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Primary fuel pressure regulator - Is disassembly possible?

Started by raueda1, 01 November 2022, 06:59 PM

raueda1

I'm accumulating evidence that mine isn't working right.  Specifically, that it isn't closing fully when the engine is off.  This would cause static fuel pressure to immediately drop to nothing, which it does.  And that would explain my hard hot starts.  It would also explain why my static pressure = cold control pressure when the fuel pump is running and the pressure test valve is open.  With test valve shut the static pressure is good and holds indefinitely, so accumulator, fuel anti-return valve etc are all good.

The fuel pressure regulator is the only place I can see to release fuel to the return and depressuriztaion of the system.  The regulator contains at least 1 o-ring and they somehow assembled the damn thing.  Can it be non-distructively taken apart?  I'd like to see the guts of it before dropping a lot of $$ on a new one.

"Nothing works unless everything works."  Thanks and cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Randys01

If you are referring to the pressure regultor valve in the back of the fuel distributor then the answer is yes they can be pulled apart/serviced/recalibrated.

raueda1

Quote from: Randys01 on 01 November 2022, 11:35 PMIf you are referring to the pressure regultor valve in the back of the fuel distributor then the answer is yes they can be pulled apart/serviced/recalibrated.
Thank you, that's encouraging (and a bit surprising).  Is this something I have any hope of doing?  Seems like special tools would be needed.  And would this explain my symptoms?  Cheers
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Randys01

To give the component it's correct name "System Pressure Regulator" ..this is a screw in device at the rear of the fuel divider. It is largely best described as a long thin piston device.

These are easily serviced. This device could be contributing to your woes.

raueda1

Yes, yes, we're talking about the same thing (see pic from ebAY).  The picture shows it being sold with a bunch of o-rings and pressure adjustment washers.  One is for the piston inside the FD (1 on 'not running pic).  I have no idea what the others are for (maybe you do?). 

And you're confirming that maladjustment &/or internal damage to the hidden o-ring (2 on 'not running pic), or its seat, or whatever else, could cause leakage with the symptoms that I have.  So far so good.  And I also know that the gap between the spring-loaded plunger and the cylinder needs to be right (past experimentation and measurement).  I guess the gap could be changed by varying the copper washer on the valve threads. I also discovered that length of the skinny shaft can vary from unit to unit and that this has to be right.  This could result from long term o-ring compression I guess?  So it seems like there's plenty to go wrong here.

But what is there to adjust or calibrate?  Spring pressure?  And do you actually know HOW to pull it apart without damage?  And how to calibrate?  Sorry for kind of getting into the weeds here.  W116 generally promotes diagnosis and understanding instead of blindly replacing stuff.  So I'm trying to actually understand what's going on.  Thanks again and cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

rumb

Dave, look in the 100.985 Combustion manual job 7.3-210 Reconditioning and adjusting.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS
'21 E450 Cabrio

raueda1

Quote from: rumb on 02 November 2022, 04:32 PMDave, look in the 100.985 Combustion manual job 7.3-210 Reconditioning and adjusting.
Thanks Robert, but it this refurbishment isn't complete.  It doesn't get into the refurbishment of the system pressure regulator itself (the pointed threaded body with the hex head, item 10 below).  4 is the pressure setting washer(s), 8 is the green washer in my first pic and 9 is the copper sealing washer.  There's another o-ring inside the body (10) on the other end of the pin.  If it is damaged the system won't hold pressure.  Randys01 seems to be saying that it's replaceable but I can't find anything on that.  It's easy enough to replace the whole unit but they're very expensive for what they are.  I've already replaced 0-rings 1 and 8. I've got a spare regulator, though I think it doesn't work at all.  I'll retest it and maybe risk trashing it in the name of science.  It's worth noting that the hot start issue appeared quite abruptly.  That's not inconsistent with a sudden o-ring failure, like chunk breaking off. We see that all the time. Cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Randys01

This device does a no of things and is generally not considered a home handyman adjustment but we can do it.! :P
The whole thing about the fuel distrib [and its assocaited hanger on bits ] is that it is restored at specialist centres with flow meters and God knows what else.
So that's part of the reason it is hard to find info  about them.

Anyway, for the moment let's concentrate on setting the system fuel pressure.
ASSUMING you have assembled this correctly  and ASSUMING that all the O rings are in place and serviceable,ie as per the drawings.. it is the shims that set the pressure. You only need 2 as a rule to obtain a good ave fuel pressure of 5.6 bar.
Until you have that and 1 litre per 30 seconds flow: they are the cornerstone settings.......the rest of it will be like wrestling with a column of smoke.

daantjie

From memory there is a push valve inside the unit with a very tiny oring.
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

Quote from: daantjie on 03 November 2022, 08:56 AMFrom memory there is a push valve inside the unit with a very tiny oring.
Yes!  Thank you!  That's exactly what I'm driving at here!

Quote from: Randys01 on 02 November 2022, 11:05 PMThis device does a no of things and is generally not considered a home handyman adjustment but we can do it.! :P
The whole thing about the fuel distrib [and its assocaited hanger on bits ] is that it is restored at specialist centres with flow meters and God knows what else.
So that's part of the reason it is hard to find info  about them.

