oops - ran out of fuel...

davidsl500

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I haven't been using the SL for a while with the weather and workload etc., So last weekend I thought I had better kick it in to life and do an oil change, clean out dizzy caps etc., So I started it and left it running whilst assembling the tools and 5 mins later the engine slowly died. Restarted it and it ran for a few seconds then promptly stopped, same procedure again, turned over fine, ran a few seconds normally and died. At this point I spotted the fuel gauge needle hadn't got off zero.....duh! I left it last time with the fuel gauge on reserve light so it was low and I seem to have run it empty!

The first time I turned on the ignition I did notice the normal hum of the fuel pumps appeared a bit "strained" rather than their pleasant whirr before shutting off as well.

I have ordered up a new fuel filter to fit this weekend (that's different to what is supposed to be as well!) and fingers crossed I have just drawn 22 years of sediment through it.

Do you reckon I am going to get away with the fuel filter swap or is their a possibility that I have trashed the fuel pumps running them dry? Also, is it worth trying to backwash the pumps as the fuel tank connects to them before the fuel filter so they would receive the rubbish first?
 
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davidsl500

davidsl500

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I'd just put fuel in and start it personally.

Ah, that's the bit I forgot to mention! After realising that the tank was empty, I got 20 litres of fuel. Ignition on and the pumps whined into action - still sounding strained too me and then started it. Ran a few seconds and cut out, repeat the operation and same again. Any touch on the throttle kills it immediately. If I leave it for 5 mins and restart it, its lasts longer - 10 seconds maybe and cuts out. When its running its 1000RPM and stable. Hence ordering the fuel filter thinking (hoping!) it must be blocked and I haven't trashed the fuel pumps in the process!
 

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What year is the car please 96?
 
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brandwooddixon

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A blocked filter is possible, but are you sure that you're getting a strong spark? Or indeed it's not over fuelling (1000rpm seems pretty high for idle speed)?
 
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Richard Moakes

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When I changed the fuel filter on my 1991 car, it needed a plastic adapter to make it fit in the metal bracket on the car. Seems they have shrunk in size?
 
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A blocked filter is possible, but are you sure that you're getting a strong spark? Or indeed it's not over fuelling (1000rpm seems pretty high for idle speed)?

Definitely fuel related. I could weld with the spark!

1000RPM from cold is normal on the 500's with choke, settling to 500RPM when warm
 

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You can unplug the fuel pump relay and bridge out pins 7 and 8, this will make the fuel pump relay run all the time, to test that fuel is OK,, do not run it like it for too long as excess fuel will wash the cylinders
 
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When I changed the fuel filter on my 1991 car, it needed a plastic adapter to make it fit in the metal bracket on the car. Seems they have shrunk in size?

Got it off last night....

They seem to have got bigger! The Mann reference for mine is supposed to be WK845 or Kneckt KL38 which are 82-85MM Diameter 169mm long filter whereas mine is 74.5mm 146mm long. The KL54 on mine isn't made any more. I have tracked it down to a Mann WK830/3 which appears to fit certain AMG W124's, W114's and W123's and a load of ferraris! Mine is obviously a very early R129 - actually made in April 1990 but not registered until April 1991 so who knows what other goodies I am going to come across!

 
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I see you did the rotor etc as could have been that, do note the filter has an arrow on it for the direction of fuel travel and on a twin pump system it often points to the rear
 
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I see you did the rotor etc as could have been that, do note the filter has an arrow on it for the direction of fuel travel and on a twin pump system it often points to the rear

Malcolm, yes the arrow points to the rear, I have followed the plumbing from the tank through the two pumps and into and out of the filter.

I am a bit concerned that I have dragged rubbish through the pumps as the nice whirring noise when switching the ignition on sounds rather strained!
 

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Got it off last night....

