S54 fuel system in a 325es

[Flug540]

Hi everyone,

As per title, I'm swapping an S54 into my 86' 325es coupe.

I am confused about the fuel system that I would need to put together.
The car came with a single hole fuel tank, one opening on the passenger side rear bench. It has two pumps, one in the tank and an inline one next to the tank on the driver's side.

I know that I would need a 5bar fuel pump, but unsure if I would need to get the newer fuel tank with two holes/pickups? Do I still need the original inline pump or the new 5bar will replace both existing pumps? Can I reuse the fuel lines (not sure if they have adequate diameter)?

Any feedback is greatly appreciated,

Thanks!
Alex.

[R3VM3UP]

I've just been working on figuring this out myself since most people don't give too many details on it. I have a late model with only the in tank pump, but the process is pretty much the same. This is a standard return style fuel system that uses a vacuum reference on the regulator. The only difference is that the regulator is not located on the rail like most older vehicles. I haven't installed all this stuff yet, but this is all pretty straightforward.

You only need one fuel pump in tank and it needs to have adequate flow for the S54. A Walbro 255lph or similar from TRE or something should do the job. I ended up buying an Aeromotive 340lph which is overkill, but the Walbro is known to be noisy, which I didn't want. There are also tons of walbro knockoffs floating around so it can be tough to know you are getting a real one.

From there you should be able to eliminate the stock inline fuel pump as it won't be needed. Install a filter of your choice. I'm planning on using a stock late model E30 one, but I'm sure there are tons of other options if you want. Stock E30 lines on my 318is are 8X13mm which is pretty much equal to 5/16, so any filter with a 5/16 barb could be plumbed in.

The E46 M3 also uses 8X13 lines, so you don't need to go to a larger diameter. You can just use an E46 M3 fuel pressure regulator and line to the fuel rail. The M3 regulator has a threaded inlet where the filter screws on. You'll likely want to unthread it and install a barb fitting. Thread size is M12X1.5. I purchased a vibrant M12X1.5 to 5/16" barb adapter that I'll be using.

[Flug540]

Dude!

Thanks for sharing, awesome detail, this will allow me to move forward.

I'm currently working on rewiring the entire car and needed to know if I still need the wires going to the inline pump. Looks like not.

The question that still remains whether the older style tank can be used for this. In your setup does the new pump go on the passenger side? If so, what do you have on the driver side of the tank?

Also I read somewhere that there might be differences between the older and newer tanks in how tolerant the car is to fuel starvation in hard cornering. And I believe there was a suggestion that the older tank is more tolerant. Does anyone have any feedback on this?

[R3VM3UP]

IIRC yes, the pump in the stock location is on the passenger (right) side on my 91 318is. There isn't anything on the driver's side of the tank.

As for fuel starvation that's not something I've looked into. Maybe someone else can comment.

[Flug540]

Found some references to people reporting fuel starvation at autox/track.

Here's an interesting post: DIY - Walbro 255 fuel pump retrofit.

SURGE TANK FOR BOSCH 044

[R3VM3UP]

Looks like I spoke too soon on the barb size. I got the 5/16 barb fitting and I think it's a bit loose. It slides into the 8X13 hose and stays in, but I'd feel better about a tighter fit for a fuel line, even with a hose clamp. The barb on the E46 M3 fuel pressure regulator was a significantly tighter fit. I'm going to try out a 3/8 fitting and report back.

[FredK]

I used a 5/16" to M12x1.5 adapter to plug into the FPR block and it wasn't really loose. I didn't get the Vibrant brand, but I don't think it'd be much different for other brands.

The stock dual pump will work better to prevent against fuel starvation, at least as far as I recall. If you go with a single pump setup without a surge tank setup, you'll have fuel starvation below half a tank.

[R3VM3UP]

Does the inline pump pull from another location in the tank, or does the early tank just have a better baffle/surge tank setup?

The vibrant barb wasn't super loose, but the bump on the return side of the regulator the the hose slides over definitely has a larger OD and is much more secure than the 5/16 vibrant barb. I can take measurements and or pictures later when I get a chance.

[FredK]

I'm not quite sure if there's an actual difference in the tank with baffling, but the combination of a lift pump feeding a high pressure pump may have just enough fuel volume in the line feeding the pressure pump to prevent fuel starvation. Just a wild guess, though.

[R3VM3UP]

Good point, the combo of low pressure in tank pump and high pressure external pump could potentially be helpful. I also read about some people installing a swirl pot in between the two to alleviate starvation.

[TobyB]

The early 2- pump tank is physically different, too, so that plays some part in it...

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