280i Fuel System

[pasogrande]

I've started back on the fuel system. I decided not to remove the fuel tanks, and they seem in good condition.

So far I have removed the swirl pot, fuel pump and accumulator, and the 5/8" hoses that connect them. At first sight everything looks good, except the hose pipes, which had disintegrated badly - probably the cause of old petrol smells.

My first three questions:

1. How do I check the swirl pot? I can blow easily through any pipes with no resistance.

2. How do I check the fuel pump off the car? Would it be safer to pump diesel instead of petrol? The pressure valve seems good. I am not worried yet about the exact psi or flow it produces.

3. How do I check the accumulator? Should I be able to blow through it?

Thanks,

Wilf.

[mrzigazaga]

Hi Wilf..I will try not to scare you this time......Not to sure as regards to the swirlpot as i dont have one but i should imagine if it rattles then the mesh filter may of corroded..Not sure what blowing through it would determine unless its blocked..The fuel pump should be ok..I think they can leak if the check valve fails..Not sure about using diesel through it..Its probably best to test it once all the hoses have been replaced and it has been put back on the car..The accumulator probably wont show any result by blowing through it either..The spring in the diaphragm is massive..again the only way to see if it is working would be to clamp the feed from the accumulator to the metering head/Fuel distributor and then operate the fuel pump to see if any petrol leaks out from the rear of the accumulator if it does then it is kaputten as it should maintain fuel pressure and help filter out any pulsing of the fuel pump...I have removed mine and have had no issues starting hot or cold..Cheers..Ziga

[RCK974X]

Swirl pot is really just a local reservoir for the pump to stop cavitation (as far as I know), so if fuel goes right through, should be OK.

Pump - I put hoses on mine with fuel in a 2 litre ice cream tub, and just gave a quick 'shot' of power to make sure pump ran. Much more than that I reckon is up to preofessional testers - just put it on the car....

Agree with Zig about other stuff - replace the pipes/hoses and see if engine runs, is probably the simplest....

[pasogrande]

Thanks Mark & AndyP. Pretty much what I thought.

The swirl pot's main purpose is to get air bubbles out via the small hose to the top of the left tank; that hose is also clear.

Andy, I just hope that the pump won't blow up from petrol vapour!

I already have the new hose and hope to get it back together this weekend.

Expect more silly questions next week!

Wilf.

[RCK974X]

My wedge hasn't got a swirl pot at all....Don't know if that's original or not !!

On mine, the feed pipes go to a 'T' piece, which then feeds straight to the pump....

[Danny Hoffman]

The original swirl pot on my car only had 2 connections, I know some have 3. When mine rusted through and I couldn't find any with only 2 connectors I replaced it with a large fuel filter as I figured it would do the same job for a fraction of the cost.

[mrzigazaga]

I believe that the swirlpot is to help maintain a supply of fuel to the pump, Especially when cornering..I only have a "T" piece instead of a swirlpot and i have only ever experienced about two seconds of fuel starvation when cornering but if im honest i was going way too fast... ..Within the speed limit of course... ..The accumulator however when that was leaking was causing serious cavitation of the pump..
I thought there was a wasp behind me!......

Fuel Diagram:

Edited by mrzigazaga on Thursday 17th January 09:34

[pasogrande]

At some time they added a fourth line from the swirl pot to take bubbles to the top of the left tank; but got rid of the small hose from the back of the accumulator, which may have served the same purpose. That is what I have, and is as shown in my July 1985 diagram, maybe USA spec.

Wilf.

[pasogrande]

I'm ready to put back the swirlpot/fuel pump/accumulator with new hose. The difference from Mark's diagram is that the return to the tank is from the swirlpot, not from the accumulator.



Wilf.

[pasogrande]

This diagram is how mine is laid out.



Wilf.

[mrzigazaga]

Hi Wilf..I cant see a return being on the swirlpot?, There are three hoses on it..2 X feed from tank and 1 X feed to the pump..The pipe from the rear of the accumulator i believe is to release excess fuel pressure once the ideal pressure has been maintained in the system..The fuel return should be from the metering head/Fuel distributor..Ziga

[pasogrande]

Mark,

My photo isn't very good. The small diameter pipe connection on the swirlpot is not visible. This is clear on the 1985 diagram and leads to the top of the left tank, presumably to let any air out before it gets to the pump.

As you say, excess pressure is relieved from the fuel distributor (#12 on my diagram) Nothing from the back of the accumulator on mine.

Wilf.

[mrzigazaga]

Hi Wilf..I guess the swirl pot on yours has a breather..Some swirl pots have a return fuel line from the fuel pressure reg or the metering head going into it but it is clearly an air breather as its a small diameter hose..In effect its a small fuel tank and i suppose as you have a roll over valve fitted to your atmospheric fuel breather then you need it to avoid vacuum building up...Although i could be wrong..Ziga

[RCK974X]

Yes, seen those diagrams before....

