Fuel pump enigma

Paxmanmerv

Active Member

Posts

171

Location

Bredon Hill.

• Nov 24, 2018

• #1

Afternoon all!
As we all know, there`s a lot of Defenders getting stolen at the mo. Thought to myself I better get a bit of home made security at the very least on it.
Logical line of thought went that if the fuel pump is not running, the engine wont..
So! Seat out, start the motor & pull the Fuel Pump Relay out.....Engine kept going. Put it back in & pulled the Fuel Pump Fuse, just the same....
Any thoughts on this? Seems to make no sense what so ever....

 

jamesmartin

Well-Known Member

Posts

91,879

Location

louth lincs

• Nov 24, 2018

• #2

which engine

 

Paxmanmerv

Active Member

Posts

171

Location

Bredon Hill.

• Nov 24, 2018

• #3

Hiya Jamesmartin!
It’s a 2007 TD5.

 

L

lynall

Well-Known Member

Full Member

Posts

26,725

Location

Kent

• Nov 24, 2018

• #4

Have you actually tried to drive it with a dead fuel pump? might find it wont make a few hundred yards, whcih is excellent as they wont hang aorund trying to fix it!

 

Paxmanmerv

Active Member

Posts

171

Location

Bredon Hill.

• Nov 24, 2018

• #5

Pulled the relay & ran fine for a few mins. Popped the seat back in & did a mile or so. Wouldn't rev past 2000 i guess so a bit sluggish. Getting splinters under my finger nails from scratching my head with this one.....

 

L

lynall

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Full Member

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26,725

Location

Kent

• Nov 25, 2018

• #6

Well thats no goof then, maybe a fuel cut off solenoid in the main feed line.

Iirc the Td5 has a quite a complictaed route for the fuel to flow, maybe that has a bearing on your ideas?

 

G

guineafowl21

Well-Known Member

Posts

3,360

Location

Inverness

• Nov 25, 2018

• #7

Do we think the high pressure pump has enough suck to keep the thing running without the tank pump?

I take from your previous posts that you got it started, then pulled the relay. What if you pulled the relay, then tried to start?

My guess is that if pressure is allowed to bleed off the high side, then it won’t be able to start. Especially after a few hours or an overnight sit. You could even make a fake relay by gutting one, to sit in place so all looks well.

That would narrow down the potential thieves to those with a test light, multimeter and a knowledge of basic diagnostics (or a big tow rope, I suppose).

 

Paxmanmerv

Active Member

Posts

171

Location

Bredon Hill.

• Nov 25, 2018

• #8

Tried a few different things, First thing i tried was simply a switch in the power supply to the fuel pump relay. Flick the switch so it is off & turn the key. Burst into life without the relay being energized. Stoped it then pulled the relay incase it was faulty. Turned the key & it started right up.
Time to think again.
Quick look at the electrics schematics & changed my home brewed security to cut off the main relay. Stops it dead.
RESULT!
Still not sure why the TD5 can run with the fuel pump not running though. Got onto the South Africa LR Club forum pages & it’s mentioned on there. Several theory’s bounced about but nothing conclusive....