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Hello, I am a new member to your site. I am hoping that some experts out there might be able to help me diagnose a problem I have been experiencing. My '99 ML320 has 76K miles on it. All regular maintenance has been performed by Mercedes up to and including 60K mile service. The spark plugs were part of the last service. They would now have 15K miles on them. They were replaced with Bosch plugs just like from the factory.
I noticed yesterday the engine was missing like a cylinder wasn't firing from the moment I started the car. It doesn't seem to make any difference what temp the car is running, it is consistenly missing even after it has reached running temp. The check engine light has never come on since this problem has occurred. I pulled all the ignition wires and tested them with a multimeter. All were between 2100 and 2300 except one which was only 8.9 so in other words basically a dead wire. Rather than messing with replacing only one wire I replaced the entire set with new wires. I am still having the same problem even with new wires. Took it over to a buddies house who is a mechanic (but not a Mercedes mechanic) who said he thought that a fuel injector may be clogged. I know Mercedes doesn't recommend using fuel injector cleaner but I dumped a bottle of Valvoline cleaner into the tank anyways to see if it helps out.
I drove through the McDonalds drive through today and since I was right up against the wall I could more easily hear the engine sound reflect back to the car. I could hear a fluttering sound come from the engine which definately is a wierd sound and overall it just has no power. Under heavy acceleration on the highway it almost sounds like a Chevy small block V-8 with a manifold leak or something. That's about the best description I can come up with as to how it sounds. I can smell gas fumes after I've parked it in the garage which isn't normal.

Any ideas? Thanks in advance!
John
 

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It's oftentimes difficult to diagnose smooth running complaints without the aid of the MB tester. The tester allows you to observe all the actual values the different modules are reading in real time. That being said, I would start by dissconnecting one coil at a time to see if it runs worse. If there is no change, it is likely you have a bad coil. It is also possible you have a malfunctioning mass airflow sensor, which would definately contribute to your lack of power. I rarely if ever have replaced a bad injector on one of these vehicles, but I suppose there is a first time for everything. It boggles my mind that you still have no malfunction lights, as this would happen almost right away if there was a spark or fuel delivery problem. It is also possible that your fuel filter has become clogged up, but I would imagine that would have been taken care of during your regular maintenence. The only way to confirm this sort of problem is to hook a fuel pressure gauge up to the rail. It's quite easily done on your vehicle (there a little cap with a schaeder valve at the end of the rail). You should read right around 4 bar at all time while the system is active. Beyond that, you would really need a printout of your faults/actual values from a Mercedes SDS tester to tell for certain. At this point, randomly hanging parts on with the hopes of diagnosing your problem is going to run you quite a bit more than having a qualified technician with the right tools for the job do a real diagnosis (those supressor wires are not cheap!). You always have the option of declining the work after you've gotten your diagnosis. Best of luck, please post your findings.
 

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I think I probably should have posed this question in the Technical form instead of under the general ML class forum. I reposted my problem there hoping that some techies might run across it.

Thanks!
 

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PHAEDRUS, thank you for your help. It's not what I was hoping to hear but it'll probably come down to just going and getting it diagnosed. For the time being it's just sitting in the garage and I'm riding my Harley as a daily driver but sooner or later I'm gonna have to get something figured out. I gotta say I didn't realize what I was in for when I bought this vehicle. I was a former BMW owner so I know what it is like to pay high $$ for parts and service but it's uncommon to go a month without something going wrong on this ML320. Anyways thanks!
 

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hello all,new guy here...owner of MB BMW shop for quite some time.my dad has a 00 ML320,,49k on it,called me and siad it wont run.got it towed to shop,hooked up scanner,found bad alt,,replaced alt,,still poor running,,only on 123 cyls...456 cyls were dead,only 70 lbs comp,,123 had 135lbs comp.only thing i can see is cam timing has jumped.it has had service ,oil changes @every 5 k with synthetics,and a very strick service code.in all of my 28 years of MB BMW repair this is a first.i can just hope that it is not another 117 like timing chain problem.any one else have this type of problem?i am eager to know, as our local MB dealership is,of coarse, no help.any help or info would be cool.thankx...ken [email protected] MB BMW of orlando,fla
 

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That's definately peculiar. I've only seen a few 112 motors fail over the years. I suppose, if your compressioin test confirm it, you need to pull the head and go from there.
 

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thanks for input.not reeely wanting to pull heads,i dont have an e z bake oven you need to remove/reinstall rocker assem.if you dont mind,what kind of 112 engine failure have you seen?thanks again
ken [email protected] MB BMW orlando,fla
 

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Most every single one was due to overheating. The heads will warp under high temps. There is also the notorious oil sludge failures, although those would be pretty obvious due to very high oil consumption. I would just pull the head completely and send it to your machine shop to have them do a valve job, etc. When it's off, it'll be quite easy to ascertain the cause of the compression loss. Worst case scenario will have you doing seom re-ringing.
 
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