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#581614 15/06/19 09:42 PM
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John V6 Offline OP
Member of the Inner Circle
Fuel cap seal

I have been having for the last twelve months an intermittent but increasing ECU fault on lean mixture on bank 1 and or bank 2 (P1071 & P1074). This can be caused by a small air leak. Dealers told me to ignore it & to cancel the fault via the OBDII dongle I have as they could find nothing.

A chat with Simon Daunt over dinner at the Anglemog trip to Scotland helped track down a possible cause to the seal on the filler cap.

Mine was badly perished & a loose fit in the groove. I had assumed the locking cap was the pressure & venting valve so didn't think it an issue and that this seal just allowed the cover to lock down.
But it seems this seal & the spring loaded inner pad do act as the pressure & venting valve.

A replacement was sourced from Melvyn Rutter, but they commented they were over size. This new seal has stopped the error most of the time. But fails when you stop and refill the tank.

I can obviously cut the seal to make it shorter but I am unsure how tight it should be. I am concerned that it needs to be loose to let air back into the tank when / if it pulls a vacuum Is there a kind soul out there who has a newer car & can let me know their seal diameter?
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John V6 #582107 19/06/19 02:01 PM
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John V6 Offline OP
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Cheers Mike


JohnV6
2022 CX Plus Four
2025 MG ZS EV aka Trigger
teknome #757564 07/10/22 04:37 PM
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Originally Posted by teknome

Won't win concours with a dirty cap !

These fuel caps are made by Newton Automotive, tracking down the locking inserts on the Car Builder Solutions web site, they are available as non-venting, and as venting.

In the case of emission control they need to be non venting inserts so the carbon filter stores the fumes.

For older vehicles they would normally be vented inserts. In that case the large disc and o-ring would become the primary seal and release fumes once the pressure is high enough to lift the disc.

The Newton locking inserts come in two styles, the older type has a sort of rubber band style of gasket

The un-vented https://www.carbuildersolutions.com/uk/un-vented-lockable-insert-for-aston-necks-excl-2

The vented https://www.carbuildersolutions.com/uk/vented-lockable-insert-for-aston-necks-excl-2

I have purchased the non-venting and it did fit my old filler cap.

The later (current) style of locking insert has an o-ring seal, the part number on the insert here on my desk, for the non-vented is #Z45LT. I haven't yet found these on a re-sellers site, There was a thread some time ago on Talkmorgan where someone got hold of Newton and purchased an insert.

Assuming your cap is in good shape, it may be worth getting a new locking insert as this should be the primary seal for a non-vented system.

Another thing to check would be the fuel hoses to see if there are any cracks. My old hose looked OK but I did find some fractures although they were under the hose clips.




That's the great thing about forums that have been going a while and you join as a newbie there is just so much information available.

Ive been having a problem with the filler cap on my 2006 4/4 where the cap has been really difficult to open and close. Caused, I was sure, by the filler cap itself not searing fully. Which in itself was as a result of the rubber seal expanding over time - and looking at it having then had the edges shaved away to help with fitting.

I was at the factory spares desk last week and asked how much for a new filler cap - £136. I was surprised to see that the keys were labelled with Newton and not Morgan but that my Morgan key would fit this new cap. Apparently they are all the same key - many might already know this but it was news to me.

I chose not to pay £136 but resolved my self to try and find a new rubber seal and maybe repair the fitted cap.

With the luxury of time and few gins I can across this thread with the really helpful links - ordered an unvented cap for £34.39 delivered and fitted it just now. Problem solved.

I also ordered the large o ring from simplybearings.co.uk for £6.16 delivered as mine was completely perished

[Linked Image]
[Linked Image]
[Linked Image]


4/4 70th Anniversary
John V6 #784531 26/08/23 11:15 PM
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It is possible to make a new seal. I have made a couple by buying lengths of round material, cutting to length then supergluing to form circular o-rings. Our factory engineers used to do similar when no replacements could be found.
I have a box of o- rings in various sizes but needed some odd sized ones. If I remember correctly 1.5mm dia material and 2.5mm dia. material.
You could buy in square extruded material and do similar to copy the failed seal in the photo. Two (or three?) round material home made rings side by side might also work.


Plus Four MY23 Furka Rouge
John V6 #784532 26/08/23 11:23 PM
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John, the filler looks like the one I had on my Plus 8. “Monza “ name, I think. Quite a big filler! Can you get some sheet material and cut one out? Use the original to make a template. I’ve done similar to make gaskets from sheet material. A scalpel used carefully gave good curve cuts. The gaskets were paper ones though not rubber,


Plus Four MY23 Furka Rouge
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