Wont Start - Fuel Pump Relay Grounding Issue?

dthomp87 · Jul 18, 2016

Truck wont start. Cranks fine. I've found some strange behavior in the fuel pump relay socket. the voltage is there but the ground must be bad because it wont trigger the relay, but when i jump the relay ground to proper ground and use 12 volts from the relay socket, the relay triggers. This leads me to believe that the relay socket has a grounding issue? I tried to jump the pump relay (to actuate the pump) and the pump didn't seem to turn on, which I assume may mean the ground for the pump may be bad as well.

Could this be a computer issue? are there multiple relays controlled by the computer before the pump?

Trynian · Jul 18, 2016

Could it be the pump itself?

My fuel pump ground shorted out at the wiring harness plug in the left rear wheel socket that couples the main harness to the frame harness. Once I traced it there, just opened it up and cleaned contacts and it solved it.

You can also test the pump from there.

dthomp87 · Jul 19, 2016

It could be the pump itself. I would like to give it power to test it to be 100% sure before I order and replace, and most likley wont do the job myself. From the strange relay behavior, I'm wondering if its a grounding issue. The information you have given me is very valuable. I will look around there today, Is the socket behind the plastic splash gaurd accessable by removing the wheel? whats the best way to find it? When you say left im sure you mean, drivers side(US) rear.

dthomp87 · Jul 19, 2016

I found the Connector, its pretty large and easy to find. I'm not sure which wires are for the pump. I'll try to clean it out if that changes anything, if not I need to figure out which wires to connect 12v to test the pump.

Trynian · Jul 19, 2016

If I recall, the ground wire was a fairly heavy gauge black wire in one of the corner pins.

I used the wiring schematic from topix electrical section.

http://topix.landrover.jlrext.com/topix/vehicle/lookupForm

I have seen the manual out there on the net. not sure if it had a the electrical connectors but a cheap one month subscription can get you all you need.

FYI the fuel pump only engages for a few seconds when the ignition is turned on to pressurize the line. It does not run steady until the car is started so it is hard to hear as it is very quiet. The only way to tell for sure is to hook up a fuel pressure gauge to to the fuel schrader valve under the hood. Depressurize it then when you hit the ignition on without starting the car you will see the pressure go up if it is working.

Houm_WA · Jul 20, 2016

I don't know if you saw my other post (your suspension fault one) but the RF Capacitor for the Ignition can produce the symptoms you are experiencing, too. If this fuel pump investigation doesn't bear fruit, you may want to look at that.

dthomp87 · Jul 20, 2016

Thanks for your always valuable information Houm_WA. I will investigate the capacitor. When the car is in the ON position, I hear a little buzzing in the engine compartment that I couldnt find. I wonder if it is in fact this capacitor. I am getting close to having it towed to a shop, but still have slight hope I can solve this myself. If the fuel pump is very quiet its possible that it is working and I think it isnt. I will use a fuel pressure tester as I couldnt figure out where the wires to the pump were.

Is it possible to just remove the capacitor completely to test if this is the problem, or does the car not work without it?

dthomp87 · Jul 20, 2016

I unplugged the Capacitor and still no start. Should I try to replace?

I found the buzzing to be the Throttle Position Sensor. When I unplugged it, the sound went away. Plugged it back in, no sound, start attempt says HDC Fault.

Should I look into the Throttle Position Sensor noise? Could that cause a no start?

This afternoon ill do a fuel pressure test. Im sure my battery is going to go bad after all this troubleshooting and no starting. If the fuel is good it maybe something simple like position sensor.

Also, I often would get a CEL code the past several months that said Throttle/pedal position sensor/switch A/B voltage correlation General Signal Falure - P2135-28

Houm_WA · Jul 20, 2016

Not sure on the throttle position sensor. As for the RF Capacitor....I don't remember if unplugging it is supposed to by-pass it, but that IS true for the one on the tranny. It is a cheap part though, so replacing it wouldn't be too painful.

dthomp87 · Jul 21, 2016

I ordered the ignition capacitor the part number is LR004160

Wont Start - Fuel Pump Relay Grounding Issue?

dthomp87

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Trynian

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dthomp87

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dthomp87

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Trynian

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