W113 280 sl

[Markbrock]

My injection pump overflow valve seems too stick open then sometimes shut.i now there is 19mm disc inside ,and is spring loaded .can any one tell me how it should be working ,when I turn key too start.....all the best.

[mbzse]

There is a System description of the Bosch Injection pump in the Technical Manual on this Forum.
It is not a trivial system, see picture attached. A bit like a Swiss watch inside...

The Owners manual for your SL has a useful FI system overview in it.

A more detailed system description can be found here. It is in German, perhaps you can use translator tools
http://sterntwiete.mparschau.de/html/einspritzung_2.html

Where in your engine bay would this valve you mention be situated?

[Markbrock]

The valve I’m talking about is the return valve on the injection pump.i think it open and closes ,but I’m not sure how it works as fuel goes through it.my problem is my return too fuel tank valve.it has an open and shut disc in it. Need too no how this works all the best....mark

[mbzse]

Hmm, not clear to me...
Are you perhaps referring to the fuel damper(?)

If so, there is information in the Tech Manual. Also, see for instance this posting:
https://www.sl113.org/forums/index.php?topic=30698.msg222916#msg222916

[mbzse]

Or, is it this guy? (Valve outlet fitting marked in blue)

[Markbrock]

Yes marked in blue how does this valve work.mine seems too be closed.asked a lot of people about it but no one has an idea.strange.oh well,it’s been sent away for repair and this how it performs.all pump lines and rails have been replaced.....has me baffled.

[Dave H]

Hi Mark

This is the best explanation I could find .
This fuel by-pass valve on the injection pump outlet opens between 0.8 to 1.1 atu (about 11 to 16 psi).

The measuring point (for pressure) is by fitting a small gauge  on the line just before the cold start valve.

The valve ensures the feed pressure is a constant  0.8 to 1.1 atu.

The BBB mentions another value with the measuring point the same as above and that is the final feed pressure.
That value is a minimum of 1.3 atmospheres (about 19 psi) when squeezing the fuel return line. Don’t recommend doing this for more than a couple of seconds ,just enough to get the reading as you are dead heading the pump .

A point to note is the early fuel bypass valves had a tiny hole in the middle of the disc allowing vapour to escape preventing warm start problems, the next generation valves had no tiny hole but needed a T piece fitting on the return line at the fuel pump.

Lastly, the measurements are performed with the engine stopped and a minimum voltage of 11 V at the terminals of the fuel feed pump.

Others hopefully ( Joe, Stick, Dan, Mbze )will jump in here if my explanation is wrong .

Regards Dave

[Pawel66]

I think it is good you mentioned the hole/no hole topic - I think it is not so commonly known and if someone replaced that valve with a newer one (no hole), might not have added T-piece to the equasion.

[Markbrock]

Thank you......good info.we have just found the valve is faulty.so hopefully new one in place should clear this problem up....

[GM]

I also posted this in another thread. It's been a slow weekend in quarantine, so I took the liberty of translating the German document that Hans provided earlier in this thread with Google translate. I didn't translate the items in the pictures. I'm not the expert that others here are, but hope I can help in other ways.

[Dave H]

Wow, that’s fantastic Gary, looking forward to reading that when it quietens down tonight. What a great document 👍

[mdsalemi]

...description of the Bosch Injection pump...like a Swiss watch inside...

Don't involve the Swiss with the Germans here; conflating one with the other is just wrong. It has been said in jest that had the Germans invented a paper clip, it would have a dozen moving parts...my good friend, a Bosch engineer, said "truer words were never spoken".

I don't think a Swiss fuel injection system would look anything like the Bosch. It might be every bit as good, would give the Bosch a run for the money on precision, be a bit simpler and probably even more costly! 

[Bonnyboy]

Swiss fuel injections?   At a "carBS & coffee" event last fall a guy was showing his kid the fuel injection system on my Pagoda and he was comparing differences to the common rail system on his diesel which he said was developed by the Swiss.  He said the common rail system ran at very high pressures (20,000 psi?) which gave more precise metering of fuel which helped with performance and emissions and it had way less moving parts.    So I guess if this guy was correct, the Swiss did make a better mousetrap or maybe just different

The guy really didn't like the injection system on the corvette which they had just finished looking at.  Something about electrical gremlins - he did like the Mercedes injection system as there was very little electronics to go wrong and said that they were bullet proof and proper German engineering.     

[mdsalemi]

Swiss fuel injections...common rail system on his diesel...developed by the Swiss.

Yes, that's right. Indeed developed by the Swiss. Worked on by lots of folks, but the technology was purchased/licensed eventually to...yeah, that's right--Bosch. My friend worked on these and indeed they do operate at astoundingly high pressures. I got a tour of some test cells at their facility in Michigan for fuel systems. Amazing stuff. Not surprisingly the Japanese are up there too and Denso has the technology. My guess is there's a lot of patents on the technology.

Gone are the days when we would say "high pressure" is 200 PSI. 20,000 PSI is a whole different kettle of fish; different tolerances, different manufacturing, different materials.