Vilpo

I have had a strange problem with the car for a while now. It runs fine most of the time, but accelerating hard on boost makes it bog and sometimes its as bad like hitting rpm limiter..
There is no error codes and i've checked values while driving with star and everything seems ok, though it seems when it does this, O2 sensor shows lean.. But i know this is not the real issue since i've already replaced fuel filters and injectors and tested the pump flow to be more than enough.
Now i started scoping some of the ecu signals to see if there is something out of the ordinary..
So i found injector signal has a random "glitch" in it for all cylinders..
Here is a picture of the waveform:


http://i1354.photobucket.com/albums/...psfto2no1p.jpg


So it seems like its giving extra signal for the injector when it has to peaks so close to each other.. This happens all the time, no matter what load/rpm.
And this seems to happen totally randomly for all injectors.
Everything else i scoped, looked fine. Like ignition and ckp sensor and cam sensor.
So should i suspect the ecu, or is there anything else i should look at?
Also, i tried upping the fuel pressure by an adjustable regulator, but this did not help the lean issue..

A1EK

One thing you haven't mentiones is the MAF, have you tried unplugging it and trying the kick down?

Vilpo

I don't think i tried this yet.. I'll give it a go and let you know if this changed anything.

A1EK

I had simliar problem and found the MAF sensor was very oily and when I accelerated hard, it would make the car bog down and I could only accelerate slowly. This then made me look into the cause of the oil and thanks to the forum discovered 2 blocked breather nozzels on the fuel intake, once cleared no more oil contamination and sharp acceleration.

Vilpo

Ok, pulled maf and the car was working fine through the rev range, but i don't know if it's the real reason since i don't get any boost while maf is disconnected...
So it can be either maf or something causing bogging under boost.


I tested the injectors during disconnected maf, and i'm still getting the glitches.


I'm thinking i'll test the coils for spark voltage, since i've heard weak spark could cause this..?


And i wonder how could the mixture go lean, if i get extra signals for injectors, not too little...

A1EK

That’s correct, the MAF will cause the SC to disengage so it will not kick in at all, however when you did accelerate hard was it consistant, smooth albeit without boost? If so then if you could get anther MAF it would be a good test to see. Also was the MAF clean or was there any oil on it inside?

Vilpo

When i accelerated without MAF, acceleration was smooth. No problems at all.
This leads me to conclusion, that maybe the injector "glitches" are not causing the jerkiness..
I did not check yet the MAF for oil contamination, i'll do that next. I'm not sure right now, where i could get another MAF to test for difference.

A1EK

Thats good so we are getting closer to the cause perhaps.
Its quite common for a diagnostic to not fully pick up a fault with the MAF, as its could be still operating but not too the right spec. If the MAF fails fully there is a descirption used like 'Hot Film Sensor Fault' .
Personaly I would work out how old the MAF has been on the car and if it has oil or dirt.

If it is dry dirt you could possible give it a gentle clean and see.
If its oily then this could indicate a blocked airbreather on the intake fuel side.
If the MAF is clean, but is over 7 years old or so then its done well and I would personaly buy a new one. However PLEASE DO NOT buy an aftermarket MAF, THEY WILL FAIL. (Trust me the amount of people who have experienced this including me is high !)
If you are on a budget then buy second hand off ebay theres loads and they are cheap enough, but get the original Bosch or Mercedes, just check your part number on your existing one.

