Mercedes 300CE rough idle

Maintenance/Repairs
21

@PvtPublic:

“… that membrane serves no purpose that a fixed solid partition would …” (PvtPublic)

“solid”: ok, if you want
“fixed”: no

If it were fixed, then with rising pressure in the dark colored chamber, it could not be pushed downward in order to leave space for the valve body (10) to move away from the valve seat which valve plate seal (5) is pressed onto.

There could however be a “solid” spring loaded piston (like a brake piston) instead of the membrane.
But 2 reasons led the designers of the regulator to go for the membrane:

  • leak tightness
  • manufacturing costs

If you just need something like a “flexible and tight chamber wall” which is pushed aside by internal pressure for less than 0.15 inch, a membrane screams for application.

@insightful:

“…I’m used to seeing the bottom tube under significant vacuum, thus pulling the membrane down and reducing fuel pressure. ………” (insightful)

That’s a widespreed misconception.
The pressure regulator doesn’t need “any vacuum” input for it’s function. As part of a “closed circulatory system” it keeps the pressure of this system at a certain level, no matter how big a hole someone rips into it. In case of the CIS that someone sits in the center of the CIS and is called “control plunger “.
That’s where the intake vacuum of the engine gets into the game, because that’s what “urges” the control plunger to “rip or close holes” in the “closed circulatory system”.

Oh – and thank you for correcting me: Of course it’s “excess” not “access”.
To my defense, please keep in mind, that my wife was pushing me to come and have dinner all the times while I was typing.

@everyone:

Talking about the CIS pressure regulator – I think it’s one of the most underestimated components in cars.
It is quietly and reliably doing it’s job continuously – not only when the engine is running, also when the car is parked in the garage and we are in beed sleeping (remember: it is also part of the “pressure preserving system” during engine shutoff).
The pressure regulator (which should actually be called “pressure and volume flow regulator”) certainly cost the designers some sleepless time before they had it working as well and reliably as it does.

Talking about the CIS in general – I don’t want to know how many times the designers were very depressed and thought: Oh man! What were we thinking? We will never get this working well and reliably enough for an affordable price.
So let’s esteem these people – they suffered for us car drivers.

@insightful:

No, I didn’t install the new injectors yet.
After this posting I will go to pick up new engine mounts + transmission mount from the local Mercedes dealer.
I want to install them first, because after further inspection I found out that the left engine mount is definitely damaged. Probably I will get the time to do that on Tuesday.
And I want to see what effect the new mounts have on the shaky idle. You know – if you fix something by renewing 3 or 4 things at a time you will end up not knowing which of these things caused the problem.

22

I’ve read through the thread carefully, and you are definitely more qualified to be doing diagnostics than the average mechanic. Perhaps far more so.

Getting back the original post, have you put a scope on the ignition system to see what the spark pulses are doing? This all sounds eerily to me like an ignition component becoming heat soaked.

I’m almost embarrasses to suggest it, because you have given the ignition system a cursory look and someone with your level of expertise clearly must have considered this, but sometimes when ones focus gets sidetracked it can become myopic as if it were on rails. It happens to me occasionally. Can’t see the forest for the trees.

23

@the same mountainbike:

Thank you very much for the compliment!

I like it, when someone reads my postings carefully, because that way there is a good chance that someone discoveres mistakes in them.
Maybe I didn’t concentrate well enough, or maybe I have a misconception about something, or maybe I should just improve my English (especially in writing).

“…have you put a scope on the ignition system to see what the spark pulses are doing? …”
Yes I had that done about 2.800 miles ago. It didn’t look like a brand new ignition system, but it also didn’t display anything that could be the reason for my car’s behaving. At that time the problem(s) already existed, but the shaky idle has become a little worse since then.

“…This all sounds eerily to me like an ignition component becoming heat soaked. …”
Yes, I have the same feeling – at least sometimes.
Especially this morning I had the feeling that there was occasional misfire involved at idle (which is 540 / minute in “D”). But you can hardly determine that. One moment you think “now I can clearly feel it – it must be the motor mounts, that feels like mere vibration”. 10 minutes later you think “hm, I couldn’t see any movement on the rev meter just now, but that felt more like slight misfire”.

