DME Repair ???

[E39MGirl]

Hi Chris,

In normal running valves 'ramp up' and 'ramp down'. Modern low inertia valve trains keep a very tight control on acceleration and deceleration rates with very carefully designed cam lobe profiles and base circle diameters, and initial lift and the final runout to seating is comparatively slow when compared to peak rates. Valves spend much of the percentage of the 100% total of their cycle at comparatively low ramp rates and low lift, plenty of time for the build up of carbon.

If the deceleration rate isn't controlled appropriately you end up with 'valve bounce' or float. Remember valve bounce from the good old days of pushrods and heavy pressed steel rockers? What fun it was to rev those old engines until they 'hit the wall', well, until you bent a valve or the big bang happened!

When you tap valves with the hammer there is no controlled deceleration - they are basically behaving like 'poppet valves' and being snapped back very fast against their seats with no cam lobe to slow the impact. As a result the carbon is broken off the head of the valve and off the seats.

It isn't going to hurt to give them all the same treatment and clean things up a bit.

Andrea

[MarcoZandrini]

Chris,
It sounds like you're making progress. My question, and ignore my ignorance, but how could the issue of carbon build up impacting compression be intermittent? It would seem that this would be a continual problem. I think you're on the right track with swapping out all of the lifters. rereading this thread make it seem that erratic lifters could be the cause of your misfires.

[bmwdirtracer]

Hi Mark,
Really, until the engine is running with zero misfires showing, all this is supposition.

I was showing intermittent, but all-too-common misfires on 2 cylinders. I ruled out coils, plugs, injectors, intake leaks, and wiring harness. That leaves either the DME, or a mechanical issue. The DME is pretty unlikely, because the previous engine didn't set any misfire codes ever, and the DME is unlikely to have been hurt by the engine exploding. In the period of inactivity, the DME lived in a big ziplock, inside the nice dry car.

The engine passed compression tests, so I thought valve and piston issues were out of the question.....until I found 25% leak down on #2, with the leakage coming out the intake valves. Certainly, that's cause for misfires.

Why intermittent misfires? I can only guess: because the DME has some threshold for seeing the torque delivery of a cylinder's firing as a misfire, rather than just an "imbalance". Again, this is just my guess.

Why didn't cylinder 8 have similarly bad leak down numbers? I have no idea, but I'm hoping it's because the bad lifter at that cylinder hyperextended when it was operational and pumped up, but then leaked down sometime before my leak down test. (I did not see any difference in the lifters, as suggested in the S.I.B.).

Again, all this is pure supposition, and that's why I'm looking for thoughts, advice, and theories from you and all my other wonderful friends here.

If I have leak down numbers of 3% or less on all cylinders, after yesterday's hammering experiment, I'm not seeing the justification for pulling the engine (AGAIN), and removing the cylinder heads. Unless someone here has some thoughts about why I should??

As Andrea mentioned a while back, the normal failure of lifters is that they don't pump up -- and this won't cause misfires, just noise.


I've used an old-school technique for cleaning combustion chambers and valves, many many times in the past - and I would have likely tried that already on this engine, but the layout of the S62 makes it somewhat difficult to do water injection. That said, I will be attempting that after reassembly, assuming I don't pull the heads. (On my old S38, it was easy to do this, because there were little vacuum ports on each throttle body, perfectly accessible....not so, on the S62)

[WadiM3]

When will you have everything back together and test drive it ? I really believe in you Chris like your reputation. Your damn good at everything you attempt and do! I hope this sorts it for good and you don't have to take this engine apart ever again! You went through some hard time recently and I hope it all goes well for you

[bmwdirtracer]

I wish I were half as good as you think I am, Mohammed. I am, forever, a student, and I'll always try to keep the open mind necessary to that cause, so I can keep learning.

[E39MGirl]

Hi Chris,

Your guess about torque delivery to detect misfires is pretty close to the mark. As far as I am aware the DME detects very small fluctuations in crankshaft rotating speed to identify misfires on individual cylinders. Obviously when the engine is under load (i.e. in gear), the fluctuations in rotating speed will be greater because the driveline drag creates a bigger crank speed difference between firing and non-firing cylinders.

Andrea

[WadiM3]

Update us Chris!!!

[bmwdirtracer]

The post from the 10th is my update, Mohammed. I have to work on other people's cars during the week, not my own.

Okay, update: It's my Birthday. (I forget how old I am.)

Oh, and I got another 24 lifters in today; they'll be installed this coming weekend, and then I'll try to reinstall the cams, vanos, and time this critter.

[E39MGirl]

Happy Birthday Chris! It's not the miles, but how you do them that counts

Andrea

[WadiM3]

Happy Birthday Chris!!!

