John Hamilton

C320 Wagon, 2002, 105K miles
Excuse the long post, but I know many knowledgeable folks are on this forum and I think the more info I supply the better the advice I receive. Also, folks like me trolling for clues may also be able to get something from my post. Thanks in advance
OK – I am a newbie on this forum and my issue seems to be a variant of many a misfire at high revs - posts. I am loathed to take it to the stealership for the obvious reasons of maintaining control. If I take it down there the first behind closed door gesture is a conspiring rub of the hands as they figure how to maximize their return at my expense. No thanks!! I enjoy the tranquility of working on my car as I listen to my audiobook. A therapeutic work depressurizer. Downside of course is that they may be able to quickly diagnose and figure things out. Call me a skeptic, but I don’t think so. Instead I think I would get a $1500 “quote” to make things right – yeah right mr. stealership !! Instead I have spent many hours trolling for clues, hints, help, and solutions and in the process have learned a ton as I will explain below.
To my issue: At high revs at ~ 4k and under load (generally going up a hill or accelerating) I hear what I believe is engine knock, sharp rattling or ping – then engine hesitation, surge, more hesitation, check engine, power loss. ECU disables what I believe is cylinder 1,2,3 and I need to turn the engine off then on again. Back to normal until the next time. Codes are always P3000,1,2,3 and occasionally 6. No other.
Some environmental facts
1. CEL occurs always at load (accelerating on a hill) and never stationary high idle rev >4k RPM
2. Idles @ 680RPM smooth, no stutter (after plugs and leads replaced)
3. Smooth engine revs when stationary up through 4200 RPM
4. Car will operate normally until I get close to 4k revs under load
5. Accelerates from stop with no issues as long as stay 3500 RPM or below–
a. At start I use to have a quarter second delay but that is now gone.
6. Temp OK
What I have done to try and address the issue
1. Installed 12 new Bosch plugs after installing new champion pugs (indie recommended)
2. New 12 leads
3. 1x New O2 Sensor Bank 1 pre cat
4. Switched coil packs around – no change
** note combo of the above fixed some rough idling – now as smooth as silk at idle **
5. Removed plugs – 1,2,3,6 after ~ 20 miles – look clean
6. Checked Fuel Rail pressure - 55PSI at idle and maintains ~55PSI during stationary engine rev thru ~ 3k. Note did not check under load…
7. Had the injectors cleaned and Meineke – please don’t shoot me but this is in a full disclosure post
8. Tired Techron Fuel Injector cleaner on 2 tanks – no change
9. Checked PSI of each cylinder (crank engine, no pressing the pedal) - all between 165-175PSI
10. Removed and cleaned the MAF even though it looked as clean as a whistle – no change
11. Checked for vacuum leaks – none detected
12. Removed EGR , cleaned, ensure diaphragm operation, inspected, cleaned pipe (minimum build up) - Reinstalled = No change
13. Check air filter – OK
14. Checked air pump hoses – OK
15. Checked air filters – clean
16. Ran with no air filter – no difference
17. Ran with disconnected MAF - still same CEL at ~ 4K RPM
18. Replaced fuel filter ~ 1 year ago
Other things probably not related but in full disclosure
1. Recently replaced the alternator twice – now OK
2. Recently replaced fuse (57 I think) as it had blown due to , I think, a bad replacement #1 alternator
3. Battery disconnected for at least 2 weeks as I battled my alternator issue
My ODBII learning’s: All the way along my frustrating and perplexing experience I have been using the OBDII scanner and my PC to monitor and record the codes and values of the sensors as described below.
1. CEL always points to misfire on 1,2,3 and occasionally 6. No other codes.
2. I am using my USB ODBII scanner with Scansoft software which allows continual monitoring and recording of the MAF, O2, Fuel Trim and other values. I am no expert but here is my layman’s observation:
a. MAF values seem consistent with air flow rising and falling in relationship with throttle position, engine revs and also engine load. SO my assumption is the MAF is working – at least its not dead.
b. 02 sensor voltage values seem to jump around between 0 and 0.8v. Both Bank 1 and Bank 2 have almost identical profiles and tend to jump up and down based on the pedal depression. Note: I compared the general profile of the Sensor 2 (post cat) on the C320 with my Jag XJ8 and give or take the general profile looked similar in that the Jag also jumped up and down and it doesn’t have an CEL misfire issue. Again my assumption is that the O2 sensors are OK and again at least not dead. Also I am making an assumption that the cat is also OK as I don’t observe abnormal values in either as compared to my Jag.
c. Fuel trims Long and Short for Bank 1 and 2 have the same profile in that the rise and fall at the same rate. Again I have no idea what I am looking at but it looks like its responding and is not dead.
Other Observations
1. Car flat lines going up a steep hill around 3300 RPM no matter how much pedal is pressed.
2. When depressing the pedal to accelerate aggressively, giving it some throttle, there seems to be a low dampening sound. Could it be an exhaust leak or air flow issue? – I am not sure !!
a. Or am I just imagining it?
b. Could be but doesn’t feel right!!
3. Seems to have less power than it used to. Not sure tho… !!
4. I hear a small faint hiss from around the air pump area at Idle (front). I can’t see any obvious leaks. There is a black pressure valve thingy on the RHS behind the air pump that it may be but I am not sure. Anyone know what that thingy is and what it does? As I mentioned above I did check for vacuums leaks but can’t find any obvious ones other that this faint hiss.
5. I am not sure, but I feel the C320 is downshifting more that it should do - or use to do. Is this because of a general lack of power?
a. Or am I just imagining it?
My Thoughts
1. God forbid a bad cat,
2. Valve issues
3. Possible bad wiring on injectors under load,
4. Fuel pump/ pressure /regulator or line issue under load
5. Faulty injectors
Any Ideas?