I went to several Mercedes dealers and let the mechanics with the most experience on these older cars drive with my car, and guess what – they all came up with a different suspect. And they all said that this kind of behavior can have several different reasons or also compounding reasons (which is certainly correct).

So don’t be hesitant with your suspicion on the ignition system!

24

@‌HD

AFN radio . . . that brings back memories

I also listened to Cartalk on AFN, when I was still living in Kaiserslautern

Anyways, I haven’t lived there since 1999. I’ve been in Los Angeles since then

Sorry I haven’t been able to help you, but it seems like you’ve already “covered a lot of the bases” yourself.

Perhaps this website can help . . .

http://www.startekinfo.com/StarTek/outside/12264/?requestedDocId=12264

25

@‌HD

By the way, I regularly read Oldtimer Markt . . . I have a subscription . . . and in the past year they had a few articles about the various older Bosch fuel injection systems, including troubleshooting and adjustments.

Perhaps you could find a way to log onto their website and view the past articles for free?

As an interesting sidenote . . . according to Oldtimer Markt, Bosch introduced L-Jetronic and K-Jetronic at the same time, give or take a year or two. In hindsight, I can’t understand why they would have introduced 2 fundamentally different systems at the same time. Now, years later, the L-Jetronic system, is much easier for mechanics to work on, because it’s an early EFI system. Whereas the K-Jetronic . . . and KE-Jetronic . . . are often considered to be exotic and temperamental.

26

2014-05-11

@db4690

You had lived in Kaiserslautern? Then I bet that the “AF” in AFN had to do with that!
So you can probably speak German!? Your German is obviously at least good enough to read the “Oldtimer Markt” magazine. I hope you had a good time in Germany!

I haven’t been to LA since 1990. But I’m thinking about going on a trip through California again in the not too remote future.

I also read “Oldtimer Markt” (irregularly), and I do remember these articles about the Bosch fuel injection systems.
I don’t know either, why Bosch introduced these 2 systems at the same time. Maybe they thought that possibly both systems could be further improved as time passes, which would change the pros and cons. As I said in an earlier posting - during the development stage of the K-Jetronic they must have felt already how risky it was to design that system. I’m very impressed and surprised, that it works as well and reliably as it does.

Thank you very much for that really interesting link you posted!!
I only had a quick look into it so far. Since I’m planing to install my new engine and transmission mounts on Tuesday or Wednesday, I browsed to “removing and installing front engine mounts”. The content looks exactly the same as on the CDs with the original Mercedes Benz workshop manual!
I tried to find an online resource with such detailed information about the maintenance of Mercedes cars several years ago – but couldn’t find it. That’s amazing!
So much for “…Sorry I haven’t been able to help you, but…” … !
I have the feeling you know more interesting sources, which I’ve never heard or seen of !?

If you want to keep a 26-year-old car on the road, getting equipped with everything neccessary yourself is a good way to do that. And knowledge about sources for spare parts and usefull tools and (most of all) knowledge about the car’s technology are part of that.
As you know – with the time passing you find less and less experts who are still familiar with the older technology. Most mechanics today, if you ask them what the reason for your engine problem is, they get their OBD2 code reader, plug it to your car, let it scan, and then they tell you what the code reader tells them. They are scared of cars which - due to their age - don’t have a code reader plug socket.
In the old days mechanics learned to first “diagnose” depending on the car’s behavior, second “what to do” depending on their own diagnosis. So they needed to know what each component of the car exactly does.
Today they learn “what to do” depending on what the code reader tells them.
I don’t say that I don’t like todays diagnosis technology – on the contrary – I think it’s an enormous time saving invention. These code readers (for around $ 50 or so) are a must for every average DIY mechanic who owns a 15-year-old car or younger. They are really easy to handle.

It seams to me that you are a Mercedes owner too. Could it be that your username “db….” reffers to “Daimler Benz”?

