Try to notice if milage is better or worse and post on this thread. You might help a lot of people. Do you remember your average milage prior to stretching the spring?

What I still think is occuring is the injection pump elements are fuelling better or more equally. If the loading quantity is greater as well than design the timing relationship of the pump to the engine is changed as the injectors pop off earlier. Timing is in effect advanced.

The important item is before the spring was stretched . What was the release pressure point of that return valve? What is in now I wonder? Is it possible to put a gauge somewhere between the lift pump and the injection pump to read it? I an kind of hoping some old 240d and 300d engines have a substandard release pressure on their relief valves becuse af aging and usage.

If either of you where to presently read abouit 14-15 pounds pressure now it would mean before your spring stretching the pressure release was low. I am pretty certain that if you drip timed an engine with a substandrd release pressure. You are wasting your time. When that pump is returned to running you would have retarded timing in reality.

A lesser quantity of fuel is being loaded into the elements than the pump designers intended. So the injectors pop off later. If the presure is really low erratic loading may also occur from what I have observed on earlier posts. This at present is the best current possibility of where the missing miles per gallon might be on some of those 240ds.

It did occur to me since the pump and relief valve was simular on the 300ds the problem should be almost identical. . Milage loss for example would be simular. Instead it appears a somewhat lesser problem on them. The reason I suspect is more power strokes on a five cylinder than the four I think. The inefficiency is less pronounced with them perhaps.
The relief valve release pressure may have quite an effect on the quality of operation as well it is starting to look like. I originally thought the residual fuel pressure was just there to make sure fuel was available if needed.

Too bad we do not have a member with extensive pump knowledge. With a little time the answers will emerge anyways. You did not mention if your car is a 240d or 300d.

Any more black smoke than normal at startup and running? It is also quite possible for there to be less than before if efficiency has increased.

The curse of this may turn out to be be that before we all set our engine timing you should probably make sure the residual pressure in the injection pump is correct on all 123 diesels.