gpaolo79

Hi all,
I would like to ask you some suggestion.
Many years ago I had some problem starting up the engine of my car, which were discussed here ( https://mbworld.org/forums/e-class-w...problems.html# ). At the end, the mechanics fixed the car as no one else did in the past and it had been running perfectly for the past eight years. What he did was changing the injectors that were leaking and adjusting the engine, basically. At least, this is what I managed to get from him.
Recently, almost from one day to the other, the engine is a bit slow to start and, in idle, the economy gauge started to be at about 1/6th of the scale, going up to 1/4th when I turn on the air conditioning. If I increase the RPM, the gauge goes back to the full left. And this is the same thing that the car was doing before the mechanic fixed it the previous time.
What happened? Well, believe it or not, the only thing that happened was that I moved from UK back to Spain.
So I have started reading (again) about this and I have seen a lot of people saying that a high economy gauge in idle indicates a vacuum issue.
However, I have the feeling that this is not my case. It's just a feeling, but I suspect that it's an issue of mixture in idle, which might need to be re-adjusted. Why? Well, first of all, as I said, it's the same problem I had before and the mechanic didn't mention anything about fixing vacuum leaks. Second, because I have taken the car from a sea level, very wet air location, to a 1000m above sea level, extremely dry conditions.
Before I try, I was wondering if someone think that this is a complete nonsense and that I might end up screwing everything even more... I have seen a few videos of how to adjust the plate of the air intake, and the warning about marking the original position and not moving the screw more than 1/8th of the turn at the time, but before touching it I was also thinking to try to push it slightly manually to see if the engine runs any better. If the gauge goes back where it should be and it doesn't change in idle when I increase the load by enabling the air conditioning, then I would have found again the right setting, that would be my success criteria.
Any idea before I try?

PS; concerning the obvious question "why are you not asking again to the mechanics to fix it"... I took the car back to him when I moved back to get it ready for the inspection, but he made clear that he doesn't have time any more to deal with old cars. It's a pity because he was really good and he knew what he was doing, so I guess I will have to find someone else, but it takes time... I can try begging, but I still have some self respect left

dolucasi

I would not try to adjust anything based on your vacuum gauge issues. That is not mixture related. It is all mechanical, and could either indicate vacuum leaks in your intake (most likely), or engine mechanical issues (valves and pistons) or a simple leak between your intake to the instrument cluster or the gauge could be wearing out.

You do not strike me as a DIY person, but if you want to check things you will need a fuel pressure meter meant for these cars as well as a digital multimeter to take measurements.

Unless any of the emission components are changed, adjustments are generally not needed or desired with these systems.

I am the original owner of mine and in the past 34 years the only time adjustments were needed was when the following components were changed/serviced:
Fuel Distributor
EHA valve

But you should always take some measurements to make sure everything is in order.

-Cheers!

gpaolo79

Hi, thanks for your feedback.
I am quite a DIY person, but I tend to be cautious on things where I don't have experience...
The reason why I would look first at adjustments rather than broken parts, as I said, it's because in the past the same situation has been solved by just adjusting the engine, not changing parts (except for the injectors, but they were more than 20 years old at the time).
I have plenty of multimeters, but no fuel pressure meter.

dolucasi

It is good to know you are a DIY person. In this case do not adjust anything, just take measurements and post it here in a table form. Avoid sentences just tabulate things. Makes long distance help a lot easier.

Report on your Duty cycle measurements:
(1) Engine off, ignition on
(2) Cold Idle right after start: rpm number + duty cycle
(3) After warm up: idle rpm number + duty cycle range (min max)
(4) After warm-up immediately after taking the idle measurement: duty cycle at 2500rpm after 2-3 seconds and keep it there for 20 seconds and report duty cycle after that..

There could also be other issues like O2 sensor problems etc. so adjusting the screw prior to checking out all the components is a very bad thing.

Like I said, the most important part about taking these measurements is not to be tempted to turn that screw.
You will not dig yourself out of this by adjusting. Trust me. I have taken measurements dozens of times on my car, and only adjusted it once after an EHA valve replacement.

