hey just bought a donor car that has a completly standard motor it is auto (not for long) but want to get it running right to sell engine . it has the problem of when u get to 2500rpm under half load it seems to die -feels like an ignition or fuel cut -it will accelerate but just not under any real load -and will do it at any revs when put under load -it recently had a rebuilt motor put in and a new leading coil im wondering if could be something to do with that or a faulty hold button on the auto?-
any help would be much appreciated

 

Check the battery. If it doesn't put out enough voltage the fuel pump won't go into high speed.

 

It's in limp mode. No fuel or ignition advance unless the manifold is under vacuum. If you've got a boost gauge you can confirm.