Engine quits after a few miles

[n/a]

I realise that this topic has been discussed in this forum before and I thank all those who have contributed as their advice has been very helpful in on my w113. I have recently bought a 1967 250SL and I suspect that the car has been standing idle for some years.However the car was running fine when I got it as the seller had previously done a fair amount of work before I got it.

Recently however the car has developed a fault and here are the symptoms:

After a cold start the engine will run fine and pull smothly. Throttle response is good. After a few miles ( and obviously after warming up completly ) it starts to miss badly and then the engine will lose power and quite quickly stall.

When the fault first occurred leaving the engine to cool down would then allow the whole sequence to be repeted. But now the fault seems to be more persisitant and I need to leave the car overnight to allow the engine to run for a few miles.

So far I have concentrated on the fuel supply as this would seem the problem. I found the fuel tank was rusting internally and have had it cleaned and relined. All the fuel lines have been checked and are free flowing. The filters were blocked (all 3 of them full of grit and the bottom of the main filter had lots of silt) but they have been cleared and the main one replaced. the fuel return line has been disconnected and running the fuel pump for 15 sec gave approx 1 litre of fuel (I hear we need min 750 ml )so every thing seems ok here.

As the fault did not clear I have replaced the fuel pump to eliminate any chance of the fault being an intermittant fault in the fuel pump, this still made no difference.

Next I investigated the ignition system and have replaced distributor cap, Rotor arm, Condenser, Coil and HT lead. Each one was done independantly but none cured the problem.

So finally my question....!!!!
Where next?

I am considering the fuel injection pump but really don't know what to look for. As it is expensive to replace I would like to here from anyone if there is any test I can do with it to prove it is in fault before exchanging it. Thoughts and ideas much appreciated.

John McGinley
Ireland

PS I am supposed to travel to France today in the SL but obviously that is not going to happen. A friend has offered to lend his 1984 Ferrari 308. Hopefully it won't make me want to give up on the Merc!!!!

[Ben]

John I'm sorry to hear you still have trouble. As I mentioned to you before it would be a good idea to drive it and when the fault occurs whip out the plugs. They will tell you whether your mixture is rich/weak or if you have fuel starvation.

When the fault occurs you could disconnect the coil, then loosen an injector line and see if you have fuel !

Did you ever check the Warm Running Device ??

Regards,
Ben in Ireland.
'64 230SL 4sp.
'03 CLK Kompressor

[Naj ✝︎]

John,
If your car starts and runs well for a while, I would not suspect the inj pump.

I still think your problem is with fuel vapor lock. To test this, when the engine stalls, leave the ignition 'on' and bleed fuel from the little bleed screw on the main filter (near inj pump).You will find first cold fuel runs out, then warmer fuel and back to cold. Now tighten up the bleed screw and the engine will restart.

I had the same problem with my 230 which had been stored for 12 years. The tank was cut open and cleaned inside but the problem persisted. I would make sure the return line from the damper back to the tank is clear of debris AND the bit inside the tank!! Although my tank was clean, the return line inside the tank was still clogged up hard and I could not manually clean it. The tank was opened up a second time and the pipe had to be desoldered, removed and drilled out.Now it runs fine

Hope this helps
naj

65 230SL
68 280SL

[n/a]

Ben
I did try look at the plugs and they seem normal light brown ( not whiteish )
As for the fuel injector;-I thought about doing as you said but don't know what to expect in relation to amount or size of fuel spray. Someone told me each injector should be checked and they all should give equal amount of fuel. This won't help if they are all down on volume due to a faulty FI pump. Does anyone know how much should come out when cranking the engine?
Thanks for the advice.
Regards
John
PS Ben, I should be back from france Tuesday so should make the M-B owners meeting.

[n/a]

Naj
The fuel return line into the tank seems clear as I can blow air into it with little or no resistance. This was done with the tank out of the car so I am fairly sure it is not blocked.
Thanks anyway for the advice and I will loosen the filter and double check for vapour lock as you suggest. Will let you know
Regards
John

[Ben]

John the meeting is on tonight, June 2nd at 8PM ! !

If the plugs look okay, as you describe, when the problem manifests itself then it does sound like fuel starvation. If you open the lines at the injectors themselves you will only have a small amount of fuel. It'd be no harm to have an extinguisher there though as the hot exhaust is literally underneath. It sounds dangerous but I've done it lots of times, just wrap a rag around the pipe !

Regards,
Ben in Ireland.
'64 230SL 4sp.
'03 CLK Kompressor

[hands_aus]

Hey John,

You seem to have eliminated most possibilities.

Before spending money on replacing the inj pump, have you tried adjusting the AIR SCREW on the inlet manifold?