- Cheers!

gpaolo79

[edited]
(1) Engine off, ignition on ---> 30% duty cycle
(2) Cold Idle right after start: rpm number + duty cycle ----> 50% duty cycle, about 1200 RPM
(3) After warm up: idle rpm number + duty cycle range (min max) ----> 22-32% duty cycle, about 900 RPM
(4) After warm-up immediately after taking the idle measurement: duty cycle at 2500rpm after 2-3 seconds and keep it there for 20 seconds and report duty cycle after that.. ----> 31-32% duty cycle at the beginning, then about 28-29%, but fairly stable

gpaolo79

After the table with the results, I'll add separately a few sentences and details.
This is the measurement with ignition on and engine off:

gpaolo79

This is the switch on at cold:

gpaolo79

This is after warm up in idle

gpaolo79

And finally, this is at 2500 RPM.

gpaolo79

Sorry, I have realised I misunderstood what you meant by warm-up. I thought it was when the revolutions in idle were going down but it should have been when the car was actually warm. I have updated the measurement with the correct values, apologies for the mistake.

dolucasi

All good data and summary. Pictures help! It appears your EHA is well mated to your FD as the drift from idle to 2500RPM is minimal (better than mine really).

Indeed your mixture coarse adjustment appears to be too lean and the ECU is having to enrich it quite a bit. With your meter it needs to be adjusted down to bring it to about 50%-55% range in your meter (this is opposite to the mercedes definition of 45%-50% which is 100% minus a normal meter)

Not sure how it changed and you have to make sure your O2 sensor is working properly BEFORE you make the adjustment.
I assume you know the method to measure the O2 sensor output. It needs to be cycling around 0.5V, up and down perhaps 0.2-0.9 volts.

Once you verify that the ECU is getting the correct information, I would try to adjust the screw.

- Cheers!

gpaolo79

Thanks!
I have been looking about how to do it, as I suspected this was going to be your next instruction. I need to understand in my engine where to take the measurement, as I can't see where the connector from the probe is.
I'll see what I can do tomorrow and I will let you know. Thanks again for the indications!

gpaolo79

It might be a silly question... but I prefer to ask.
My engine is a 102.963, but almost all information are for the 103 model.
I see one sensor on the exhaust manifold, while all the guides I'm finding are talking about a sensor that needs to be accessed from below the passenger seat.
Do you know which sensor should I check and from where I could access it in my car?

dolucasi

Yes most W201's and W124's no matter the engine size have the sensor wires enter the car under the passenger side floorboard for LHD. I have no idea about the RHD cars. You pull the carpet carefully without damaging the foam, they tend to be brittle after 30+ years.

There is a barrel connector in there (single wire - hot) you can insert a thin copper wire in there, make sure you are making good contact. The ground is any ground you can find. The Door latch is a good ground normally.

Let us know what you find out. Make sure the engine is in operating temp (hot) when you take the measurement.

- Cheers!

gpaolo79

So, the sensor on the manifold is really easy to measure, as the connector is near the battery. So I took that measurement, in the meanwhile.
Ignition on, engine off, car hot, 497mV stable:





Idling, slow fluctuations between ~200mV and ~800mV:





2500 RPM, faster and regular fluctuations, same amplitude:





This sensor looks good to me, as far as I understand. Does it make sense that I try to dig out also the connector of the sensor at the exhaust?

dolucasi

Can you send a photo of this sensor on your exhaust manifold? I'm not used to seeing one on the manifold.
But yes those values look normal. Better measure the other one by the floorboard as well.

gpaolo79

Sure, this is the sensor on the exhaust manifold



and, as I remembered, there are no connectors under the foam on the passenger's side:



So I tried to adjust the screw, but I think something is not right.

