Misfire, Running Lean --> how should I prioritize the following steps to take?

[MichaelWilkens]

Hello all and thanks for clicking...

BACKGROUND INFO
Just bought the '02 325Ci for dirt cheap. 162k miles. Going to work my magic... (which means ask you guys for help).

Codes:
P1349 – Misfire cylinder 4 with fuel cut-off
P1347 – Misfire cylinder 3 with fuel cut-off
P1345 – Misfire cylinder 2 with fuel cut-off
P0300 – Random misfire detected
P0174 – Lean conditions detected

It is misfiring, and its lean...

I have ruled out coil packs. . Cylinders 1, 5 and 6 are not missing. Switched coils with with 2, 3 and 4. Same misfire codes on cylinders 2, 3 and 4. Not the coils. Also the engine drops revs upon unplug of every single one.

I have replaced all spark plugs with the NGK manufacturer recommended part.

I have installed a new DISA valve. The original wasn't holding vacuum with my finger over the hole and was snapping open.

I performed a cylinder compression test with engine warm, throttle open and fuel pump unplugged. Here are the results:

Cylinder	Psi
1	116
2	95
3	90
4	110
5	150
6	165

Not great but not extremely horrible.

Here are the next things I was going to do. Please response with the order in which you would do them.

NEXT STEPS:

a) Check the fuel injectors
b) Check the CCV
c) Valve cover gasket
d) Fuel filter
e) Test fuel pump
f) Smoke the intake system to check for leaks
g) Camshaft position sensor
h) O2 sensors
i) Timing

I was thinking d-e-b-a-f-h-c-g-i

[MarcoZandrini]

Those compression numbers are pretty bad. A 10% variance between the high and the low results is fine. Notice that the misfires correspond to the cylinders with the low compression numbers. So, my first question is how much time and money do you want to put into the car?

Low compression is usually caused by worn compression rings. Now, on the off chance that those cylinders’ rings are gunned up you could try a 24 hour piston soak using a top end cleaner such as the GM Top End cleaner, if it’s available. What’s the condition of the rest of the car?

[jclausen]

Squirt oil in the bad clyinders and see if the numbers go up, ring problem, check the fuel pressure, I've seen those faults so up with low fuel pressures. Had the car been sitting for awhile?

[Muzz258]

Smoke test the intake as a first step and get rid of the lean codes. The misfires may be sorted as well if they are the result of the lean condition.

If you don't have a smoke tester then check your fuel trims with the scanner. With a warm engine at idle, look at the fuel trims. If any are >8% then you have a vacuum leak to find.

[MichaelWilkens]

I did the oil-in-cylinder test. It was funny when I started the car afterwards and crazy amounts of blue smoke came out, probably pissed off some neighbors. Check out the results:

Cylinder --- Dry test (psi) --- After dropping oil in (psi)
1 --- 116 --- 145
2 --- 95 ---- 110
3 --- 90 ---- 115
4 --- 110 --- 120
5 --- 150 --- No test performed
6 --- 165 --- No test performed

Well, they all went up, however notice that even with the higher numbers, cylinders 2 and 3 are still lower than the others.

I am also losing coolant. So, dear bimmer gurus, could this be a bad head gasket around cylinders 2, 3 and 4?

I am still working towards the easier fixes. Could be a fuel delivery problem, or unmetered air is entering the system.

Today I removed all the injectors and tested the resistance, it came up as 1 ohm across the board. Then I made an injector cleaner setup like my man here recommended: https://www.youtube.com/watch?v=8rk0tKtiVic which cleaned them out nicely.

Since cylinders 2, 3 and 4 are my misfires, I moved around the injectors to see if the misfire follows (#1 to #2, #3 to #5, and #4 to #6). I'll start it up tomorrow and record the DTC's.

Next steps in fuel testing is testing the fuel pump and getting a new fuel filter. But it's probably not the fuel delivery, more likely from what I've read is the unmetered air entering the system.

Tomorrow I will remove and clean the idle control valve. I will report back.

[MichaelWilkens]

Those compression numbers are pretty bad. A 10% variance between the high and the low results is fine. Notice that the misfires correspond to the cylinders with the low compression numbers. So, my first question is how much time and money do you want to put into the car?

Low compression is usually caused by worn compression rings. Now, on the off chance that those cylinders’ rings are gunned up you could try a 24 hour piston soak using a top end cleaner such as the GM Top End cleaner, if it’s available. What’s the condition of the rest of the car?

Time is not a factor really, but money is. I can't pull the engine (I live in an apartment complex) but can do pretty much everything else.

I have the piston soak on my list of to do's, but it's pretty low on the list. Maybe that's because I don't understand how cleaning combustion build up would improve compression.

The rest of the car is pretty solid, good brakes, suspension, body, convertible top, interior is decent, tires good.

[MichaelWilkens]

Smoke test the intake as a first step and get rid of the lean codes. The misfires may be sorted as well if they are the result of the lean condition.

If you don't have a smoke tester then check your fuel trims with the scanner. With a warm engine at idle, look at the fuel trims. If any are >8% then you have a vacuum leak to find.

Should I smoke it like this dude? https://www.youtube.com/watch?v=GOhl4r0GSiE

He mentioned opening the throttle... not sure how to do that on the m54.

[MarcoZandrini]

The M54 is throttle by wire. That is, the gas pedal’s position is constantly read by the DME and the DME controls the throttle body. When smoke testing via the upper intake hose the smoke goes through the idle control valve. It’s open.

[MichaelWilkens]

The M54 is throttle by wire. That is, the gas pedal’s position is constantly read by the DME and the DME controls the throttle body. When smoke testing via the upper intake hose the smoke goes through the idle control valve. It’s open.

Ok cool, so I'll clean the ICV and then smoke it. I'll report back.

[MichaelWilkens]

So the ICV was cleaned, the gas pressure was tested, and the DISA valve has been replaced, no improvement. I smoked the engine and it held pressure and did not come out of any obvious areas.

I think MarcoZandrini is right, it's a compression problem. I will probably tear down the engine. My question is, would a head gasket job make this problem better enough to drive the car?