43167-43170 were used as test beds for engine trials, first up were Mirrlees Blackstone MB190 engines which were not successful (anybody seen the picture of all 4 lined up at Bristol St Phillips Marsh), the next engine tried was the VP185. These proved much better and Great Western (before First bought them out) started to fit them to a lot of the fleet, 43173 was fitted about 3 weeks before its crash at Ladbroke Grove and it was removed for re-use). 43167 was then transferred to GNER and after awhile had the VP185 replaced with a Valenta to standardise the fleet. Midland Mainline then started to fit the VP185 to their power-cars.
First Great Western then decided to try another engine, the MTU, and fitted them throughout the fleet, the VP185s removed were taken on by East Midland Trains for their fleet and now all their power-cars have the VP185. GNER then decided to fit the MTU to their fleet as well.
43167 has had- Valenta, MB190, VP185, Valenta and MTU engines fitted.