First of all, with then engine off, I inserted the hex key on the slot, pushed it until I felt it was engaging (air plate was not moving), then I pushed slightly with my hand the air plate and the hex key has been pushed off the car as if a spring suddenly released. I put it back, repeated the same operation, but it didn't happen again.
So I thought, ok maybe something was latched, let's check the duty cycle. I let the car warm up, but it was still around 30%.
So I started trying to turn the screw, 1/8th of turn at the time, but nothing was changing and the screw feels like it's not encountering any resistance, no matter in which direction I turn it.
I tried up to four turns in each direction and nothing changed, still 30% and no visible change in the air plate position.
I put it back to the original position now, so there should have been no harm done.

Just a curiosity, you were mentioning that Mercedes gives an odd definition of duty cycle, i.e. Toff/Ttotal instead of the usual Ton/Ttotal. This means that the duty cycle I'm measuring would actually be 70% according to Mercedes definition, is that correct? And that would mean too much air in the mixture?

Now it's raining and I can't work on it, later I'll get some tool to measure the free movement of the plate and see if it actually changes moving the screw.

dolucasi

Seems the oxygen sensor in your car is located on the manifold instead of near the passenger floorboard. I suspect this from your description.

That adjustment screw is very sensitive because of the trigonometry of the lever. So it seems like your screw is either stripped, or you are not pushing in the allen wrench deep enough.

Yes mercedes defines the duty cycle as off time. So 30% means 70% in Mercedes service manuals. And that means mechanically it is adjusted lean so the ECU is having to correct it by pushing the duty cycle to 30% in your oscilloscope (70% in mercedes definition). This will cause minor running issues but you may not even notice is except cold running.

gpaolo79

Thanks.
So I have made one further check, after ensuring that the key is properly inserted in the screw. I have checked with the micrometer, which stops where the air plate starts making resistance (which I understand is the point that you set by moving the screw) and I have tried two turns in both direction and the micrometer doesn't move from zero, so I suspect there is something wrong with the mechanism or the screw.
I have measured the deflection of the plate from rest position to the position where it starts making resistance and it's 2.09mm. I understand from other online tutorials that it should be 1.9mm, which would be consistent with the observation of too lean mixture.
I guess I'll have to find a mechanic after all... I still have to check properly, but I think the car is consuming more since this issue started.

dolucasi

As far as I know, that is the sort of rough setting you do for a non-running car. I mean it is just a starting point. You are not in this situation.
From your description it appears your set screw is stripped and is not doing anything useful.

First convince yourself that this is the case though, as we are not there to inspect things.

If this is the case and you can not make it adjust, you may have to replace your tower. That requires removal of the tower and tapping threads in your aluminum throttle body and screwing in a new tower. So it is a bit involved but it seems you are well equipped to do this.

But before considering that, make sure that this is indeed your problem. This may also explain why things got out of alignment on their own over time.

- Cheers!

gpaolo79

I guess it can be done, but that would be way out of my comfort zone. "know your limits" is my starting point when working on my car as it's the only one I have, and dismounting is a lot easier than mounting back.
Also, as you say, no one is here to inspect things and this situation seems to me that it starts to require a degree of experience that, honestly, I don't have.
There is one thing that I want to check, anyway, before doing anything else: the air intake sensor. Years ago I had to change the potentiomenter since the contacts were completely gone and it was reading open circuit. The diagnostic was indicating a sensor issue tough, which is not the case now, and of course that was still the original potentiometer more than 20 years old at the time. But we all know what happened with the quality of newer parts... so ten years for a new potentiomenter might be like 20 for the original one.
Anyway, that should be easy to check if it's working and giving the right reading.
And, I suppose, I could try to turn the screw until I eventually see any change. If I don't see any, then I know for sure it's gone.
Well, I'll let you know what happens.
Thanks a lot in the meanwhile for the guidance, it has been precious!

