M54 Engine Lost Compression on Cylinder 6
 

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?

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

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.

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.

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.

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???

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).

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

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

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.

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.

I've done a few swaps but never an M54 to S52. Is it pretty much bolt up?? Besides having to swap the oil pans etc.

Physical fitment wise the S52 will bolt in identically to the M54. Use the engine mount arms, oil pan, etc - everything from the M54 on the S52 including all accessories. It all bolts up, the engine will then bolt up to the chassis.

I am betting you have a burnt or chipped valve....I have seen a few on M54's...although that usually results in zero compression.

Oil gets in through the CCV over time and eventually burns up the exhaust valve. At least that is the theory...

Regardless, if it is something in the cylinder head, I would slap a good used head on there and put it back in service. The M54-equipped E53 X5 takes a cylinder head or head gasket pretty well. The car stays on its wheels the whole time, and you have good access.

Alright, after some marvel mystery oil in cylinder 6 soaking overnight, no change. Pretty much confirmed the engine is toast. I never saw it coming.. no clue what happened. No warning.
Compression numbers as of yesterday...
Cylinder #1: 168psi
Cylinder #2: 145psi
Cylinder #3: 147psi
Cylinder #4: 100psi
Cylinder #5: 168psi
Cylinder #6: 12psi

So pull the head off.

Three different age coil packs? The spark plugs show some serious ceramic burn through. I think most engines don't get enough rear cylinder cooling. Ram's diesels are notorious for it. Same I6 design.

On the M52TU and M54 the cold coolant flows to the rear of the engine first, then flows forwards to cool the other cylinders. 6 receives the coldest coolant

Have you checked the DISA valve for missing pin?

Yes I have replaced a couple of the coil packs over the years of ownership as needed. But never replaced all. My conclusion was, they either work or they don't. Cylinders 1-5 plugs look very similar, #6 is darker. 1-6 from left to right.

I have not checked the DISA valve for a missing pin. Can you elaborate?

Very interesting on the DISA valve. I had it off when I did the plastic coolant pipe under the intake manifold earlier this year and it seemed to work and seal properly then. I'll see if I can get it off and apart today and report back.

I couldn't wait. DISA valve looks ok and seems to function, doesn't look like any parts have broken off. It's just dirty.

Is it feasible to pull the engine without the oil pan? In other words, could I essentially leave the cv axles and oil pan in place and just pull the engine? Or am I wishful thinking?

I'm not excited or convinced to swap engines yet...

I would take off the valve cover next. Try to find a cause before pulling the head off.

I don't really see a big obstacle on lifting up the engine. Well, maybe a good rear point for lifting. Definitely a two man job this way though. I've pulled engines by myself. However, none were a cradle book removal type.

Would a bore scope go all way down to the valves through the intake?

Think I would see anything with the VC removed? I could see the valves with the intake off but I need to commit before I remove that. Plus I guess the intake has to come off before the engine can be pulled anyway.

Maybe I'll do a compression test on the S52 engine before I do anything to the X5.

I'm reluctant to pull only the head in case the rings let loose.

Ive never seen a single documented case of an M54 ingesting a DISA pin. If you look at how it's assembled and installed it's clear it's not possible. The only people that claim this can happen are people that sell DISA upgrade kits.


You could pull the engine with the oil pan left behind. I wouldn't, it's going to add a lot of complexity to reinstallation and a little to removal as well

The amount of time spent thinking about it and checking other random things at this point could have just gotten the engine out. It's about a 5-6 hour job. Faster if you have a lift. Hardest part on an X5 is getting it over the radiator core support due to how deep in the engine bay it is. With a lift you drop the subframe and lift the car up over the engine/subframe assembly (the inverse of how they are installed at the factory)

I wonder how many people suggesting you remove just the head have actually removed and reinstalled an M54 head before.

It seems easier to just remove the head because it's only removing "one part" but in reality I think it will take more time and end up being more complicated compared to pulling the engine. Having the engine out will also give you a chance to re-seal the rest of it for new gaskets all around to end up with a nicely refreshed engine.

I have a lift and have considered dropping the engine that way. At the factory, it's literally the entire drivetrain though, rear axle (brakes diff etc) to front axle with engine trans and t-case, along with radiator.

In my case, if I were to drop the engine from the bottom, what would you drop and what would stay with the body?

I would drop with transmission but separate the driveshafts so it's just the front cradle you drop. Engine, transmission, front diff will come out. Then split the trans and if you want to remove oil pan you can do that, with the subframe dropped you have good access to make reinstallation easier.

With a lift it's a few hour job, just a little longer if you've never done it before and really take your time.

So basically, transfer case, transmission, engine, and entire front subframe with steering gear front struts/brakes etc would drop, the rest would go up with the car body?

I'll need to remove exhaust, drive shafts, AC compressor, steering shaft from gear, wires/harness connections, transmission cooling lines, radiator connections, oil cooler lines, etc.

Alright guys, sad times here. I have made the decision to part out my X5. No one local wants to buy it on FB, even for $1000. I sold the hood, tailgate and steering wheel yesterday.. so officially it's the beginning of the end.

I'll be listing a JL Audio Stealthbox on eBay (contact me asap 😉) and probably a few other parts that can help me recoup some of my costs over the last 5-6 years. It is actually an interesting feeling pulling parts off of the car you've put so much time and parts into over the years, then to hand them off to a stranger for a fraction of what it cost you. Similar feeling when I watched the kid drive off in my e36 M3 that I 6 speed swapped. But you can't keep everything and I have too much stuff and not enough hours in the day for it all.

My suburban gets a solid 10-11 MPGs but can haul anything you attach it to 😂. I have my e39 M5 and my wife's 07 X3 M-Sport left as far as BMWs go.

Thank you all for the advice and recommendations and information from this site and I hope my previous posts help someone in the future.

Sorry to hear - Did you ever figure out what caused the loss of compression in cylinder 6?

I did not. For it to still have some compression (12psi) I would guess the rings went. It sucks. The guys that bought the hood and stuff had a nice titanium Silver 6 speed! So at least some of the parts went to a good donor.

I am not disagreeing with the recommendation of swapping the whole engine here.

But I was one of the people suggesting OP remove the head in this situation, and I still think it was also a reasonable way to go, particularly if OP does not have a lift (not sure if that is the case).

I don't have a lift, but I have done in-car M54 head replacements about six times...E46, E39 and twice on E53's... There is really good access on an E53... I have also done a couple of engine replacements.

I've got a lift but man that's a lot of work with no guarantee that I'll be able to salvage the engine. And to do it on a vehicle that has 214k miles and very little value to most and still wouldn't pull a camper was kind of the reason I decided to part ways. Just replacing those plastic coolant lines under the intake was a PITA (intake removal was the PITA part) that I didn't want to do again, much less removing the head. It basically came down to time and end result and value for the money for me. Hopefully I can get some of my money back with a high level part out.