Its a 1998 528i bmw that will start but wont stay running also there is a loud kind of backfire noise from one of the cylinders . the engine wont rev up proper even though i keep pressing the throttle and eventually just dies until i start it again .

Could you give me a more detailed description of what kind of noise it is? Is it a bang like a gun? A thump or 'clonk'? Or a machine gun like rattle? Is it as you turn the key or after the car has started? These details can help work out where the problem is.

The lifter rod is out or you cracked your piston mine did the very same

any time an engine that was taken apart and put back together backfires, the first thing to do is double or triple-check the timing.

Engines runs for a couple of seconds then loudly backfires with a flash of flame out of the exhaust followed by a plume of black smoke. Then runs sort of ok for a couple of seconds then repeats the backfire again AmanStino Lightning Cable Apple MFi Certified 1M Nylon Braided Charging...

How is the oil level in the engine? Have you actually checked that? Also, what kind of oil (and what weight) are you running in the engine, and how many miles are on the car? You may be running oil that is too thin for the amount of wear on the engine parts! oil leaks cause low oil levels!

I had the same problem. My car sat for a few days and when i went to start it i heard an extremely loud pop (kind of like a backfire). After that it would start and sound fine, but die 2 seconds later. Thank god my bf is a mechanic he knew instantly that the pcv valve hose that connects to the intake manifold unplugged itself. He plugged it back in and it runs fine now. I didnt however get a check engine light, but i only tried to start it twice before he fixed it because i was scared it jumped time.

I think your problem is injectors not firing, and is linked to the Powertrain Control Module. Disconnect the battery for 30 minutes to reset the PCM. Reconnect the battery and try to start the car. If it still doesn't start, pull a spark plug and see if the tip of the plug is wet with fuel. If it is dry, then you are not getting fuel to the cylinders. If you have fuel pressure and spark, but noe fuel in the cylinders, it has to be computer related.

this is a very common issue with any of the bmws with n52 and n52k engine,as long as oil level is ok and is being changed regularly than than a "blleding proceedure" may solve this problem, when the engine has been running long enough that it is hot run the engine at idle to 4500 rpm for 10 to 12 min to start, if is still present after this attempt again.It has been said that this could take up to 30 min at longest.The reason for the ticking noise is a very tiny air gap in the hva and or lifters, try this and if does not work than the lifters should be replaced, although this noise doesnt really hinder the performance it does take away from driving such a nice car and having a loud noise come from the engine, good luck

sounds like eithor you blew a cylinder or a head gasket might have been a spark plug blow out
look under your hood when the car is running you will see the problem if it is one of theise

other wise 1 plug might have craped and the raw fuel was dumped down the exhaust and you got a backfire

If you've never replaced the timing belt or chain,That would be my first thing I'd check is the Timing belt or chai, just aline the timing marks on crankshaft and then look at the position on the distributor to see if it's pointed in the #1 firing position .