Glyn M Ruck

Wow. You have done your homework & thank you.

I believe some of your coil packs are breaking down under load. Remember compression suppresses spark.

If it's not that then a clogged Cat or exhaust is certainly a possibility.

From a diagnosis perspective the trouble is that both conditions could be the cause with a combo of attempted high RPM & WOT.

I think I would have a go at the electrical side first. Did you get decent new plug leads? Replace some or all coil packs.

Does the car wheeze at all through the exhaust?

John Hamilton

Thanks Glyn
To add a spot of humor I have to disclose that I am a Scottish and the Scots are cheap. I did buy leads but there were relatively inexpensive at $140 / set. I am hesitant to purchase a new set of coil packs as that is a pricey move. Heh - I can’t alter my makeup and DNA. It's the haggis and Irn Bru.

Seriously - I'll go there but only if I run out of options and I have a high probability of success. There is a few things I can try including shifting things around and seeing if I can move the misfire around. Stay tuned on that. I have some pesky curiosity questions that will help my thought process.

1. What is the science or theory behind what happens to the coil/leads/plug/spark at load. A spark is a spark is a spark me thinks. What electrical spark phenomenon changes or is changed by the system at load?
2. What is the science or theory behind the pinging/piston rattle at high revs under load? Can lack of fuel cause it Pinging/Piston. Could it be an Ignition timing thing? I should have disclosed that I ran the wagon in 2nd gear playing with 4k RPM on a rolling straight (light load). I’d take it up to 4k @ ~ 35MPH – would hear pinging/rattling, would let of the gas, ECU did not record the CEL. 3-4 times same, no CEL. Load it up on a steep hill or moderate uphill at speed acceleration and CEL every time.
3. Any thoughts on my O2 voltage readings? All I can say for sure is that they are reading values up and down the voltage ranges, but is there a way to definitively call them good and by default call the cat good. What does a shot or clogged cat do to the O2 voltage values?

I’m thinking fuel starvation/mixture at this point. What other tests could I do in this area? What ODBII measurements/values should I hone in on? The Scansoft s/w allows me to take it out on the road connected to my laptop while I monitor each reading at ~4 readings per second. But again If I don’t know what to look for the data is meaningless…

Oh I haven’t touched the cam position sensor, should I? Where is it? I did replace the Crank Position Sensor (blindfolded – coz you can’t see it.) – made no difference…

Thanks

John

Glyn M Ruck

On a M112 it is unlikely that cam sensors would have anything to do with what you are seeing or misfires. Only driveability problems.

Running cheap leads on a Benz is asking for trouble.

Air is a very poor conductor of electricity. A spark plug at a specific gap that fires at atmospheric pressure will frequently not fire at pressures many times atmospheric unless the voltage & current available from the ignition system is adequate to achieve this. You need very high voltage & adequate current - sometimes up to 45,000 volts as an example. A lazy coilpack & voltage loss through poor leads can lead to misfires when you increase cylinder pressure by going WOT. Remember that petrol engines suffer pumping losses at partial throttle.

