "oil" light would be on on the dash. Am I right?

The previous owner did some weird wiring on this thing, trying to hook up a god-awful stereo system in it, so I have wires going all over the place, with fuses here and there and everywhere in between. I'm going to end up just ripping it all out and doing it over (eventually).

Again, thank you for the help. Hopefully I'll have it running again here this afternoon.

[crawfw]

If the jumper wire on the oil pressure switch plug allows the pump to run. You might want to consider hooking up an oil pressure guage to make sure its not actually low oil pressure causing this. I had this issue but it was just the switch so I just left it bypassed with a jumper wire since my oil pressure guage showed good oil pressure. mine was intermittent though and would die while driving it. lol. It very well could be a fuse since it happened so suddenly. I thought my issue was in the tilt steering column since it was loose and thought it was pinching a wire in the ignition or something. So I replaced the steering column first. Man, what a debacle thas was. Then I decided to start reading the repair manual, And voilia, there it was in black and white. Oil pressure switch. lol Good luck with the fix.

[cosvega76]

Now for my NOOB question of the day, where's the fuse box on these things? I would assume it's somewhere under the dash, near the firewall, but I haven't found it yet in digging around under there.

On the firewall, right above the dimmer switch.

HOWEVER, I would also assume that, if I didn't have power going to my oil pressure unit (and in turn no power to the pump), that the red "oil" light would be on on the dash. Am I right?

The oil light circuit and the fuel pump circuits are separate. If there were no oil pressure, that switch in the sender would be grounded, turning on the light. Once it has oil pressure, it closes the contacts in the sender for the pump circuit.

Check out the pump first with the jumper. If the wiring is as cobbled as you say, you need to check to see if the wiring is sound.


Chuck

[CK88]

OK guys, new developments, and still no solution.

I changed all of the fuses in the panel, even ones that weren't blown, and still no success. I checked and rechecked all of the wiring to sensors and switches, everything (upon first look) was connected.

After that didn't work, I did the bypass of the oil pressure sensor with the 12gauge wire and 2 fork terminals between the two parallel ports in the plug. No oil light on, no fuel pump... No success.

Tonight I decided to just wire the pump solo on its own switch. I used a ring terminal and tapped in to power on the starter, where the previous owner put on the power for the electric rad fan. I used a 3/8 ring on the bolt, with 12gauge wire to a single 10A blade fuse box, then to a toggle on/off switch. From the toggle switch I ran 12gauge to the back of the car, where the pump wiring comes up through the floor. I spliced in to the pink wire coming off of the pump housing. I left the ground as it was, connected to the floor pan. Blue wire is still going through wiring harness as it was before as well. By doing this, I bypassed the internal wiring for power to the pump, which I assumed would give me power via the toggle. However, I'm not hearing the pump come on with the switch, while at the same time my rad fan will work. I missed something somewhere, or something is messed up... I noticed the radiator fan is running through a relay AND a toggle switch, is this needed for me with the pump situation as well? Did I need to run blue separate from harness also?

I am by no means a wiring expert, so forgive me for any silly mistakes I might have made.

I decided to run it off of a toggle because it gives me one more mode of control over the car. I can turn it off if I ever have an emergency, and it provides an added security measure, in that people won't stay running long if they don't know about the switch and decide to take it.

Anyway, any input?

[CK88]

One other thing... Do all 72's have inertia switches? Could this have gone bad and caused my problem? If so, where the he** is it?

[firebird77clone]

Bad ground.

Remember always, for a motor to run, it has to have potential... That is what the voltage is, a measure of potential.

Anyway, the voltage has to return to the battery.

It sounds as if you have the positive voltage to the pump, but it can't get back to the battery.

Btw.. did you bench test it while it was out?

[cosvega76]

One problem I had with the Cosworth was that the flat conductors between the sender plate and the pump are secured only with push nuts. When I replaced the pump it wouldn't work. I ended up cleaning the connections and using new push nuts so it would make contact.

Of course, that means you'll have to drop the tank again and pull the pump/sender unit to check.


Chuck

P.S.: Silly question: you did install the wiring connector to the sending unit when you installed the tank, right?

[CK88]

I kind of thought about the bad ground also. I checked it on the floor pan in the back, but I guess I could run a wire back up to the front and ground it with the radiator fan at the front of the engine bay. I know, I don't HAVE to run it all the way up there to ground, but at least then I know I have a good ground connection.

I didn't bench check the pump before I installed it. I just assumed that a brand new pump would work as new.........

And yeah, I double and triple checked the plug on the top of the sending plate. It was plugged in correctly, but I'm now wondering if maybe you're right, and I have a bad connection in those push nuts... I think today I'll try and run new wiring all the way to those prongs on the sender plate and make sure that those are cleaned up and looking good. If that doesn't work, I'll pull the pump out and run power straight off it to make sure its working at all. If this turns out to be a bad NEW pump, I'm going to feel really dumb...

I'll update again tonight after new wiring is done...

NOOB question for today. Is the blue wire just a negative, or is it running to the float sensor?

[firebird77clone]

Automotive typically uses black for ground

[CK88]

Just wanted to let everyone who helped me out know that I got the pump running again. Apparently the plug going into the sending unit on the top of the tank was bad. I had to take the plug apart and rewire it because I couldn't find a new one anywhere. Anyway, got it all hooked back up and the car purred like a kitten... For a while...

Then it died on me going down the road. Felt like it was starving for fuel and then would die. It would start right back up, putter for a couple seconds and then die. I opened up the fuel lines right behind the carb, and even with the pump running, I wasn't getting any fuel. Something is backed up in the line somewhere. I can't blow air down the line anymore... I'm thinking I'm going to just redo all of the fuel lines and make it all new. Any recommendations on dimensions for fuel line? Should it be 1/4 inner? 5/16 inner? Any benefits to putting in larger diameter lines?

[CK88]

Turns out the fuel line that ran up behind the wheel well got pinched between the metal line and the sending unit. the pinch + pressure caused the line to rupture. I replaced that 8" section and it started right up and ran great. That problem is fixed...

BUT with the new wiring I did, something got messed up with my sending unit. It is reading at a full tank no matter what. No fluctuation or anything. I don't know if something is messed up with the sending unit, since I removed it from the tank to replace the pump, or if my wiring is messed up and causing a faulty read. Any ideas?

[Monza Harry]

That is usually the ground not functioning. Check clean and re-pinch should get it going again. Harry

[CK88]

I should have also added that, since this newest issue occurred, the pump is running as soon as the key is turned from the off position to the on position, and is not responding to my toggle switch anymore. I guess that kind of confirms the bad ground. There should be only power coming through the toggle circuit. EVEN with the toggle unclipped (no power supply running to toggle switch) the pump is running WITH NO POWER SUPPLY wire. Something is still hosed up... Ill check grounds.