[zhengbob]

I bought a 2009 e93 335i from Facebook, the seller has stage1+ tune on it.

Randomly, it has multiple cylinders misfire at cold start, the car shake a bit due to the misfire. But the engine is perfectly fine after warm up.

Wonder if this misfire is due to the stage1+ tune.

Anyone has some idea?

[GSB]

There are many possible causes, but the one I'd suspect first, is oil fouling from the terrible PCV system. Direct-injection engines like the 335i suffer chronic oil fouling of the intake ports, valves and spark-plugs. My valves were so badly caked that airflow was impeded, causing spluttering misfires and hesitation at low RPM. My intake valves and ports have needed to be thoroughly cleaned - twice.

Another source of trouble, is the valve cover gasket leaking oil into spark-plugs and ignition coils.

Another potential issue, is a weakening battery. It may have enough capacity to crank, but low battery voltage causes failures with fuel injectors, ignition coils, oxygen sensors, and many others.

[Gizm0]

Leaking injectors is the most probable cause for misfire on cold starts. Monitor the fuel pressure (on the high side, it should be around 750psi) when the key is in accessory mode, if it drops quickly to zero, you have a leaky injector.

[lowrydr310]

Originally Posted by zhengbob

I bought a 2009 e93 335i from Facebook, the seller has stage1+ tune on it.

Randomly, it has multiple cylinders misfire at cold start, the car shake a bit due to the misfire. But the engine is perfectly fine after warm up.

Wonder if this misfire is due to the stage1+ tune.

Anyone has some idea?

Misfire most likely isn't caused by the tune, but it wouldn't hurt to flash back to stock while you're diagnosing the issue.

As others have already said, first things to check are plugs, injectors, and coils.

[zhengbob]

Originally Posted by Gizm0

Leaking injectors is the most probable cause for misfire on cold starts. Monitor the fuel pressure (on the high side, it should be around 750psi) when the key is in accessory mode, if it drops quickly to zero, you have a leaky injector.

leaking injectors will be a $1500 nightmare.
Will check the HPFP pressure as suggested. The seller listed index 11 injectors it has, also new Dalian coils and 1 step colder NGK spark plugs.

I also checked the valve cover, it has a pretty nicely fitted aluminum valve cover, I see no oil leak around the mating surface.

Currently I am more inclined to injector leak theory - the cold start misfire only happens if the car is parked in garage over night, but never happened during the day when I started the car after work, which the car sits less hours than over night.

Will tear down the engine cover in summer time, will check thoroughly by then.

[lowrydr310]

After driving and letting your car sit overnight, you can remove the plugs from the cylinders that are misfiring. If they're wet with fuel then you know for sure you have a leaky injector. If you do have a suspect leaky injector, I wouldn't recommend waiting too long. If the leaks are severe enough fuel can leak into the cylinder past the rings and accumulate in the crankcase diluting the oil. A $300-400 injector isuch cheaper than replacing a crankshaft because of a spin rod bearing. Not trying to scare you, but something to be aware of.

It's my understanding that colder plugs are not needed with just one of the standard off the shelf "Stage 1+" tunes and might be worse.

What coils are you running? Is that a typo? I never heard of those. Most folks run Bosch, Delphi, or Eldor.

[Cloverdale]

Plug access only requires coil removal.

[zhengbob]

Originally Posted by lowrydr310

After driving and letting your car sit overnight, you can remove the plugs from the cylinders that are misfiring. If they're wet with fuel then you know for sure you have a leaky injector. If you do have a suspect leaky injector, I wouldn't recommend waiting too long. If the leaks are severe enough fuel can leak into the cylinder past the rings and accumulate in the crankcase diluting the oil. A $300-400 injector isuch cheaper than replacing a crankshaft because of a spin rod bearing. Not trying to scare you, but something to be aware of.

It's my understanding that colder plugs are not needed with just one of the standard off the shelf "Stage 1+" tunes and might be worse.

What coils are you running? Is that a typo? I never heard of those. Most folks run Bosch, Delphi, or Eldor.

Here is the screenshot of seller's post with all mods. It says 'Dinan coils'.

[lowrydr310]

Dinan coils are good.