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4.0 SOHC Fuel System 'Hack'


JonC

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'99 UK spec - LPG soon!
Hi guys,

had a bit of a result this week which I thought worth sharing with the wider community. The background to this is that my 1999 UK-spec 4.0L Explorer 'gently expired' recently whilst driving in that it just stopped. Something told me it was the fuel pump but at the roadside, I couldn't prove it.

I'd had the presence of mind to buy a recovery package some time ago so I had the truck recovered to home but on a large, ramp truck, it could only be unloaded onto the road outside my house and not up the drive where I can work on it more comfortably.

So what do you do? There's only me and the ladies and 2 1/4 tons of dead truck - not something you want to push and even if you did, you're not going to push it up the ramps for getting underneath!

I did the required electrical inspections and convinced myself it was a dead pump so one last check, I took the Schrader valve out of the left-bank fuel rail and using a funnel and hose, poured some fuel in. It tried to fire and run so at that point, I'm more convinced about the pump but as injectors have no suction, gravity isn't going to get me enough fuel in there to drive it.

Enter the hand-held garden spray...

Ditch the nozzle and adapt a hose onto the fuel rail valve, pump up the gas and sure enough, we have enough fuel - under enough pressure - to drive the truck across the road, up my drive and onto the ramps where I have subsequently successfully replaced the duff pump.

So now you know!

Pictures
 


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dezufo

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Very interesting work around which I shall probably end up doing to mine as it will turn over but not fire up. Can you tell me where your fuel pump relay is situated as layout of relays in the main box on my '98 are not the same as in my owners manual + haynes manual
 




JonC

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'99 UK spec - LPG soon!
Very interesting work around which I shall probably end up doing to mine as it will turn over but not fire up. Can you tell me where your fuel pump relay is situated as layout of relays in the main box on my '98 are not the same as in my owners manual + haynes manual
No problem - just uploaded a drawing under the same link as the photo. Strangely enough, I had exactly the same issue - don't think I've found anything in the Haynes manual that actually relates to my truck!

When you compare the fuse box drawing with your truck, it will be 'upside down' i.e. the big fuses will be nearest the windscreen. The FP relay is the 30/40A device 'on it's own' as you'll see.

I did various electrical and continuity checks, proving power at the relay terminals, pulling the relay then plugging it in with the ignition on (you should feel the relay switch over) and testing between the relay socket and inertia switch. They didn't check out exactly as I expected but then as we now know, you can't trust the Haynes manual wiring either!

In the end, I jumped 12V onto the outgoing side of the inertia switch and still got nothing from the pump. Beyond that, there's only the connector under the vehicle and compared to the pump itself, that's got very little probability of failure so at that point, I committed to a new pump. I suspect the old one died from being 20 years old, not from the 50,000 miles which is all it's done!

If you haven't already dropped your tank - DON'T - until you watch this video:

This guy will stop you breaking things (I've seen others that don't!) - notably the evap. hose which is as stiff as a board and will break it's connection if you go too far.

Good luck - and if there's anything I might be able to help further with, give me a shout!
 




dezufo

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can you tell me which colour wire you connected to on the inertia switch so I can check if pump runs or not

this is my main box and the relay on its own does the blower motor.
the one directly below is engine management, the one to the right of that is the starter
the small relay on its own is wipers hi/low
the one below that is the horn, the one to the right of that is any body's guess but I think it may be wiper delay unable to confirm because the switch has stopped working
upload_2020-1-30_12-54-20.jpeg
 




JonC

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That's strange - because that's exactly the arrangement in my fuse box. Mine is a 99-registered, 98 model. You can check the relay manually - if you pull it out, then turn on the ignition, when you put the relay back, you'll feel it switching (they go with a good clunk). I checked the continuity on mine and the 30/40A relay just below the small fuses definitely powers the fuel pump.

There's a green/yellow wire on the IFS and that's the supply from the relay. The pink/black at the IFS is the outgoing to the pump. Jump 12V +ve directly onto that and if the pump is good, it'll run.

You're right about all the small relays by the way.

Just as an aside, have you checked for pressure on the LH bank fuel rail? There's a Schrader valve just behinds the EGR valve. Give that a prod and if there's pressure, it'll either hiss or leak a little fuel. If your pump isn't delivering, there will be nothing there to speak of.
 




dezufo

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I found out mine by turning the ignition on and removing the relays one by one, Thanks for the info will try a jump lead on the IFS at the weekend if weather is nice also the valve
 




JonC

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Just out of curiosity, what LPG system do you have? I was surprised to find that some can be made to start on LPG - if you have the 'technique' for your particular system!
 




dezufo

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Its a stag 300 ecu and I lost the instructions for getting it to start on lpg but I could warm up the heat exchange valve to about 40'C so that the liquid turns to gas and then start it but I'm reluctant to go that route just incase it goes BANG!
 




JonC

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The temperature is academic (in the UK) as Propane boils at around -42C.

The liquid constantly turns to gas as in the tank - that's why you can never completely fill an LPG tank - the space above the liquid accommodates the evolved gas. As I remember, the issue is in 'fooling' the system into opening the solenoid at the 'wrong' time. My previous Explorer had a Leonardo system and there was a specific sequence which you could apply to the changeover switch which would then make the system open the solenoids and let it start immediately on LPG.

Might be worth looking up. I'd be more cautious if it's single-point injection though.Problems only arise when it doesn't start. That's when you get a build up of gas in the manifold and if you ignite that, you're then shopping for a new manifold (after you change your pants!).
 




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