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Fuel delivery issues - 280 SE

Started by Feather535, 11 September 2022, 05:50 PM

Feather535

In continuing to chase down poor running issues on a 280 SE that hasn't been on the road in 10 years (stumble on acceleration, cold or hot), I tested the fuel output at the return line and it's about 250 ml in 30 seconds - way below spec.

The seller said he replaced the fuel pump and filter and they look new, but the accumulator and damper can on the fuel pump are obviously old.  The manual says to check for restrictions on the inlet side of the fuel distributor, I removed the fuel line and the brass fitting with male threads on both ends that screw into the distributor on one side and the fuel line on the other.  It's hard to see inside that fitting, but it looks like there is a sort of soft rubber nipple in there. I can blow compressed air through it and see a bit of daylight, but it's partially blocking the inlet.  Is it supposed to be there?  Anything else to check?  Voltage to the pump is correct.


Randys01

wots the fuel volume going into the fuel distributor?

Jan S

The fuel volume going into the FD should be significantly higher than at the outlet.

I tested it on my 6.9 (k-jet) a while back ... it was around 3 liter in 30 sec. Less restriction, more flow.
1975-mod W116 450 SE with 6.9 engine

Feather535

Quote from: Randys01 on 12 September 2022, 01:48 AMwots the fuel volume going into the fuel distributor?

Don't know.  The factory manual says to test at the outlet, so that's what I did.  What should be volume be going in?

Randys01

 a litre every 30 sec would be nice

SteveDuNord

Quote from: Feather535 on 11 September 2022, 05:50 PMIn continuing to chase down poor running issues on a 280 SE that hasn't been on the road in 10 years (stumble on acceleration, cold or hot), I tested the fuel output at the return line and it's about 250 ml in 30 seconds - way below spec.

The seller said he replaced the fuel pump and filter and they look new, but the accumulator and damper can on the fuel pump are obviously old.  The manual says to check for restrictions on the inlet side of the fuel distributor, I removed the fuel line and the brass fitting with male threads on both ends that screw into the distributor on one side and the fuel line on the other.  It's hard to see inside that fitting, but it looks like there is a sort of soft rubber nipple in there. I can blow compressed air through it and see a bit of daylight, but it's partially blocking the inlet.  Is it supposed to be there?  Anything else to check?  Voltage to the pump is correct.



If I'm reading you correct there's a little metallic strainer bud in there? I changed mine recently with a Febi part that uses the later style synthetic filter found on later Kjets. Slightly different size but fits ok and appears to work.



febi bilstein 19947

'77 280se

raueda1

Quote from: Feather535 on 11 September 2022, 05:50 PMIn continuing to chase down poor running issues on a 280 SE that hasn't been on the road in 10 years (stumble on acceleration, cold or hot), I tested the fuel output at the return line and it's about 250 ml in 30 seconds - way below spec.

The seller said he replaced the fuel pump and filter and they look new, but the accumulator and damper can on the fuel pump are obviously old.  The manual says to check for restrictions on the inlet side of the fuel distributor, I removed the fuel line and the brass fitting with male threads on both ends that screw into the distributor on one side and the fuel line on the other.  It's hard to see inside that fitting, but it looks like there is a sort of soft rubber nipple in there. I can blow compressed air through it and see a bit of daylight, but it's partially blocking the inlet.  Is it supposed to be there?  Anything else to check?  Voltage to the pump is correct.
I recently went to hell and back with fuel flow problems because of that fitting.  There's a tiny screen filter inside that can clog very easily.  Mine was not completely blocked, it was possible to blow air through but there was substantial resistance to air flow.  I happened to have another on hand from my parts bin.  The replacement didn't impede air flow at all.  Swapping them instantly solved the problem, at least for a while.  Then the new one clogged up too with what looked like extremely fine rust powder, maybe fine enough to get past the primary fuel filter.  In the interim I had replaced the fuel filter and fuel pump. 

My hypothesis is that the act of changing the filter and pump somehow allowed unfiltered fuel into the system or maybe knocked loose some sludge that then reclogged the new fitting filter.  It's remarkable how many little screen filters that are in the system apart from the main fuel filter.  Seemingly somebody anticipated that junk would get past the main filter and that others were necessary.

I ended up just removing the fitting filter.  Flushing with carb cleaner wasn't enough.  The blockage was like an inorganic mud.  Fuel delivery problem solved.  The car has been driven about 1500 miles since and no problems at all.  At least not yet.  Not having the filter in place makes me uncomfortable so I'll be looking for a replacement.  It seems kind of odd that I'd never read about this filter as a potential problem or seen spares for sale or even any posts that I can recall.  Anyway, that's my experience.  Good luck and cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

raueda1

And here's more proof that searching is always successful only after you've already solved the problem.  Guess I'll order a few of these.

the forgettne filter
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Feather535

Quote from: raueda1 on 13 September 2022, 09:51 AMI recently went to hell and back with fuel flow problems because of that fitting.  There's a tiny screen filter inside that can clog very easily. 

Rust particles came out of that fitting when I blew compressed air through it--no surprised, since the car was sitting for 10 years.  The filter inside looks more like a rubber or fabric sock than a screen, but it looks like there might be a big hole in it.  Are replacements available anywhere?

raueda1

This looks like SteveDuNord's part.
https://www.pelicanparts.com/More_Info/0000746086.htm?pn=000-074-60-86-MBZ&gclid=CjwKCAjw1ICZBhAzEiwAFfvFhJxB_RHbZOKyRkOzJVvNVZL_aMCJ5kOKB1IjBg7oNz3f4F50-AcNOBoCjhIQAvD_BwE

I'm ordering a couple right now.  Website says it's not a fit but I don't believe it.  Cheap enough to take the gamble.
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Feather535

Quote from: raueda1 on 13 September 2022, 10:31 AMI'm ordering a couple right now.  Website says it's not a fit but I don't believe it.  Cheap enough to take the gamble.

Do you have a MB part number by any chance?

raueda1

-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Randys01

The filter at the entry to the FD is a known and well documented little critter. Some posts would have you beleive it was fitted from new but never intended to remain........they were to be removed after a certain mileage...they were there to scavenge any swarf from manufacture.
Whether you believe it or not, I am very keen to see mine fully serviceable and still in place..
Whilst they might look blocked etc, it's a brave man who runs without one.  With the passage of time, the grunge upstream in the whole fuel chain is breathtaking after 45 years.
A serviceable one will pass fuel freely altho it just seems so fine.
This filter is the 2nd and last line of defence in ensuring clean fuel enters the FD. So it's very important.

But it's not the last time it gets filtered. Some viewers maybe unaware that the FD has little filters on each outlet and then finally, the injectors themselves have teeny filters.


SteveDuNord

Quote from: raueda1 on 13 September 2022, 10:31 AMThis looks like SteveDuNord's part.
https://www.pelicanparts.com/More_Info/0000746086.htm?pn=000-074-60-86-MBZ&gclid=CjwKCAjw1ICZBhAzEiwAFfvFhJxB_RHbZOKyRkOzJVvNVZL_aMCJ5kOKB1IjBg7oNz3f4F50-AcNOBoCjhIQAvD_BwE

It certainly fits and I can't see the filter being any less useful than the strainer bud. I'm guessing they changed over to a synthetic filter because it's replaceable (?), or perhaps because it's cheaper?

The thread is slightly longer at one end but the same diameter/thread spacing.

I'm ordering a couple right now.  Website says it's not a fit but I don't believe it.  Cheap enough to take the gamble.
'77 280se