M54 Engine Lost Compression on Cylinder 6

[Auto Parts Guy]

Well I guess it was a good run.
Driving up to the Gem Mining place in Hendersonville NC today and the engine lost power and had a misfire on #6. Limped back home on 5 cylinders, swapped coil packs, spark plugs, no change.

Hooked the compression gauge up and only have about 12-15psi on cyl#6. For comparison, cylinder 2 had about 138psi.

So I guess the rings went, hole in piston, or an exhaust/intake valve burnt. Thoughts?

[80stech]

If you are curious get a cheap borescope and have a look.

[X5chemist]

Ouch. You can bring it to TDC. Blow low air flow into the cylinder. Does air come out the exhaust or intake side? Removing the valve cover might give a clue. A bore scope camera is ideal. No coolant in the cylinder is a good sign.

[Auto Parts Guy]

I'm going to borrow a friend's boroscope and look in there. It sucks for sure. No coolant or overheating issues or any other indications which was the odd thing. I for sure thought the trans would go first. She's right at 215,560 miles.

[BimmerBreaker]

I wouldn't spend too much time poking around now. The engine needs to come out, get it out and take a look when it's out ... everything is much easier that way. M54's are cheap. Find a good one and plop it back in. You can use ANY M54 - you'd want to keep it 3.0L due to the weight of the X5. But you can use a RWD variant and just bolt your oil pan and accessories onto it.

[Auto Parts Guy]

I've got a boroscope on the charger now so I'll know something shortly hopefully. I haven't accepted the fact that she's gone yet �� and I'm not committed to the work involved yet either.

I do have a complete S52 engine in my shop from a prior e36 M3. Any chances that could work???

[BimmerBreaker]

You can run the S52 on the MS43 engine management with a few tweaks. You need to know a good tuner for that though - I know someone who can help with this if needed.

If your X5 is MS45, you may need to convert to MS43, not completely positive, I'll talk to him (converting to MS43 is very simple anyways).

[cn90]

You need to do dry and wet compression test on #6.

If P still low with wet, then chances are burned exhaust valve.

[Auto Parts Guy]

Originally Posted by BimmerBreaker

You can run the S52 on the MS43 engine management with a few tweaks. You need to know a good tuner for that though - I know someone who can help with this if needed.

If your X5 is MS45, you may need to convert to MS43, not completely positive, I'll talk to him (converting to MS43 is very simple anyways).

That would be good to know! I would love to have a 420G in there too. At this point I'm weighing my options. Pretty sure it's MS43. That's the selection I use on my code reader. I have the S52 harness still on the engine and I think I have the ECU still. And all else is in tact. Luckily I have other vehicles to drive so I don't need a DD replacement immediately. But this X5 has been my DD for many years now..


So on to the boroscope. Not much luck there. Couldn't see much more than my cell phone would take. Once I got into the cylinder it was a dark hole. I poured a few ounces of marvel mystery oil in the cylinder and going to let it sit overnight. At this point it can't hurt. I'll put the plug back in and crank her up when I get home from work tomorrow.

[BimmerBreaker]

You could do a 420G, but you'd lose the AWD.

I just checked and it looks like E53 got MS43 until the end of production so that's good if you wanted to S52 swap it.

You would not use S52 engine harness or DME to swap into the X5. You would use the M54 engine harness on the S52, and the MS43 DME. If you've done it before it's a weekend project. If you've never done it before it will take a bit longer.