Some months ago, I decided to replace my fuel injection pump with a rebuilt one that I had picked up in Germany about two years ago as part of a package that included an engine-to-be-rebuilt that I wanted to have. This FI pump really looked great, like new (with all the right yellow chromate, yellow seal stuff, plastic caps on the valves etc).
After the swap-out, the car ran pretty rough when pulling away from idle, and hesitated slightly while driving, say, 40 MPH. First I thought the pump needed to 'settle in' (had not been used for several years after the rebuild). Then, when the hesitation did not go away, I thought it might be the ignition timing, which was not quite right before the swap of the pumps. So I tinkered quite a bit with that (and, boy, does the ignition timing have an impact on the engine performance characteristics). When this did not clear things up properly either (although it seemed to make some difference) I started looking at the linkage settings. I checked the spark plugs and the leads resistance. I also checked the CO mixture. It just seemed to me this rebuilt pump should be better than my old one? Driving the car was no fun anymore, so I barely did so the past three months (also being too busy at work to have the time to do more tinkering).
Then, finally, this evening I decided to swap them out once again, putting my old pump back in. Having done this once before, I managed to get the job done in a little under 3 hours; there are some nuts and bolts that are pretty tough to get to, and some can only be approached from underneath the car.
Anyway, I test drove the car and the hesitation is all gone. What's more, the car seems to run better than ever, probably due to my fiddling with all the other things.
As far as timing of the pump, all I did both swaps was just orientate the marking on the gear exactly the same as the pump that just came off the engine.
It's always so nice to get some performance problem resolved; also because something like this ("hesitation" or "intermittent miss") can have so many different causes on our W113's. Glad in this case it was just that rebuilt pump. Now I have to get it looked at to figure out what the problem with it is. Maybe the guy I bought it from went through the same ordeal.
Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic
