When doing autotune I get high precursor in mass 502. I get 12.79% and the limit is 12%. The manual says that it could be contaminated. The equipment has had preventive maintenance recently but it has now this problem. Previously it had a ratio of mass 503 to 502 high (18.24). I have set a temperature of 240° C from 230° C and initially the 503 to 502 climbed to 25%. But then it lowered to normal values (bellow 12.3). But now it gives me the precursor problem. Would be a good idea to bake out the MSD? I have done a bakeout on the weekend, but perhaps it needs more. The equipment has 11 years but it has only 6793 runs. Recently it was added a Tee to use a FID. Everything was OK, but the equipment was power down for the end of the year (7 days aprox) and then we have this problem. I have placed the column directly to the MSD without the Tee to see if the problem was in the Tee, but now we have this problem. Another question. The Foreline Pressure is at 0.000 mTorr. We have never had this display. Perhaps 2 or 1 mTorr but not cero. Could it mean something wrong? We have a diffusiopn pump. To check if this is an issue I have vented the instrument. I have opened the door so that it was fully vented. Then I have started the pumpdown and the pressure has been going down very quickly has been around 2 and 1 for about one hour and now it shows 0.000. We have upgraded to Mass Hunter recently, previously we had the GC/MSD ChemStation and we have not had this problems. Could it be some issue with the SW installation? We have a 7820GC and a 5975MSD. The Mass Hunter is Version 10.2 Service Release 1, Build 10.2.524.1. Perhaps somebody has had similar problems? Thank you.