Hi All, I have 2000 ML320 and its been couple year since I had it. Lately, my check engine light comes on and this start happening when I accelerate too quick/fast. Only time I did this is when I was getting on either main highway or merging with on-going traffic. I took it to Mercedes dealership and they ran the test and it came back as bunch cylinder mis fires (P0304 #4 cylinder misfired, P0305 #5 cylinder 5 misfired and multiple cylinder misfires). They told me that I need to replace my spark plugs, spark plug wires, coyle wires and oxygen sensor and that should take care it. So, I got all that replaced and thought life is good now. But about 3-4 days later same thing happen when I accelerate little too quick to merge with ongoing traffic the check engine light came on and the car was kind of stumbling and hesitated to go. Now they are not sure what's going on either and he thinks only thing they can think of it is either the engine control module or motor mount balance. And he said he is still not sure if this would fix the problem. I was wondering if anyone here had same problem or any help would be appreciated. I paid somewhere around 600 bucks and the problem is still not fixed.

 

How's your fuel filter? Poor fuel flow can certainly cause lean misfires at heavier throttle applications.

 

Well, I don't know but I am sure the dealership checked that. I don't even know where the fuel filter is at and can you check it yourself or do you have to take it to someone professional? Also, I know first he(Benz service department) was talking about cleaning my whole fuel tank but than they decided not to, so if they were going to do that than you would think they have checked the fuel filter too. Thanks for your advice.

 

I would take it back especially since you paid that kind of money to get that work done. Secondly, it sounds like a fuel problem, either fuel pump or fuel filter. Fuel filter is easy to replace, typically it is mounted on a rubber-isolated tray in front of the pax side axle. It has a plastic cover and it can be removed by three or four plastic 10mm nuts....easily accessible BTW, it's a 30-45 minute job.

 

Thanks StapleGun. I took it back and they just cleared the code and he said it can still happen again. You would think that they would be able to track the problem down by running the diagnostic too but I guess not. So, I don't know what the hack they took my dang money for. If they didn't fix the problem they said it was fix than they should give me my money back but I don't want to make a big deal about it and it's the only Mercedes dealership in town so I am going have to end-up going back there sometime. I am just thinking about selling my ML anayway. I will call them and see if they replaced the fuel filter or not and if they didn' than I will try to replace it myself. Thanks for your assistance.

 

engine control module is not the cause of misfiring cylinders.

only 4 and 5 cylinder still appears as a fault? how about the 6th? need to check the compression on affected cylinders. don't ignore defective or leaking fuel injectors which is notorious for engine misfires. OR if left and right bank cylinders keeps on appearing as the source of misfires i have a feeling it's a vapor lock- try using different fuel or the MAF.

fuel filter is positioned at the top of the fuel tank next to the delivery module.

 

Well I think according to the codes cylinder 4&5 misfired and than it says multiple misfires. I would think they checked the compression on those cylinders too, when it comes to car I don't know much about it. What's the vapor lock and can I replace that myself? I will try to use different fuel. This may sound stupied but what's MAF? Thanks for your advice.

 

Replace Mass Air and replace the air filter also..seen this cause alot of running complaints even without codes

 

My check engine light came on and I had it checked out and it turned out to be my MAS $325,.....

 

I had to change the mAS on my ML430, Stealer quoted $450 for part and labor. I bought it online for $175 and put it in by myself..its soo simple. $325, in my opinion is too much money for that.

 

This is dumb question but what is MAS? SANMAN where did you buy yours from online and is it pretty is it put on? Thanks all for the help!

 

Its the Air Mass Sensor. I think price has gone up since I purchased..for 2000 ML320 www.autohausaz.com has it for $251. I bought it from drivwire.com, Putting it in is very easy.. it resides next to air box. Unplug the wire connection. Unscre the tightener that seure the boot in the outlet. un do the latches on the intake side. It comes off. Orient the new one for plugging the connection back on.. put the latches back on.. and tighten the outlet boot and you are done. You need a OBDII code reader to clear the codes and turn of the check engine light if it is on. Or take it to autozone and they can clear it for you...It real easy.. all you need is a screwdriver.

 

Thanks, all for the help! Have a awsome week!

 

$251 seems pretty steep for a sensor. Sometimes the dealer likes to sell the housing with it, which is not necessary. One or two torx screws typicallly hold it in the housing. Get the Bosch # and cross reference it. I bet it is used on other cars, and the sensor can be acquired much cheaper.
Regards,
Jerry

 

Thanks, Jerry. I found one on the Ebay and right now it's at 135 and got about couple hours left so hoping I can get it for around 160 or 170.

The check engine light came back on week before the last week and I called the Mercedes service department that it wasn't fix and the check engine light is back on so he told me to bring it in. This time FINALLY, he said it's MAS (I should have just ask you all here before I took it to Benz service department) and he gave me quote for $545.00 for parts and labor. I told him that I will come by and pick-up the truck for now and bring it back later to replace the MAS so now he want to charge me 145.00 for labor for just to check the code for the 'check engine' light on...they are just ripping people of left and right or I guess I am just cheap.

 

I dont think trying to save money is being cheap. They told me for reading diagnostic code alone they charge $99. For that money you can buy a decent OBD II reader. If you are buying from ebay make sure, it is new and in original packing. Good luck

 

before getting a new MAF try spaying it with an electric parts cleaner... do not touch anything inside but hose it down...sometimes its as simple as some crap stuck on the sensor......worth a shot?

 

Thanks, I ordered new one but it hasn't came in yet. In mean-time I will try that out.

 

My dealer MAF story, I have always worked on cars but when mine started running like crap, I didn't know of this web site and the small town I live in had no one that even would hook it up to a OBD, so I made an appointment and took it in to the "Big City" to have the codes read and to tell me what was wrong, for the $100 shop time my service advisor came and told me it needed the MAF sensor and they could do it and I could be on my way in about a hour for $700. I said no thanks I would fix it myself, got the attitude from him at that time, after I had "free" Starbucks coffee and KrispyKremes, then had to sign a paper that they had warned me about my problems. I went to their parts department and they didnt have one? mmmhh.. and it would be $400 in the morning. So I drove it home and ordered one from another dealer for $250 and took the 2 minutes it took to install it. Anyway that was just a rambling story to get off my chest, I bought my own OBDII. I am such a redneck I shouldn't have a Mercedes. But I am sure most of the MB dealers feel the ML is the stepchild anyway, like my old 98.

 

Your problems sound like my ML320.
I replaced my MAS. Still have lots of mis fires.
Looking foreward to hearing what your cure was.

i have a 99 ML320 w/121,000 miles.
i changed the plugs,
cps, mas, plugs, fuel pump and filter.