Fuel flow - short fuel pump -1965 230 SL Automatic

[Klaus Pieper]

My Pagoda starts well, both when cold and warm.  Often however, when starting the cold engine, it revs at normal 1200 rpm and then as the engine gets warmer the revs drop to the normal 800 rpm and then the revs drop further and the engine stalls.  When starting the engine again the same procedure follows.
As a result of this I checked the fuel flow after the fuel damper return hose - the reading was 800 ml/15 seconds.  The forum suggests that the reading should be 1000 ml to 1200 ml/15 seconds.

I had the fuel tank cleaned and thereafter checked all the fuel lines and breather pipes for blockages, including the rectangular fuel inlet below the fuel return pipe to the "flowerpot".
Cleaned the filters in the fuel tank and fuel pump and replaced the main fuel filter element.
Checked fuel flow at:
      fuel pump outlet pipe - 2000ml/15 seconds
      inlet pipe to main fuel filter - 1650ml/15 seconds
      inlet pipe to fuel damper - 800ml/15 seconds
      outlet pipe of fuel damper - 800ml/15 seconds
The voltage reading at the fuel pump without the engine running is 11 volt.
The fuel pressure reading at the cold start valve was within limits i.e. 0.8 bar or 11 psi.

What are the correct fuel flow readings at the above stations. I am a little bit at my wit's end and would appreciate your help.

Many thanks, Klaus

[BaronYoungman]

Something I would do to start before  delving further is running the pump for a few minutes and then testing  the flow .   Sometimes a bad pump that has a worn or faulty Armature or bad electrical connections  inside will start out pumping the correct amount and after about 5 minutes the flow will drop off the side of a cliff and pump substantially less fuel. I have seen it numerous numerous times. I don't know if you took those readings immediately, but I would let the car ( pump ) run for at least five if not ten minutes before taking readings then and seeing what those readings are. Just trying to be helpful Bob

[Klaus Pieper]

Thank you very much Bob.  I followed your suggestion and ran the motor for 10 minutes before taking a measurement at the outlet pipe of the fuel damper.  The reading of 900ml/15 seconds was somewhat better than when I took it previously.  What I also did differently this time, was to run the pump for 30 seconds and divide the volume by two to get to the 900ml/15 seconds.  By the way, the fuel pump is still fairly new and would not have been used for more than 100 hours.  It would still interest me what the normal fuel flow at the outlet pipe of the fuel pump should be.
Klaus

[Pawel66]

I do not know if the volumes in those various places you are mentioning is correct, particularly the drop after filter - not sure if it is normal. But I remember we said in many places in this forum, that about 1l per 15 seconds at the end of return pipe is what we look for, but vicinity of 1l, such as 0.8l is ok. I htink I remember someone saying if it goes to 0.6l issues may start.

[Klaus Pieper]

Thank you Pawel, that makes me feel a little bit more at ease that the fuel flow seems to be sufficient, but I will research a bit more as to the reason why the fuel flow drops so much between the fuel filter entrance and the fuel damper entrance.  This obviously then does not explain the initial problem of the intermittent stalling of the engine which I thought was as a result of fuel starvation.  The search continues.

[Pawel66]

Klaus, I am not an expert, so be careful with what I say, but - is what you describing not a picture of a quite typical wrong mixture setting that occurs at the end of the warm up cycle?

What I experienced is that when the warm up cycle is very rich, the plugs get fouled at the end of it.

And another condition I had was that idle mixture was a bit too lean, which resulted in idle, when warm, being ok, but the engine stalling at the end of the warm up cycle.

I think if you had fuel delivery issue, the primary complaint you would have is difficult warm start. Engine hesitating at acceleration, loss of power...

[Cees Klumper]

I also think the symptoms indicate more the 'warm-up fuel mixture conundrums' than inadequate fuel flow. There's extensive write-ups here on how to manage the warm-up cycle such that the engine keeps running throughout that cycle, mostly around the two shim locations in the WRD (Warm Running Device). I would exhaust that before looking elsewhere.

[ctaylor738]

Why not try opening up the idle air valve in half-turn increments, and maybe richening the idle mixture a click or two with the thumbscrew?

[col320ce]

Another vote here for wrd and air/Fuel mix

[Klaus Pieper]

Thank you gentlemen for all your comments and suggestions.  Yesterday I checked and tested the relay for mixture control, cold start valve, time switch, warm running device, thermo time switch and the solenoid on the fip.  All seemed to me to be working correctly.  A few months earlier I had done the linkage test.                                                                 
I also adjusted the air/fuel idling mixture using a vacuum gauge as a point of reference. The vacuum reading was 20 inches or 68 kPa at an altitude of +- 1000 feet.  The engine ran well although the warm idling speed was somewhat high at just below 1000 rpm.  This morning I started the engine again and it ran for about five minutes, then slowly started stuttering and then cut out.  One hour later I started the engine again and it ran well without cutting out.
From your suggestions I should now be looking at the WRD shims. Also, what are your views of the barometric compensator regarding effecting incorrect mixture?

[Benz Dr.]

Before you go any further, check your coil wire. If it's carbon core, you'll find that it's most of your problem. I find carbon core coil wires on most cars because Bosch sets are sold that way.  A one-foot length of carbon core cable will have about 12K ohms of resistance when you should have zero. A common problem with a lot of cars.

[Klaus Pieper]

Thank you Dan,  I checked this morning and I have Bosch copper core coil wire which is connected to a red Bosch coil (without an in-line resistor) and Bosch W7DC spark plugs with a gap of 0.7mm and 123 Ignition System. Would this set-up be in order?

