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280se - new to me, warm stalling!

Started by SteveDuNord, 04 May 2022, 10:57 AM

SteveDuNord

Well, the old injectors are back out, the new ones refitted but this time using the old injectors' (correct) rubber holders/sleeves.

Refuses to start.

I am at a loss.

So far:
New injectors + new sleeves. No start.
Old injectors + new sleeves. No start.
Old injectors + old sleeves. Start!
New injectors + old sleeves. No start.

The new Bosch injectors are supposed to be the updated version of the originals.
'77 280se

SteveDuNord

The 'correct' injector holders arrived today.
They are identical to the other ones I bought, that are supposedly incompatible with pre '78 280se's.  >:(

Waste of money but I'll try installing them anyway.

Here's images of the old style holders (right) vs the new style, and then the two new style ones together (identical).





Very frustrating.
'77 280se

SteveDuNord

Well, with the new injectors and new holders fitted, I couldn't start the car. Having cracked every fuel line, at the distributor and injector end, I found fuel was indeed flowing.

Next up was to check the pressure/flow from the fuel return line. I couldn't find any specific guide for the 280se engine so here we go:

First up identify the fuel return line, here it is - disconnected at the union with the hard line going back to the tank:



Stick that into a suitable receptacle:


Next we have to jump the fuel pump relay, which is found in the fuse box:



Find a piece of wire, I used guitar hook up wire, and jump the following two holes in the female end of the relay, for illustration purposes I've held the wire up to the two corresponding prongs:


Turn the ignition on so that the red light appears (position 2?) and jump the relevant points holding the wire in place, hold it there for 30 seconds:


You should have a minimum of a litre of fuel in the can. I did not. I had about 300 mil.



Anyone know how you test for voltage at the fuel pump??




'77 280se

Jan S

You can measure directly at the fuel pump, at the rear, under the car.

Did you remove the tank cap when measuring return flow?

I would also measure the flow at supply line to FD (to see if the filter, pipe, etc is clogged).

Have you measured the system pressure? Should be in the range of 5-6 bar I believe ... please check exact spec.

A few scenarios:

1. fuel pump is ok but return flow is restricted due to a main pressure regulator that is not opening correctly (system pressure would be higher than 6 bar, I guess. The higher the pressure, the lower the flow)

2. Main pressure regulator is ok but the fuel pump is not delivering the required flow (system pressure would be lower than 5 bar, I guess). Could also indicate a clogged fuel filter or pipe

I believe you are facing one of the two ...

Supply flow, return flow, system pressure and control pressure cold/warm are the first four things I would check.
1975-mod W116 450 SE with 6.9 engine

SteveDuNord

Quote from: Jan S on 30 June 2022, 05:30 PMYou can measure directly at the fuel pump, at the rear, under the car.

Did you remove the tank cap when measuring return flow?

I would also measure the flow at supply line to FD (to see if the filter, pipe, etc is clogged).

Have you measured the system pressure? Should be in the range of 5-6 bar I believe ... please check exact spec.

A few scenarios:

1. fuel pump is ok but return flow is restricted due to a main pressure regulator that is not opening correctly (system pressure would be higher than 6 bar, I guess. The higher the pressure, the lower the flow)

2. Main pressure regulator is ok but the fuel pump is not delivering the required flow (system pressure would be lower than 5 bar, I guess). Could also indicate a clogged fuel filter or pipe

I believe you are facing one of the two ...

Supply flow, return flow, system pressure and control pressure cold/warm are the first four things I would check.

Thanks, Jan.

I'll have a poke around the fuel pump and see what wires I can connect my voltmeter to. Does the pump have to be running to get a proper reading, and is it 12v?

I did not remove the tank cap but can give that a try tomorrow.

I tested the return pipe flow as per the Kjet pressure test guide I found online. Are you saying also to check the fuel IN line? Should the flow also be minimum of 1 litre over 30 secs?

I have not measured the system pressure. I need to buy a proper kjet testing kit.

I don't know what the main pressure regulator is.

'77 280se

Jan S

The wires + and - at the fuel pump are easy to find. You have to remove the two rubber caps/covers to connect your voltmeter.

And yes, the fuel pump must be running for a few seconds. I believe you should read approx. 12,5-13,5 V.

The fuel supply line to FD should deliver more, 2-3 liter if I remember correctly from my own test, because pressure is lower, i.e. no resistance from FD incl. pressure regulator (Pump curve tells us low pressure=high flow and high pressure=low flow). If the flow from supply line is low the pump is totally shot, or the line is restricted ... clogged filter, clogged pipe/hoses, clogged accumulator +++

The pressure regulator sits in the FD at the side where the return line is. I wouldn't touch it, without knowing what to do. Plenty of people here at the forum that can help you, if you need to "open it", check and adjust it.

AND PLEASE BE VERY CAREFUL WHEN WORKING WITH FUEL, "IGNITION ON", VOLTMETER, etc. ... a fire extinguisher within reach is recommended.

