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I have a cylinder 3 misfire code changed the plug and coil. Still misfiring when cold sometimes it doesn’t. When it’s warmed up it runs perfect. I believe it’s a fuel injector. Is there a way to test fuel injector before I replace it?
 

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Best (or at least cheapest) way to test is to pull the injector rail and swap the #3 injector for a neighbor and see if the misfire follows or not.

Depending on the type of engine (can't tell...) it can be other things as well.
 

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To aid trouble shooting you need a BMW specific scan tool. There are many to choose from. If you have an Android phone I recommend Protool from Bimmer Geeks which will work with any k+d enabled OBD2 cable to USB connection. It's comprehensive and easy to use.

There are the INPA and ISTA tools available for free but you will need a cable as well as a laptop to install the software on. Quite a steep learning curve as well but very powerful.

Otherwise, you are just throwing money at the car, hoping to fix it.

If it turns out to be the injector, the replacement will have to be coded to the car based on the existing one's parameters. You will need a software tool to do that.
 

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You can code injectors with the Foxwell NT520 - I've done it. Worked well when I had to put a used injector in place of one that leaked.

To test for injector leaks, pull spark plugs on a cold engine. You'll see fuel or at least worse fouling on the one that has the leaking injector. And if you drop a hose into the cylinder head you'll smell gas when you give it a good sniff.
 

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I'd pull all the plugs and compare them. Cold engine.

My car has a mix of index 5 and 9. I got a used index 9 from a guy who'd replaced his with index 12. I got the tool to R&R the injectors and seals. New teflon rings and damper seals fitted.

That was 4 years ago and it's still working perfectly. Cost of tools and the Foxwell was less than what I'd have paid a pro, and I've used the tools on a friend's N63 to do similar work.
 
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