I can only say that with my early (1982) 2.8, and no swirl pot at all (just a 'T' piece), I've never had any engine hesitation/stall even with fast cornering and pulling a wheel off the tarmac...

Considering those dual tanks are relatively cubic in shape, and the pump is well below the tanks, I'm not convinced that it is all that likely to get fuel surge around them ?

[pasogrande]

Here's a better picture showing the extra pipe on the swirl pot, the end of the accumulator (a screw, not a pipe) and a piece of the old pipe, which is very brittle, disintegrating and probably the source of petrol smells.

[taz turbo]

pasogrande said:

Here's a better picture showing the extra pipe on the swirl pot, the end of the accumulator (a screw, not a pipe) and a piece of the old pipe, which is very brittle, disintegrating and probably the source of petrol smells.

The small pipe on the swirl pot is an air breather that should route back towards the top of one of the fuel tanks. I used to suffer with terrible fuel starvation when accelerating hard out of corners with anything less than about 1/3 of a tank.

The screw in the end of the accumulator is interesting, to my knowledge there was always a small breather, as inside the accumulator is a spring and a diaphram, the spring and diaphram compress under fuel pressure, the breather is to allow this movement without generating pressure on the none fuel side of the diaphram. BUT, check bosch fuel accumulator on google images, you will see many with the same arrangement as yours.

Re. the hard/brittle fuel hose, it could just be age OR it could be the fuel is NOT suitable for unleaded fuel and has carried unleaded fuel, this destroys the hose very quickly.

Chris.

[RCK974X]

Great reminder from Taz Turbo !!

Modern unleaded fuel has higher benzine content, and it's the benzine that rots old fuel pipe.
(and the old style rubber gaskets too, but none in 2.8i system)

The really hard plastic pressure pipe (injectors and pump to fuel head etc) is fine and should still be in good nick, but check it for surface splits, and 'pulls' (pipe stress - has a sort of whiteish sheen on the surface).

The soft 'carburettor' type pipes though should all be inspected VERY carefully....this was my problem too for fuel smells, I changed all the pipes tank to pump, and returns from accumulator etc. Big filler pipes on mine seemed OK, and get just the ocassional fuel smell now, when full.

NB. I didn't get starvation on corners, but did get flat spots on heavy acceleration, which turned out to be the fuel filter. New one sorted problem. Oddly though, never got misfire, engine just went flat and stopped accelerating.

I took old filter apart for interest, and I got about a tablespoon of sand and other crap out of it !!

[pomchal]

Greetings fellow PistonHeads. I have spent a fair amount of time on my '86 US-spec 280i recently trying to get it running after it has been sitting for ~3 years. I started by draining the tanks by removing the swirl pot, fuel pump and accumulator and replacing all the connecting hoses. It all looked pretty decent except for the hoses. I also noticed that the breather pipe out of the top of the swirl pot was broken (badly corroded). I did repair it but decided to replace the swirl pot with a 5/8" T and added a filter before the fuel pump. If I can get my hands on a new (better material) swirl pot, I will replace the set up to original.
I have used quite a bit of the info exchanged here. So, thank you for being a great resource for a guy that is trying to keep a wedge on the roads of California.

Now I am trying to tackle lack of power to the fuel pump. I have replaced the Engine Run Sensor (ERS) and checked the fuse (#1 and #2) that apparently feed the ERS. All appears to be ok, but still no power to the fuel pump.

Does anyone have any suggestions ? I have seen mention of "Roll-over Switch". How does it work and can it be the problem? Is there a relay that could be causing this problem ? if so, where can I find it (there is none in the cabin that refers to the fuel pump).
Any help will be greatly appreciated !

[RCK974X]

OK - I'm not quite sure what may have been added to US spec cars, but the european spec injection had two types to do with power to the pump.

Early type - this had a simple switch contact on the metering head, so that the pump runs whenever the metering flap is lifted off its stop. You can tell this type as it has a connector on the side of the metering head. As this switch is a 'contact to stop' unplugging it with ignition on should cause the pump to run.

Later type - this had no connector on the metering head, and used a 'timed relay' which runs for 2 seconds upon ignition power up, and then is triggered by an ignition 'pulse' from the ignition amplifier to keep pump running for another 2 secs. On Euro Cars, this was a tall relay of a purple colour.

I think (but not sure) the US ones had another unit which was an 'inertia' or 'collison' cutout, and if this has tripped, pump will not run. It may be a combined unit (ignition pulses and collision) not sure...

For wire tracing, the pump takes quite a bit of current, so has a nice thick wire which should be traceable to engine bay...

Hope that gives some clues !!

[bobs280i]

When you say ( I have replaced the engine run sensor) is it a new one or different? Bob