4.4 BMW V8 won't start after "Booster" jump start.

Hello everyone, I would really appreciate your thoughts and help here please.
My 2002 L322 has always been a heavy consumer of batteries. I went to jump start it recently as it had a flat battery and have a battery charger with a booster starter function, which I have used without problems on other cars.
When I went to start the RR with the booster function on, the car initially started then appeared to run on only half it's cylinders before dying.
The 150 amp fuse in the booster had blown too.
The old battery could not hold a decent charge after 48 hours so I fitted yet another new battery.
Now when I try to start the car, I get the same rough running before it dies, but if I let go of the key when trying to start it, the key returns to the previous position but the car continues to try and start itself for a few more seconds.
Having read other threads it sounds like I have damaged an ECU or module. I fitted a used engine ECU with the same part number, but the condition prevails.
The last time I had a similar issue is when oil from a leaking rocker cover gasket filled the plug wells and caused a misfire.
No codes come up on my Autel code reader.
Many thanks, Philippe

Have you checked the new battery is fully charged?
What do you mean by battery booster, do you connect as if you're jumping off another car? What does the booster function do?

Hello and thank you for your answer. The new battery is fully charged. The booster function on the battery charger connects as if you are jumping off another car, but really spins the engine over quickly, far more so than jump starting.
What surprises me the most is that when I let go of the ignition key and it springs back to position 2 in the barrel, the starter motor is still turning the engine over for a few more seconds. When it does fire, it feels as if it is running on only half its cylinders and will die after 5-10 seconds. The car was running fine until I tried to "boost" start it...

The vehicle has a starting procedure it goes through, you don't need to keep the ign switch turned, you initiate the start then the key returns to position 2 while the vehicle continues to try and start,

If you blew a 150amp fuse in your booster, have you checked all the fuses and connections on the car. that's a big fuse to blow.

J

marjon said:

If you blew a 150amp fuse in your booster, have you checked all the fuses and connections on the car. that's a big fuse to blow.

J

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I think the fuses may be the least of his worries.

If there are no codes in the ecu it has to be a physical/mechanical problem the ecu doesn't monitor.

Which autel are you using?

When you put the ignition on can you hear the fuel pump in the tank?

Mark Piercy said:

When you put the ignition on can you hear the fuel pump in the tank?

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Hello Mark, thank you for your support. I don't think its the pump as the car will start then runs super rough as if its firing on only 4 or 5 cylinders. It has a LPG conversion with the air suspension pump relocated to the inner wing so when I turn on the ignition I hear the clatter of the air suspension pump over anything else! I disconnect the battery every time now so am not sure if the ecu is storing any codes. I'll recheck. However the "Booster" pack might well be a red herring. I've had issues in the past with the spark plug wells partially filling with oil. I have new rocker cover gaskets and seals gaskets, just haven't had time to fit them. Previously I have wicked the plug wells clean using an old toilet paper roll slit down the middle and then rolled up tightly and slipped over each plug...wait an hour and its all mopped up. The reason I mention this is because the car has been parked for months on a slight slope (see photo), left side down and maybe the oil has seeped into all of the plug wells on the left bank causing a misfire on a number of cylinders. I'll check at lunchtime and report back. I do remember a slight misfire when the car was last used too. I really hope this is the root of the issue.

Nice mini garden .
My old omega 2.0i used to weep into the plug ways as well. Oil being an insulator also shorts the buggers out.. Quite possibly just oil contamination.. Now get those bloody gaskets sorted!!!