2,8L MFI - where to connect the fuel line of Webasto auxiliary heating system?

[atelier14]

Hi,

during the installation process of my new 2,8L MFI engine we now have to decide the right way of connecting the fuel line of the Webasto auxiliary heating system which is already in the car as I am running headers.

Because of the flow/ return fuel lines for the MFI system are both connected to the twin outlets of the front fuel tank we have to put a T-fitting in one of the lines. The question is now which fuel line to choose?

I think I once have seen a '72 911 MFI with factory auxiliary heating system which had its fuel line connected with a T-fitting to the flow fuel line to the MFI pump which also would make much more sense for me from a technical point of view...

What would you suggest here?

Many thanks,
Christian

[356RS]

I don't know much about the Webasto aux heater, but will it be able to handle the 1 to 1.5 bar of fuel pressure? Maybe the Webasto has a restrictor in the fuel inlet, maybe not, but I would check that first. Sounds like you have the answer for heat with headers.

[atelier14]

Originally Posted by 356RS

I don't know much about the Webasto aux heater, but will it be able to handle the 1 to 1.5 bar of fuel pressure? Maybe the Webasto has a restrictor in the fuel inlet, maybe not, but I would check that first. Sounds like you have the answer for heat with headers.

Hi Mark,

Our plan was to fit the fuel line of the Webasto with a T-fitting to the MFI flow fuel line BEFORE the electrical fuel pump - so the Webasto won't see any pressure...

Thanks,
Christian

[304065]

Christian,

The original Hardi pump for the Webasto, mounted up under the cowling, was very low pressure, probably only 2-3 psi. I will double check the Webasto manual for you to confirm.

Fuel pressure in the MFI loop is 1 bar with overpressure relief at 2 bar. This is too much for the Webasto system.

The MFI electric pump would ideally be situated down near the front crossmember-- these pumps are much better at "pushing" fuel vs. "pulling it." The factory relocated the pump up front in the later years from its location in the rear wheel arch.

What tank are you using? A '66 tank has two outlets and a drain. A later tank has an internal "swirl pot" which is used to prevent pressure surges.

I would route the RETURN line into the top of the tank and use one of the lower gravity fed outlets for the Webasto pump. You don't need to, and probably shouldn't, return fuel at the low point in the tank.

Grusse

[atelier14]

Originally Posted by 304065

What tank are you using? A '66 tank has two outlets and a drain. A later tank has an internal "swirl pot" which is used to prevent pressure surges.

I would route the RETURN line into the top of the tank and use one of the lower gravity fed outlets for the Webasto pump. You don't need to, and probably shouldn't, return fuel at the low point in the tank.

Grusse

Thank you!

If I get you right you wouldn't fit the fuel line of the Webasto with a T-fitting to the MFI flow fuel line BEFORE the electrical fuel pump? Do you think this solution would lead to certain problems?

Viele Grüsse,
Christian

[JFairman]

couldn't help noticing what looks like nylon water/methanol injection line, tee fittings and nozzles mounted in the top of your air cleaners above the velocity stacks that are probably inside?

[atelier14]

Originally Posted by JFairman

couldn't help noticing what looks like nylon water/methanol injection line, tee fittings and nozzles mounted in the top of your air cleaners above the velocity stacks that are probably inside?

These are just the cold start nozzles we put in the filter tops.

[Grady Clay]

Christian,

Most important – what fuel tank are you using?
I’m not clear about that.
There are two basic choices: the ‘early’ non-CIS version that has two ports with filter screen fittings (one for the engine and one for the gas heater) and a lower drain fitting, also used to return the circulating fuel.

The later CIS tank has the 22 mm wrench size screen filter in the bottom of the tank.
There are several versions of this tank with different fittings for the outlet and return.
None of these tanks are fitted with an extra port for the gas heater.
All of these tanks incorporate a ‘swirl pot’ to improve fuel pick-up during hard cornering and reduce the circulation of vapor ‘bubbles’.

I haven’t searched PET, is there a CIS (’73.5) or later engine with fuel system provisions for the gas heater fuel supply?
If so, how is it plumbed?


I know we have previously discussed your engine.
Please remind us of the configuration of the engine.
What is your intended use?


Best,
Grady

[proffighter]

I mounted a T-piece right before pump (pressureless)

[atelier14]

Originally Posted by proffighter

I mounted a T-piece right before pump (pressureless)

This is also what we are planning to do - a T-fitting in the MFI fuel flow fuel line BEFORE the electrical fuel pump so the Webasto won't see any fuel pressure from the pump. I' m using a CIS tank in the car currently.

Grady, I try to post an update on the engine when we had it on the MAHA in 2-3 weeks time...

Thanks,
Christian