MK4 Golf 1.4 fuel pump issue(one for George maybe)

Plug

Hello kids, in a spot of bother here.
This morning my father went down to get petrol, drove down perfect, start up again after filling her and it ran for a few seconds and cut out. It didn't start again. I walked down to see what was up, I had no tools, nothing as they are in work till Tuesday.

I done a few visual checks first, nothing out of the ordinary. Disconnected the fuel pipes and there was no pressure at all, turn on the ignition a few times to prime the pump but still no fuel pressure. So I checked the fuses by looking at them and they are all ok. The engine is turning over good.


Next thing I did was take off the back seat and look down where the fuel pump was. There was three philips screws so only by fluke there was a screwdriver in the boot. I removed that cover and disconnected the plug, no signs of corrosion. I got a little paper clip and shorted the two heavy wires for a split second. No sparks or anything.


Next thing I headed to Argos to buy a multimeter. Got it for €40. We then towed the car home for a bit of inspection. With the ignition on I was only getting 3.5 volts at the pump. Obviously something wrong. I disconnected the relays under the steering column one by one to see which one was the fuel pump relay but it stayed at 3.5 volts when I removed them all. I thought that was a bit strange.

Im only armed with an Argos multimeter and a screwdriver. Im not macgyver either:( Im thinking a wiring problem or the relay. Anywhere I should look, google results say the relays can give a bit of bother. Its relay 409.

Cheers.

Plug

With all the relays plugged out I was still getting 3.5 volts. I have 12 volts at the relay plugs. I have a diagram and it looks like a basic handy circuit. Heres a picture of the relay set up(not mine).

George Dalton

If you bridge the relay what happens?

Plug

1)With the plug on the pump disconnected and the relay in I was getting 3.5 v

2)With the plug on the pump disconnected and the relay disconnected but a small pin bridging 30 and 87 the voltage shot up to 12v at the plug. When I reinserted the relay it dropped back down to 3.5V.

When it was at 12v and plugged it back into the pump and it didn't operate. I don't think it would have because the pin I was using to bridge 30 and 87 was very thin, more like a spring. The pump earth wire is ok.

So my conclusion is its definitely the relay which is at fault. Im thinking the only reason the pump didn't operate is because there was not enough amps able to flow because of the high resistance of the pin/spring I used.


Im still wondering why there would have been 3.5volts even the when the relay was disconnected?

d o'c

what car?
crank the engine when rechecking for voltages. The priming will initially energize relay coil, but will need to see CAS or similar engine rotation sensor to keep the relay coil energized (86/85)
most likely 86 will be ign on +12v, and the 85 ground will be switched by ecu. I woulf check for 12v at these pins first, then you know the signal is being sent to the relay.

on the ouptut side 30 should be +12v supply and 87 to load (pump). So bridging these should run the pump.
check the relay coil with the meter,
If your careful you can usually take the cover off the relay,inspect the heavy side for cracked/dry joints.

Plug

Bought a relay this morning from the scrap yard. Fitted it and I got 12 volts down to the pump when the ignition was switched on for a few seconds and then off which is normal. Put the plug back onto pump and no joy. The plug is ok and is making contact with the pump. So looks like the pump is gone too:mad:

Plug

Ok so here is the verdict:
1)Tested for voltage down at the pump and I only got 3.5 volts when ignition turned on.

2)Crossed pins 30 and 87 and it put 12 volts down to the pump. The pump didn't run but I thought that was normal since not enough amps could flow down what I used to cross the contacts

3)Replaced the relay and I got 12 volts back down to the plug when ignition turned on.
Pump didn't run.

4) So Tuesday we picked up a second hand pump, fitted it and worked perfect. Still working grand.


Verdict, I think. Something happened in the pump like a short when brushes failed and it then burned out the contacts of the relay instead of blowing the fuses.
A guy in work thought if the relay was damaged before and sending down too less of a voltage to the pump it may of caused an issue.
Google results were showing the relays can give a bit of bother.