ML320 misfiring - PeachParts Mercedes-Benz Forum

JMyers · #1 09-26-2003, 09:15 PM

Bought the daughter a 99-ML320 2-months ago. 76K miles. She's driven it about 3000 miles including from Atlanta to NY to school. All was perfect until.... last week while coming home in the rain, the engine started misfiring badly. It was bad enough that she pulled off the road and shut it off. On restart, it was fine, but the check engine light was on. My dependable experts are in Atlanta, there are no dealers in Ithaca NY, and only a few good independents. Took the car to the guy who serviced her 260E for the past two years... he says he can't figure it out but the codes say there was misfiring on some cylinder - he says the "computer is telling the car to misfire and his recommendation is "take it to dealer - replace computer".

My local guy in Atlanta says it is probably a bad plug, or plug wire / resistor, and could have been caused or rather aggravated by water splashing up on the bad wire / plug.

Now we have moved it to the other well respected independent in Ithaca and it's been there a week. They were to start on it Wednesday and as of today, they are "still looking at it - don't know what it is." When she drove it from one shop to the other, she said it ran very rough, and seemed to surge when stopping. Any suggestions??

Gilly · #2 09-26-2003, 09:39 PM

Which cylinder or cylinders were misfiring?

Gilly

JMyers · #3 09-26-2003, 10:38 PM

I am trying to get the answer to that question, and will post it as soon as I have it. Trying also to let the daughter run interference on this one so she learns something about her car. So far she knows it has spark plugs, and if they are not happy, she is not happy! Thanks.

Gilly · #4 09-27-2003, 05:39 AM

OK, see if there are any other codes.

The tech that first looked at it could be right, there was a probem around then for the ML320 (and other 112 equipped vehicles) with the engine control unit, but usually it would happen with a cold engine at high throttle load, so ask her if it misfired at the beginning of a trip, cold engine, and if she had her foot into it.
Also is she using premium gas as required, and/or if she might have filled up at someplace that was a brand she was unfamiliar with. Could be a bad fuel issue.

Gilly

JMyers · #5 09-28-2003, 10:52 AM

I think our second independent may be on his game. He's asking the right questions and he e-mailed me on a Sat. night - that's service!

The answer to your questions about hard acceleration while cold are basically "no". She had been driving for an hour on rural roads so the car had been at normal operating temp, though she was in a small town at a stop sign when it started. As we have talked about this, there are a couple of important things I left out. The week before the event occurred, the car had a dead battery. My daughter had friends jump the car off at least twice, then realized it needed a battery, and it was replaced, about 3 days before the road trip. Now she tells me that she sensed that the car was not running right (no power on hills) as she left town on the trip. (This would have been the first significant drive after picking up the car.)

Now she reports that while taking it from shop 1 to shop 2, it was not shifting well and that she had to let off on the accelerator to get it to shift. Shop 2 confirms that , and says that it also seems to be misfiring on #4, but he didn't mention the actual codes. While he is still looking, his initial thinking is that some of it could be due to the battery change, and it may be necessary to have the dealer reflash the computer. As long as he also looks for some simple things like loose wires or cracked/loose vacuum hoses, it sounds like he is on the right track.

Gilly · #6 09-28-2003, 08:10 PM

OK, I think maybe what needs to be done is the crank angle sensor need to be "readapted" due to the loss of battery power.
They will need a shop computer to reset this setting, then it will need a roadtest to properly adapt the crank angle sensor. Hopefully the shop has the computer to do this.

Gilly

JMyers · #7 09-29-2003, 09:09 AM

Thanks Gilly! The way you said this, I assume this could be the problem affecting 'both' the misfiring and the shifting?

Gilly · #8 09-29-2003, 08:05 PM

The same problem can be described by 2 different people 2 different ways. Since she is at her destination (school) I feel the prudent thing to do is check out the crank angle sensor adaptation, and get that properly reprogrammed, if neccesary, then see what develops. Hopefully this may be what the problem is.

