nunodiasdasilva

Hi,

In my w208 55 AMG engine, on Cold start seems like misfire or wrong timing, engine shake a little. After warm up continues the symptoms.
If I restart after warm, the engine is fine and smooth.

I changed the Coolant Temperature Sensor, same symptoms but I found that if I disconnect the sensor before a cold start, it starts/works fine.
If the ECU doesn't see a temperature value or a warm value, it manages wrongly.
Sparkplugs, filters changed and coils verified...

Error Codes: two O2 sensors missing (removed after MKB headers/exhaust tuning)
These never were an issue, I even think that the ECU don't read the O2 values until it's warm.

It seems something in the cold-start cycle that is not properly working...but what?

Rgrds,
Nuno

GatorMB

Not a lot to work off of here,

My first thought is the Air Flow sensor, The crank position or a cabling problem.

Was it instantaneous after the header/exhaust mod or progressive?

Basic information about the fuel pressure is needed as well. Cold/Hot soaked etc...

Cheers, Gator

nunodiasdasilva

No it did not appeared with the modification.

Like I said it only issue when cole start, it raies the idle for 20 secs than low To normal rpm but always shaking like misfire and keeps like this even after warm. Only fine if I restart!

Rgrds,
Nuno

GatorMB

Never come across this problem but the ignition coils might be something to consider.


If one spark plug wire is bad the other will fire the cylinder. Under Acceleration spark plugs/wires give problems.


If you can isolate the cylinder that is acting up than it is a clue Coil/fuel injector etc..


Gator

MarcusF

Before tossing any cash at this problem, you may want to follow Gator’s advice and check a few things first. To try and determine if a coil is not firing, I’d use a timing light – if it lights, it’s firing. Unfortunately, you’ll have to check 16 times (just be glad it’s not a V12). To check for a dead injector, you can use a mechanic’s stethoscope.

If it's not a coil or an iffy injector . . . . . . .

Is this the first "winter" since the exhaust mod was done? If so, which O2 sensors were removed? I ask for several reasons. The primary O2 sensors (closest to the engine) are only used in closed loop mode - which is at idle and at cruise. Although the primary O2 sensors are not read until they reach operating temperature – it is the O2 sensor’s operating temperature that determines whether their input is used – not the coolant. The O2 sensors are heated/4-wire units and they are at operating temperature by the time the enriched idle circuit (high idle) is disengaged. If the primary O2 sensor signal is lost, the closed loop / feedback system is canceled, and the engine can idle erratically – especially when cold. If the primary sensors are not plugged in, you may want to weld an O2 sensor bung in each of the header collectors and connect them. The secondary sensors are only used to check the condition of the cats and have nothing to do with engine management, so they can be ignored (as long as you don't have to pass smog).

As an aside, in many Bosch injection systems disconnecting the temperature sensor causes the ECU to use default values. On early Bosch systems, the default value for a missing water thermosensor signal was to set the coolant temperature input to 176 degrees F (80C).

If the exhaust work was performed several winters ago and no mods have been made prior to this winter, I’d give the MAF serious consideration. The MAF is a normal wear item, and if this is the original MAF, it may be on its way out. The good news is they’re easy to change and not expensive (about $150). This page shows how to change it.

I hope that helps

nunodiasdasilva

Thanks guys,

I didn't check yet what are the position of sensors missing but the decription errors are:

P0150-130 G3/3 (left O2 sensor, before TWC [KAT])
P0130-015 G3/4 (right O2 sensor, before TWC [KAT])

And the car has no cat...only backbox!

Was from a family member that didn't know/care much about cars, so now it's mine and I'm trying to solve the issues...

Rgrds,
Nuno

nunodiasdasilva

I didnt check the errors yet when the idle is misfiring on cold start but I notice that as soon as the temp gauge needle starts to move a little from the initial state (40ºC)...I can restart the engine and it stays fine engine!
This meets the fact that the secondary air pump/cold start routine should stop on 53ºC.
The issue is that without restarting it will continue with the engine misfiring behavior.

Rgrds,
Nuno

MarcusF

Your car’s error codes indicate the primary oxygen sensors are missing. Putting the sensors back may fix the problem.

I know of no advantage in removing the primary sensors. Oxygen sensors are not used under WOT conditions, so they do not impact peak power. As I posted earlier, there are several disadvantages to removing them. A bad idle is one, poor fuel economy is another, and the system will never go into closed loop mode.

nunodiasdasilva

So if are those in front what missing, meeting what you ve said, make sense with the symptoms...but in that case shouldn't the system go To default after some time, without need
restarting?

I Know that the exhaust manifolds are from MKB, its strange if they remove the O2 holes. Have To check properly below the car.

