When it stops working again, check for a live on the fuel
shut off solenoid.
Carry a spare bit of wire to bypass it as I suggested. If it's working at the moment it sound like the solenoid itself might be ok.
A jump lead is not suitable, you need a wire with a spade connector on the end to plug into the fuel shut of valve/solenoid.
Have you located the injection pump and shut off valve yet?
You have had it running so the shut off valve seems to work.
I am presuming it only has 1 wire on it. When you find it post up a picture to confirm.
 
Note the alarm / immobilizer on the 300 was so rubbish that, iirc, landrover even gave a part number to the bypass loom.

Years ago I had a disco with a 300 that would occasionally fail to start (in this case it was the starter as well as the fuel solenoid, but I guess they can fail in different ways) but a thorough whacking on the dash around the head unit area would generally resolve it.

I assume the additional vibration from the whacking dislodged a stuck contact on the immobilizer unit.
 
thanks for the messages guys - appreciating all the assistance!

So by way of another update, unsurprisingly the issue has returned, I had taken out the new starter relay that worked yesterday overnight - when I’ve plugged it back in this morning the same issue has returned. I had taken out the new relay about 3 times last night to check if it worked after being removed with the Landy starting perfectly each time.

Hoping it is as simple as you suggest @lynall and that I’ve bought the wrong relays each time so they keep blowing and that I’ve been the issue here!! I’ve added photos - the yellow relay is the one that was originally in the landy when I bought it, the 3 black ones are the new ones I’ve bought which have all initially worked but then packed in.

@Anaconda - Excuse my lack of understanding and pitiful mechanical knowledge, do you think it’s worth checking the solenoid even through it started with a new relay? And what I’m basically checking, is to see if it starts with a direct connection to the fuel solenoid? I assume if it does the issue lies in the electrical wiring to this point? Next question is does a simple jump lead work and is the wire/lead to be ran directly from the battery to the solenoid?

@boguing ill check and clean these points as advised after work today - thanks!
One of them black relays says it is a 24volt version?
 
Did you just say -



Am I reading this wrong? You say it starts with the relay removed?

Surely that tells you something?



Basically, stop messing about with the relay and run a wire direct to the stop solenoid (also referred to as the fuel solenoid).

I know you're convinced it's the relay. But if it starts (when it starts) with the relay removed, you probably need to move on from your target.
I think there is some confusion, I thought the relay is for the starter solenoid, and not the stop solenoid?
 
I think there is some confusion, I thought the relay is for the starter solenoid, and not the stop solenoid?

Exactly. The chap has confirmed its cranking. The only relay in the (electrical) area has been confirmed working.

I edited the post to be clear that I didn't know if the alarm section somehow fed back to the immobilizer section, but, irrespective of that, a wire to the stop solenoid is the next stage in diagnosis.
 
I think there is some confusion, I thought the relay is for the starter solenoid, and not the stop solenoid?
My understanding is it cranks over but doesn't start, therefore the OP needs to check for fuel, live at the shut off valve, use a jumper wire to shut off valve to bypass the rest of the vehicle.
Once the fuel is out of the equation then the wiring fault can be traced back.
 
I had similar issues with my 1990 Ninety, after messing about some came to the conclusion that the cable from the ignition switch to the starter relay was duff [at first it was intermittent] As it is buried in the main loom I just disconnected both ends and ran a line direct from ignition switch via a push button direct to starter solenoid.
Same fix [no button] would sort stop solenoid. Both only need about 5amp to excite them.
 

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