Gilly

JMyers · #9 09-29-2003, 10:18 PM

Thanks for the patient replies. This is a great website. Bought some parts from Phil at PartsShop today. That was quick and easy.

roadsession · #10 10-03-2003, 12:29 AM

So any update on this issue? Curious to see what the ultimate resolution was... Gilly, does this mean that you don't need to replace the crank angle sensor, but just reset it with AAM or something like that?

Finally, I guess this speaks to the dangers of jumping a dead battery on modern engines like M112 or M113.... What is the right procedure in event of a battery emergency?

Thanks

Gilly · #11 10-03-2003, 05:10 AM

I don't know if you need a crank angle sensor or not.
The danger isn't in jumping starting, it happens when the battery goes dead, kind of like when you need to enter your radio code or set your clock.
Normally the crank angle info will get initialized by itself through normal driving. There are about (if I am remembering this correctly) 5 different load ranges and 3 different rpm ranges the engine computer remembers. If the crank angle info at some later time doesn't match the criteria it has recorded for a specific rpm/load range it will use this info to determine if the engine is misfiring.
It needs to see specific rpm and loads for 1 minute to store this "initialization" info. It needs to store load range 1 (the lowest) and rpm range 2 (the middle range), then the rest of the info will enter in by itself rather easily. What I believe MB said is drive the truck in 3rd or 4th gear for 1 minute at about 2500 rpm, should equal about 40-45 mph, but go by the tach. If I can find more concise info on this I will post it here, but "in general" this is the procedure for initializing the crank angle sesor. I will also invite other MB techs to comment on this procedure.

Gilly

JMyers · #12 10-03-2003, 09:27 AM

The ML is still sitting at shop # 2, and it's approaching two weeks. For the past couple of days, I haven't been able to get a status report, but I'm about ready to go to plan C which means towing that ML to the dealer in Binghamton, or bringing it back to Atlanta. It shouldn't be this hard. The last update I had was concerning possibly reflashing the computer.

Damn. That car was running fine before that dead battery!!

Benzmac · #13 10-03-2003, 08:49 PM

The crank angle sensor can be readapted by the push of a button at the dealer or here at MB Autowerks in Atlanta.

I have seen these exact symptoms when a Mass Air Sensor fails, the fuel pump gives up, or the filter cloggs.

I have seen all of the above.

Good luck on your hunt....

PS. I'd get it out of that shop.

JMyers · #14 10-03-2003, 11:42 PM

Donnie, Thanks for the reply. I've seen your web site and photos of your shop. Believe me I've wished I could drop it off at your place. In fact, if I need my appendix out, I might just want them to do it in one of your pristine service bays!

I got the call today, and they say the car is ready and it seems to be running fine "except" when you accelerate hard, it hesitates / seems fuel starved. For now they attribute this to the fact that they were able to re-adapt the system to shifting at the lower / normal speeds. It has to do with driving the car through all of the transmission speeds at increasing throttle settings, and so far they haven't been able to get it up the higher speeds to let it "learn" the shifting at the higher throttle settings. Of course I ask myself, "what happens if on the way home she needs to get the crap out of someone's way?" Oh well, it IS a Mercedes.... it should be able to take the shot. They did say there seems to be no recurrence of the misfiring. I think they did the best that they could, and maybe we will get lucky.

I keep thinking of my "plan" when I bought her this car to replace her 260E... it was to buy her a bullet proof Honda or Toyota that used regular and only needed maintenance every 250 years!

I'm going up there in about a week... do you think I should call ahead to the dealer in either Syracuse or Binghamton, tell then the problem and have them reset everything that needs it? I'm guessing that if they schedule me, it shouldn't take too long?

JMyers · #15 10-03-2003, 11:54 PM

Gilly - Based on your comments above... when the daughter picks up the ML, should I tell her to find the first opportunity to put it in 3rd gear and drive it for at least a minute at 2500 RPM. or 4th gear?

Or is it better to just plan that trip to the dealer ASAP?