Thanks
Nuno

MarcusF

The odd idling you’re experiencing probably is the default mode. The ECU has no way of determining the correct A:F ratios at idle or at cruise (closed loop) and determining those ratios is a requirement with this system.

If your exhaust doesn’t have O2 sensor bungs, those can be added pretty easily. Someone can weld them in - but that's an oddity. On a stock exhaust, the O2 sensor bungs are downstream of the exhaust manifolds. On your car, if everything between the exhaust ports and the y-pipe has been replaced, check to see if the tubing has bungs and they're capped. If so, remove the caps, screw in the new sensors, and you’re set. If you have aftermarket headers (not log manifolds), they usually come with a bung too.

Ausmbtech

Once a cylinder has had a number of misfires it will remain off until restart. This issue you're having causing the misfire might only be there for 30seconds but once it's reached the misfire threshold it wont operate the injector for that cylinder until next restart.

The first thing to do is work out which cylinder is deactivated (via fault codes preferably) and then if it's the same cylinder each time. Once you know if it the same cylinder or differing cylinder we can help you narrow down the problem.

Justin9212

I would assume it's a bad coil. I see this often on BMW's when they have a bad coil. Runs, detects misfire, deactivates that cylinder fuel injector until the next key cycle. Most OBD2 systems are similar on European cars. If you had multiple cylinder misfires then would I start to jump to something global like a MAF or O2 Sensor.

nunodiasdasilva

MarcusF:
But beeing the default mode, don't make sense, because if the car is warm or dont have temp information (CTS unpluged) it works fine...

Ausmbtech:
When I put in post title "misfire" I thought it was, the unstable engine is similar to it but maybe it's some kind of timing completely abnormal on cold start routine...
After some troubleshooting procedure (plugs, coils,...) the codes were clean and only show those of the O2 sensors.
I didn't have the chance yet to put online the code reader when it's on cold start.
By the other hand, what you ve said make sense, if there is some small misfire and shutdown that cylinder, it only work properly after restart...Then I only have to find why it makes the first misfire...

Justin9212:
I ve done some tests with coils, and even if it was, it shouldn't work fine at warm...
My CLK dont have yet the OBD2 plug, it's the round one...

Thank you guys,

Rgrds,
Nuno

Justin9212

What country are you that didn't have OBD2 in a CLK? Also in some conditions a coil will not work cold and only fire once warmed up, I have also had it the opposite, and more commonly where they just fail completely. How old are the spark plugs?

nunodiasdasilva

I'm in Abu Dhabi, UAE but the car is imported from Japan...W208 CLK 55 AMG from year 2000.

One of the first issues that I found, when bought the car, was bad sparkplugs that met the errors code of misfiring and they were clean after that. Around 3000 km plugs made (Champion from Mercedes).

Looking at the O2 sensors situation, today I looked to the exhaust...the manifolds until the Y is from MKB, straight to the end where's only a back box AMG (without Cats or middle box).
Have 2 O2 plugs disconnected without O2 sensors to plug and 2 O2 sensors in the manifolds (one each)...maybe the error code is correct and those 2 sensors in the exhaust are damage witch causes the fail...make some sense what I'm saying?

There is any way to test them...voltage, resistance measure?

Rgrds,
Nuno

nunodiasdasilva

Update.

The error codes when it's misfiring in a cold start is misfiring in cilindres 4, 7 and 8!
After warm up and switch off and on...no errors unless the 2 O2 sensors!

Anymore ideas?

Rgrds,
Nuno

cm60k

Nuno,

Usually; O2 sensors causes a meritorious issues to the idle & Emission system,

problem will NOT goes away, till replace all sensors, if you replace them, do a full reset, after that,

diagnose the car to see if the problem appears again....

ZAYED,,

nunodiasdasilva

Finally I can give some feedback.
After went To Mercedes garage and one more workshop outside, they couldnt figured out, unless I paid parts without 100% sure the problem was solved.
Then a friend took me To some Mechanic in a small workshop...in 20 min he said what was it and how much it cost.
2 coils and 6 plug wires...done! Now it's smooth.
I was surprised cause I changed in the beginning coils places To check and it seems ok. And issue only on cold start...well it's solved.

For the O2 sensors, he said that they were not good but was not the main cause. Only after, if I'll want I can replace them.

Rgds,
Nuno

Justin9212

I called that. I said it's the coils some time ago. You quickly shot it down. Feels good being right, because this is what I do for a living. Validation

nunodiasdasilva

As I said, had change coils from places and didnt notice changes on issue...and seriously im still confused with the temperature related...strange!
Thanks anyway.
I posted the feedback cause I just hate that people just come To forum when they have issues but then after...nothing!

Regards,
Nuno