Anyway, for the moment let's concentrate on setting the system fuel pressure.
ASSUMING you have assembled this correctly  and ASSUMING that all the O rings are in place and serviceable,ie as per the drawings.. it is the shims that set the pressure. You only need 2 as a rule to obtain a good ave fuel pressure of 5.6 bar.
Until you have that and 1 litre per 30 seconds flow: they are the cornerstone settings.......the rest of it will be like wrestling with a column of smoke.

Thanks Randy, you're preaching to the choir here.  "Nothing works unless everything works."  All my pressures are good except cold pressure.  System and hot pressures are towards the high side of their ranges but still in spec.  Cold pressure is about 0.6 below where it should be for a given temp.  The result is low idle for a minute or 2 and car runs fine otherwise. I'll attend to that later, but that wouldn't effect system pressure leakdown or the hot start issue we're discussing here.

HOWEVER, I've got a lot more than 4 washers setting the primary system pressure.  The cylinder they sit on is almost full, about 4mm or so thick.  It was always this way so I doubt it's related and the hot start/pressure loss problem is quite recent.  Still, maybe this suggests a connection or that something else is amiss?  Weak spring on cylinder (#3 in pic above).

Anyway, absent anything else, I guess path forward is
  • Sacrifice my spare to see if I can get it apart without destroying it (unlikely) and then
  • Bite the bullet and get another regulator assembly  >:(
Stay tuned.  Thanks and cheers,


-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

raueda1

Quote from: Randys01 on 02 November 2022, 04:01 AMTo give the component it's correct name "System Pressure Regulator" ..this is a screw in device at the rear of the fuel divider. It is largely best described as a long thin piston device.

These are easily serviced. This device could be contributing to your woes.

I just went back and reread the thread.  It suddenly occurred to me that I may have misinterpreted "easily serviced."  That could mean serviced as in simply removal and replacement of the valve assembly (maybe a more common usage in the Anglo-english sphere?).  I took it mean refurbishment or repair of the valve assembly itself!  In hindsight I think you meant the former.  And all the while I was going nuts trying to figure out how to do the latter.  Now I wonder why the answer wasn't "just unscrew the damn thing!"  I'm usually my own worst enemy.  :-\  Cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

raueda1

Some progress to report.  It turns out the valve actually IS easy to take apart.  This is done by pushing down on the ferrule at the end of the spring thereby compressing the spring.  This exposes an absolutely tiny c-clip that keeps the ferrule and spring in place.  Carefully remove it with all due caution because it wants to get away.  If it does you're screwed.  Anyway, the o-ring in question and discussed above is towards the left.  It's about 7mm OD (hard to tell exactly with old o-rings, they can swell from fuel, shrink, harden etc.). 

When removing the long plunger the o-ring came out distorted and twisted.  I'm not sure how this happened.  Maybe sticking to the valve seat and twisting on the way out?  Whatever the case, it's clearly not good and points to the source of leaking. Just for fun I took apart the spare valve (on top in pic).  Looking back at my records that one didn't work either.  The o-ring there was totally shot - rock hard and triangular shaped from sitting against the valve seat.

New o-rings are now on order.  I was going to wait to post until testing but got too excited cause failure points were so obvious.  Let's hope I'm right.  If so, and anybody else has similar symptoms, the lesson is do NOT pay US$150-250 for a new valve.  Just get a few 7-8mm o_rings and do it yourself.  Will report back....  Thanks and cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Randys01


raueda1

Quote from: Randys01 on 03 November 2022, 09:50 PM.you're gettin' there!
HeeHaw!  I got there.  Ticket closed.  Replacement of the o-rings did the trick.  It was certainly the tiny one on the valve needle that was bad but I replaced them all anyway.  The small one is NBR (as might be expected) but I upgraded the other 2 to HNBR (for improved heat stability and compression set).  No static pressure drop for over an hour at which point I stopped the test. I still need to bump up system pressure and cold pressure a little.

It's worth noting that the valve assembly certainly IS serviceable,  but it's in no way adjustable (apart for the pressure adjusting washers, but they aren't part of the valve itself).  All you can do is replace the o-ring.  The spring isn't really doing anything except keeping the needle in position.  It's worth noting that at some point I mentioned that the total valve assembly length varied by about 2mm between my 2 units.  I assumed that this was just one of those arbitrary MB spec changes.  Not so!  The difference was entirely the result of o-ring compression on one unit. 

At the end of the day chasing down to o-rings saved me lot of $$$ by not buying the whole damn valve.  Trouble with hot starts and you know your accumulator is good?  Then this might save you $$$$ too!  I had to buy a bunch of o-rings to meet the vendor's minimum sale, so now I have extras.  If you're interested in the o-ring kit PM me on this site.  Cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Randys01

  "The spring isn't really doing anything except keeping the needle in position".

Not quite right mate.......the spring and the shims are the only things doing the work!!  The O rings are passive in the scheme of things. By adding /reducing the no of shims, they are tensioning the spring. More tension, higher fuel pressure etc.