adjusting fuel mixture during warm up

[handyandy]

Hi

I am working on a late 280SL, the car was restored about 2 years ago at huge cost (not by me) but has only done 100 miles since and hasn't been running properly. we have set all the linkaeges throttle valve etc etc as per the various tours on here. When you drive the car its not nice when its cold but as soon as it has warmed upit drives perfectly

When the car is hot and you do the split linkage test the car is perfect both at idle and at revs.

My problem is that when the wrd is actually working (ie you can hear air being drawn in through the WRD filter) the mixture is much to rich, I know that I can remove oval shims to weaken the wrd mixture but as I understand it this doesnt alter the ration of air to fuel that the WRD actaully provides to the engine, if you split the linkages when the wrd is operating you have to open the thottle butterfly quite a lot before the the mixture is correct

The question is what is the answer!

Thanks for looking

Andy

[glenn]

HandyAndy, The fuel/air ratios(FAR) for hot vs. cold engine are two different worlds.
    The FAR for a warmed engine at idle is set by the idle air screw and the idle fuel knob on the FIP.  The WRD has closed its air flow and the heat pin is extended to max, thereby pressing the FIP lever to no additional fuel.  The CSV is closed.   Throttle pedal movement  now  opens the butterfly and FIP pistons in a precalibrated, synchronous FAR manner.

    The FAR for a cold engine???   Air? Fuel?   Air is coming in thru the idle air and the WRD.  The WRD air is gradually closed over 1 or 2 minutes as the engine warms up.   Fuel is initially max on FIP via 'Start'.  The CSV squirts for a timed length based on temp.  How this results in the correct FAR??
     Questions?  Is the WRD calibrated to provide the correct FAR as it gradually reduces fuel and air flow simultaneously?  What about all that fuel coming from the CSV and FIP Start relay??  Where is the air for this fuel??

     "Lurtch" took the WRD out of the picture by removing it and installing a bolt that pushed the FIP internal lever to the hot position of the WRD. 

[wwheeler]

The oval shims between the WRD assembly and the pump body DO change the mixture. It reduces the fuel input but does not effect the air. Take away shims to lean.

The round shims in the WRD piston DO NOT change the mixture but alter when the WRD shuts off.

Try removing oval shims first.

[twistedtree]

Ya, what Wallace said.

[ja17]

I agree, remove oval shims.

[glenn]

Re: WRD.  The WRD operates from -20 to +25 C(or so).   At -20 the air valve is wide open and the lever in the FIP is at max effect on FIP fuel adjustment(increase).  At -19 the heat feeler in the WRD begins to expand, the air valve starts to close, and the lever in the FIP starts to reduce fuel flow.   The engine continues to warmup and the WRD moves the air valve closed at 25 C and the internal FIP lever to max reduction of the added cold fuel adjustment.   Shims are added or removed so this happens.
     I assume Bosch/MB sized the WRD's air flow curve to the fuel curve as each are reduced during engine heat up of a couple minutes

     The FIP 'Start' relay and the CSV add much fuel on initial start.  Where does the air come from for this flood of fuel?
   
         

[wwheeler]

I would think that the fuel from the CSV and start relay are similar to the fuel bulb you manually squeeze on your mower or edger to get it to start right away. A concentrated shot of fuel to get it started, and then let the running engine sort out the correct mixtures.

[glenn]

Aye yes...   The 'Start' relay on the FIP moves the rack to enriched output until key returns to 'Run'.  Rack then returns to where the WRD says to.  Kinda like the squeeze bulb.
      Meanwhile, the CSV squirts away depending on the temp, thermal time delay, EPA reg, etc.(determined by what wiring scheme was in vogue with MB at the time).  This is a lot of fuel with no accompanying  air.

     But, by the 60s I would have hoped that Bosch/MB would have a better Fuel Management System than my Sears lawnmower.........

     The car cost say 5 grand in the 60s.  The FIP/fuel control probably cost nearly as much as the engine, $500?

     What a breakthru to have the feedback of engine rpm in the control system.   A 50 cent chip in today's computer control.

[Naj ✝︎]

Hi, Glenn,

CSV only squirts while cranking and controlled by the thermo time switch.

Under cold idle, both extra air and fuel are provided by the wrd settings/shims, so removal of oval shims would lean out the cold idle mixture.

Naj

[glenn]

Naj, I think the CSV squirts after cranking stops- until the thermo switch times out and temp rises.  This all depends on the many ways the relays, s/w, timers, etc were wired.   I think every car was different, figuratively.   MB believed in 'diversity'........