O2 sensors cease to function properly when they cycle too slowly. Your friend Google will give you many references to the operation of O2 sensors. Read the Bosch material & here are some good basics.

http://www.picoauto.com/applications/lambda-sensor.html

A shot Cat will give a high voltage reading on the post Cat sensor. A clogged Cat however can mess with the upstream sensor but give a totally normal reading post Cat.

Ignition timing too advanced for Octane rating of a fuel can cause knock. Knock is merely preignition of the fuel under heat & pressure without spark exactly like a diesel (sometimes called detonation). The rattle you hear is the preignition shock wave hitting the spark ignition shock wave in very basic terms. Incandescent combustion chamber deposits can also aggravate this. As engines age & foul their octane tolerance increases & they need higher octane fuel. Octane of a fuel is purely it's resistance to knock. Your car should never suffer knock. If it does you are either using fuel of too low an octane rating or your knock sensor has failed & timing is not being retarded at the onset of knock or your car has the wrong ECU map & can't retard timing sufficiently when it gets a signal from the sensor.

Running lean can aggravate knock in that it increases temperatures. Getting the car onto an exhaust gas analyser might be a good idea.

There is no difference between low & high speed knock. High speed knock can be more difficult to detect & very damaging when it resonates piston & rod and erodes holes in things.

You had better check your knock sensor.

Good luck!

Be careful that the Scottish traits don’t prevent diagnosis of this problem. We DIY’ers do not have the dealer pleasure of being able to try things from the parts dept.

sammydragon3

switching around the coil packs wouldnt work

i'd replace all coil packs at your mileage

fuel filter can cause a misfire if its clogged

cleaning your injectors was a waste of time

check both banks of exhaust with a back pressure gauage

and also run a vaccum test on the air lines

John Hamilton

OK

Great information and advice. very much appreciated. The O2 sensor tutorial was extremely informative. Based on what I read and observed with the ODBII and the Scansoft SW I am going to call them good for mow and look elsewhere.

I ordered 6 new coil packs. Stay tuned.

I'll separately read up on the knock sensor.

Again, many thanks. Forums like this are a life line to folks like me...

Glyn M Ruck

Good luck! - Benz knock sensing is excellent which is why they are able to get the "diesotto" to work. On my M112 that I have recently sold in the eight years that I owned it I never detected even a hint of knock & I'm trained to listen for it due to my job. See my profile.

In the very worse situations you should just pick up a trace of knock & the knock sensor will detect it & the ECU will immediately retard timing & it will disappear. Any prolonged knocking or pinging is a sign of trouble. Please only use the highest Octane pump gas you can buy. US gas is not the best.

Coilpack life is a crap shoot. I have seen them last many hundreds of thousands of miles while others fail early.

Switching them around can be a guide if the misfire changes cylinder as long as the one you are switching out with is good.

Careful ultrasonic cleaning of injectors is not a waste of time. Techron, however can achieve the same thing, it just takes a little longer without the risk. Ultrasonic cleaning can damage coils in the injectors. I good injector shop knows this however.

If you are maintaining 55psi or > 3.8 bar rail pressure it's unlikely you have a filter or fuel pump issue as long as it is maintained at high demand.

I note you have had alternator issues. I hope it was not overcharging at any time. This can damage electrics.

John Hamilton

The short - bottom line: Problem fixed - catalytic converter(s)




The long: Here is my story.. It has some key learning’s that hopefully will help someone in the future with the same issue.... Warning - I have some good things to say about my dealer experience... Read on at your own risk

