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Fuel pushed from one tank to another - Induction/Turbo/Chargecooler/Manifold/Exhaust - The Lotus Forums Jump to content
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Fuel pushed from one tank to another

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Yesterday (Cromer run) was the first day for a long while that I've used the car, but it highlighted I need to fix the issue (I think it is all related), so thoughts?


Right hand (one with submerged pump) fuel tank pressurises.

Fuel moves (I assume via the balance pipe ( to the left hand tank (one with fuel sender unit)

The dump valve does not function, most of the time.

The right hand tank becomes low on fuel, the car splutters and misfires.

I release pressure on the RHS tank, fuel flows back to it, car runs OK, for a while.

I have checked the breather pipes, and they are clear from obstruction. I have even blown air through one end and it has come out of the tank filler pipe (with cap off). I've checked the one-way valve in the line from the charcoal cannister to the induction manifold, it allows gas to move to the engine, but not away. The one-way valve is between the canister and the T for the dump valve which is where I believe it should be. The solenoid for the charcoal canister seems OK. I am getting no freescan errors reported.

I had initially thought the dump valve issue (and yes I have swapped if out for a known-good one) was a separate issue, but I think it may be related.

I am now wondering if an issue with the pipe from the canister could be causing all symptoms. If the silicone hose (not reinforced type) is collapsing under external atmospheric pressure and so blocking it. This could cause the fuel vapour to be blocked form leaving the canister. It would also result in the pressure on either side of the dump valve to be very similar, close enough so that the spring keeps the valve closed.

The one thing I cannot explain to myself is why ONE tank pressurises, not two. This is despite the fuel balance pipe and the small bore (8mm) air breather pipes allowing fuel & air movement between the tanks. I did check, and if I remove the cap from the left hand tank there is no apparent air movement, but then if I remove the right hand filler there is air movement out of that right hand tank.

So, thoughts?

I'm considering replacing the vacuum pipes and the one way valve (just in case it's sticky), and possibly the charcoal cannister and solenoid, but want a second (and more) opinion in case I've missed something obvious, or even remotely possible but plausible.


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Hi Andy

Just a thought, I believe the engine you have normally works with fuel tanks that have an external fuel pump.

What about disconnecting the internal fuel pump and trying an external one in case the problem lies within ?

Edited by Newts


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Hi Andy, how you keeping.

Gut feel says you have a kinked / collapsed pipe but I cant believe you wouldn't have found it. Have you checked the fuel cap. Some cars have a breather in the cap, generally to allow air to enter the tank and stop vacuum. I cant remember if they let it out again but I would check the valving. At least try to run it with a dummy cap. Still puzzled as I would have thought the balance pipe would have equalised the pressure. I would also be a bit suspicious of the canister as on your car if the caps aren't dsigned to vent then the fumes should be being pulled through the canister, another possible kinked or blocked pipe or perhaps an NFG cannister.



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Well I have checked the breather pipes, both manually by sucking and blowing gas (not petroleum, but the state of matter other then solid, liquid and semi-solid)through the pipes,and with the use of a vacuum pump & gauge. The sucking manually was not nice, short breaths so as not to inhale it fully is better.

The pipes seem OK, but I'm wondering if one of the roll-over valves (right hand tank is the suspect) could have moved from vertical, it's hard to tell, so I'm going to re-locate it.

I suppose that if that ROV was in a closed sate, and an amount of pressure builds up in the tank it could push the fuel so far that it reaches the vapour pipe take-off on the fill neck (not difficult when tanks are full). If it reaches that point, it would be a lot more fuel reaching the (potentially NFG) charcoal canister, and so getting pushed down the purge pipe, and reaching my dump valve*. I guess I'll simply have to work on the process of elimination, replacing components when suspected.

* see post about dump valve.

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