They seem to have got bigger! The Mann reference for mine is supposed to be WK845 or Kneckt KL38 which are 82-85MM Diameter 169mm long filter whereas mine is 74.5mm 146mm long. The KL54 on mine isn't made any more. I have tracked it down to a Mann WK830/3 which appears to fit certain AMG W124's, W114's and W123's and a load of ferraris! Mine is obviously a very early R129 - actually made in April 1990 but not registered until April 1991 so who knows what other goodies I am going to come across!


Interesting, the old filter on my car was larger than the new one from ECP, I ended up ordering a collar from MB to adapt it to the bracket on the car.
 

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David what you can do is take the air cleaner off, bridge pins 7and 8 on the relay and slacken the inlet pipe on the fuel distributor and see it fuel is coming out 8 pipes I think fuel in,return to tank and 6 for the engine
 
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The fuel filter is "in the post" so probably have to wait until the weekend to attempt the next stage. Whilst I have the tank empty, I think I might as well have a good look at the pumps as well and do a proper job. So I think I will take the pumps off and see how they each run off the car and check for blockages on them both. As they are vane types, they will have a non return valve in the outlet so I don't think they will back flush successfully. Whilst I am at it i think I will run some fuel through the tank and see what comes out the disconnected pipe to fuel pump 1. I am convinced I have probably taken one or both pumps out so I will have to wait and see until the weekend when I can listen to each one off the car. I am thinking about running paraffin through them rather than petrol as I think I would like to keep my eyebrows with them running off temp cables! Then maybe a good flush with carb cleaner. I dont suppose for one minute I will be able to dismantle the fuel pump - they aren't like a good old SU pump of the 70's !

The pumps do kick up when the ignition is turned on and shut off after a few seconds as normal - what I don't know is whether they are providing sufficient flow.

I would love to drop the fuel tank as well and clean it out, still thinking about that one and haven't checked how difficult that is! I was thinking about attaching my airline to the fuel tank outlet pipe and giving it a blow - but I think that may just disturb the rubbish which will no doubt cause more issues...
 
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davidsl500

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And the saga continues........So, whilst I am still waiting for the new fuel filter to arrive, I decided to drop the fuel pumps off and have a look at them. Although I had siphoned off the fuel, I was expecting a little more to come out when I took the pipe from the tank off pump no1 - and I was correct. About 4 litres of fuel came out (plus half a litre down my sleeve!) and it was far from clear - more of a translucent yellow colour... and another couple of litres of the same from lowering the car off the axle stands.

I made a temporary feed pipe so that I could attach each pump inlet in turn to a temp fuel supply ( clean parrafin rather than petrol)

So I gave pump1 a direct power feed and nothing, totally dead! Pump 2 gave a groan and a kick and then nothing.... So, I am pronouncing both pumps as dead. I think pump 1 died first and then pump 2 had a struggle to draw fuel through pump 1 and expired as a consequence after it ran dry? Thats my theory anyway. Since the fuel running through these vane type pumps is used to cool the pumps, they wont survive long if they are run dry.

Looking at the quality of the remnants of fuel that came out I am glad that I decided to take the pumps off! Methinks I will be flushing some fresh petrol through the tank before reconnecting the new fuel pumps and filter.

Fuel pumps ordered from GSF since Eurocarparts don't seem to list stuff for older vehicles...
 

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David try running the pumps backwards with the head in a bowl of diesel and they could come back to life
 
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davidsl500

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Thanks Malcolm. I was using paraffin to run through the pumps as it has lubricant properties as well as degreasing. Pump1 is totally dead. I can't even get a spark if I brush one of the temp power leads across the battery terminal.

I think that, given they have done 100,000 miles now, I am going to replace them both. £69 each from GSF so not the end of the world. Also, they are a not that pleasant a job to do given their location and having to drain the tank so even if I could get pump2 going, I wouldn't want to have to do the job again later!

( I have also resisted the temptation to put my head in a bowl of diesel :D)
 
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OK David, the pumps are plumbed in series, the idea was to stop the fuel from foaming, this was dropped about 1998 and back to 1 pump
 

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