Try giving the engine more air when it is hot and see if it idles.
If it does, this will indicate that it NOW needs that air. Of course you can adjust the screw the other way also.

This sounds like the Warm Running Device as Ben suggested.
It could also be the inj pump thermostat that is not working properly. (Fortunately on the 250 sl these are not expensive to replace.)

I have added 2 of Joe Alexanders’ pics in case you don’t know what they look like. The Warm Running Device provides additional air and fuel when the engine is cold and should shut off completely when the engine is at operating temperature.

If the 'WRD' is not working properly your car will run great while cold because of that additional air and fuel but it will run poorly or if at all when hot.

Often when the 'WRD' is not working correctly the fuel inj pump air/fuel mixture can be adjusted to make the car run acceptibly. It will be alright for a while and will get you home if caught away from home BUT….

Maybe that is what has happened to your car.

Eventually the WRD will not work because the little aluminium valve will bind in the aluminium housing due to lack of lubrication.
See the component parts in the pics.

Also it has been found that if the engine coolant gets into the valve of the WRD it will gum up and stop the WRD from working.

To TEST if the WRD is working you can remove (22mm, THIN spanner) the Inj Pump air filter and then start the cold engine. You should hear a loud sucking noise. This will indicate that additional air is being drawn into the engine via the WRD. As the engine warms up to operating temperature that loud sucking noise should be eliminated completely.

If you still hear some noise then you have possibly 2 problems.

As I said earlier it could be the WRD or it could be the Inj Pump Thermostat.

There are usually not expensive to sort out.

I suggest you try the air filter removal first and let us know of your findings.

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Download Attachment: AirScrewInletManifold.jpg
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Bob (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[ja17]

Hello John,
I agree with Ben, the warm up device should be checked next. It sounds like your car is starving for fuel after warm up. Also the intake fitting of some original  electric fuel pumps have a wire screen which can get plugged.


Joe Alexander
Blacklick, Ohio

[n/a]

The ideas listed below are helpful but none have fixed the problem. Thanks anyway.

It's nearly a month now with this problem still keeping the car off the road. I have enlisted the help of a local "Old Merc Garage". The owner has tried to replace the fuel Injection pump with one from a 280SL ( mine is a 250 ) and the car will now run without stalling He had it running for three hours without any problems.

The only problem now is the car doesn't want to start when cold. It will turn over for a long time and even then may not catch. He says it is over fueling on cold start but admits he is not an expert on this type of FI pump. Does anyone know if the 280 pump is really the same as the 250? ( It looks the same on the outside) What might be the problem with the cold start?

Is it worth getting my original pump reconditioned somewhere? The mechanic said that the regulator at the end of the pump had a broken spring. I guess that was there to restrain the governor weights. Problem is the whole unit is in a pile of bits in a box.

Anyone know where could a rebuild be done and how much should it cost? Will a specialist bench test it and set it up just to bolt back into my car? The 280 pump will cost me €500 if I keep it. This will obviously mean it has to work first!

Any thoughts or advice much appreciated.

[Cees Klumper]

Your old pump can be checked and tested by a number of specialists - check the vendor database here:

http://www.sl113.org/data/show_table.asp?table_name=usr_parts_and_service_suppliers

A specialist will have the test equipment necessary to check all functions. If I were you I would send in my original pump rather than the 280 replacement. Only if the old one is too costly to calibrate/repair, can you consider getting a proper replacement. Rebuild cost is quoted at Euro 2,500 at SLS here in Germany (ouch!) but a new one from DC for the 280 lists at Euro 5,900 (ouch!!).

Alternatively - apparently these pumps do not typically break down. If you can find a used one in a breaker yard for, say, $300 you could give that a shot too. Over the past two years I have collected 11 engines (10 M130:280 and one M129: 250) for future rebuilding and each came with its FI pump. One pump was overhauled and never used! So if you look around you may come across a functioning pump for relatively little money.

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[mdsalemi]

For those NOT interested in complete originality but simply good functionality, think outside the box...

Years ago, I had a 1966 Austin Cooper S which had a Lucas ("Prince of Darkness" fuel pump.  The fuel pump, like most Lucas products of that era, was expensive and unreliable.  It had points, like a distributor, and they too burned out regularly.  So my smart thinking father went and picked up a new, but "good old made in the USA" SW (Stewart-Warner) electric fuel pump, and all the troubles went away.

What many of you may not (maybe you do) realize is that to feed the enormous custom street rod and stock car business there is a plethora of manufacturers out there that make ALL KINDS of stuff and it shouldn't be too hard to find a reliable electric fuel pump for something less then a king's ransom.  Do a google search for electric fuel pumps and surf.

Of course this is ONLY if you don't want or need originality.


Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored