I recently changed the plugs on my 03 coupe to Iriduim IX NGK's. After about a week, the SES light came on and the engine began misfiring. Took it to my mechanic. He wasnt there, and so this new guy works on the car......tells me I have a bad ignition coil, P0300 code. He also tells me he has a spare from another VQ engine he just worked on.

He swaps the coils, and everything is fine for about 2 hours....then, on the highway, the car shuts off and will NOT turn back on. I have the car towed back, and notice the ignition fuse it burned out.

Take it to a specialist who tells me I may have a bad timing circuit board, and code P0300, which makes him suspect another coil, injector, and possibly a couple of sensors. I left it with him to do the motor teardown and see whats wrong.

Yikes. Anybody have any ideas of what might be bad? I dont know what to do. The car only runs rough at idle, all power seems to be there, but it stumbles badly at idle with the SES on......any guidance would be great.....thanks.

 

Update: the 2nd mechanic gave the car back....he says that the electronic signals governing the entire left cylinder bank are running with a very low current compared to the right cylinder bank. He says he now thinks that the wiring on pin 6 (which is slightly exposed) grounded against the chassis ground and shorted out ECU terminal #66, which controls the sensor gound for the throttle position sensor at idle. He suggested swapping out ecu's.

Yesterday, went to the dealer, and the service manager confirmed pin 66 was burned out on the ECU as well as pin 67, which controls the ground circuit for the throttle body actuator at idle.

He also suggested an ECU swap and a new harness, because he cant probe for continuity on the harness itself because of the melting (according to him). The harness doesnt look bad, so I am going back to my main mechanic with this into to see if he can get the harness sorted out.....ECU may or may not work once this is done. I hope that does it.

Any ideas as to what could have done this???

On the plus side, the car runs better, only the idle is rough.

 

ECU price: $946......
Harness price: $1051.......

Plus labor (15 hours at $150)....what a ripoff!

 

Man that is expensive.. If I were you I would just inspect the harness and tape up any exposed wires and install the ECU yourself. I can't imagine that would take 15 hours..

 

I think I will let my mechanic open the harness and trace any exposed wires there.....maybe the harness is worth saving. As for the ECU, found a couple of spots that will rebuild it for me.....

 

Got the ECU rebuilt for $395 with a lifetime warranty at ECM Depot in Texas....waiting for it to get back. Found a short along the idle control solenoid on bank 1, that likely is what fried the ECU.

Ah well....looks like I'll be getting a 335i soon, this sh*t really changed my attitude about the car, and the bimmer is easy to modify anyway, lol!

 

I'm kind of in the same boat you are. I just replaced an ignition coil Thursday and the car started misfiring again yesterday... I hope it's not my ECU

 

Yeah I know.....the tech also find an unsecured main ground along the passenger side inner fender, which he said probably caused the ECU to malfunction over time.