My 1984 Volvo 240 DL wagon with 168K miles cranks well but will not start. The fuel pump relay under the dash (passenger side) can be heard chattering (i.e. rapidly closing and opening). In-tank pump and main pump are working. Switching fuel pump and system relays give same sympton. Chattering is present in intermediate and start position. Engine wiring harness wires are brittle in some areas especially at connector on engine firewall. Is this the classic electical short or is something else?

my 240 dl wagon did the exact same thing...there is a short somewhere in the wiring going to the main pump.. i made an aligator clip jumper between fuses 5 and 7 and it started right up.. just remember to disconnect the jumper or your fuel pump will continue to run after the car is shut off.

some one will tell you to resoulder the fule relay - ignore them

thank you sir!!

It sounds like the classic syndrome of corrosion in the EFI power circuit, namely the 12 gauge wire that originates at the battery cable and passes through a troublesome 25A blade fuse at the driver's fender. Clean, clean, clean.

Ron Schuyler II

great advice to clean that 25 amp fuse.
you can also swap the main relay and the fuel pump relay - they should be right there side by side - and see if the chattering moves with the relay.
personally I don't believe in repairing relays, but there are lots of posts on this so you can evaluate the issue yourself.
I would buy and install new main and fuel pump relays for reliability.

Thanks!

I have switched the fuel pump relay and the system relay. The chattering remains in the fuel pump relay side, which leads me to believe both relays are good. Both relays were replaced. 25 amp fuse is good and no sign of corrosion is apparent.

Toano3

The 25 amp fuse itself may be OK, but carefully examine both ends of the 2 wires connected to it. Although that fuse feeds through the relay, it is not involved in the relay's operation, so I don't think it is causing the chatter

The Chattering is caused by low voltage — enough to energize the relay coil, but when the points close, the load (fuel pumps) is more than can be handled, so the relay drops out. The cycle repeats rapidly, causing chatter or buzzing relay.

So you should also check fuse contacts for #13, which powers the fuel relay COIL (Blue/Red wire on terminal #85). The fuse (along with 11 and 12) gets power on the hot side via a Blue/Yellow wire from the ignition switch.

The Ignition Switch gets power from the small black plastic terminal block on the fender rail, near the battery.
--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

Harvey your right about these relays - theres nothing to repair theyre just generic cube relays cheap to replace and available anywhere. This is peculiar to the 83-84 B23F. One thing you learn about relays when youve been around them long enough: a chattering relay is a good relay and the problem making it chatter is elsewhere.

But the other relay repairing you read about is worthwhile because theyre more than just relays theyve circuits inside with cracked solder, and not so cheap or generically available. Reflowing the solder actually makes them better than new.