[ja17]

The CSV is activated while the ignition is on depending on engine temperature. The WRD draws in extra air through its own air filter until the engine warms.

[ctaylor738]

It doesn't make sense to me that the WRD would supply too much fuel during warm-up but then be OK when fully warm. 

What is the CO reading when warm?

Have you checked the current at the cold start valve?  Maybe the thermo-time switch is bad and causing the CSV to operate too long after starting.

[jacovdw]

Naj, I think the CSV squirts after cranking stops- until the thermo switch times out and temp rises....

Naj is correct.

The CSV only squirts whilst the ignition switch is in the start position and then only for the duration that is allowed by the TTS in terms of engine temperature
(irrespective of how long you operate the starter at that point).

If you look carefully at the respective wiring diagrams (versions 1 to 3 of the cold start system), then you will see that the TTS only receives power from the ignition
switch when it is in the start position.

[handyandy]

Hi

Thanks for all the input.

I have ended up removing all the oval shims between the wrd and the ip, the car runs much better during warm up but I am still confused/worried on 2 points

1) This car has had an exyensive rebuild by a reputable company and the pump has been rebuilt, It seems very odd that I should have to remove all the oval shims to get the mixture correct at warm up

2) even thou it runs much better it still goes through a very short stage during warm up when it is too rich (as prooved by doing a split linkage test) It occurs to me that if I play around with the number of round shims in the wrd I may well be able to "tune" this anomally out so I will probably give it a go (always assuming the owner is prepared to let me!) I have tested the CSV and it operates as it should and is not leaking

I will let you know what I find.

does anyone else run without any oval shims under the wrd?

Regards

Andy

[Cees Klumper]

I have now no oval shims and am planning to add one because mine starts running rough after a while, before the engine is sufficiently warmed up.

[Benz Dr.]

Engines are like people. Some are fun and some are nothing but trouble. They all use the same parts but every one of them seems to have a different variation to a common theme.

Is it any surprise that yours works differently than the one down the street or thousands of miles away? Yet they are still the exact same model made only days apart - 40 years ago.

[handyandy]

Hi

Its not the fact that the set up on this car is different to the setup on somone elses that bother me, I have worked on classic cars for over 20 years and dont expect any commonalities between them,(I work on a lot of Lotus and they couldnt even fit the same parts to 2 "identical" cars !)

What does surprise me is that on a pump that was rebuilt less than 100 miles ago I should have to make such a large alteration to the fuel metering to get it to run nicely.


Andy

[twistedtree]

What does surprise me is that on a pump that was rebuilt less than 100 miles ago I should have to make such a large alteration to the fuel metering to get it to run nicely.

Good point, and it suggests the problem lies elsewhere.  Have you done a real thorough check for vacuum leaks?  They can create all sorts of wacky behavior.  I recently had the IP rebuild on one of my cars and found it running lean.  A quick phone call with H&R resulted in a recommendation to enrichen by 2 clicks.  10 clicks later it was running better but still not right, at which point I stopped and started looking for other problems.  So far I've found dried/cracked vacuum hose for the brake booster causing a leak, and a leak at the manifold/head joint.  I'm optimistic that once I replace the manifold gasket I'll have a much better running car.  I'll let you know if about a week....

[glenn]

Re: The FIP.  The position of the rack determines the amount of flow from the pump.  At minimum(toward rear of car) the rack rotates the pistons to minimum flow for idle.  The internal lever for barometric and WRD compensation is at zero.  At higher altitudes(less fuel) and cold engine(more fuel) this lever compensates fuel flow by moving the rack back or forward.   The only other ways to move the rack are the 'Start' relay, the throttle, and on some the 'decel' relay.  (And with the 5 mm screw.)
  The WRD theoretically depresses the internal lever to move the rack backwards as the engine warms to operating temp(60 C or so).  The WRD's heat feeler pushes the WRD's slide piston against a spring loaded pin(to return the slide valve when cold) which pushes the lever down(against the barometric compensator pressure).  How much, etc, the lever moves versus the temp change is dependent upon the geometry of that stuff -  plus any shims, washers, etc. added to the mix.  Ideally, you want a direct proportional relation between the heat feeler movement and reduction of fuel flow.   Or,  at -20 C and max additional fuel,  meaning a little forward rack movement. And at 60 C(or so) no additional fuel flow compensation(rack movement back to zero).   The trick is to get this all working right with the air flow thru the valve.