Not sure where you are in the world but just checked ebay and they have a genuine one for £25 delivered.
http://www.ebay.co.uk/itm/MERCEDES-C...item259f318357

Vilpo

Ok, thanks A1EK for the info.
I checked MAF and it had no contamination. I'm not sure how easilly would it get dirt on it though because it sits so far from the intake, right next to the radiator..
Anyways, i just received spark tester i ordered so i decided to test it also.
So the result was interesting, it's a screwable model to see the spark strenght so i turned it to 2,0cm (0,8 inch) and no spark at all. Then i twisted to 1,5cm (0,6 inch) and got spark but it was intermittent. I had to go down to about 0,5cm (0,2 inch) to get constant spark.
It was about the same with all cylinders.
From what i understand, the spark is a little weak? The instruction says i should get normal spark at the range of 1,5-2,5cm with this type of coil (wasted spark).
I'll recheck tomorrow just to confirm it..
I forgot to mention, not sure if it has anything to do with this problem but the car bogs also on normal driving when the engine is cold/just started in the morning (not on boost).

Vilpo

Ok, i had a closer look at the MAF and i noticed it had some oil deposits on closer look.
So i took it out and cleaned it, but i think i did something wrong while cleaning, since after i put it back in the car it wasn't running quite right and no boost.. So i read out the codes and there is maf code.
I measured the maf signal with a multimeter while revving the engine and no fluctuation in the signal, just constant 1 volt..
So i'm pretty sure i did something wrong, i used a flattened cotton bud to clean the sensor tip, im suspecting this was something i shouldn't have done..
Anyways, i've ordered up a used Bosch maf online. I ended up to this after A1EK giving hint about this and also read a lot of horror stories about aftermarket MAF:s..
Also, redid the spark test and actually i got consistant spark on 0,6 inch setting on two of the spark plug wires and 0,4 inch on two. According to the instruction, i should get 0,6 inch minimum so i suspect the two with 0,4 inch are weak. Those two are the ones connected directly to the coil.
If anybody knows some good performance coils that will fit CLK, let me know! Help would be apreciated..

A1EK

HI

Really if truth be told you should not really clean the MAF with anything touching it as they are delicate, a spray or blowing air is really all you should do as they are not deisgned to be cleaned. They either work or they don’t.

Good for you in getting a used original MAF, I know it is tempting to buy a cheap non brand one but you done well to avoid this and trust me you’ll be thankful.

GatorMB

Other symptoms of power loss, clogged exhaust (cats) and fuel pump volume (filter)

The MAF can cause a multitude of problems including power loss and I agree with A1EK. Stay with quality parts especially when chasing problems.

A vacuum reading from the engine will help to diagnose many of the related symptoms.

Cheers, Gator

Vilpo

Yes, learned that the hard way. Was just thinking to be thorough, but obviously it was more sensite part than i thought..
Yes, i hope it works. It's hard to find a used Bosch though, since sometimes the internal part could already be replaced on a MAF, being an aftermarked after all.. Just tried to look for a one that the center part didn't look too new..

Vilpo

Yes, i didn't include it here but actually i already tested the exhaust for backpressure by connecting a pressure gauge to the O2 port. Didn't find any backpressure at all, even at high rpms.
Fuel pump volume tested to be in spec from the return side.
Also fuel pressure tested during driving, found no drops or abnormal behaviour. Also, fuel filter replaced a year ago (also the small inline filter this year).

GatorMB

There are many parts vendors accommodating the DIY Benz fan.

www.Autohauseaz.com Amazon, Partsgeek and mbpartsonline.com.

Be weary of uro brand electrical parts.

With a vacuum gauge we read engine condition. All naturally aspirated engines will read 17" - 21" The higher the better condition the engine and Fuel management.

With Turbo and Supercharger engines we utilize the same observations at idle but under acceleration and load boost will be read instead of vacuum.
Boost is read in PSI or positive pressure instead of negative pressure.

Vilpo

Thanks for the hint, GatorMB.
Has anybody replaced the original coils with performance parts?
I mean, what would be the best option that would work with the original ecu without getting error codes?
I don't mind fabricating mounts, etc.. as long as it wouldn't cost too much.
Thanks.

GatorMB

Coils and electronics are not normally on the to do list for these cars.

It is best to just maintain it properly and it will outlive most of us. Mods are best found by just searching your model and desire in the forums or the www.