 
1975-mod W116 450 SE with 6.9 engine

revilla

Hi,
It seems like your mixture is off. I'd leave the pump and injectors aside for now. You have fuel going and your injectors even if not perfect would be enough to at least start the engine running rough. Weak pump and bad injectors/adaptors set would make your engine start even if rough. I would concentrate in the 3mm allen mixture screw that you played with.
Follow the thread below to find a baseline where at least the engine starts. Then focus on fine tuning. You can add a few drops of fuel directly into the FD plate while someone else cranks the engine. You don't need to jump the relay, there's a much easier technic described in the post:
Good luck.

https://forum.w116.org/mechanicals/1979-280-se-not-running-on-fuel/msg153464/#msg153464





 
Robert
W116 1977 280SEL & 1979 280SE
[img width=150 height=100]http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG[/img]

SteveDuNord

Quote from: revilla on 01 July 2022, 12:59 AMHi,
It seems like your mixture is off. I'd leave the pump and injectors aside for now. You have fuel going and your injectors even if not perfect would be enough to at least start the engine running rough. Weak pump and bad injectors/adaptors set would make your engine start even if rough. I would concentrate in the 3mm allen mixture screw that you played with.
Follow the thread below to find a baseline where at least the engine starts. Then focus on fine tuning. You can add a few drops of fuel directly into the FD plate while someone else cranks the engine. You don't need to jump the relay, there's a much easier technic described in the post:
Good luck.

https://forum.w116.org/mechanicals/1979-280-se-not-running-on-fuel/msg153464/#msg153464





 

Excellent, thanks.

I wonder if the new style injectors and holders require a slightly different mixture?

The old ones were working fine just the other day and the mixture was dialled in for them.

I will try adjusting the mixture screw for slight enrichment today after charging the battery.

If I get it running, I'll test the fuel delivery again.
'77 280se

revilla

Perhaps your low fuel flow is related to the battery voltage being low (?)...
When removing the injectors, perhaps you removed the distributor cap and/or cables to gain access to injectors 1/2 ? If yes, were them reinstalled in the correct order?
I'm just guessing. Dropping a bit of fuel directly into de FD plate while cranking will give you an indication.
Definitely do the plate slight depression test described in the post to confirm gas in coming in the right proportion through the injectors and you have spark. This is key for combustion. I would avoid touching other components until you set the mixture first, otherwise you might loose traceability of the changes and the engine will never start. I'm confident you will get there.
Robert
W116 1977 280SEL & 1979 280SE
[img width=150 height=100]http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG[/img]

SteveDuNord

Quote from: revilla on 01 July 2022, 06:40 AMPerhaps your low fuel flow is related to the battery voltage being low (?)...
When removing the injectors, perhaps you removed the distributor cap and/or cables to gain access to injectors 1/2 ? If yes, were them reinstalled in the correct order?
I'm just guessing. Dropping a bit of fuel directly into de FD plate while cranking will give you an indication.
Definitely do the plate slight depression test described in the post to confirm gas in coming in the right proportion through the injectors and you have spark. This is key for combustion. I would avoid touching other components until you set the mixture first, otherwise you might loose traceability of the changes and the engine will never start. I'm confident you will get there.

Eureka!

A quarter turn of the mixture screw and it started up first time.

Not only that, after a long run I tried to recreate the initial problem encountered before fitting injectors and spark plugs. Fixed!!

There is still a drop in revs when you take it out of park, but no stalling. Thank. God.

Next up I need to fit the new shocks I bought and change the transmission fluid and filter. Then I'll get back to the fuel tuning.

Many thanks.



'77 280se

gurrier

This is like a TV Serial - finishing on a happy ending.  I preview of next season now provided.
Thanks for the infotainment SteveDuNord.!!
1973 350SE

revilla

Robert
W116 1977 280SEL & 1979 280SE
[img width=150 height=100]http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG[/img]

SteveDuNord

Quote from: gurrier on 01 July 2022, 09:17 AMThis is like a TV Serial - finishing on a happy ending.  I preview of next season now provided.
Thanks for the infotainment SteveDuNord.!!

Haha. Don't worry I'll be breaking something else soon.  :D

Just washed it for the first time in weeks and ignoring the various spots of rust, I'm reminded of why I bought it in the first place.

A good day.
'77 280se

Jan S

Wonderful indeed!

When you are ready for the next step the low return flow needs to be tackled. And system pressure and control pressure cold/warm need to be measured. Very important for a well functioning k-jet system.

We look forward to "next season"  :)
1975-mod W116 450 SE with 6.9 engine

revilla

And with that wash, the frustrations that invade us all sometimes wash away too, at least temporarily... :)
A side effect of that joy is ignoring the "little" defects (eg rust spots, etc) that they might have. To wrap up the successful episode, a nice ride of a few kilometers is highly recommended by the doctors... :)
Robert
W116 1977 280SEL & 1979 280SE
[img width=150 height=100]http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG[/img]