I'm in the middle of dealing with the M&D people on Shepherd. Background is that about two weeks ago they installed new Monark nozzles (supplied by me) onto my injectors, and also cleaned, tested and balanced them. Cost was $27.30 per injector (not including the nozzles, of course) and turnaround was one day.

I installed the injectors and one of them nailed. I pulled it and took it back to them and asked for an explanation. They took one look at it and concluded that the injector tip had not seated properly against the heat shield and detonation was sneaking past the heat shield and hitting the nozzle. They told me to (again) clean the surface where the heat shield rests, drop in a new heat shield and reinstall the injector. I did that and it still nailed.

A few days later I noticed that this same injector was leaking from between the top and bottom half. Pulled it, took it in. They had it for a few hours and determined that, once again, it was not seated properly against the heat shield, was being exposed to detonation and this was causing the leak and the nailing. They cleaned up the injector, tested it and pronounced it good. I reinstalled with a new heat shield and - surprise - it still nails. That was yesterday.

To their credit M&D has turned my injectors around in one day or less both times they have had them (once for the nozzle install and once for the repair), and they haven't charged me for either subsequent service on the faulty injector even though (a) they explicitly disclaimed any warranty because I provided my own nozzles, and (b) they seemed convinced that any problems were my fault and not theirs.

I don't yet know if the nailing issue is truly due to my own faulty installation (three times in a row??) or due to some sort of shortcoming in the quality of their service. I am in touch with a mechanic who is going to diagnose the problem for me (he seemed convinced based on my description of the problem that the injector spring settings are amiss) and if it truly is an issue with the injector he is going to "raise hell" with M&D until they fix it properly.

Also note that they will not work on Mercedes automobiles. They will only service the injectors themselves, meaning that you have to pull them and take them in yourself, and reinstall them yourself, and be comfortable doing everything that those actions entail. And if something isn't working right, you can't just drop your car off there and tell them to "fix it."