TD5 110 fuel pump earth location?

Filbee · Aug 19, 2020

Hi folks, I've done a search and looked through loads of threads but not come up with an answer...
My fuel pump relay gets red hot after a few minutes running to the point where the relay socket is turning s nice shade of brown. I've changed the relay and put a new spade connection on the wire that's getting hottest after cutting out an inch of wire to make sure the wire is good and clean. But still it gets hot.
Before I go down the route of dropping the tank and fitting a new pump, I wanted to check the earth from the pump. I looked at a couple of wiring diagrams and it just shows the earth from the pump joining a load of others, but no explanation as to where this earth point actually is on the vehicle.
Can anyone enlighten me please?

jamesmartin · Aug 19, 2020

it aint going to be a poor earth

Filbee · Aug 19, 2020

Any thoughts on what it could be?
Pump sounds fine. No funny noises. Changed the filter last week. She runs fine and pulls well. The only reason I checked the relay was that one day she cranked but wouldn't start. Pulled the relay and put it back in, fired first turn of the key...

Filbee · Aug 22, 2020

So where does the fuel pump earth go to? I want know now out of curiosity, whether that's the issue or not. I assume it's somewhere on the rear chassis but I can't see it.

mystery · Aug 23, 2020

has the correct relay been fitted and the wires you say got hot the colours were ? ,did you use open barrel crimps or the crappy colour coded crimps .is it the relay base that has been overheating or the relay overheating

Filbee · Aug 23, 2020

Many thanks for the reply Mystery.
I'm pretty sure it's the correct relay fitted. It was an OEM yellow Ford one, which I've changed for a pattern replacement with the same spec.
The wires that get hottest are the bigger white and purple ones. Both the relay and relay holder had brown scorch marks. The worst marks where on the side leading from the fusebox, but the side that goes to the pump also shows signs of overheating. I replaced the female spade connectors with proper uninsulated open barrel ones (with locking tabs), crimped with the correct crimping tool that folds the ends overs, and I fed some solder down the end of the wire to make sure the connection is as good as it can be. I don't use crappy colour coded jobbies on any of my projects.
Thanks for the diagrams. Any idea where the earth actually attaches to the vehicle?

mystery · Aug 24, 2020

MYSTERY EARTH HEADERS defender td5 (1999).png

Filbee · Aug 24, 2020

Ah-ha, that's useful, thanks for including the pic. I must get myself a full copy of the workshop manual...
What is perhaps a bit odd is that my 110 (ex utilities hardtop) has the three earth posts seen in that picture, but they are all capped off with plastic caps and there are no earth connections going to any of them. Nor do there appear to be any wires that could/should be connected to them! The plot thickens...
Here's what it looks like under my seat if it's any help

Filbee · Aug 24, 2020

As said previously, the truck runs fine, pulls well, starts first flick of the key and the fuel pump isn't making any funny noises. The only issue I had was the one occasion when she cranked but wouldn't fire. Since I've changed the relay and renewed the connectors she starts without issue. The relay is still getting hot though.

mystery · Aug 24, 2020

On the earlier 300tdi the earth point C556 was on the right hand side of the bulkhead ,you could convert to a solid state relay (no doggy contacts) but bear in mind they will operate a their set minimum voltage which I believe is 3 volts plus less
drain through the ECU and good for when the battery voltage drops due to cranking

Filbee · Aug 24, 2020

Thanks for the tip, I've not come across solid state relays before. I'll check it out and see if I can find one suitable

Filbee · Sep 5, 2020

I've got an update of sorts...
Since my last post I've fitted a new VDO fuel pump, filter and filter head ( so the bleed valve and one way valve are new). The bleed valve turned out to be fitted in the wrong union so I've put it in the right one now and eventually got it up and running again.
While I had the fuel tank and pump out I checked the continuity in the power and earth cables from the relay to the pump, and they were all good.
However, the relay is still getting very hot...
I even treated myself to a little AC/DC clamp meter so I could measure the current in the cables to the relay. It's showing between 13 & 14 amps whilst stationary. It seems to be around 13 when first started and settles at 14 when warm. It doesn't seem to increase when revving the engine but I guess it's not under any load.
Does 13-14 amps sound ok? The relay is rated at 40 amps so it's well within its capability.
Any other ideas why the relay is getting so hot?

Jurels · Feb 23, 2021

Filbee said:
I've got an update of sorts...
Since my last post I've fitted a new VDO fuel pump, filter and filter head ( so the bleed valve and one way valve are new). The bleed valve turned out to be fitted in the wrong union so I've put it in the right one now and eventually got it up and running again.
While I had the fuel tank and pump out I checked the continuity in the power and earth cables from the relay to the pump, and they were all good.
However, the relay is still getting very hot...
I even treated myself to a little AC/DC clamp meter so I could measure the current in the cables to the relay. It's showing between 13 & 14 amps whilst stationary. It seems to be around 13 when first started and settles at 14 when warm. It doesn't seem to increase when revving the engine but I guess it's not under any load.
Does 13-14 amps sound ok? The relay is rated at 40 amps so it's well within its capability.
Any other ideas why the relay is getting so hot?

Good day. Any feedback on finding a solution for the relay getting hot?

My Defender Td5 has got the exact same issue. Fires first time, no noisy fuel pump, continuity in the cables 100%....but the fuel pump relay gets very hot after some driving.

LandyAidso · Jun 24, 2021

Glad I found this thread. I am having the same issue except I have been through 2 relays in the past 8 months and currently have not been able to start the landy in a few days. When the ignition is turned my fuel gauge and temp gauge both go to 80% approx, Engine light does not come on or the coil light on the dash. I'm going to start running some new earth cables on my next day off. Has any one got any new information on this fault?

Many thanks

Filbee · Jun 24, 2021

I'm afraid I don't have anything new to add. As per the earlier posts, I've been through the whole fuel system and replaced the pump, filter head + filter and the fuel pressure regulator (all genuine LR or OEM parts). I've replaced the injector loom and cleaned the bit of oil out of the ECU plug. I've replaced the spade connectors on the wires that connect to the relay and soldered them as well as crimping them. I bought a clamp meter to check the current going into and out of the relay and it doesn't seem excessive.
The relay still gets hot but I don't really do many long journeys to see how hot it would get after running for more than an hour at a time.
So I'm going to see what happens for now, and I make sure I've got a spare relay in the cab just in case...

TD5 110 fuel pump earth location?

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