27

@HD

I am German, actually

As a matter of fact, I got my kfz-Mechaniker Gesellenbrief in Kaiserslautern. As it turns out, I did my apprenticeship with the US Army . . . they were, and maybe still are, a large employer in the area, as you may know . . . then stayed on a few years as a heavy duty mechanic in their Depot.

But I really wanted to work on cars, not heavy vehicles, and job prospects were grim at the time in Germany. So I moved to the Los Angeles area, where I worked in a Mercedes-Benz dealership for several years.

But I’ve since moved on and am now a civil service fleet mechanic in the area.

As for those cars, I’ve owned 2 W202s. A 1998 C230 naturally aspirated and a 1999 C280. The amazing thing is that the C280 is better equipped, faster and gets better fuel economy than the C230 ever did.

As for those interesting resources, I still have a few tricks up my sleeve. But they are of more use to US domestic vehicles and heavy duty trucks.

Unfortunately the db in the username doesn’t mean anything. I wasn’t even thinking of Daimler Benz when I chose those letters. Total coincidence.

28

@db4690:

Ha! That’s interesting!

That explanes the experience and knowledge that I thought you have.

And it explanes the feeling that I had about you being very familiar with Mercedes cars. I already thought that after your first comment on my thread.

Since you told me about parts of your cv, I want to let you know something about mine.
Since my early youth I tinkered with old motorcycles and cars and sometimes rode / drove them. I grew up as a country boy – you know. I was not the only one in my environment who did this in the early 70s.
After high-school I first passed through machine fitter training (Maschinenschlosser Gesellenbrief). After that I worked several years as a machine fitter assembling and installing production equipment mainly for the car industry, worldwide.
Than in the early 80s I thought it’s time to upgrade and went to study Mechanical Engineering.
For the past 30 years I have been a designing engineer, designing special purpose machinery, mainly for the production of combustion engine parts (crankcases, cylinder heads, crankshafts, camshafts, pistons, valves, …) for the global car industry. For the past 20 years I have been doing that as a freelancer.

By the way, I also had a US car once: a black 1990 Corvette (the last year with the completely round rear lights). I sold that one 15 years ago.

29

@‌HD

“country boy” . . . the town I lived in before Kaiserslautern had less than 5000 inhabitants. Quite rural. We literally lived on the edge of town, and I have good memories of taking strolls in the forest. Our cats could stay out all day and night . . . no coyotes, unlike Los Angeles!

You’re braver than I am . . . motorcycles scare me!

But I have a class B commercial driver’s license, so I’m allowed to drive pretty massive air brake vehicles for my job. It’s a lot different driving a 8 or 10 speed dump truck with straight cut gears, versus a car with a 5 speed synchromesh

Those big trucks never scared me as much as a motorcycle

30

@db4690

“…motorcycles scare me! …)
That’s good - for your health. They really are dangerous!
From the mid 70s to the late 80s we were a bunch of real racing bike enthusiast. As you probably know – there are several racing circuits around here at the border triangle of Belgium, Netherland and Germany where you can ride or drive anything with powered wheels for a fee. We had several 2-stroke race bikes (around 300 pounds with 90 - 120 hp at the back wheel). Oh boy – don’t get me started on that toppic! My guardian angel will probably want to have a word with me when I come back from my trip on this planet.
I kept riding such bikes occasionally until 2005. Then a friend of mine who still had several race bikes died on one of them and I decided to put an end to this activity for good. After the age of 45 it’s better to stay away from toys like that.

“…It’s a lot different driving a 8 or 10 speed dump truck with straight cut gears, versus a car with a 5 speed synchromesh …”
Tom and Ray from Car Talk Radio would probably now say something like:
“Hahahahaha!
I can literally feel myself bouncing up and down on the seat!
Ahahahahaha!
And painfully hear the straight cut gears – finally - snap into each other.
Ahahahahahahaha!"

31

I want to keep everybody informed – especially everybody who contributed to my thread:

Today I renewed both engine mounts and the transmission mount.

Based on what the old ones look like after disassembly and what the car feels like with the new ones, it was high time to renew them. (See pictures!)

