N54 ZERO PSI cyl 3 :(

inline6xi

Lurker
Apr 30, 2019
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2008 BMW 535xi
Hey guys, I'm a bit baffled regarding the current state of my N54. I'm reading 0 psi in cylinder 3, and I mean you would think the gauge is stuck. Not even the slightest flutter. I checked the adjacent cylinders and cylinder 1 as a benchmark, and they were all normal, within 2psi of each other.

The strange thing is that I took it out for a nice little drive, nothing crazy I don't go super hard with it, and parked it in the garage, all good. Logs look good. Next time I go to start it- it's stumbling, running like **** and wants to die. throws misfire cylinder 3. Now at this point since it ran so well literally the last time I drove it I'm thinking it's got to be a leaky injector that finally went to ****, a mosfet or some sort of ignition problem. I troubleshot all of those things first, systematically finding they weren't the culprit. Coils good, plugs good. I even have msd81 and I checked mosfets (I know I'm an idiot msd81 doesn't have the same mosfet problem).

So even though it seems unlikely to be something mechanical inside the engine i figure I should do a compression test.

0 psi cyl 3.

No oil in coolant, however I haven't drained oil yet to look for coolant in oil. I confirmed the piston is moving inside the cylinder.

Car is basically fbo, pure stage 2, however I only run about 18-20 psi max with e30. I've been holding off on going more boost until I upgrade fuel pump. What the heck.

I guess next thing would be to do leakdown test and my friend is gonna let me use his fancy snapon inspection scope. Bummer.

Any guesses or similar experiences?
 

inline6xi

Lurker
Apr 30, 2019
11
1
0
Ride
2008 BMW 535xi
0 psi is suspiciously low. Like someone removed the piston low.

Broken valve?

Right??? I made a rig to test my compression tester.

Valve issue is what I'm leaning towards. But still bizarre how I park it one day and no big deal, then go to cold start and all hell breaks loose. Must be a problem that is accentuated with cool engine temp.

Going to pick up the snap on scope tonight.