engine starts then stops with a thud!

[frank galager]

Hello, ok so heres the score! Just put a new engine an transmition in my 8v gti, No real issues, started first time an ran really well. I then stopped the car to fit the battery, restarted it an now it either just turns over an wont start or starts then after a second or two stops with a thud! Sounds  really bad! tHE immobilizer is playing up but my thinking is that if it was that it either wouldn't turn over at all. An even if it was for some reason kicking in after it had started it would just idle down not stop suddenly. Is that correct? The only other thing is that the down pipe gasket isn't fitted correctly yet just left the old one in to test the engine while i wait for the part, so its not got a good seal there, would that cause this fault? I am Vexed! Any ideas?

[Wayne]

It will not be the immob, sounds more like a mechanical problem, timing maybe

[Jasikasisback]

yeah disconnecting the battery shouldn't have anything to do with the immobiliser as the transponder in the key is the boss there...

[Rmachines]

Sounds like timing,  Its it going with a Thud/pop and an abrupt stop?   Mixed up HT Leads will do that, or timing belt slipped on the intermediate shaft...(unlikely to do that without slipping the camshaft though lol)

Check firing order, and check timing belt condition and timing marks just incase, double check dizzy is all lined up.

[frank galager]

Yeah was a mixed up HT lead, feel proper stupid now lol. cheers though guys.