The engine mount with the ripped out bottom part is the one which was installed on the left. When I checked the engine mounts last week from under the hood I could already feel that the left one was definitely not good any more. But when I took that one out – which is not so easy with access from the top completely blocked by the CIS – I was really surprised that the vibrations at idle were not worse then they were. I hardly understand how the engine and the whole car could run so smoothly above idle with that torn apart engine mount.

Since I didn’t see any Mercedes label on the old mounts, I thought they were probably not even hydraulic ones, but just rubber mounts. But standing underneath the car and taking out that damaged mount, oil which was dripping in my face told me: I was wrong.

The old transmission mount was about one third of an inch lower than the new one.

Remember:
3 Mercedes dealers – including one of the biggest in Germany – suspected all kinds of components, but none of them suspected the engine and transmission mounts!

With the new mounts the engine started almost without any shaking!
Then I went on a test drive with a cold engine. With a cold engine idle was also okay with the old mounts.
The result at 185°F:
80% of the rough / shaky / vibrating idle is absorbed by the new mounts!
But obviously the old mounts were not the source of the vibrations, they just couldn’t absorb them anymore (or only very poorly).
A little shaking is still detectable. You can feel “tiny kicks” every 2 or 3 seconds (only with the warm engine at idle in “D”).
Above idle and moving the car really feels like new.

So, I guess I’m not done yet!

32

Danke Herr Deutscher.

33

This is my method for evaluating those hydraulic motor mounts

Look at all parts of the mount, with a mirror, if necessary

If there is any liquid coming OUT of the mount, it’s toast

If it’s BADLY cracked, it’s toast

I then put a screwjack or jack under the pan and SLOWLY raise the engine or trans a small amount, while carefully observing the mount, with a mirror, if necessary. Sometimes those cracks which you thought were insignificant turn out to be quite severe. Sometimes it’s obvious that the mount is collapsed.

34

Sincere thanks on the update.
It always amazes me how much vibration mounts absorb that we’re oblivious to until they fail and/or we change them. That goes for engine mounts, spring bushings, strut mount busing, and all the other rubbery bits.

I’ve no doubt you’ll find the vibration source soon. You definitely know what you’re doing. Your level of expertise leaves me humbled.

35

@insightful

That’s a good one! Reveals humor and intelligence!
Leads me to a little side note: I wonder if my humor is well received too!? I’m not sure – being not a native English speaker. I may be a lot funnier than it appears!

@db4690

“…my method for evaluating those hydraulic motor mounts.”
That’s how a professional does it!
In my case you could already see and hear from the top – by manually moving the engine to and fro sideways – that there was a problem with the left mount. But then I didn’t see any oil on the white (well, dirty white) traverse which the mounts rest on.

This experience with the old aftermarket mounts shoes again – as you already mentioned earlier – that it’s better to choose genuine Benz parts for a Mercedes.
However the Bosch parts in a Mercedes, I think can also be bought from Bosch directly. They are about 10-15% cheaper and I think they’re not any different. What do you think, as an ex insider?

@the same mountainbike

“……Your level of expertise leaves me humbled.”
Tooooo much for me to handle!
I’m just one of the guys here who try to fix car problems and exchange some information and experience – best with a little fun, of course!

Talking about “…rubbery bits…” (the same mountainbike)
The rubber and plastic parts on my car are the ones that worry me the most.
I want to keep this car maybe for another 10 to 15 years or longer, because it’s very nice to cruise around with it and it’s still in really good condition.
But 95 % (or maybe more) of the parts on my car have been installed at the Mercedes plant when Ronald Reagan was still in office as President of the United States.
Age is the main enemy of the rubber and plastic parts - the material becomes dryer and harder over time.
Just 2 months ago I found out that the top plastic neck of my original watercooler was halfway broken off and sticking in the hose. I opened it in order to renew a leaking plastic breather fitting which can only be removed (without braking it) by pushing it out from inside. I couldn’t manage to reattach the coolant hose securely enough on what was left of the neck. So I had to throw away a perfectly working cooler and buy a new one, because of some broken plastic attached to it. Besides age, probably the damaged left engine mount (which also broke due to fatigue of the rubber material) contributed to braking it. The engine’s vibrations due to the mount’s disability to absorb them must have been tearing to much at the cooler neck through the coolant hose which - with an open thermostat - is quite rigide.
I wonder how much longer all these rubber components of the suspension will do their job properly. Surprisingly they still look okay and work well. And there are many of them, especially in the multilink rear suspension of the Mercedes W124.