[Fx323i]

Happy birthday! Wish you the best present coming from your car

[MIKYZZ4]

Well, I'll throw my $.02 in after the fact. Chris, your problem had me stumped, as well as everyone else it seems, but that hammer trick is pure genius, or most probably due to years of experience! I agree with E39MGirl-"It isn't going to hurt to give them all the same treatment and clean things up a bit." I will add, and sorry I didn't think of this earlier, that I would put your boroscope to work, and observe the effects/effectiveness of this procedure. Maybe a boroscopic examination of all cylinders for comparison would have revealed the extent of the carbon buildup. Before the hammer trick revelation, I was going to agree with a complete head removal and cleaning, but now after, I also see no justification, unless the boroscope reveals another hidden ghost. BTW, Happy Belated Birthday!!

[dworthy]

Happy B-day Chris!!

I am sure you have more miles than my old E-28! hahaha

What I see as an issue with the carbon build up on the newer cars, is from the hydraulic lifters. On the old school spring, you would have the same amount of tension thru the whole range, so once the cam was off, it would snap shut faster. On those hydraulic lifters, it will slow the valve down by a split second at WOT vers idle, so you don't get the same Italian tune-up that you would from the older motors. But like yourself I am still a student, and that is just my thoughts on the subject.

[bmwdirtracer]

Thanks Darin! I'm also older than your E28.....and yeah, many more miles than that.

I've seen bunches of carbon build up; but I've never seen it hold the valves open. On newer, direct injection cars, I've seen accumulated crap (oil residues) clog the intake passages to the point that you couldn't put a pencil through them. (Hence, walnut shell blasting).

I'm going to refrain from further disassembly, and install the 32 new lifters this coming weekend, then the cams, then try to get the beast retimed and back together. (It may take more than one weekend). After I get it running again, I'll get the engine up to full operating temp, and do my old-school carbon cleaning. (You'll all know the process, I think, with a bottle of water and a vacuum hose?)

[WadiM3]

No familiarise me with this old school method. The only one I know is 160 mph on the autobahn for atleast 10 minutes lol

[bmwdirtracer]

It's dangerous, friend. You get the engine hot, suck water into the intake, rev the motor while it's all happening, and try to avoid hydrolocking the engine, because that makes it break permanently. Done properly, the steam cleaning breaks off all the carbon deposits. Done improperly, it bends connecting rods.

[shadowpuck]

A belated birthday as well!! Here's to many more laps around the sun.

[328 Power 04]

It's dangerous, friend. You get the engine hot, suck water into the intake, rev the motor while it's all happening, and try to avoid hydrolocking the engine, because that makes it break permanently. Done properly, the steam cleaning breaks off all the carbon deposits. Done improperly, it bends connecting rods.

Can you use a household clothes steamer, or is that just too weak?

[bmwdirtracer]

The theory is to suddenly shock the deposits and the metal parts into departing their bond. Hot metal, sudden influx of cold water, engine revving so the explosions don't die. Half the time, you see a huge cloud of black smoke, and suddenly, the engine feels new. Sometimes you do the whole procedure several times nearly stalling the engine.....then you go drive, flat out, through four gears.....and suddenly, that huge cloud comes out the exhaust,,,,,and your engine is new again. Yeah, no $#!+.

But the process is dangerous, You need to control water flow vs airflow and combustion.

This is a "quick-fix". You can put a can of Jectron, techron, or similar in the tank every other fill up for the slow method, at least on a non - direct injection car.

Oh, by the way: I've never ever heard of, or seen this method hurt an engine, but it scares me when the engine stalls........

[dworthy]

+1

I have used a spray bottle, like an old Windex type so you can control the amount of water that is allowed to enter the motor. 1 to 2 squirts, then wait a second or two, three, four, then a couple more squirts. I like to keep the rpm's around 3k, and take care with the MAF, as if you have a hot film type, it can mess with it.

[WadiM3]

Update us Chris!!

[328 Power 04]

He's probably in Maui without a care in the world.
Man I miss Ka'anapali/Lahaina. Can't wait to go back.

[MauiM3Mania]

I feel sure that Chris is not on Maui as I would've expected a call to pick him up at the airport. Chris, are you here? I just picked up TT from OGG, a stop at Costco and the fridge is stocked with local brew.


Abel, headed this way soon? Come to the south side to visit!

[bmwdirtracer]

I love ya, buddy! And please tell wonderful TT that I said she's magnificent! And, damned sure, you'll know FIRST, the very second that I make that reservation, for me and 5 cats. Wish I could bring the snakes..... (Oh, for those who don't know how weird I am, I have 5 cats, 5 Drymarchon couperi. The latter can't go to Hawaii....and even the former have "issues" making the move, from here to there.)

Abel, yeah....if you go to Maui again, you need to see much beyond the western shore. If you get there before me, Scott will be your ambassador. Otherwise, we'll both show you around....

And yes, dammit, I need to be living on Maui again. Tomorrow. Tonight would be better.

[328 Power 04]

I've driven the whole island (seriously, whole figure 8s) on 3 separate trips. I'm that one tourist tearing up the rentals on the unpaved roads past Hana. And my wife did not get one bit of nausea. I'll dig up some pics tomorrow. We don't do tours, we explore.