To recap the symptom; at 2500 revs under load the car has no guts or torque. Engine sounds like crap. At 4k revs under load I get a knocking of engine, CEL comes on - misfire cylinder 1,2,3. Occasional 4,5,6. Under no load - engine sounds and behaves OK. Not going anywhere but sounds OK.
First Indie I took it to concluded it was the plugs. "Gotta be Bosch”, "Pretty sure that will fix it!!" - Replaced, no difference. Even tho they advertised themselves as German car experts I concluded I had more knowledge than them. So I said polite thanks but no thanks!!
As I describe in my first post I worked myself through part after part, attempting to fix. All shots in the dark including a MAF and all and sundry related ignition and fuel parts including throttle body cleaning, fuel rail pressure check and on and on... On the plus side I now understand what makes a C320 run and frankly I enjoyed the education.
So off to the 2nd indie she went where I have had recent +ve experience of honest and transparent dealings in my past on other cars...
I explained everything I had replaced to the mechanic/technician who promised me he would get to the bottom of it as they had the "latest diagnostic equipment for the Mercedes". OK I thought; for $90 to find the problem - go for it. I'll be brief but in summary 5 days and many hours later they concluded it was the computer after a session with Mercedes support team. A smoke test found a leak in my MAF body and they proceeded to replace the MAF throttle body seal --- convinced that was it. It was not! They ran a running compression test - OK. They removed the upstream O2 sensors and no luck - "so it’s not the cat" they concluded... Seven days later I was handed my car back, still with the same issue and $250 out of pocket. I had authorized a "not to exceed $250" mid-week as the technician was now many ours into - what was to become - a failed effort.

So off to the dealer I trotted - Wilsonville Mercedes in the Portland Oregon area and ~ $8-900 into this mystery.
Now I have to say I was dreading the experience. Dealer = Stealer -- I say. But as my son proved to me, the dealer is not always the evil empire. He always said I should take it to the dealer. I had resisted, coz I knew best as after all I am the dad with years of experience!!! Well as it turned out much to my pleasant surprise my time at the dealer was OK. To summarize; the service adviser was actually very pleasant to deal with. He had no problems with me poking my nose in and talking with the technician as he plugged the car into the Mercedes Start Diagnostic system. The mechanic/tech quickly concluded the computer looked and was behaving fine. I mentioned that the indie had removed the O2 sensors ruling out the cats. And then came, what was to be the pivotal moment As the technician explained the O2 sensor hole is too small to rule out a clogged cat. "I like to loosen the exhaust manifold to eliminate the effect of clogged cat back pressure". He did that took it out for a ride and was able to red line with no CEL. Bingo - we were onto something...
OK I thought here comes moment I was dreading - a huge bill for replacing the cats. I had done my homework coz I always had the cats in my sight but was hoping, because of cost, it would not be the issue. So with my son, myself, service manager and mechanic all discussing the issue, and myself being completely in the loop we proceeded to discuss options. Worst case, including diagnosis (3 hrs. at least) + 2 cats installed the total would be $1475. Now I had previously done some homework and I estimated $565 each from the internet. + My pain and suffering should I do it myself I quickly concluded - "Heh they are not trying to rip me off" “They are actually being honest and transparent". They explained they will replace the one causing most of the issues and see if that fixes it and it not, replace the other. We had a plan. So the mechanic removed the first one and sure enough as he showed me - cracked honeycomb cat inside the chamber with pieces rattling inside. So he replaced the 1st cat and took it out for a test drive, came back and said much better, but still giving a CEL on 4,5,6 although at much higher revs. Replaced the 2nd one, took it out and cured the issue. So in summary diagnosis ~ 3 hrs. Replacement ~ 2hrs install/test time + 2 new cats for $1475 at the dealer was very fair IMHO. They were honest transparent, friendly and approachable. My son smiled but said nothing. I got it.
What did I learn: Dads don't know it all? Find an honest dealer and they can be your friend. Indies can work sometimes but not all the time. Shot gunning can be expensive. Use the sniper rifle for tough targets.
Way to go Wilsonville Mercedes!!

Glyn M Ruck

Thanks for letting us know.

RedStripe

Excellent thread!

KHARBAT1

excellent knowledge !!!
I am a new owner , doesnot know how many Air filters the 2002 c320 has !!!
I see one filter over the battery in the engine compartment . Any other Air filters ? Auto parts say it takes 2 filters . where is the 2nd one located ? Thank you for the help .

gngrbrdman

[QUOTE=John Hamilton;5038668]The short - bottom line: Problem fixed - catalytic converter(s)k
I think I am having the same problem but mine is a sadan..I think its the bank thats on the odd side bc its doing it under load.. its high mileage...
has similar symptoms going to hobby shop to run car on lift to get some ir temp readings.. I think the driver side cats are bad... probly high heat.... in that tight section..was making crank sensor fail this is why I wish I had a proper data logger I only saw egt readings on snap on reader think it was at 300 something.. where is the egt prob on this car
I like to use a sniper riffle on all targets. I am going to loosing.. cats too see what i discover....also was the fuel light on before starting engine?

notice that when crank position sensor fail

Q
using stupid tablet to post..........
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