Chasing a mystery

[phr0stByte]

I am scratching my head.
I am getting codes P0174 and P0305 and have a rough idle.

I have replaced:

• plugs
• coils
• injectors
• O2 pre-cat sensors
• MAF
• Secondary MAF

Did a smoke test and fixed all the vacuum leaks and no longer releases any smoke during a smoke test.

Seafoamed the cylinder

Compression is solid at 167 on cylinder 5, while the rest are around 165-170

Short Term fuel trim for Bank 1 is 0, while fuel trim for Bank 2 is ~26% until a misfire code is stored at which point it goes to zero

Fuel rail pressure is solid at 50psi with key-on or running down the road

Runs the same with or without MAF hooked up (except for the tranny going into failsafe mode while detached)

I'd appreciate any thoughts you have on what may be going on here.

[andrewwynn]

Adding fuel like crazy on bank 2 only suggests O₂ out of whack or injector not putting out.

You said you removed cleaned replaced injectors? Did you swap locations? I would swap 5 and 2 (center each bank).

What scanner are you using? Can you watch the smooth running live data to see what's going on with 5 before it's cut off?

Front O₂ are identical you can swap those. For some tests you can swap the connectors just mark correct position to get them back when done.

If the O₂ is reporting the wrong air mix you should quickly see the fuel trim go max on "bank one" if you swap the pre cat sensors or connectors.

Is there oil on the O₂ wiring? O₂ sensors get their atmospheric O₂ reference through the cable going in and head cover leak can easily get enough oil on the wiring to throw off the reading.

The DME is convinced the engine is lean and is adding tons of fuel.

If it adds enough fuel it will misfire. Maybe the center cylinder has an easier path to suck in that too rich fuel mix so it gets the misfire.

I didn't know about the 26% when I suggested CKP. Def need to solve that bank crazy lean first.

I would swap the pre cat connectors and if the error moves to bank one means O₂ bank two is defective.

To confirm unless it's also covered in oil I'd swap the two pre cat O₂ put the connectors back and see if the lean follows to bank one.

The good news is you have an extreme case of repeatable error you will find the source.

[X5chemist]

What is the rear O2 sensor reading? Is it steady or follow B201? When you pulled the plugs, what did #5 look like? What brand of spark plugs did you put it?

[80stech]

It sounds like there is some history like you are coming from another forum? Your first post ? and you don't have anything listed about the vehicle??

Compression is solid at 167 on cylinder 5, while the rest are around 165-170

What the heck ??
Seafoamed the cylinder ??
I imagine fuel pressure is 50 PSI engine running and not with just key on ??
Get something that can scan BMW specific codes and post the descriptions.

[phr0stByte]

Sorry about the lack of other info, this forum gets a lot more traffic and has been where I have lurked unregistered for several years. One of the FB groups is where I had been posting.

2005 E53 3.0L

I have both ISTA and INPA and their readings are the same. lean on bank 2, misfire on 5 with no other real information.

The smooth running values are in the 0-3 range for all other cylinders with 5 being at 7.8 - 8.9 with A/C off.

Plug #5 doesn't show much in the way of oil, rather clearly getting too much gasoline.

Plugs are NGK

The O2 sensor wires are pristine (brand new) and I will have to watch the voltages again as replacing the old ones was one of the first things I did.

Edit - Just realized there may be PEBCAK on the fuel pressure readings.. going to redo those.

[80stech]

Concentrate on the mis first. There is going to be gas on the plug of the cylinder that isn't firing properly so don't let that bamboozle you into thinking that excessive fuel on one cylinder is the problem. Maybe redo the compression test and do 4 compression strokes instead of the 10 seconds or whatever. Does number 5 seem to run for a while after the codes are cleared before it starts to mis again?? Any black smoke ?

As far as fuel pressure, the gauge needle should shoot up quickly when pump starts with key on then drop a chunk when the fuel pump stops after a few seconds. If it rises slowly or doesn't drop when pump shuts off then you don't have a good connection to the rail. After that check that the rail holds pressure. with the pump off.

[phr0stByte]

The pressure on the rail dropped from 50 to maybe 46 and then it held. With the car running it is at 50 idling and under load after re-testing.

[80stech]

Perfect

[phr0stByte]

Not sure what you imply with perfect?

As for frequency, if the engine is at idle, it will run for a bit, up to 3-5 minutes at times, before misfiring. under load, it is almost immediate.

No black smoke.

I actually removed the valve core from the fuel rail for the second test to ensure there was no restriction, It still held 50 at key-on with a slight drop to 46 and then back to 50 while running at idle and under load.

[phr0stByte]

Here are readings from ISTA on O2 sensors and smooth-running. both of these are with the misfire cleared.