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Premium Member
560SL 1986 244k miles astral grey / black
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389 Posts
Discussion Starter #1
Never a dull moment. Decided to have a look at the small filter on the fuel distributor as I couldn't see if the filter was dirty or not and a new one is only 3 euro I decided to replace it. I left the main inbound fuel line disconnected (with a plastic bag around it) and order de the new filter. This evening installed the new filter, 4 days later and tried to start the car, nothing.

The engines cranks, there is spark, the fuel pumps start up, there is fuel pressure, but it looks like the fuel is not distributed evenly to all injectors. I loosend 1 by 1 the full lines on the FD to the injectors and cranked the engine to let any air out. This helped a little bit and with pedal to the metal the engine started, but as soon it drops under the 2k rpm, it dies out instantly. See movie.

What can I furthermore do?

 

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1986 560 SL
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7,300 Posts
I didn’t know there is a filter in the FD inlet line. Is it just a metal mesh? Could it be improper in some way or clogged somehow? Perhaps try running without it, as the upstream fuel filter at the pump cluster should be effective on its own.

You say you loosened the injector lines to purge any air. Did fuel weep from all the junctions? If not, perhaps some debris entered the FD when you removed the old filter?

You say there is fuel pressure. Did you actually measure it to see if it meets spec?

I dont see any movement in the intake plate until you push the pedal. I believe it should open slightly when you crank the starter.

Sometimes there are multiple coincident faults in old cars. Something else unrelated to your filter change may have occurred by chance. It certainly presents as a fuel supply problem but I would pour a little fuel directly into the intake to confirm.
 

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Premium Member
560SL 1986 244k miles astral grey / black
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389 Posts
Discussion Starter #4
@jsebastian, No about the fuel distributor, the spider.

@dugald, The new filter is good. Didn't measure the actual pressure, as I don't have the meter for it, but when I unscrew the inbound fuel line from the FD gas quits out, so I don't think it's the fuel pressure.

I just watched the below series on YT, he purges the lines from FD to injectors as well, I try that tomorrow as well as checking the intake plate.

 

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Premium Member
560SL 1986 244k miles astral grey / black
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389 Posts
Discussion Starter #10
Were you able to get the car running?
Yes when starting the engine with full throttle and keeping her above 2000 rpm, she would run. As soon as I let her drop below 2000 rpm, the engine dies out instantly.

Yesterday I purged air all the way up to the injectors 2 by 2, all injectors receive gas, but no damn start unfortunately.
 

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1986 560 SL
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7,300 Posts
Seems unlikely that it has been affected by a simple fitting swap, but I think you may have to try adjusting that intake plate.
Do it in much smaller increments than that bold fellow in the YT video and remember where you started so you can return there if it doesn't work.
 

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1967 250 S (sold) 1986 560 SEC 1987 560 SL
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1,282 Posts
A Mystery! I agree with Dugald. The plate looked "closed" but why would it be different from before? And thanks for the filter info. I had no idea it was there. Wishing you a fast solution. Please keep us posted:smile

John
 

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1984 380SL
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2,288 Posts
Agreed, Dugald is on the money.

I would first make sure you're actually getting the right amount of fuel pressure. Maybe Murphy paid you a visit and something is causing the pumps to pump less.

One tip I may add, unbolt the injector hardlines and adjust the air metering screw until you reach the point that fuel dribbles out of the top of the ports.

Then hook everything back up and see if it starts. The car should fire up, but you'll need a duty cycle meter to dial it in further.
 

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Premium Member
560SL 1986 244k miles astral grey / black
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389 Posts
Discussion Starter #14
Ok, thanks guys. I am going to follow that route. This YT movie also points in the same direction.

I don't have the car next to my home, so I'll refer back to you guys in the weekend.

 

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Premium Member
560SL 1986 244k miles astral grey / black
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389 Posts
Discussion Starter #15
Didn't have much time last weekend, but did a few test and it I start to have the feeling that there might be not enough fuel pressure to make it all the way thru the FD to the injectors.

I ordered and fuel pressure gauge to obtain a reading, but the have the fuel pumps running constantly is there really only one way to jumper them by diving deep into the dash and jumper pin 30 with 87? No easier way?
 

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1986 560 SL
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7,300 Posts
You can jump 12v directly to the fuel pump terminals.

Did you ever try putting the old filter fitting back in?
 

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560SL 1986 244k miles astral grey / black
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389 Posts
Discussion Starter #17
Did you ever try putting the old filter fitting back in?
Yes, no difference. I have fuel on the cold start valve, but not on the lines to the injectors, so I am suspecting that I don't have enough pressure to push the fuel thru the FD.
 

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Outstanding Contributor
1988 300CE
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1,424 Posts
Hello Bauk18,

I‘m actually not active in this forum … I just wanted to browse a little in it and the first thread at the top (this one) caught my eye.

I suggest the following:

1.) Check if the air flow meter plate moves (about a centimeter or so) away from it‘s (correct) rest position when you (try to) start the engine, and check if it moves further down if the throttle is completely opened during starting.

2.) If that‘s the case, check the fuel pressure … “system pressure“ (SP) and “lower chamber pressure“ (LCP).

... I start to have the feeling that there might be not enough fuel pressure to make it all the way thru the FD to the injectors. ...
Assuming that there were no issues before you replaced the FD filter fitting, there might be too much fuel pressure … in the lower chambers that is. … With ignition off and fuel pumps running, LCP shoud be at least 0.3 bar (4.5 psi) lower than SP.

If the difference is smaler … and I‘ll have enough time :D … I‘ll explain a possibly helpful next step.

If that step will be successful, I‘ll tell you what happend when you replaced the FD filter fitting. … :wink_2:

H.D.
 

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Premium Member
560SL 1986 244k miles astral grey / black
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389 Posts
Discussion Starter #19
Danke shön H.D! I have a pressure meter underway, estimated delivery end this month, so I'll get back to you asap op step 2. On step 1 I'll make a movie later today and post it.
 

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Premium Member
560SL 1986 244k miles astral grey / black
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389 Posts
Discussion Starter #20

The air flow plate moves when starting and it moves deeper when throttle is further open.
 
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