My M129 engine has been working perfectly since I purchased the car about a year ago (I have driven it some 600 miles) and has always started without any problems. When I checked the fluids recently I noted that ther was no oil in the FI pump (this is the model with its own oil reservoir and dipstick), so I filled it up to the correct level on the dipstick. A week or so later when I tried to start the engine it was very difficult to start when cold - when cranking it "almost" fired for a long time until it started but ran very poorly for 5-10 minutes with a lot of misfiring. Once warm it worked very well, good torque and no misfiring even on low revs, as usual. A few days later it would not start at all, but I could hear that it "almost" fired several times.
I made several checks:
-Ignition works, good spark and the timing seems right (can't check properly as the engine won't start, but once it did the first time the engine went well after some time).
-Fuel pressure and pump capacity measured at the cold start valve is within specs.
-Cold start system seems to work - cold start valve sprays as it should and the solenoid on the FI pump clicks when I crank the engine. (In any event, a defect cold start system would as I understand it not cause poor running for several minutes after start since it is only in operation when the starter motor is running and possibly for some seconds thereafter.)
-I suspected that the warm running device was stuck in the hot position which could explain the problem (too lean mixture for cold running), but it moved freely and the "heat feeler" thermostate expanded according to spec when submerged in hot water.
I now suspect that this may have something to do with the oil that I filled in the FI pump. Is it possible for the oil to leak from the reservoir in the FI pump and into the pump elements so that the fuel is contaminated with oil, which I suspect could clog up the injectors? This might explain why the engine ran properly after some time when the oil had been flushed out by clean fuel.
Has anyone out there experienced similar problems? Any input or thoughts would be most appreciated.
Thank you!
