E46 3&4 Misfires

[chrisefird]

Getting misfires on 3 & 4. Have done the following:

1. Checked coils
2. Checked plugs
3. Checked fuel pressure
4. Changed intake manifold gasket
5. Checked MAF

I'm thinking about picking up an ignition wiring harness from the pull a part for $15. If that doesn't work I'm out of ideas unless the DME isn't telling the coil to fire

[ross1]

Try swapping coils/injectors to other cylinders and see if the miss follows them.
If correct fueling and adequate spark* that leaves compression
*confirm signals from DME

[chrisefird]

Try swapping coils/injectors to other cylinders and see if the miss follows them.
If correct fueling and adequate spark* that leaves compression
*confirm signals from DME

Yeah swapped around coils and injectors and plugs. Stays on 3 and 4. Getting a No Ignition Spark code on 3 and 4 as well. Also pulled an ignition harness from the junkyard but the issue continues

[MarcoZandrini]

The coils (and injectors) get 12VDC as long as the ignition is in the run or start position. The DME provides the ground to fire the coils (and the injectors). The electronic component that momentarily provides the ground is called a complementary metal oxide substrate field effect transistor (MOSFET). Each coil (and injector) has its own MOSFET. If this coils aren’t firing I’d start by checking the harness with an ohm meter. Pull a coil’s connector, turn the ignition switch to run and see which pin has 12VDC. I don’t remember if there are 2 or 3 wires in the coil connector but one of them goes back to the MOSFET in the DME. Ohm out that wire. If the wires check out then the problem may be the MOSFETS. You’ll need to have an oscilloscope to see if the MOSFETs are bad. They are available at www.mouser.com.

[chrisefird]

The coils (and injectors) get 12VDC as long as the ignition is in the run or start position. The DME provides the ground to fire the coils (and the injectors). The electronic component that momentarily provides the ground is called a complementary metal oxide substrate field effect transistor (MOSFET). Each coil (and injector) has its own MOSFET. If this coils aren’t firing I’d start by checking the harness with an ohm meter. Pull a coil’s connector, turn the ignition switch to run and see which pin has 12VDC. I don’t remember if there are 2 or 3 wires in the coil connector but one of them goes back to the MOSFET in the DME. Ohm out that wire. If the wires check out then the problem may be the MOSFETS. You’ll need to have an oscilloscope to see if the MOSFETs are bad. They are available at www.mouser.com.

I picked up another harness from the pull a part but 3&4 still aren't firing so I might just send the DME off to get tested.

[MarcoZandrini]

See if you can find a shop with a portable oscilloscope. It will allow you to see the ground pulses coming from the DME.

Are you handy with a soldering iron? Open the DME cover and get the part numbers for the CMOSFETs. Order them from mouser. Alternatively, you can send it out for testing. If a CMOSFET is bad I’d have all of them replaced.

[chrisefird]

It was the DME. Acquired a new one that had the EWS deleted and the coils are firing now

[MarcoZandrini]

Great news!

[ross1]

It was the DME. Acquired a new one that had the EWS deleted and the coils are firing now

Glad you got it sorted.
Oil in the spark plug wells? Good "boots" on the coils? Either can kill coils and coil drivers in the DME.