36

@‌HD

Here’s my take on Bosch parts for a Mercedes-Benz vehicle

If Bosch is the manufacturer who originally made the parts for the car, they are more than likely just fine. If they did not, it’s a gamble, which you will probably win

Unfortunately, I have had some bad luck . . . both in the shop and on some personal vehicles . . . with some German aftermarket parts. In this case, they were not the original manufacturer of the part. I suspect the parts were reverse engineered, and maybe not very well, at that. I’m not referring to Bosch, but some of the “lesser” auto parts manufacturers

“top plastic neck of my original watercooler was halfway broken off and sticking in the hose.”

That sure brings back some memories. I replaced lots of those radiators when I was working at the dealer. And most of them had the same kind of failure. If you want to save a little money, buy a Behr radiator . . . minus the star . . . because that is who originally made it. You will find that the new radiator has a metal sleeve in that area where yours broke . . .

37

Rubber parts constantly under compressions, such as the spring bushings, undergo another change called “cold flow”. The material actually changes shape to try to comply with the cavity into which they’re compressed. That’s largely why gaskets lose their ability to seal (they lose their compression, they stop “pushing back”) and a part of why spring bushings become thinner at the portions of their anatomy where it counts the most… those areas that absorb vibration. As regards their becoming harder, that changes their density and reduces their ability to absorb vibration and convert it to heat energy.

My feeble brain keeps going back to that comment you made in your original post that the shaking gets a lot worse at operating temp. I keep feeling that it might be heat related. I know you said you’d checked the ignition system out, but have you tried actually monitoring the ignition system while the engine heats up and the condition develops? Being a 1988, I’m guessing that it’d take some inductive pickups on the ignition wires… if there are any. I don’t know how you’d accomplish this with COPs with a pre-OBDII engine. You might know better than I.

There are so many things in the ignition system subject to heat sensitivity, especially things with coils in them (which, actually, the injectors have also), that if you could rule the entire ignition system “in” or “out” at least that would eliminate a lot of possibilities. Monitoring the voltage spikes would do that definitively.

38

@db4690

“…If Bosch is the manufacturer who originally made the parts for the car, they are more than likely just fine….”

I attach a picture of the “Bosch”-injectors I bought from this dealer:

Their main focus is parts for elder Mercedes models and they started their business (I think 30 years ago or so) as a supplier of spare parts to cab companies in Berlin. I never bought anything from them before, and I don’t know anybody in my environment who did. Judging from what some people say about them on the internet they seem to be okay. Some say “Don’t buy their 25-50 Euro engine mounts, they’re garbadge”, which I certainly belief too. They have a shop close to Düsseldorf, where I went to pick up the injectors.

It’s not about the money that I’m hesitating to install those injectors. It’s about awareness of the behavior of injectors in general.
Is it normal, that they drip a little during the engine’s coast-down to idle from higher revs?
I asked several car mechanics in my environment here in Germany plus the mechanics of one of the biggest Bosch service workshops in Germany. They all (say that) they can’t answer that question. Of course they all use a separate test apparatus to test injectors. Bosch of course offered me to test the 6 injectors on their test apparatus for 65 Euro ($90), which is different from the way I tested them (connected to the fuel distributor with the engine running).
One mechanic said that as long as the injectors don’t leak after engine-shut-down, they are probably okay.

