Hard start when hot- leaking injector?

Perform leak-down test of fuel pressure; however, if the injector was weeping and bleeding down, you'd also see extra cranking on a cold start. The raw fuel smell is probably due to the extra cranking, not a leaking injector, but that's just guessing without data.

Check for DTCs (even hidden ones), look at your fuel trims, MAF flow rate and A/F & O2 sensor data. The hot start issue is probably due to the vacuum leak that every 173k mile car, especially BMW, is going to have; a cold start is open-loop with a purposefully enriched mixture and can mask an air leak, but a hot start would not see the same. If you disconnect the MAF before the hot-start, and the hot-start issue goes away, that is additional data pointing to an air leak.

All of the above diagnostics are free.

The IAC valve on an M54 is also a maintenance item, either cleaning or replacing.

no spare said:

Yeah, I figured that would be a likely solution. Any idea how these outfits "clean" the injectors? At $20/injector, there can't be much labor involved. I have a sonic cleaner at the shop and was thinking of soaking them in it for a bit...

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Replicate the no-start hot-start, and stop cranking the engine before it fires. Pull the plugs and look for the wet or rich-mixtured one. If an injector is weeping, you’ll see it.

Alternatively, pull all six injectors, but leave them connected to the rail. Place the set on a newspaper. Turn the key on and find the wet spot.

To clean them, step-up the tube from a spray can of carb/injector cleaner using rubber hose until you can attach the injector, and use a 9v battery to sporadically fire the injector. When it emits a clean spray pattern of cleaner, the injector is good. Just remember to cycle the injector, or you’ll burn it out.

Or, on your next fill-up, pour 6-8oz of Marvel Mystery oil into the fuel tank. It’ll safely clean and lubricate the fuel system and upper cylinder. I’be got some in my own 195k mile E83 tank right now, and do every oil change. With it running, listen with a stethoscope to each injector, noting the loud one(s).


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