A paperclip as a Fuel Pump Relay bandaid?

Post by **thecheat** » 03 Sep 2010, 09:13

Nobody mentioned so I'll chime in. The fuel pump always runs with the key on, it doesn't work like a thermostat and cycle on and off as fuel pressure dictates. The pump sends gas to the fuel rail and the fuel pressure regulator operates by vacuum and allows the correct amount throughnand bypasses the rest back into the in a loop.

You should have switched 12 volts on one leg and constant 12 volts on another. Then the relay closes the electromagnet and completes the circuit sending 12v to the pump. If you have the switched 12v present the relay itself is probably bad since the constantn12v isnrunning the pump.

It is possible that the switch side isn't working or the magnet side isn't engaging the switch. Sometimes there is a broken solder joint and you just need to reflow the solder. Common problem on older bmws.

Post by **renns** » 03 Sep 2010, 10:13

thecheat,

Your description is missing some important points. The key on will energize the fuel pump relay, but only briefly to pressurize the rail in case pressure has bled off over time. Then it turns the pump off until the engine is cranked. So long as the engine is running, the pump/relay stay energized. If the engine stalls with the key on, the pump will be turned off. This is to ensure in an accident that the fuel pump will not continue to run emptying the fuel tank out a compromised fuel system.

Post by **thecheat** » 03 Sep 2010, 10:30

Good point. So then the switched 12v should be powered briefly then always on with the engine. Presumably if it does not remain on, the ecu is to blame?

Post by **renns** » 03 Sep 2010, 11:37

ecu, or more likely wiring harness. Also, if cam/crank sensor(s) are not functioning properly, then the pump may not engage when cranking, as the ecu won't know the engine is turning over.

nightc1 · Post by **nightc1** » 03 Sep 2010, 20:11

The drive home was smooth as ever with the paperclip installed for the ~40 mile ride.

Even though the abs flaked out a few times (thus hurting the calculated miles per gallon in the computer, not the actual MPG), I managed a whopping 33mpg calculated average ... which means it was even better than that for real

. I guess the maf cleaning, electronic throttle body cleaning, o2 sensor cleaning, new plugs, fully synthetic oil, new oil filter, new fuel filter, mass air sensor cleaning, cleaning of the air hoses between the engine/maf/throttlebody, and so on helped something out. I averaged close to 30mpg for my drive to work before all this and my tires are really bad... but now I averaged over 33.

This fantastic mpg lit a fire in me to get this car back on the road and sell off my suv (though I enjoy that vehicle, I could do without the payment). Maybe later when I feel my v70 is up to snuff I'll look into buying another (maybe in white) and get it into tip top shape for my wife as a daily driver so she can leave her suv in the garage

.

Anyway, I pulled the paperclip when I got home. It wasn't hot or anything.

I can't recommend more having a small paperclip as an emergency tool for this very purpose. If something else causes this relay to not get it's signal then no amount of backup relays is going to get you going again.

I'll find out this weekend if I'm getting the signal on the other pins for the relay to close with the engine running. Thanks again for everyone that chimed in on this thread. I had seen many people recommend using a paperclip for testing, but not on possible longer term use in an emergency (get me home) kind of situation.

Wongster · Post by **Wongster** » 24 Oct 2012, 09:46

The paperclip trick worked for me! Ordered a new relay and replaced it. Everything is running A1

Post by **rmmagow** » 24 Oct 2012, 10:23

Personally, I bought two used relays via ebay, less than 30 for both. When I got them, I tested each one by running for a day in the car. Both are in my glove compartment. Cheap insurance.

Melisalynn · Post by **Melisalynn** » 28 Jan 2021, 08:26

Hello just wanted to say I did the paper clip thing for my ac compressor and ended up doing the wrong relay my car will not start no fuel pump noise. I checked all the fuses. My car has been sitting for 6 months now bc of it and I still don’t know what to do.

Post by **volvolugnut** » 28 Jan 2021, 10:06

Welcome to MVS.
Help us help you. What is your car model? What relay did you alter? Other details?

Starting a new thread in the proper model/year forum will keep things neat for others.

volvolugnut

Post by **abscate** » 28 Jan 2021, 19:46

Melisalynn wrote: ↑28 Jan 2021, 08:26 Hello just wanted to say I did the paper clip thing for my ac compressor and ended up doing the wrong relay my car will not start no fuel pump noise. I checked all the fuses. My car has been sitting for 6 months now bc of it and I still don’t know what to do.

Where are you, in the beautiful Magnolia State ?

We might have a MVS person nearby!

There are two sets of fuses to check, especially if you’ve been paper clipping

A paperclip as a Fuel Pump Relay bandaid?

Re: A paperclip as a Fuel Pump Relay bandaid?