periodic signal decrease with FID

Question

I was experiencing ghost peaks in my water blank shots so I decided to do some maintenance. This included a new S/SL liner and septum, removing the first inch or two of the column, FID disassembly and ultrasonic cleaning of the jet, and reassembly. Now I have a different issue. At rest, my signal decreases periodically, then returns to zero, only to decrease again. See picture. 
 
 Any ideas what could be causing this new issue?

CMZainea · Answer

Hello karrun 
 
 I&rsquo;m sorry for the delayed reply to your message. Do you still need assistance with this? If you do, please take into consideration the notes below. However, if the issue was resolved, could you please share what the resolution was? 
 
 My first thought would be to re-seat the FID castle, as it could be that it was improperly assembled. However, I feel like this would not cause this sort of...cycling, let's call it. 
 
 Did you change any gas tanks? Maybe even change from one gas type to another? 
 
 Other things I would be curious to know is whether you have gas generator for either Air, H2 or both. Also, what pressures do you have going to the GC from the gas tanks/regulators?