gpaolo79

Oh I made it!
When I tried to move the screw to see if it was eventually going to do anything, I realised that I actually had to push the screw down until it was engaging "something" rather than just engage the key in the screw.
The thing is that all the instructions I read were saying "do not push it too much or you will push down the plate", so I thought I had to be really gentle... and it turned out I was wrong.
So I set it to about 1.9mm and then, with the engine running warm, I set it to 50-54% (so equivalent to 46-50% according to Mercedes definition) at idle, which goes to 45-48% (again, 52-55% on Mercedes convention) at 2500 RPM.
It looks good!
The vacuum gauge is still not much at the left as it used to be, so there could be something else -for example the vacuum leak I have been reading about?- and that might explain why the mixture setting was not correct any more?

gpaolo79

oh this was luck.
I searched for w124 vacuum leak and the first video coming out was about headlight connections.
And I realised that I just had my headlight replaced (I had to remove the UK headlight and install back the original EU headlight)!
So I checked and moving the headlight height control the economy gauge was moving as well. One of the seal of the vacuum pipe were not entirely plugged in (and it can't go fully in, apparently), but now the gauge stays a lot lower, and duty cycle is still good as before.
I'll get hold of a vacuum tester and test them for leaks.
Oh this has been indeed a productive morning

dolucasi

This is great. I did not mention about pushing down the screw that is spring loaded for adjusting because you said you read instructions and you mentioned in your post that you actually pushed it down while adjusting. Most instructions warn against pushing down too much, it could cause a stall because when you push down you are also moving the plunger in the FD.

Anyway, glad is is sorted out.

As I was saying much earlier, the intake vacuum issue you have which is hovering around 14-15 inch mercury instead of the desired >17 inch in neutral idling has to do with vacuum leaks or engine mechanical problems. For NA built cars with all vacuum HVAC controls that our down stream from that gauge us a very common problem. The actuator pods develop leaks and it manifests as a low vacuum in the intake but it is not. I have not seen a picture of your center console so can not comment on your model.

Just remember the AFM Pot you just checked out has very limited operation (if any) on a warm running car. If it is not working, you will notice ill effects when you start driving a car when the engine is cold. Because it is the only way the system can enrich your air/fuel ratio as you press the gas peal as there is nothing else in the system that can do it. So if you accelerate in cold you will have no power and it may even hesitate. And the originals go a long way. Mine is original at 205K miles, but I understand yours developed opens most likely due to crud in and around the AFM plate.

I would strongly recommend acquiring a hand vacuum pump with a built in gauge to chaise down the vacuum leaks and also look for inoperable appliances like HVAC, heater valve, adjustable headlights (you mentioned this) an others. I think I mentioned this very early on as well.

And also remember the duty cycle adjustment you just made will hardly ever be noticeable by an average person because the system does what it is supposed to do and center things in this closed look system. Unless that duty cycle is in the 70-90% range in which that is too close to the systems ability to center. And again the off adjustment will most be noticeable during cold running during the first minute of operation. Because that is where the closed loop system is not adjusting anything at all.

Good to see you are making progress!
Happy motoring!

gpaolo79

I know! I did read the instructions, but I misinterpreted the warning about pushing.

Sorry, I don't get the acronyms, what do NA and HVAC mean exactly?
Oh I'll take a picture of the console later, now I have a thunderstorm just passing above me...

When I checked it, the carbon track was completely consumed and the wiper was not making contact any more.

Yep, it was already in the Amazon basket this morning
My heater valves are electrical (I had my share of issues with those, I had to change them a few years ago and they got stuck open and I had the heating always on... which was not good while driving in south of Spain with 40 degrees in the shadow...), so that would be one less thing to check. I'll start reading a bit how to check the rest.
When the mechanic fixed the car years ago one of the things he mentioned was that the injectors were leaking. I thought that they were leaking fuel, but now I wonder, could that mean that the seal was leaking and it could have caused the vacuum issue? Also at that time I had the economy gauge high at idle.

Yes, I understand.
I imagine it matters also when you start the engine, which is another thing that had become slower than it used to be. The engine used to start at cold after a couple of turns of the starter motor, lately it has been taking a few seconds. I haven't tried at cold yet, I'll check tomorrow if it has improved.

Thanks!