tim687

I have got issues with blue smoke coming out of the exhausts upon cold start.
This morning I undid the oil filler cap and cranked the engine; the oil filler cap started to dance around for a brief moment. By the time the smoke was stopped, the cap settled.
I suspect that I might have a blow-by issue, which is quite common for this engine.

The car also starts to misfire when the temperature is rather low; at around 7 degrees C. When the engine warms up a little, I can restart the engine and the misfires are gone.
I'm not sure if the misfires are caused by the oxygen sensors getting fooled from all the oil burning.

I've cleaned the PCV system venturi valve about 10k~15k km ago and it stopped to produce smoke upon cold start after that. But I'll undo the PCV tube next time I start the engine.
I did notice that the PCV tubes where a little oily at the outside, that an pool of oil has formed on the intake manifold and that some of the clothwrapped wiring was moist due to any oil.
I undid pipe #230 from the engine and gave it a quick blow to check the flow. It wasn't great and I was expecting a higher flow for such diameter, but again I'm not sure what the normal flow should be.

Last november, one of the coil packs went and the car started to gradually produce more and more blue smoke upon startup. I guessed this was due to fuel and oil mixing or something.
It took me about 1 to 1.5 months to order/receive/install the new coil pack and I was driving around with half an engine until that point. I did not disconnect the injectors, so the cylinders probably got washed everytime on startup.

I did notice that the oil was had a nice metalic cloud, during the last oil change. I thought that those where the ZAS actuators since they wheren't getting operated properly due to a vacuum leak.

I tested compression on all cylinders and there where a few lower ones.

Values are in bar
1: 9.6
2: 8.2
3: 6
4: 9
5: 10
6: 10.1
7: 11
8: 11
9: 10.5
10: 9
11: 10.1
12:8

I did an oil change after the test and the engine performed much better.
Currently I'm using 5W40, but the MB 229.1 spec that the M137 should use, lists many 10W40 oils. So I might switch to 10W40.

Any suggestions? I'm kind of lost at this moment as there where a lot of problems summing up at this point. (Ignition coils, voltage transformers, oxygen sensors)

tim687

The cats are what's wrong. Someone who saw me driving reported a rotten egg smell and the engine seems to run much worse now the previously lose lambda sensor was tightened

CaliBenzDriver

Hey Tim, my tailpipe experience is fairly limited. I can't help much in a muffler thread.

It's not uncommon to have cats meltdown with a fresh supply of unignited gasoline, heat goes up. That's one good reason to go easy with known bad ignition...

Make sure all your ignitions work before swapping any good cat. Deal with the root cause before the many consequences... is my "good advice" #2!

Try to compare the data of your secondary O2-sensors to see what they are saying about the cat's work.

kraut56

search for my postings on misfires that are due to the ECU shutting down cylinders to protect the associated cats (TWC DAMAGE coded visible in DAS only)

tim687

I met up with a few car enthusiast and mechanics today and they told that the ignition of the right cylinder bank is not quite how it's supposed to be. It runs a little rich.
The cats are probably fine, since one was not overheating and they look to have the same color

I will, thanks!

I now have a new suspect, they told me they it is most likely going to me something mechanical that only happens on cold starts.
One thing sprung to mind, I mishandled the valve that switches the secondary air injection output, quite a little.
I also think that the right valve cover head (venturi valve) is leaking as there is oil all under the engine on the right hand side
They gave me throttle body cleaner, which I should also inject into the vacuum system and spray the rest in the intake to get it cleaned up.

I'll try to get some readings of the ECU upon cold start

tim687

By the way, on a cold start the car starts up and goes to around 1400 rpms, after a second or 5 the rpms drop down and the engine is barely able to keep running. You really need to try in order to get the revs up again.
That is the point where it shuts cylinders down and starts to misfire.

That is why the suspecion is that the secondary air intake system is not behaving properly

tim687

I undid the PCV tube, engine side there wasn't alot of pressure, air intake (oil cooler) side there wasn't any pressure at all, I actually hooked my vacuum gauge onto that PCV tube and nothing happened. I was expecting to be a vacuum, but I think @kraut56 has more knowledge about this.

Upon startup the vacuum gauge connected to a vacuum line read this



Eventually the vacuum went up a little, or down, I mean, more vacuum. I think it stayed steady at 48cm/Hg.
I did not notice anything strange when blocking the PCV or plugging/unplugging the oil cooler PCV tube.
I'm not sure how much the throttle body should be open at idle but it was open for 5 degrees (guestimate)

I'll start the car up tomorrow with the PCV disconnected, to see if there is any smoke.

I did notice a burst of air moving in/out of the engine PCV tube. The engine started nicely today. Which is should do as it's 20 degrees outside

tim687

The car had some smoke, but it there was noticeably less smoke than usual.
The engine ran fine, loads of power and the accelerator pedal felt rather light.
The brake pedal felt a little firmer than usual, so I might still have a tiny vacuum leak somewhere in the brake system.
I'll keep starting and stopping with the PCV hose disconnected to see if the smoke goes away.

