Fuel pump relay question? Topic is solved

Post by **June** » 27 Feb 2023, 16:04

Here on MVS I have read 200, 700, and 900 series cars have known problems with the fuel pump relay. I did notice the in tank pump only runs a few seconds with each key cycle. Does anyone know if this is normal? Or do I have a problem? Do both pumps run continuously? Or just the main pump? Is the in tank pump just a initial prime pump? I assume the relay controls both pumps?

Anyway I bought a replacement relay on FCP Euro and finally I got around to putting it in. Surprisingly the original Volvo relay looks nearly new physically. Really everything wires/electrical on this car looks nearly new. I did install the new relay since I was there. Here are photos of the relay I removed from my car. The original relay has copper prongs and the replacement has steel prongs. Both have the same part number. The in tank pump still only runs for a couple of seconds. Is this normal? June

Addendum: Robert has videos recommending relay replacement every so many years to circumvent getting stuck. His video on the subject is the main reason I bought a new one to begin with. Also the 1990 240 with the buzzing relay leaving it's owner stranded. My car is a 1991 with 202K. So the original did it's job and now will be the spare in the glove box. June

Post by **volvolugnut** » 27 Feb 2023, 16:36

It is my understanding the in tank pump and main pump should both run as long as the engine is running. The in tank pump is a booster to get fuel to the main pump without the main pump needing to pull fuel, especially when the tank level is low. Most pumps of all types are better at pushing fluid than pulling fluid.
How did you determine the in tank pump only runs for a short while?
volvolugnut

Post by **June** » 27 Feb 2023, 17:04

volvolugnut wrote: ↑27 Feb 2023, 16:36 It is my understanding the in tank pump and main pump should both run as long as the engine is running. The in tank pump is a booster to get fuel to the main pump without the main pump needing to pull fuel, especially when the tank level is low. Most pumps of all types are better at pushing fluid than pulling fluid.
How did you determine the in tank pump only runs for a short while?
volvolugnut

It is audible with the door open. Like a humming sound for maybe two seconds. That is cycling the key from off to run. With the engine running I cannot hear anything from the tank. Perhaps it quiets down? The pump under the car is silent always. I don't wish to find myself stuck somewhere. What has me concerned beyond all the hoopla about these cars eating relays is the fuel line from the fuel pump to the engine has a continuous pronounced pulsation. Shouldn't the fuel line from the pressure pump to the pressure regulator have a steady pressure? That line nearly vibrates!?

The S80 fuel line doesn't do this. I know it's a different system. Perhaps the pulsating fuel line is normal. Sometimes the car starts in a split second. Other times it cranks several seconds before starting. Cold or hot doesn't matter. June

Post by **volvolugnut** » 28 Feb 2023, 08:08

Bentley manual says you should be able to hear a buzzing sound at the fuel filler opening when the engine is running IF the in tank pump is running. There is also a fuse (#4?) for the in tank pump. You can also lift the carpet in the trunk and test the current to the in tank pump. Your pump should have 3 to 4 amps. This will also check if it stops running after the engine starts.
If the in tank pump is not working, the main tank will struggle to pull fuel when the tank is low. This may be the cause of pulsation in the fuel line. You could also test fuel pressure at the fuel rail to see the variation.
This information is for 240 cars, but 740 are very similar.
Since you like to maintain your cars very well, you might consider dropping the tank and replacing the in tank pump and prefilter just because they are old.
volvolugnut

WGFP · Post by **WGFP** » 28 Feb 2023, 17:04

I kept the functional but very old relay when we replaced it recently on advice from this forum. I haven't tried opening it up yet, but has anyone had success rebuilding/refurbishing one?

BTW, we've also started marking the sides of relays and other suitable items (like the alternator) we replace with a date and mileage. We're keeping good records, but it's a good backup.

Post by **volvolugnut** » 28 Feb 2023, 18:15

I have not tried it, but the relays are said to often be repaired by resoldering all the internal connections.
volvolugnut

Post by **volvolugnut** » 28 Feb 2023, 18:16

I have not tried it, but the 240 relays are said to often be repaired by resoldering all the internal connections.
volvolugnut

Post by **June** » 01 Mar 2023, 12:09

volvolugnut wrote: ↑28 Feb 2023, 08:08 Bentley manual says you should be able to hear a buzzing sound at the fuel filler opening when the engine is running IF the in tank pump is running. There is also a fuse (#4?) for the in tank pump. You can also lift the carpet in the trunk and test the current to the in tank pump. Your pump should have 3 to 4 amps. This will also check if it stops running after the engine starts.
If the in tank pump is not working, the main tank will struggle to pull fuel when the tank is low. This may be the cause of pulsation in the fuel line. You could also test fuel pressure at the fuel rail to see the variation.
This information is for 240 cars, but 740 are very similar.
Since you like to maintain your cars very well, you might consider dropping the tank and replacing the in tank pump and prefilter just because they are old.
volvolugnut

Thanks, opening the fuel door, removing the fuel cap, and the in tank pump is then audible. So the pump is running continuously as it should. My next step is to check the pressure at the rail. I did change the filter a few months back. June