Here is what I think:
When you take your foot of the gas pedal at higher revs, the idle switch of the throttle valve tells the CIS-ECU that you did that. With that information plus the ignition-ECU telling the CIS-ECU, that the engine is still at high revs, the CIS-ECU gives order to the EHA of the fuel distributor to completely block fuel supply to the injectors.
BUT – with the pressure in the injector pipes still being at “control pressure” level (76.8 – 80 psi) the injectors are urged to “pee out” some of the fuel until the pressure dropped down to the “opening pressure” of the injectors (50 – 60 psi with new injectors).
Now - in case of anybody who reads this, saying: “wait a minute – liquids are not compressible! So how is that possible?”: When the injectors are open, the valve needle inside the injector with it’s spring plus the plate which holds the spring are pushed a little to the direction of the injector’s outlet. By that the inner space of the injector is a little bigger, which results in a little bigger fuel volume. When no more fuel is being supplied to the injector and the valve needle (including spring and plate) travels back to it’s rest position it pushes out fuel which occupies the space that the needle with it’s spring + plate requires for itself. And that’s what can be observed by the dripping of the injectors during the engine’s coasting down toward idle.

I belief I would observe the same phenomina with injectors I would buy directly from Bosch for double the price.

I also bought a “Bosch”-coolant circulating pump for the heater (see picture) from their shop, because the original one doesn’t run anymore and is very slightly leaking. I payed 59,98 Euro, which is less than one third of what the local Mercedes dealer charges for it. What do you think about that?

“…buy a Behr radiator . . . minus the star . . . because that is who originally made it. You will find that the new radiator has a metal sleeve in that area where yours broke . . . “

“A metal sleeve!!!” – Oh man! - When I attached the coolant hose to the newly installed new radiator, I was considering to fabricate exactly that. I wish, someone would have told me 2 months ago, that Behr radiators come equiped with such a sleeve now. The original radiator was – as you say – a Behr radiator (with the star).
I didn’t have the time to do thorough research, so I went to a local car part supplier who has a good reputation, and bought a “Wezel” radiator (250 Euro).
I was hesitating to put a self-made sleeve into the radiator neck, because I thought maybe it’s not so good to diminish the opening cross-section of the neck. After your note about such a metal sleeve, I will make one myself subsequently. I’m thinking about 1 mm thick sheet metal – what do you think? And do you know which material Behr uses for the sleeve?

39

@the same mountainbike

“Rubber parts …… ……As regards their becoming harder, that changes their density and reduces their ability to absorb vibration and convert it to heat energy……”

That’s detailed knowledge! And especially “…and convert it to heat energy.” is the kind of words which come from someone who is very familiar with physics.

So much for “… my feeble brain…”.

”… have you tried actually monitoring the ignition system while the engine heats up…”
No, I didn’t do that. I only monitored the ignition system when the engine was at 185°F. Then there was nothing suspicuous on the display.

“…things with coils in them (which, actually, the injectors have also)…”
Not CIS injectors like the ones in my KE-Jetronic (“K” stands for “continuos injection”, “E” stands for “electronic auxiliaries”). (See picture)

Besides the ignition system there is another suspect for the difference between cold and warm engine:
This “E” in KE-Jeronic causes more fuel to be supplied to the injectors during the engine’s warming-up time (which is monitored by the coolant temperature sensor).
So, maybe with less fuel being supplied to the injectors when the engine is hot, the spray pattern is bad and unconstant enough to cause the “tiny kicks” that I detect at idle.
With idle being a little higher during the warming-up time, (almost) no kicks can be detected.
I certainly wouldn’t blame the injectors for that behavior. They have already sprayed more than 4 cubic yards of fuel each. They’re old, they were already spraying fuel when Ronald … well … you know …

40

Yeah, physics is my “thing”. The thing that gets my blood rushing is being confronted with something I don’t understand. I need to know not only how something works, but also why. I have an enquiring mind. An engineering background helps.

Re: the problem itself and your question about whether the injectors “drip a little during the engine’s coast-down to idle from higher revs”, it would seem that being as their fuel flow is modulated by varying the fuel pressure (thanks for that correction, by the way) it would seem that they’d need to be prevented from closing entirely to prevent stalling, which would by definition be “dripping a little” albeit with sufficient pressure to vaporize.

It’ll be interesting to see how the new injectors work out. It would seem that erosion would allow more fuel to pass than is intended by design, and springs do weaken over time. The injectors themselves would be a critical component of fuel management, unlike a solenoid-operated injector.