Mfi fuel pump not working (getting hot)

[pszemia]

Hii everybody, i tried yesterday to start the car after a 2 years work and everything is working except the fuel pump.

The engine spins, the oil circulate (found 2 loose hoses), but the electric fuel pump is not working.

I suspect a problem with the wirings, because the pump gets hot, there is no noticeable noise or spin when I touch it. If I try it with 12v directly it spins ok. I have 2 pumps, same sinthom with both. The fuel hoses are new, if I blow through them I hear bubbles in the tank, and if I suck, I get fuel.

One of the pumps was recently rebuilt to factory spec.

Could it be something wrong with the wires? I have disassemble and assembly again because of full body work.

Thanks a lot,

Ariel

[RSTarga]

sounds like a weak connection. bad ground.

[pszemia]

And any ideas where should i track the ground problem?

Thanks,

Ariel

[RSTarga]

I doubt you have 2 bad pumps at the same time. If they work ok when you give them outside power then the problem is in your wiring. Check voltage and amps at the pumps and follow it back. It could be bad ignition switch. Grab a wiring chart and follow.

[Porboynz]

The fuel pump earth is at that stud behind the fuel filter bracket. The other thing to check is that you get a full 12V at the pump through your wiring to the pump. The pump 12V comes direct from the ignition switch, via the feed side of the front fuse block. #7 fuse on my diagram, the fuel pump feed is the Red Green wire. (feed side not fused side.) There is a red feed wire to fuse #8 from the ignition switch and a link in behind the fuse panel joining #8 to #7 fuse feeds. In fact this could be the problem, if this link has developed a hi resistance dry joint you will read 12V at the pump OK without the pump, but loading it with the pump will cause the joint to go hi resistance and the 12V drops away. You can prove this really easily by taking a screwdriver and shorting #7 to #8 on the fuse block (remember this is the feed side, lhs as you look at it) If this is the problem simply take a short length of wire and join #7 to #8 so you no longer rely on the copper strap under the fuse block. This is a common problem. If this is the problem its likely that your windscreen washer pump does not work as its fed by the #7 fuse. (black wire)

[pszemia]

Hi, and thanks for the reply.

I've been playing with the pump the last 2 hours and found the following things:

Pump electric connection:

Key off and No pump connected --> 0v
Key off and pump connected --> 0v

Key on and no pump connected --> 12v
Key on and pump connected --> 9v

12v direct feed to pump: I can hear a click and feel the pump moving

key on, pump connected and a 12v bypass direct from the battery --> 10.5v

Tried to get the 12v from fuse #1 in the engine bay --> 9.5v

All this tests were made with the #7 and #8 fuse feed line connected with a cable.

Also i found the feed line in my car is the right side (near to battery), because if i remove the fuses and turn the ignition on, i get 12v on that side and 0v in the opposite, is this ok?

Any ideas? My mechanic told me to add a relay and a new cable from the battery, but i want to keep the car as original as possible.

The pump keeps getting hot when i do this tests.


Thanks,

Ariel

[Porboynz]

Progress but confusing. Please confirm that the pump runs normally when 12v directly connected. The pump will get warm or hot if it is not running normally and pumping fuel, it's cooled by the fuel it's pumping. If its stalled because of low feed voltage then yes again it will get hot. A running pump is quite noisy, maybe a bench test pumping some kerosene or petrol (be careful) is a good idea. Anyway, the feed side is closest to the battery, I took a photo of my 1972 fuses for you to compare. If you are only getting 9.5v with the pump connected its either jammed or you have a hi resistance somewhere. If you have bypassed that link between #7 and #8 then it will not be that. Check you are getting 12v at the fuse block, maybe you battery is run down after all this testing. There is a fuel pump connector inside the engine bay, LHS right near the shock tower as you look at the engine. Make sure that's not corroded as well. I would also clean all the wire ends where they attach to the fuse panel, any corrosion is bad.

It is possible your pump is failing and you have faulty wiring, they are the worst faults when there are 2 things wrong. Keep at it, you will succeed I am sure. A relay is not needed if everything is clean and connected tightly with no corrosion. If the battery is freshly charged you should have about 12.6v not just 12v.

[pszemia]

going for a test this week, have a question related to your picture.

Why you have a joint between fuse #4 and #6? i can't see the joint between 7 and 8 on your fuse, i guess you don't need that bypass.

Also, to check for corrosion on engine bay, what do you mean with shock tower? (FOUND IT)

One more addition, i have forgot to say i have made all the tests with a car charger connected, so i get 14.5 at the battery, and only the measured values at the pump.

Thanks,

Ariel

[Porboynz]

The join between 7 and 8 is there, its a metal link riveted in behind the fuse panel. If you unscrew the fuse block and look in behind you will see it. This is the sort of link that can be a problem, but if you have linked #7 and #8 with a wire at the front then that's eliminated. The large red wire link on my fuse block between #4 and #6 has been like that since I got the car, the schematic shows #4 #5 and #6 bonded together so maybe a previous owner added the link or its from the factory, I never checked. I see you added an edit to your last post to say you found the fuel pump connector in beside the shock tower, that's another good test point. Its also another fail point to check for good connections and crimps of wires into connectors. All of these joints attract corrosion and can cause hi resistance which causes voltage drop.

Battery chargers are interesting gadgets, some only trickle charge and will not sustain a serious load. What voltage do you have at the battery terminals with it disconnected after an hour or so? You should get the same or very nearly the same at #7 and #8 with the ignition on. You should also get the same at the pump with or without the pump connected, or at most 0.5V or so drop.

Here is a picture I took of my repair to the #1 and #2 link.



If you look closely you can see that link between #5 #6 and #7 in behind my thumb and that #5 looks corroded so I bet the link was added to bypass a problem. I chose to solder #1 and #2 to fix a different problem. In fact if I look real close I can just see the link between #7 and #8 we have been discussing and the Red Green wire that goes off to the pump.