overheating fuel pump relay

connect an ammeter and measure it.

You can put the ammeter across the fuse to check it there too... but also at the pump of course.

Is the pump noisy?

 

Thats the go FF, basics first

Do you find it only overheats when the fuel level is low in the tank? The fuel in the tank keeps the pump cool, I never let my cars fuel tank level drop below 1/4 to try and extend the life of my fuel pump

 

when pumps and motors start to wear out they heat and start drawing more current....
typical of a fan motor on a radiator.
you know if you overload a motor the current draw increases.

but you can check all the connections in the circuit make sure the are all clean
and tight.
electrical connection that is corroded or loose will pull more current because the resistance/heat of the connection goes up.

 

Check the fuseblock. If you have a dirty fuse contact or melted fuseblock, the resistance drops the voltage to the pump and it has to draw more current under load at reduced voltage.

Birdman

 

(If the current measurement Phil suggested doesn't show something particularly "wrong", and the running noise isn't bad), one thing you might try is "reshaping" the female sockets that engage the male relay tabs so that they have a good physical connection/grip on the male tabs of the relay (since you've been doing a lot of removal/insertion they've probably loosened up some), and get a new (fresh) relay (for a price comparison www.importeccatalog.com -- search by typing in the Bosch 10 digit PN on the relay case).

Even when working well (i.e., the CIS fuel pump drawing 9~11A thru the 30 terminal to the 87 terminal path of the relay), these relays run very warm. Once you have an "overheating" incident, this further increases the oxidation of the 30-87 switch contacts inside the relay, further increasing the I^2*R heating generated at the contacts, so the whole thing gets caught in a death spiral (Your observation that the relays work OK in other slots is an indication that they are not obviously bad, but these other locations might not be passing such big current thru the relay -- and, since you're not blowing the 15A? fuel pump fuse, it's a little strange that a relay rated at 30A is having trouble).

Just a thought if the pump/current seem OK...

 

Steve, this sounds like the script for a porno flick!

 

The bearings in the fuel pump may be going because of dirt or (my bet) Your fuel filters are dirty as hell and are creating too much restriction/load for the fuel pump.

I would replace them either way, If your pump is going bad it may be letting debris into your filters...

 

I guess it does, but it's surprising how well this "anatomical" terminology works in communicating the technical details (even IME when dealing with German and Japanese engineers -- everybody gets the meaning ).

The current here is just almost unbelievably powerful. If you get just a 0.1 Ohm resistance in the path from:

pcb trace -to- female terminal 30 -to- male terminal 30 -to- internal relay switch contacts -to- male terminal 87 -to- female terminal 87 -to- pcb trace

you dissapate ~10W (at 10A) which is a lot of heat energy to put into a space less than 1 in^3 volume.

John -- Another way to confirm/deny if the relay is OK is to only partially plug the relay into the socket so that it makes decent electrical contact but you can still make electrical measurements on the partially exposed part of the male tabs. If you measure the voltage between the 30 male tab and the 87 male tab in this manner, while the engine is running, it shouldn't be more than a few tenths of a volt DC (and ideally would be 0 volts).