Pfaff stitch problem

[Ploshkin]

My neighbour has a problem with her Pfaff Ambition 2.0.
She has been sewing lightweight canvas bags and the issue started on the very last seam.
I spent an hour with her this morning and we've done all the standard things - cleaned between the tension discs and under the needle plate, changed the needle (twice), changed the bobbin, threaded and unthreaded many time, sused different threads etc.  I don't think the timing is out because I looked in the bottom while turning the handwheel and it appeared to be picking up ok.

There are no clunks or rattles and the machine is running smoothly and quietly.
The top stitching looks perfect from the top, the bobbin thread is navy and the stitch looks normal.

This is the UNDERSIDE of the stitching and the pink thread is the top thread.
Every 3 or 4 stitches the top thread is pulled through in 2 chained loops the first lying flat and the second sticking up.  It is very consistent.  It has me completely baffled - I suspect something going wrong in the thread path but why it should suddenly go wrong is beyond me.
Any suggestions or thoughts?
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[Ohsewsimple]

Mmmm weird!   
Things that I would try are using a different brand of needle,  try a sew sample on a simple cotton rather than a thick fabric.  Use the same thread top and bottom.  Make sure tension  is at normal setting.  And I’d do a zig zag stitch test on the widest one. 

I’m assuming you have tried turning it off and on?   

[Efemera]

Bottom being iffy is usually a sign of the top thread, either not threaded correctly or not sitting between the tension discs. Floss the discs.

[Ploshkin]

Tension discs have been flossed and same thread used top and bottom.  I think she has tried it on various bits of fabric.  I am a bit suspicious about the metal plate /strip just before the tension discs - it seemed a bit loose and flappy to me.  I checked on my machine and although i can move mine to each side it springs back to a middle position.

[Gernella]

I've got an Expression 2 and recently had trouble with a different thread creeping in, but that was clunking after a few stitches.  However it has never worked well with top stitching thread so now I've just given up using it with that machine.

[Ohsewsimple]

When was it last serviced?

[Ploshkin]

@Ohsewsimple from the amount of fluff I extracted from the bobbin area I don't think she ever cleans it out.  I know she won't have had it serviced - there's no one round here that does it. 
I have bought all my machines from an elderly man who has a little shop in Carmarthen because he services and repairs machines that he has sold.  I did recommend that to my neighbour but she didnt heed my advice.  I think she got the Pfaff from e bay about a year ago (second hand).

[Ohsewsimple]

Quite honestly I think that’s what it needs then.  If you’ve exhausted all other options.  I can’t think of anything else to try.  It’s at this point I would have admitted defeat and handed it over to the engineer.   :)Sometimes it just all needs putting back to where it all should be.  There's a huge difference once they’re serviced. 

[Gernella]

When was it last serviced?

Service, what's that

[So Chic]

New needle and a thorough clean and if that doesn't work, a service will probably sort the problem out.

[Ohsewsimple]

Service, what's that

That’s what you do if you don’t want your bearings and cogs to go in your expensive machines @Gernella        I know you’ve heard of it. 

[Gernella]

That’s what you do if you don’t want your bearings and cogs to go in your expensive machines @Gernella        I know you’ve heard of it. 

If I'm going to get a new one I need sooner rather than later or I'll be too old @Ohsewsimple , I'm not prolonging the agony.

P S  I started typing this for your name -Obi-Wan Kenobi -  hadn't quite got the spelling right though.

[Ohsewsimple]

     
Nice one @Gernella i hadn’t thought of maybe needing a new machine.   Well in  these times it may not be wise to have them serviced just in case they aren’t sanitised before being returned.  A new one would be much safer all boxed up!    :thumbsup:  Of course I always had my machines serviced and repaired for free whilst working.  I would never have got away with using something not right.  Different now!