A while back, I did notice a vacuum leak coming from around the intake manifold's gasket.
Upon inspection, I saw a puddle of oil around one of the injectors, last night I was wondering; how high are the odds of a failed injector o-ring that allows seepage of the oil on top of the injectors.

CaliBenzDriver

Tim, this is your engine, personally I ignore cosmetic leaks on mine.

If you had an active vacuum leak near your injector then there would be no oil pudling there. It would just get sucked right in.
​​​​​

tim687

Well it's starting to get less cosmetic, this weekend I looked underneath my car and the starter motor was covered in oil.
When I replaced the O2 sensors of cylinder 1-3 and 4-6, the exhaust and old sensor where covered in oil stains, which resulted in some smoke upon startup.

Of course
On your M275, is there an vacuum in the PCV tube that connects to the throttle body?

I'm not sure if the PCV fumes are getting pushed into the throttle body by the engine (due to the Positive case ventilation) or if the throttle body pulls the pressurized fumes into the intake.
If there should be an vacuum pulling the fumes into the intake and there isn't one, I can imagine that the venturi might look blocked.

To further check this, I'll start the car with both the PCV tube and the oil filler cap removed and opened.
I assume that if the filler cap dances, the problem might still be in the venturi valve, if the oil filler cap does not dance, there is a chance that something is clogged further down the line (oil cooler )

I would like to know your thoughts on this

tim687

The oil filler cap dances alot less with the PCV tube removed.

I also noticed one thing, my engine is running a little hotter than usual.

Also what is the engine load upon startup?
When driving back home I felt a vibration together with an loud hum. It could be that the water pump is putting to much load on the engine at cold starts.

The average engine load is around 25% when idling at a cold start
I also needed to fill the coolant level up a little a few weeks back

CaliBenzDriver

I am going to agree with your finding the Benz PCV is a joke. The lack of proper separation between crankase blow-by vent and engine oil cause oil to swamp the intake plenum.

The consensus seems to be adding catch-can in the PCV line so the oil is captured before contaminating the intake plenum.

Pressure or vacuum:
Renewing all PCV parts won't help stop this problem. Some people manage to blow their dipstick right out of the engine from crankcase over pressure.

With a well designed PCV separator, oil should not leave the crankase. My M276 engine intake started gulping a quart of it's own oil every 8000Mi when still new.... my intake oil swamp is underwhelming

tim687

I might consider an catch can, but I hate to do this to the engine as it's not original anymore.

On the drive towards work this morning, I read an P0410 (SAI faulty) error code.
The mechanics I spoke to this weekend already suspected that it might have something to do with the air injection system, as they could smell alot of unburned fuel in the exhaust fumes.
Presumably, the left bank is overloaded with air and isn't able to maintain a proper mixture (due to the lambda's correcting for the extra air)
As I've smacked the valve on the picture below rather hard (to the point that the top started to collapse) , I'm assuming that it is no longer valving around and needs to be replaced



Therefore I'll replace cylinder head front cover (including the venturi) as a whole

tim687

In addition to my previous post; I think I finally found the problem.
The right front cylinder head cover is held down by a few bolts, the hole for the bolt on the left top side of that cover has broken off.
Since the serpentine belt is attached to it via an pulley, I can only imagine that the whole cover get's pulled to the bottom right when the engine speed changes, due to the momentum of all the devices attached to that belt.
Thus, the secondary air injection port that goes straight into the exhaust, doesn't seal properly, letting exhaust gasses by, straight into the crankcase; thus whenever the engine speed changes by quite a bit, exhaust gases enter the crankcase.

Which is exactly what I was experiencing lately.

I'm hoping that replacing this cover will finally fix all my problems, as I'm tired of this thing not running great

tim687

Replaced the right cylinder head front cover (venturi) with a brand new one. I needed to thread the holes for the oil dipstick guide and for the pulley myself.

The timing advance was -20° at normal driving, -40 to -50° at coldstart and -10° to -7° when giving it a lot of gas
I've measured the output of the voltage transformer, the repair was successful.

Replaced the oil with a semi synth 10w40.
Last error codes where on cylinder 11 and 12 and a code for cat efficiency for that bank.

I did get some misfire counts on cylinder 2,7,11,12

Again, the short term fuel trims are between 10% to 20% high when the engine warms up
Any ideas?

Rockster

Read your thread. But I'll reply to the 1st post....

This much

6 bar = 87psi.
11 bar = 159psi.

difference between the compression of various cylinders is not good. Not good at all. Generally if the difference in compression test numbers gets to around 10% under nominal and if one or more cylinders differ by around 10% that's not "good".

Think the low and quite different cylinder pressures are what need attention. With low cylinder pressure that suggests ring/cylinder wear and smoking on startup, and at other times, is going to happen. The low cylinders will have more blowby which can overwhelm even the best air/oil separator.

