Just started writing and the IE decides to start Not Responding! Bloody thing.
Anyway here is what I can tell you:
06.56 2N09 MBR - CAR is normally a 142 and is diagrammed to be one. To my knowledge it is the longest regular diagram for a 142, being 3 hours exactly and last time I checked about 150 miles.
This then forms 2N20, 10.33 - CAR - NCL fast. Once it gets to Newcastle it is normally stabled in one of the bays for use later on. The next train CAR - NCL has been a 142 the last few times I've seen it, so this means 2N13 09.23 NCL - CAR and 2N24 11.34 CAR - NCL are a 142.
13.32 will more than likely be a 142, during the day the Pacers stick to MBR - HEX workings and the 156s take over NCL - CAR workings. However they do change around so it is not uncommon to find a 156 working MBR - HEX and a 142 going all the way back to CAR.
14.50 MPT - MCE will be a 142, hardly ever see a 156 on the Morpeth - Metrocentre trains these days. Might get lucky though, could change.
14.54 2N35 NCL - HEX comes from MBR and therefore is likely to be a 142.
17.24 2N43 NCL - HEX starts at Newcastle, so this could be a 142 either that has been stabled at Newcastle since the morning or something running ECS from Heaton. Not entirely sure what it could be, so might be either a 142 or 156.
17.35 2A40 MCE - MPT, 142 on this. IIRC it does go ECS from Newcastle, goes in front of 2N43, passes Metrocentre and turns at the points just past the station. Think this is either the only one or one of a few ECS workings that go past Metrocentre during the day, all other trains stop there.
17.42 will probably be a 142.
This info may be out of date but on average there are 30 142s based at Heaton. From time to time they move around and go to Leeds and Manchester, and we get a Neville Hill or Newton Heath 142 back. Recently there have been a few in the NE that have the bus type seating, which are rare in this area. At best I'd say you'd be able to see 20 of these in Newcastle as there are a few that run the DAR - SLB trains, and these 142s are either stabled overnight in Darlington or Middlesbrough, and also there are some early morning ECS trains from Heaton.
Out of interest, if you could send me the 156 diagram that would be great. The one I have is a few years out of date (but just about accurate). Again do expect a working to change at short notice.
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I'm not sure how many units are allocated to Heaton, but it must be a fair few. Hopefully 142094 (the RailUK user not the unit

) will see this thread as he is part of our resident pacer veg and may have some idea.
THink that label is beginning to stick!
I have a feeling there is still one run per day that is Boro - Carlise on a 142 all the way. Might have to try it out one day when I'm feeling adventurous
You'll probably think I'm mad but I've done it twice as part of a NE Pacer bash. Up at 5, drive from York to the Boro, breakfast, 3 hours to Carlisle, back to Newcastle and a few stops in between. Then get the last train of the day NCL - MBR via DAR, drive back to York.
Way I see it is that in a few years time I'll not be able to do things like that so might as well make the most of it.