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MX5 VVT Fuel Pipe Layout
albertz - 15/2/20 at 08:34 AM

Hi, I have been looking for a diagram of the fuel system layout for the MX5 1.8 VVT engine (2004, mk 2.5). It is confusing as the tank has two hose connections, but there only appears to be one connection to the fuel rail.

Iíve read that the lines tee together but I canít work out where. Also I think only one pipe runs through the tunnel to the engine?

Iíve searched on here (and the net) and have seen others having the same problem, but I canít see a conclusive answer or better still a simple diagram.

Is there anyone out there that could please clarify this by sketching out the layout, or describing it? It would be much appreciated.

JonBowden - 15/2/20 at 11:45 AM

I have a 2005 VVT 1.8 West of Glasgow (Alexandria).
If you are ever in this part of the world, you can come and have a look
This site has service manuals if it helps:

peter030371 - 15/2/20 at 02:02 PM

Sounds like a simple deadhead fuel system to me, like this

Obviously they missed out the need for a fuel pump but you get the idea

[Edited on 15/2/20 by peter030371]

albertz - 16/2/20 at 07:51 AM

Hi, thanks for the replies. I have found a decent diagram on the site. I have tried to include the relevant photo/diagram here but canít work out how to do it!

Anyway, it appears that the engine uses a single fuel line straight to the rail, via fuel filter and pulsation dampers. I think there is a pressure regulator in the tank with an integral return/overflow within the tank. The second hose connection outside the tank I think is for some sort of fume return (?) from the charcoal canister. If I could post the diagram it would be clearer, but thatís what I think is going on.

JonBowden - 16/2/20 at 11:12 AM

This is a link to a picture of the fuel rail with the regulator attached.
I'd say that it is more like the first type in Peter's diagram
The small pipe is probably connected to the plenum to allow correction for varying pressure there.
But there are a lot of complicated air valves around this bit and I don't understand them.

So, high pressure fuel from the pump goes in to the hose on the left, the return to the tank comes from the big outlet from the pressure regulator on the right.
It's the little one that is a bit confusing

[Edited on 16/2/20 by JonBowden]

Angel Acevedo - 16/2/20 at 02:13 PM

For a Normally Aspirated engine, Charcoal canister would be OK.
I donīt think connecting to a plenum would be too much of a difference.
Going turbo then you are better off connecting to plenum as at high boost levels the injectors may not be able to flow enough fuel against plenum pressure.

albertz - 16/2/20 at 02:32 PM

Yea, the fuel rail on my car only has one connection, so I think mine is more like the second diagram.

If I can work out how to get photos off my iPhone and into my photo archive I can hopefully share a diagram that makes clearer what I am trying to say in my previous post. Any tips on iPhone to forum would be appreciated. Seems like the site doesnít accept .png files (iPhone camera)?

Thanks for the help so far.