With those compression numbers a leak down test can shed some light on what's going on. You don't have to leak down test every cylinder just the lowest one or two cylinders and maybe the one with the highest compression.

Take the plugs out. Turn the engine over by hand. You want the cylinders/rings "dry".

While the cylinder is under pressure give a good listen at the oil fill hole -- with the cap off. Any sound or feeling of air leaking out is probably air leaking past the rings/cylinder. At the throttle valve that's intake valve leaking. At the exhaust that's exhaust valve leaking.

You can get fancy and check leak down with the piston at TDC then by turning the engine by hand with the piston down its cylinder about half way then as far down as the piston can go but stopping before it gets low enough the exhaust valves open.

After you get the initial leak down results add some oil through the plug hole. Turn the engine over 2 revs by hand to distribute the oil.

Then do a 2nd leak down test. If the leak down rate is better this is a sign the rings/cylinder wall are to blame. The oil through the spark plug hole helped the ring/cylinder wall seal.

The only cure I know for compression test results mismatches and poor leak down performance is an engine rebuild.

A catch can is like putting a band aid on a heart attack. It ain't going to help.

Changing oils is not going to help.

tim687

I'll try to do a leak down. Is it common that the engine is not misfiring on the cylinders with the lowest compression?

tim687

I did an extensive test with a friend of mine and my STAR system.
Full throttle test and idle test all showed the parameters to be within spec.

However, he discovered that a few hoses where leaking vacuum, on which the engine responded when you moved them around.
I did a 8 degrees C cold start this morning and the engine did not sound like it wasn't able to hold itself alive.

The car felt great on the way to work and required no restarts; which has not been the case with these cold start temperatures for a while.

Any tips on tracking down a vacuum leak, other than smoke test and brake cleaner?

CaliBenzDriver

Good to read you're making progress. Learn to learn from your own experience.
Once you've figured out that something sucks (bad spark-plugs, aged O2 sensors, vacuum leaks....) YOU REPAIR ALL OF THEM as a serie of the same problem.

You don't want to take 6 months to pin point each individual leak, plug or coil! Instead you figure what' leaks and fix every instance of them✌️

kraut56

Open the hood.
On the crossmember above the radiator is a decal with a schematic for all the vacuum/air hoses for your car.
Check these one by one.

tim687

Unfortunately there is no such diagram inside my engine bay.

I replaced all the hoses a while back, together with some of the connecting pieces. The connecting piece that has a hole through it is actually a new piece, so I'm amazed that I need to replace it again

Any tips to find leaks without a smoker/brake cleaner?

CaliBenzDriver

Smoke machine vs. hand-pump:
Obviously you use different tools according to what you are in search of:

-- A smoke machine will show you leaking valves and gaskets under large volume of low pressure.

-- A hand-pump will produce low volume of high vaccum.

To find leaky vacuum line circuits, you can use a vacuum hand-pump with gauge to spot leaks then proceed by elimination with vacuum plugs to close branches you want out during testings.

​​​​​Thank God, I haven't had to deal with vacuum lines in the past 20 years as Bosch electronics took over automotive signaling.

tim687

Thanks Cali!

How does a smoke machine show leaking valves? Where does the smoke need to come from in order to indicate that those are leaking?
I found a cheap smoke tester which requires a air compressor to use it, would that be any good?
The air compressor I have, has a variable pressure regulator

CaliBenzDriver

Hey Tim, if you think a smoke machine can help you pinpoint your engine leaks, spend couple hours around YouTube to learn how people use it.

All I know is it's pretty low-tech but powerful in locating large air leaks. You inject smoke into the intake and look where it comes out of.
Rotate the cranckshaft to actuate valves shut: no smoke should come out of spark plug hole then. Repeat next cylinder -- This is faster than having to remove engine heads only to evaluate leaky valves.

Knock on wood, I have never had to deal with any of that. 🤞

Rockster

No not that common in my (limited) experience. Typically a misfire is triggered by a cylinder under performing. Much less common if one is over performing. The engine controller measures -- via the crankshaft position sensor signal -- the acceleration imparted to the flywheel when each cylinder is on its power stroke. If the acceleration is below a threshold (or above) and for a number of successive power strokes a misfire error is logged.

It is not unknown for a weak or bad cylinder to affect neighboring cylinders. The weak/bad cylinder upsets/interferes with the air flow through the intake and into the neighboring cylinders. But this is rare and I don't like it as an explanation as to why the weak cylinders are not triggering misfires.

That the cylinders with the lowest compression are not generating the misfires does hint, sort of, that the compression tests were not performed correctly. Not saying you are guilty of this. Just want to highlight it is so important that any test performed be done correctly. Bad test results due to bad testing can send one on the wildest of goose chases.

However, a leak down test of at least one or 2 weak cylinders and at least one of the stronger cylinders I think worth the effort. If the leak down test results don't find that much leak down between the weak and strong cylinders that points to bad compression testing. It is either do a leak down test or 3 or redo the leak down tests on several of the weakest cylinders and one strong one and see if the results are the same.