Fuel Injection Adjustment: three turns to improvement.

[mdsalemi]

Folks,

My car, since its restoration in 1999-2001 (yes, approaching 9 years now) has always suffered a series of little issues that impacted drivability.  One by one they are being solved.  To review:

1)  I had a bad fuel tank, oxidizing minute rust particles into the fuel system.
2)  I had an intermittant problem with the Crane ignition.
3)  I had an intermittant fuel pump problem caused by compromised power connections.

All three of those were happening at the same time, and STILL I managed to drive to many events in the midwest.  All those are in the past.  Since those issues were solved however, I've never been 100% satisfied with the drivability of the car.  It always sounded and felt like there was slight misfiring; odd shifting, and poor fuel economy combined with a penchant for rising temperatures in stop and go driving in the summer.  Still, the car drove better than many.

At Blacklick this past weekend, Joe did an advanced version of his [what has become known as] the "Blacklick CO Test".  This is where you separate the accelerator linkages right above the fuel injection pump to separate the action of the air intake and fuel delivery.  By advanced I mean he extended this test over three ranges: idle (700 RPM); mid range (2000 RPM) and high range (3800+ RPM).  What he found was the mixture (fuel-air) was perfect at idle.  However we were lean--very lean--at mid range and high range.  Not wanting to start monkeying around with ajustments moments before I left, he did a quick fix: 3 turns of the linkage to the FI pump to enriched the mixture at all ranges.  Worked like a charm--but idle is a bit rich, so this is temporary.  However, all the drivability problems went away.  Fuel economy improved, temperature was steadier, smooth over entire highway driving range, and all shifting improved, too.

Apparently I can enrichen the mixture with a shim under the WRD.  I can lean it out at idle with the adjustment knob.  However the Technical Manual and others indicate that there are mid range and high range mix adjustment screws on the "governor" on the FI pump?  There does not seem to be any more photos or info.

Can anyone tell me how to access these adjustments?  Which screw is which?  Which direction to they turn to achieve rich/lean?

[al_lieffring]

Michael

First, thanks for providing the PUB shirts, It was a pleasure meeting you.

Next, because your mixture is lean in both mid and high range I would suggest using the main rack mixture screw. this is  behind a port covered with a 5mm allen headed bolt, located between the two solenoids on the back of the injection pump.
with this screw out you can insert a long narrow strait tip screw driver in and turn the screw one click at a time to the left (countercloclwise) to richen the mixture in the entire RPM range. this screw is on the end of  the main rack, you will feel the rack move as you press against it with the screw driver.
because this richens up the entire rpm range once you are satisfied with the upper and mid range adjustment, you can then set the idle mix knob.

Al

[Naj ✝︎]

Michael,

Picture of the screw in Al's description

[ja17]

Hello Michael,

Yes, I agree with Al, a "total range" adjustment makes more sense than tampering with the pairs of range screws. The rack adjustment screw will work fine as Al metioned.  I suggested the shims, since most techs hesitate to do internal pump adjustments. The shims will do the same thing and can be undone more easily than other adjustments.
However if you find someone comfortable with a rack adjustment it will also do the trick. Remember to turn the rack screw counterclockwise to lean. (just the oposite of the thumbscrew).

Thanks for everthiing Michael!

Joe

[geezer]

JA, Al,

I'm having a similar problem with my '72 280SE.  Starts right up idles smooth, accelerates smooth but as soon as I let up on the throttle pedal it begins to run rough and backfires out of the intake.  The engine runs smooth as long as I am depressing the throttle pedal.  The backfiring out of the intake indicates to me that the midrange is lean.  It has new points & condenser, timing is set, new fuel filter, most new fuel hoses, & clean gas.

This car has been in a barn for 6 years.  I also discovered that the idle mixture screw has been screwed all the way in.  I'm am comfortable making internal FI pump adjustments Is shimming the WRD best for enriching the mixture or is turning the screw at the end of the rack?

Looks like I'll have to get my CO meter out of retirement.

[ja17]

Hello geezer,

Before you make any internal adjustments, Is your WRD working properly?  You should be able to hear the "suction noise" when the engine is cold and hear none when the engine is warm ( use a section of hose on the WRD air filter, for a stethescope).

[geezer]

Hello geezer,

Before you make any internal adjustments, Is your WRD working properly?  You should be able to hear the "suction noise" when the engine is cold and hear none when the engine is warm ( use a section of hose on the WRD air filter, for a stethescope).

JA17,

Thanks I'll check the WRD today.  I suspect that the WRD is working since I get fast idle upon start up that gradually settles down to about 700rpm as the eng temp rises.  I will also check the flow from the electric fuel pump.   The pump does run & circulate fuel I just don't know how much flow.

[janpomerans]

Excuse my total ignorance, but what does "WRD" stand for?

[w113dude]

Excuse my total ignorance, but what does "WRD" stand for?

 I think, Warm Running Device, Right?

[ja17]

Yes,

Warm Running Device  (WRD) is the official factory term.  It is a regulator on the top of the injection pump which regulates additional air and fuel on a cold engine. As the engine warms the WRD adjusts the fuel and air mixtrue in accordance with the engine's coolant temperature.

The similar componant on later type fuel injection was called a Warm Up Regulator.

[menesesjesse]

JA
Just to be clear you mention listening to a suction noise.  I have heard this before but want to be sure from where.  Do you remove the air filter on th IP to check this sound?  If not where do I place my ears to verify that noise.  Thanks so much.
Jesse

[Cees Klumper]

The little air filter on the injection pump has inlet openings around its circumference, close to the pump body. Just try different places to hold the makeshift stethoscope right after you start the engine from cold, and you will hear a loud hiss - really can't miss it it's that loud. Should go completely away after 'a while'.

[ja17]

Yes, a two foot long section of water or air hose 1/2" diameter works as a stethescope. Listen at the bottom rim of the small round air cleaner on the WRD.
I guess mercedes should have called this a CRD (cold running device) because it functions mainly when the engine is cold ! ?

[J. Huber]

I may have confessed this before but when it came time for me to listen to my WRD, I looked around and spotted my 3 year-old daughters pretend doctor's kit (playskool). I strapped on the little stethoscope -- and it worked perfectly!! so did the WRD 

[J. Huber]

And in case you thought I was kidding... I just found it in the garage! Of course, if my daughter (or wife) sees this picture, I got some explaining to do.