19J strange fuel fault at high speed

I've got an odd fuel problem with my 1988 19J 110. It will travel along quite nicely at 50mph all day and not miss a beat. As soon as I take it above 55mph, after about 5 mins it starts to exhibit signs of fuel starvation, ie it slows to under 50mph and then takes up the drive again and then runs fine until I go above 55mph once more.

So far, I've checked the basics:-

New fuel fuel filter fitted
Fitted new lift pump and output from lift pump seems good
tried running without the filler cap to check for breather problems - no difference

As this happens at speeds only above 55mph, I was wondering if the lift pump is unable to push enough fuel through to the injector pump and therefore creating a vacuum in the line. Is this possible? Although as I said it's a new lift pump and the diaphragm is fine. Otherwise, I'm stumped so any advice gratefully received.

Could b e a restriction in the fuel line, making it too narrow for a full flow.
Dirt or a crimped pipe.

Billggski said:

Could b e a restriction in the fuel line, making it too narrow for a full flow.
Dirt or a crimped pipe.

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I've thought about that, but wouldn't the problem appear on acceleration or whenever the fuel flow was maximised if that was the case. I have done a quick visual of the fuel line and it looks ok. This is quite a specific thing. ie. it happens at 55mph plus and only after a few minutes of driving at that speed. That's what sort of led me away from thinking it was a blocked fuel filter, even though I changed it anyway. I'm still thinking that it's something to do with the injection pump or the lift pump.

I'll check the fuel lines again just in case and I'll let you know the result. Thanks for the reply, I really appreciate the help.

G

garfie said:

I've thought about that, but wouldn't the problem appear on acceleration or whenever the fuel flow was maximised if that was the case. I have done a quick visual of the fuel line and it looks ok. This is quite a specific thing. ie. it happens at 55mph plus and only after a few minutes of driving at that speed. That's what sort of led me away from thinking it was a blocked fuel filter, even though I changed it anyway. I'm still thinking that it's something to do with the injection pump or the lift pump.

I'll check the fuel lines again just in case and I'll let you know the result. Thanks for the reply, I really appreciate the help.

G

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If there is a restriction it might not show on acceleration as the fuel filter acts as a reservoir and you'll only lose power as the level drops.

Have up checked the pick up pipe for blocked gauze/crap, also there have been a lot of recent reports of new lift pumps failing so don't discount it because it's new

Will probably be the boost Diaphragm. Was on mine with similar symptoms

blue beasty said:

If there is a restriction it might not show on acceleration as the fuel filter acts as a reservoir and you'll only lose power as the level drops.

Have up checked the pick up pipe for blocked gauze/crap, also there have been a lot of recent reports of new lift pumps failing so don't discount it because it's new

Click to expand...

Thanks for that. I suppose it's the logical thing to do, really. Start at the back and work forward. Looks like I've got my weekend planned then

craigyb said:

Will probably be the boost Diaphragm. Was on mine with similar symptoms

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Cheers. I've had a quick look at a how to posted on LR4X4.com It looks simple enough but very fiddly. It does sound a very likely candidate though. Yet one more thing to check over the weekend.

Well, it took a while, but I finally got around to checking out my fuel fault. I started by bypassing the lift pump with a hand primer I had kicking around. The fault was, if anything, worse than before, so the lift pump was re-instated. So then I started at the back and worked forward. Everything checked out visually as OK at the tank end. After following the length of the fuel pipe along the chassis, just at the point where it lifts up into the engine bay was a short piece of hose let into the line as a joiner, (I hadn't noticed it previously as it was obscured from above and you had to get right under the old girl to see it sitting just on top of the chassis rail ). I don't think it's meant to be joined at this point but can only assume it was done by a previous owner to repair a rubbed section of pipe. On close inspection, it seemed that the hose section had a larger internal bore than the external diameter of the fuel pipe and although it was clamped with hose clips, I wasn't happy with it. I found a piece of hose of the right bore and fitted that instead and it seems, problem solved.

I've had her touching 70 on a nearby dual carriageway and all appears good. I can only think that the pump was able to pull fuel through with only a little air at lower speeds and was getting enough fuel to keep her running. Whereas at higher speed, it was pulling in too much air that was then causing the problem. It even seems to run better at lower speeds and tick-over is improved too. All in all a good result for a couple of hours of arseing around under a Landrover

Thanks to everyone for the advice given, it's appreciated.