Fuel Pump Relay Issues

[cactus]

Howdy All

Have had an issue with the Q-Banger for about 2 years - and finally had a break through.

Started out when driving in summer, and typically coming up Welshpool hill, car would lose what I figured was fuel or ignition, and engine would literally stop and I would have to pull over. Would wait about 20 minutes, and then car would fire back up again but only last another say 5 mins before same thing happened again. Would repeat over and over until I would manage to get it home.

Originally, only occurred on hot days and coming up the hill. Frequency started to increase and would do it on the flats, and finally, on cooler days.

Changed all sensors, tested different fuel and lift pumps but same thing would happen over and over. Had ECU tested several times and wiring checked but nothing came up.

Happened to be playing with relays the other day, when I grabbed fuel pump relay (while car was warming up) and it was extremely hot (too hot to touch). All other relays were cool.

Drove car and it broke down. So noting relay heat, I switched it over and low and behold she started straight away. Broke down after about 5 mins, put another relay in it and away it went.

So, confident it is a relay issue.

However, fuse for fuel pump melted - but didnt blow.

It seems very odd that the relay would be over-heating without the fuse blowing first?

Any thoughts on what it could be? Have had voltage read outs on fuel pump wiring and it is only about 15 and well below 30amp relay/15amp fuse. Thinking we are going to increase size of wiring from pump to relay, but still very surprised by fact that the relay is cooking and the fuse isnt blowing.

[Tre-Cool]

found the same a few times. relay and holder would melt together but not blow.

upgrade your wiring size & check your earthing for the pump & relay.

[S85FI]

Fuses in cars are a slow blow so not uncommon of relay and fuse too small for circuit.
Is the relay rated for amp draw?

Just looked at a mates v8 on e85. Pumps draw 36 amps and has same problem.

55 A/H battery with wiring too small
Battery too small
Relay too small
Fuses not popping because just on threshold
Wiring hot
Relay hot

He needs wire 13.6mm2. One fat wire. One big relay.
Has 40 amp relay. 2.5mm2 wire.

CAR eventually will catch fire.

[Bram]

See stuff like that all the tine as an auto-elec. Surprisingly, undersize wire usually holds up ok, its the connections that fuck up. Melted plugs, melted terminals/connections, crimps etc. But if you gonna try and fix it you really need to replace it all with something that can take the current, and then some.

To get any kind of decent power out of low voltage, you need plenty of amps. Amps needs conductors that can carry it.

Had a horrible job the other week where a Mack truck cooked all its wiring to the starter. 4x n70s, with the terminals melted into a puddle of fail. Battery cables (plural) each 000b/s cooked at every lug. Isolator wiring literally blowing the lugs off the cable is what eventually open circuited it and stopped. You know you have some current flowing when its enough to turn 000 into fuse wire.