News:

www.W116.org
The #1 resource for our W116! Established 2004

Main Menu

1979 280 SE not running on fuel

Started by Bobe, 27 April 2022, 11:10 AM

Bobe

Hi There,

 a few weeks ago, i posted on my 1979 280 SE fitted with a LPG tank and vaporiser not running on fuel after a few hundreds kilometers running fine on its petrol tank. I have changed the strainer in the tank - not easy, having to cut a 46 mm socket to ensure it would have grip on the strainer base - then the fuel pump (i struggled to find the required M12 fine thread (150) nut to lock the fuel pipe as the system was different from that i removed), changed the fuel filter and the accumulator, but it still won't jump.

When i start cranking, the engine seems to cough the first time, as if there was fuel, but then nothing - no matter how often I crank, the engine won't start.

How can I test if fuel comes to the fuel distributor - could anyone tell me  where the fuel line connection is located on the FD ? and any idea of  what should I look for next ?

With many thanks !

'79 280SE Champagne 473
'67 250SL Horizon blue 304
'83 Citroen 2CV Villalunga red

revilla

Hi,
There are only 3 things needed for combustion: spark, fuel and air at the correct proportion (mix).
I'm guessing you have checked spark by disconnecting one of your six cables and cranking close to body/ground and seeing/hearing the spark jumping.
For fuel disconnect the CSV (cold start valve) near cylinders 1-2  then crank and check if fuel comes out. Use caution by capturing the fuel with a rag. You can also disconnect the fuel return hose at the distributor, crank and check. There are 2 hoses connected to the FD left side with a 17mm. It's the one towards the front. Lastly, your mixture can be out of range to create combustion. Too lean or too rich not good, engine won't start no matter how hard you try. On the top of the FD there's a hole covered with a screw. Inside, not visible, there's a 3mm hex type screw which you can turn to adjust the mixture. Clockwise richer, anti-clockwise leaner. You can go all the way up and then gradually in quarter turns make it richer. Be careful not to exceed about 100 quarter turns because the internal screw will fall into the FD body in the air metering chamber. It's not a big deal to recover it but it requires disassembling the top of the FD. Not difficult but time consuming. This adjustment screw is extremely sensitive, so each quarter turn requires cranking to check. Once it coughs (good sign) you can fine tune later.
Checking these 3 things should get you there. Or at least determining the next path to check (WUR and fuel pressures for example...).
Good luck
Robert
W116 1977 280SEL & 1979 280SE
[img width=150 height=100][url="http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG"]http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG[/url][/img]

Bobe

Thank you Revilla, all good advice !

it runs fine on LPG, and the ignition distributor was changed recently, so the issue probably does not come from here. Sparkplugs are all new too. I will check whether fuel gets to the FD and out through the return line.

Thanks !
'79 280SE Champagne 473
'67 250SL Horizon blue 304
'83 Citroen 2CV Villalunga red

revilla

Ok I see, so it runs on gpl meaning you don't have a spark issue. Good. Fuel at FD/injectors and mixture is the natural next steps to check. Let us know please.
Robert
W116 1977 280SEL & 1979 280SE
[img width=150 height=100][url="http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG"]http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG[/url][/img]

Bobe

I have checked the fuel line to the FD as you suggested and it provides a lot of fuel when cranking, and i have also checked the small filter and cleaned it with compressed air. Plenty of fuel also returns to the return line. I guess it points the finger at the FD itself.

At some point it ran on fuel for 10 seconds or so - it could not have been residual LPG as I had disconnected the hoses -  but then stalled again, and nothing happened with any further cranking.

'79 280SE Champagne 473
'67 250SL Horizon blue 304
'83 Citroen 2CV Villalunga red

revilla

Hi
That's a partial good sign.
Having fuel at FD inlet and at the FD return point doesn't mean you have fuel at the injectors (where is needed).
Disconnect one of the lines to the injectors or as suggested from the beginning at the csv. That's your next test point. Then mixture.
Good luck.
Robert
W116 1977 280SEL & 1979 280SE
[img width=150 height=100][url="http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG"]http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG[/url][/img]

Bobe

Some update on the issue - I guess I got to the bottom of the problem but I don't know the solution.

There is fuel getting out of the pump into the pipes leading to the injectors. When i depress the air flap of the fuel distributor, there is a good amount of fuel that gets out of the distributor. It looks like a good news.

When I pour some gasoline in the FD through the air flap, the engine fires very well, but stops shortly after that, obviously when the fuel is burned.

I disconnected the injectors of cylinders 1 and 2  and put a recipient at the end of each of them. Then I cranked the engine but there was no fuel getting out of the pipes. I cranked several times and hardly any fuel got out, just one or two drops. No wonder the engine does not start !

What would be the solution to that ?

Many thanks!