As some wisely indicated that I most likely had "warm-up fuel mixture conundrums" I checked my spark plugs and they were all black with carbon deposits.  So, I guess it's time to learn about the warm-up cycle and the WRD.  I will trawl this forum for information, but also would appreciate your help very much.

[Pawel66]

Spark cup connectors at 1k - just to be totally sure about ignition system.

[Klaus Pieper]

Hi Pawel, sorry, but I am a little dumb.  What do you mean by spark cup connectors at 1K?

[Pawel66]

No, I was not precise, apologies. The ignition leads connector caps on the plugs should have 1 kohm resistance. It is stamped on them.

[Benz Dr.]

Thank you Dan,  I checked this morning and I have Bosch copper core coil wire which is connected to a red Bosch coil (without an in-line resistor) and Bosch W7DC spark plugs with a gap of 0.7mm and 123 Ignition System. Would this set-up be in order?

As some wisely indicated that I most likely had "warm-up fuel mixture conundrums" I checked my spark plugs and they were all black with carbon deposits.  So, I guess it's time to learn about the warm-up cycle and the WRD.  I will trawl this forum for information, but also would appreciate your help very much.

I would try going up in heat range on your spark plugs. W7DC is what you will see for our applications but I've found that 7 is too cold for most engines. I've been using BP5ES which is equivalent to a W9DC in Bosch. You need hotter plugs.

[Klaus Pieper]

Hi Pawel,  no need to apologize at all.  The connector caps are 1k ohm resistance - thanks, again learned something new.

Hi Dan, I replaced the plugs with NGK BP5ES.  Should I notice any difference in the way the motor runs?

After replacing the spark plugs, the engine started well and idled (room temp. 25 degrees celsius or 77 degrees F) at 1150 rpm.  The airflow at the air inlet at the WRD was strong.  After about 3 min and with the engine temperature at 60 degrees celsius (140 degrees F) the engine began to splutter and stalled.  Restarted the engine after about five minutes, at first running rough, but getting better and and after a while settling at 1000 rpm, the engine temperature now being 85 degrees C (185 degrees F).  When placing the finger over the WRD opening there was slight suction, however when blocking the opening of WRD the revs did not change.  I also reset the fuel/air mixture with the aid of a vacuum gauge.  So, the symptoms I mentioned before are still there.  From the smell of the exhaust gasses I believe the engine is running rich at idle as well as at higher revs, but there is no smoke.  Maybe I also need to mention that the car has not been on the open road for a while.

In the meantime I have read up about the WRD on the forum.  Most of the information unfortunately seems to relate to the 280 SL WRD and fairly little about the 230 SL.

Any help or suggestion would, as always, be much appreciated.

[mrfatboy]

After about 3 min and with the engine temperature at 60 degrees celsius (140 degrees F) the engine began to splutter and stalled.

Did you happen to pull the plugs at this point? This would give a clue if the engine is stalling because of being too rich or too lean.

About at this time the WRD is closing and there is a “lean” period before it fully closes. So if going too lean during this period could be causing the stalling.

Check out the FIP simulator and you can see what I mean.

https://www.sl113.org/fip/index.html

[Klaus Pieper]

Thank you mrfatboy.  No, I did not pull the plugs at this point.  If I had done that, what would/ should have happened to indicate if it was running rich or lean?

You hit the hammer right on the head, it is in the "lean" period before it fully closes when it stalls - the FIP simulator clarified that for me (thanks for the tip).  What puzzles me however, is that when I "help" the engine through this lean period by pressing the accelerator slightly and the engine reaches normal operating temperature, it idles at close to 1000 rpm.  Is that not an indicator that it is running too rich?

Whereto from here?

[mrfatboy]

Assuming you are going too lean during the “lean” period of the cold start process you would need to add oval shims under the WRD.

A quick test is to slightly loosen the 2 screws that bolt the WRD to the fip. This will simulate enriching the fip during warm up ONLY. This is a trial and error process and tedious because you always have to let the engine get cold before you can test again.

Once you get your warm up process working the way you want to you will put actual shims in.

I prefer to actually remove the two screws from the WRD and carefully lift it up and add/removed shims. It’s a more precise method for me and I know exactly what shim thickness I’m dealing with for each test.

Be careful lifting up the WRD to remove shims. Some people have to pinch off and remove coolant hoses. More of a pain and more messy.

To answer your plug question they would be white if you went too lean and not black and sooty.

[Klaus Pieper]

Thank you very much mrfatboy.  I will give this a go once we are back from our short getaway next Friday and I will keep you informed of progress made. What thickness should the shims ideally be? 

[mrfatboy]

People on this forum over the years have reported seeing the following shim sizes for individual shims. You can use multiple shims to come up with the desired total thickness. I believe most FIPs use 1-3 shims to come up with the total thickness.

I am using a total of .3mm under my WRD now. Every FIP will be different.

I have heard people use somewhere between 0mm (no shims) and 1.2mm.

WRD shim sizes
---------------
.12mm
.63mm
.5mm
.3mm
.2mm
.1mm

[Klaus Pieper]

Thank you, much appreciated.

[kafsan]

Hello Klaus,
Looked it up in the MB Werkstatthandbuch and here is how the fuel pump should be checked:
- motor not running
- battery voltage minimum 11 V
- pressure measured just after the fuel filter 0.8-1.1 kp/cm2
- flow directly after the overflow valve on the injection pump return line minimum 3.0 liter/min

Hope this helps.

..Karl

[Klaus Pieper]

Hi Karl,

Thank you very much for taking the time to look up this information - it is very helpful.  It also confirms that my fuel pump works within specifications.

Klaus