e90 328i n52 sometimes not getting injector pulse

[markstaa]

2007 328i I am having an issue where the injector on cylinder 1 is not getting power or pulse sometimes.

Here's the full story. She starts up fine, no codes or service engine soon light. Drive around, works fine. Let it sit at idle for a while, it starts dropping rpm suddenly then revving up past and then back down to ~600 rpm every 10 seconds or so.

If I step on it, the service engine soon light comes on and there's a misfire on cylinder 1 and it continues misfiring on cylinder 1 even when I pull over and park it and let it sit at idle for a while. Can feel shaking consistently. I open up the hood and stethoscope injector 1 and its not clicking. I check if it's getting power compared to ground on the block and its not getting power.

I turn off the engine take the key out, immediately put it back in and start the engine and no misfire, no service engine soon light, injectors clicking and going fine. I drive around a little bit, then step on it and get misfire again and injector #1 has stopped.

Is this something programmed in the DME to stop sending the pulse to an injector under a certain condition? It seems weird that it seems to fix itself when power cycling it. It's also weird that it works intermittently at idle after a while.

Anybody have any ideas?

[White94RX]

The DME stops firing the injector when it detects a misfire. This is to prevent raw fuel from washing down the cylinder walls, and damaging the catalytic converter.

The injector and DME is not likely your problem. What's more likely is a failing ignition coil. If they're original, you're long overdue to have them replaced with the upgraded Delphi coils.

[JDStrickland]

You're describing something with the ECU.

Before you do anything else, turn the engine off and on again, no wait -- just off then on -- and see if the trouble clears up. If yes, then you have isolated the ECU about 90%. I don't know what's happening, but this is the sort of thing that can come from faulty programming, and they (you) might be able to cure it by flashing new firmware into it.

[White94RX]

First, it's not an ECU, it's a DME. I'm not sure where you're getting your info from. Turning the engine off and back on, that doesn't isolate the DME. Stopping the engine, and restarting it can eliminate a misfire if the coil is failing intermittently. When you turn the engine off and back on, the DME will once again try to fire that cylinder. It will continue firing that cylinder until it misfires again. And when it does, it will stop pulsing that injector. Exactly as the original poster has described.

In my 15 years of repairing BMW's professionally, I have replaced maybe a handful of DME's. 99.9% of the time, it's not the DME. Start with the basics. Don't condone the DME unless you've eliminated everything else as a possibility.