'79 280SE Champagne 473
'67 250SL Horizon blue 304
'83 Citroen 2CV Villalunga red

rumb

At first I would say you need new injectors, but the I think you should check system pressure first.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS

Bobe

The injectors are new and the accumulator is new, there seems to be no issue with the return line. Injectors do not get fuel, as I tested by disconnecting the lines of two injectors. I understand from a few videos i saw on the K-Jetronic distributor that the air lever must deliver fuel to the injectors lines on the fuel distributors  as soon as it is depressed and this can be tuned with the richness screw as suggested by Revilla: i will try that. As i understand it, i need to first remove the screw in the hole between the air metering and the distributor to access the hex and adjust the mixture ?
'79 280SE Champagne 473
'67 250SL Horizon blue 304
'83 Citroen 2CV Villalunga red

revilla

Hi,
There are always 2 ways of tackling technical issues like this. One is guessing and changing parts left and right (e.g. injectors) until mother luck strikes and the engine miraculously starts. The second one is by understanding first how/why a system works, the principles, the work done by each part/element individually and their mutual interactions. The path selected is exclusively the choice of the owner.
I have done the following when faced with similar situation:
Keep one or two injectors lines disconnected. Put a cloth rag underneath them. Turn your key to position 1 until red light on dashboard are illuminated but without cranking the engine. Right on top of your FD there's a blue connector. Remove the security clip around it. Then carefully disconnect it and you will hear the pump start. Observe the tips of the disconnected line(s). Fuel? If nothing if coming out, as I believe was suggested in previous post, then depress (slightly) the air metering plate under the LPG nozzle assembly. Use plastic to avoid scratching the surface. After a few millimeters of vertical displacement you should see fuel coming out of those lines. Approximately the same distance needed to observe fuel coming out is the distance you need to displace the mixture adjustment 3mm hex screw to enrich the mix. As said much earlier in the chain, too rich not good, too lean not good neither. Fuel not coming out in the above test means too lean. The screw needs to be turned clockwise to allow the FD piston to deliver fuel. As said earlier too, there are only 3 things you need for combustion: spark, fuel and air in the correct proportion (mixture). Spark isn't an issue because engine works on LPG. There's fuel delivered up to the FD but not at the injectors lines. Fuel is needed there which can be accomplished by adjusting to the right mixture. If after adjusting the mixture screw (remember in quarter turns) there's still no fuel at the lines you have unfortunately an issue with the internals of your FD. In my experience this is unlikely seeing that the engine was running ok recently on LPG and gas.
Once fuel is coming out then reconnect the blue connector and reassembly the lines and injectors. Repeat the test with injectors is position. Depress the plate until you hear the injectors click (open) this should happen with a slight depression of the plate (1-2mm if the screw is well adjusted). Re-adjust the screw and crank until the engine starts coughing. Continue until it runs then fine tuning will start...
Robert
W116 1977 280SEL & 1979 280SE
[img width=150 height=100][url="http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG"]http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG[/url][/img]

johnnyw116

Did you also checked the stuwschijf if its not bended ? i dont know the english name for this part but the partnumber is A0000745376 , and in the pic you can see a bended one who had an backfire so it may not look like the one in the pic  
JohnnyW116

Bobe

Thank you. The injectors were changed as initially when i bought the car the engine turned on 5 cylinders only, and one was failing, so all were replaced as they are not very expensive and it solved the problem. I will do the test in the next few days as suggested and turn the hex screw clockwise and see if/when fuel comes out. I guess the blue connector is the one that can be seen clearly on johnny's picture above.

To Johnny, I don't know what a stuckschijf is ("stuck disk" according to my online tranlator), but I would say that the fuel lines and the air metering disk all look in a better condition than on the picture.

Thanks for your great and valuable advise.

'79 280SE Champagne 473
'67 250SL Horizon blue 304
'83 Citroen 2CV Villalunga red

Bobe

Hi there,

I am delighted to say that after doing what Revilla suggested, and turned the screw clockwise until one of the injector lines started to drop fuel, the car started almost immédiately, and kept running albeit with some "pops" when accelerating. The idling rev seems ok (there is no rev counter on the instruments panel), however the car stalls after a few minutes idling, though it starts again without difficulty. Has that to do with the mixture or with the idling screw (and if so where is it ?)

The fuel pump however is very noisy, although it is brand new.

Great help so far from you guys! I never thought I would come around this without spending a few hundreds euros on it!
'79 280SE Champagne 473
'67 250SL Horizon blue 304
'83 Citroen 2CV Villalunga red

johnnyw116

#13
Here you can find your idle screw (turning it counter clockwise gives you an higher idle) but when you adjust this idle screw it also effects the adjustment on LPG
JohnnyW116

revilla

Quote from: Bobe on 05 May 2022, 05:58 AMHi there,

I am delighted to say that after doing what Revilla suggested, and turned the screw clockwise until one of the injector lines started to drop fuel, the car started almost immédiately, and kept running albeit with some "pops" when accelerating. The idling rev seems ok (there is no rev counter on the instruments panel), however the car stalls after a few minutes idling, though it starts again without difficulty. Has that to do with the mixture or with the idling screw (and if so where is it ?)

The fuel pump however is very noisy, although it is brand new.

Great help so far from you guys! I never thought I would come around this without spending a few hundreds euros on it!

Hi,
Those are excellent news.
What the engine is doing is absolutely normal. The Warm Up Regulator (WUR) enriches the mixture when the engine is cold to facilitate starts when cold. After about 5 minutes it reaches a "leaner" condition and that's why the engine stalls again. Keep going delicately clockwise to enrich the mixture a bit more until it starts and runs fine when hot too. You can increase the rpms (plastic nylon screw shown in previous pic) anti-clockwise a bit too to help make the idle stable.
Good luck.
Robert
W116 1977 280SEL & 1979 280SE
[img width=150 height=100][url="http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG"]http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG[/url][/img]