Cheers

Vilpo

Ok, i'm just planning to put performance coil to get better spark since it seems now it is too weak to cope for high boost.
And also i have already a bigger s/c pulley so it would support this mod also..

Vilpo

Ok, after some testing i'm starting to think the spark is not the cause of the problem.
New MAF arrived and after installed it runs normal, but the problem is still there.
So what i did was i floored the throttle on 3rd gear and instead of lifting off when it starts the bucking i kept flooring it and i noticed that the bucking is worst at 3000-3500 rpm, right there it feels like it doesn't want to rev more but when i kept flooring the throttle it, after 3500 it runs smooth again and continues to rev normally till about 5000 (that's when i lifted off)..
Another thing i tried was, i raised fuel pressure some and did the WOT test again. Now i did the same, but revs recovered faster after 3500 rpm..
In my understanding, this tells me the spark is not the problem since after 3500 it revs normally again, with a too weak spark i don't think it would recover at all..
And the fact that it would run slightly better with raised fuel pressure would tell me that for some reason that rpm range is slightly lean?
I have a new wideband waiting for install so i put that in next and see what i get for AFR ratio in that rev range.
I'll post back results..


Ps. Also tried running it with O2 sensor disconnected, just to verify that i don't have excessive exhaust backpressure. And that did not have any change of behaviour.

GatorMB

Observing the scope reading from the first post: The 3rd scribe is likely the last cylinder which has double peak indication. This is from a short or failure in the secondary ignition or a cracked spark plug. cylinder 1 is the last in the firing order.

All tests you have performed show no fault relating symptom. Keep going and keep us posted.

Cheers

GatorMB

I am not sure of the DAQ (data acquisition type). therefore it is assumed the digital scope follows the guidelines of an analog scope projecting samples one cylinder behind.

A double image near the same time is a digital correcting factor. An analog image would spike high when we have secondary ignition problems. It depends on the scope configuration.

regards

Vilpo

Hello and thanks for your reply GatorMB.
Ok, so do you mean that ignition problem would show up on the injector waveform? I mean, i also tested the primary ignition side and that had no "glitches" in it...

Vilpo

I'm not sure if the case could be a correction factor, since if i read the waveform, the timing is the same after the "glitch". I mean, if it was correcting something, wouldn't the waveform "shift" acordingly..?
I mean, if i measure the distance between the peaks, it seems like the "glitches" are extra not effecting the normal waveform in any way..
Even the lenght of the pulses are the same during the glitches..


About scope configuration, i'm just using a soundcard oscilloscope software and a simple circuit connecting the soundcard mic input to the signal. I've been meaning to buy a better scope hardware, but this one has been working well in the past, with cars..

GatorMB

You are very creative in developing a circuit to emulate the engine firing.

We can isolate the problem child cylinder with a 12 volt test light at this point if the mirror image is constant. Probe one cylinder plug wire at a time through the boot if accessible. This will isolate the problem cylinder. Observe scope while probing.

Oscilloscope readings have quite a range in detection low kv to high kv readings are required.

Your circuit might need some tweaking to allow multi range display, nice work though

Ps: I used to drive the tractor close to the TV and get a pretty good scope pattern

Vilpo

Ok, back with this issue after some delay..
Thanks for the help GatorMB, i'll scope the secondary ignition pulse shortly..
I finally got my wideband working, had a lot of trouble with it since i had to replace both, controller and sensor to get everything working again.
So now i notice that at normal fuel pressure (3,7 bar), i get wideband pegged over 19:1 if i go wot at about 2000 rpm. But interesting was that after turning up the fuel pressure to about 5 bar, i was able to get the afr to about 17,8:1 at the same conditions.
So i'm suspecting a lean condition after all.. But how can this be? Fuel pump flow was already tested a while ago to be about 110-120 LPH. Fuel filters replaced, how can i still be lean with stock injectors?
Ecu issue or maf issue causing the injectors not opening at proper pulsewidth?