Lean Dip - Is there a definitive solution?

[Tomnistuff]

I think I have read every thing here on the subject and run weeks worth of tests, within my abilities, and still have either lean stalls or fouled plugs or both.  Is there a definitive solution for the Lean Dip, or should I just give up and get on with life?
Tom Kizer

[wwheeler]

Are you talking about the time period between when the WRD shuts off and the engine hot? If so, I would just move on. That is if you have done every tweak known and it sounds like you have.

I am a perfectionist as well but have come to realize that the extremely precise devices on these injection systems have worn over the decades such that events like this happen. Since many parts are not available new, possibly no way to fix it. You can shim and adjust a multitude of things but many not. This maybe where an original low mileage engine has a real advantage.

I compare this six plunger to my two plunger injection pump. The six pump provides more power but also at a cost of greater complexity. I think that it is this complexity that is causing the random issues that pop up. My engine with the two plunger pump has about the same mileage on it but starts and runs flawlessly. Firing three injectors at once into the manifold may be a less efficient method, but is simpler and not as sensitive. 

In the end, I just know the lean period is coming and adjust my driving pattern so that I am not idling much when that happens. Then all is good.     

[Peter h]

if everything is set correctly and there are still problems, the ESP should be overhauled, by the right specialist
Peter

[Tomnistuff]

Thank you both for your replies.  I am not familiar with the acronym ESP.  What do the characters ESP stand for?

Apparently until I can learn how to create a function that provides better and more flexible control of the A/F ratio from the Warm Running Device, or as some people say,"the "Won't Run Device", I'll just have to get on with my life and drive my Pagoda like wwheeler.

Tom Kizer

[WRe]

Hi,
ESP is the German acronym and stands for "Einspritzpumpe" which means "Fuel Injection Pump" (FIP).
...WRe

[Tomnistuff]

During my restoration, that was completed just before Meeting of the Clans II (2019), I sent the engine to Metric Motors for a long block rebuild and the Injection Pump to Fairchild Industries for a complete rebuild.  It came back running rich and with a typical WRD lean dip, still better than when I sent it.  I suspect that 50+ years of obscure internal wear did not allow the rebuilt pump to tolerate a resetting of the pump to factory specifications as well as it should once it was back on the engine.  I will stop working on it for now and just keep thinking about it.
Thanks for your comments.
Tom Kizer

[wwheeler]

The pump on my 280SE was also rebuilt around a 1000 miles ago by Pacific fuel. Probably not going to find a better rebuilder here or in the world. Without certain new parts available, the rebuilders can only do so much. All mechanical devices will wear over time and without enough new internal parts, they can never be as good as new. Will always have some quirks.

I drove the W111 yesterday in fact and ran very well. It probably had the lean period but was able to "drive through it" and didn't notice it.

[Tomnistuff]

wwheeler, I know that you are intimately familiar with the workings of the IP and the WRD, because I follow your posts among the discussions about Lean Dip, as beautifully shown graphically by running the TM Engine Fuel System Simulation.  Is there a good source to go to for sketches or photos or cutaway drawings of the WRD and its interaction with the IP?  In particular, I'm looking for a good understanding of exactly how the WRD and the Barometric Compensator act on levers to control the fuel enrichment.  I'm familiar with how the WRD works but I'm trying to understand the Lean Dip (mechanically Why, How and How Much it affects the IP fuel).  Bosch and Mercedes are probably the two most secretive of how their parts work.
If I knew how they interact, I could maybe figure out how they wear with time if not how much, and then try to imagine a way to compensate for the wear, even if it means fabricating new ways to compensate for the wear that causes the Lean Dip and the stalls.  Example: How does the WRD pin spring "stop" work to shut off the fuel while still allowing movement of the air control piston?
Anyway if you know where I might find assembly drawings of the IP internal parts, it might help me to educate myself further.
Thanks for the comments so far.
Tom Kizer

[Benz Dr.]

I find that I often have to do final adjustments to IP settings. I add or subtract shims under the BC until I hit the sweet spot and then I fine tune with the knob at the back of the pump. Every engine runs differently and you often have to adjust for that.
Ignition systems have to be set up right or you will have running problems.

[wwheeler]

I think I can find some of these sketches of the inner workings. It is complicated and looks like the inside of a swiss watch. I do know how the spring stop works on the WRD and there is a post around here from Jeff280SL or something like that. He did a deep dive into the pump and found all kinds of hidden jewels like this.

Essentially the air valve and spring loaded pin below are pushed down by the ever expanding wax bulb in the thermostat. At some point, the bottom end of the pin hits the stop in the bottom of the pump (there is an adjustment there) and well, stops. However the upper portion of the pin just below the air valve has a spring on it. Once the pin hits the mechanical stop, the pin spring starts compressing. At some temperature, the pin's spring force balances the force from the expanding wax and the whole assembly comes to a rest. But at that time, the air valve should have long covered the air ports in then housing.

BTW, my lean mode never was so bad that it would stall the engine. It did and does run much slower and rougher during that time though. Dan makes a good point in that if all the other systems are top notch, you should be able able to minimize the effect of the lean period by making the cold running mixture richer. Seems to help. But if the spark is weak or plugs dirty, the engine won't handle the extra richness when cold as well.

You might see if Pacific or Fairchild will talk to you about this. maybe they can give you some direction.