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Had a similar problem with my 2.5l td 90 ,when you opened the fuel cap it hissed like opening a can of coke!.Thought it might be a blocked breather tube, spoke to my mechanic who had a similar problem with another 90 and he sugested drilling a hole in the diesel filler cap wich i did and it seemed it cure it,i dont know if this helps

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These filler caps have a vent, a ball held down by a spring, built into them. Sounds like yours has jammed shut. They aren't easily fixed, but you could try giving it a soak in petrol followed by a very good shake.

I don't like the drilled hole idea much though ...

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These filler caps have a vent, a ball held down by a spring, built into them. Sounds like yours has jammed shut. They aren't easily fixed, but you could try giving it a soak in petrol followed by a very good shake.

I don't like the drilled hole idea much though ...

Yep. What errol said. Take the cap apart clean it, oil it, soak it etc to try and free up the vent. I had this problem - the fuel tak pressurised so much that it created a fuel block effectivley and the vehicle would stall as if it were starved of fuel (which it was effectivley).

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i had the same problem new caps didn't sort it so in the end i extended the breather on the filler neck all the way up to the snorkel never had a problem since all good ;)

if the engine is pulling fuel out of the tank then shouldnt it be creating a vacume rather than pressurising the tank? surley the ball in the cap is only to let air in and thats why it has a spring behind it?

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if the engine is pulling fuel out of the tank then shouldnt it be creating a vacume rather than pressurising the tank? surley the ball in the cap is only to let air in and thats why it has a spring behind it?

You also have a return to the tank from the spill pipes on the top of the injectors. If it pulls air in as it moves fuel to the front and returns fuel to the tank, you get a pressurised tank (If the ball wont allow it to vent out again, just in if it is corroded). Also, as fuel heats slightly, it will create pressure, probably more noticeable on petrol engines.

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The turbo won't work, so you effectively have an N/A engine that's a bit choked. Turn the engine off and disconnect the boost pipe. If fuel is pushed out, then the diaphragm is split.

It won't push more fuel out - the lift pump valves will prevent that from happening.

Les.

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if the engine is pulling fuel out of the tank then shouldnt it be creating a vacume rather than pressurising the tank? surley the ball in the cap is only to let air in and thats why it has a spring behind it?

sorry meant to say it was vaccuuming on mine took the cap of and you could see the diesel disappeering back down the filler neck!
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  • 2 years later...

Hello - I've just fixed such a problem on a 1989 2.5TD 90. As Les said, it was the Injection pump boost diaphragm, and after changing it (1 hour, following the instructions posted by Les), the engine is transformed, with top speed up from 60 to 75 and far more power with less smoke and easier starting. Drilling holes in the fuel cap to stop pressurising seems like treating the symptom rather than the cause. I followed a post on another forum to find the part, and I got mine easily from Atlantic Diesel Services in Southampton - tel 023 8066 3990. Cost was £21.95 including postage. They know the part number, but it was a Delphi - 7243-006 / ADNSCJ 595699. As a footnote, to help diagnosis, I held the revs high for a minute whilst stationary, then stopped the engine and removed the fuel cap, which almost blew off, which confirmed pressure.

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Strewth - here we go again :( If the tank breather is blocked, then the tank would have vaccuum - not pressure. When the diaphragm is split - boost pressure that would otherwise operate the turbo is going to the tank, which pressurises it and blows the cap off when you remove it.

sounds like your fuel cap is a non vented version, check the tank breather hoses are not crimped & are correctly routed 7 connected.

Ralph - what are you on about?

Les :)

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No you bluddy don't. Blocked breather or filler cap will cause a vaccuum, so no rush of air when you remove the filler cap (unless you are on another planet). The ONLY way the tank can be pressurised is via the fuel pipe from the engine, which on the 2.5TD engine - is always the boost diaphragm.

Simple science here - if air doesn't replace the fluid being sucked out of a container - then it creates a vaccuum.

Les.

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Les - i agree with you 101% but in my petrol i sometimes get a pressurised tank after it's been used. I've got a one way valve to allow air in but not out. God knows why ! ? But after an event, i leave the lid loose to allow air in / out.

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Les - i agree with you 101% but in my petrol i sometimes get a pressurised tank after it's been used. I've got a one way valve to allow air in but not out. God knows why ! ? But after an event, i leave the lid loose to allow air in / out.

Maybe the 1 way valve is to keep fuel in if you roll it or go fast around a corner. One other way that a tank could theoretically pressurise is through fuel expansion if parked in the sun, but it wouldn't happen if the engine was running.

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Again, i totally agree. But when we stop to refuel there is sometimes a pressure build up. And yes, the valve is for when i roll. My tank is not a normal LR tank, merely an ally tank with a couple ports.

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Maybe the 1 way valve is to keep fuel in if you roll it or go fast around a corner. One other way that a tank could theoretically pressurise is through fuel expansion if parked in the sun, but it wouldn't happen if the engine was running.

Thats what i was going to add - my petrol BMW used to do that occasionally, particularly on hot days. I miss that car (replaced it with a freelander for SWMBO - horrid mistake)

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My Micra and the Focus both have pressure in the tanks when I refuel, never caused a problem. :)

The 90 doesn't get pressurized, I assume being due to the second breather/ expansion pipe on the TD5 tank.

Mo

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Surely there should be a distinction between petrol and diesel here? It was my understanding that petrol always pressurises a sealed container - and it is called the 'vapour pressure'. I have a jerry can for petrol and one for diesel - alway pressure in the pertol one....

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