Any Mercedes Benz Techs out there?

JB · Aug 11, 2003

This seems to be the place to look for vehicle help. I don't know if I have a vehicle problem, but I have had a few incidents of misbehavior from my 1998 ML320 this year. I have owned the vehicle for 5 years and have 113,000 miles on it. This has not happened before this year. Mid-June: SW Utah, crossing mtns at about 6,000ft, burning NV "Premium" gas (90 octane), on Cruise at about 80, climbing about 5% grade. Tranny downshifted to fourth and immediately to third (not unusual on steep grades) then lost power for an instant. . . .rythmically, about a second apart. Had to take her out of cruise and finish the grade at about half throttle in 3rd to finish the climb. Behaved okay the rest of the way to iboats (SLC). Bought 92 octane fuel in SLC and returned to TX with no repeat, including altitudes of about 13,000ft, but at rural scenic highway speeds. July: Towed boat to and from Canada at 70-75. Burned 92-93 octane midwestern gas. No repeat. August: Western NM and all of AZ crossing mountains on I-40 several returns of the problem. Burning 90 octane "premium". Added octane booster to the tank and no further problem until the return trip from CA. If I didn't add octane booster to the 90 and 91 octane "premium" the problem returned at any altitude over about 5,000ft when climbing grades. When I got back on TX 92-93 octane the problem did not recur. I know this seems like a straight forward lousy gas problem, but I have made that same trip at least twice a year since I got the truck and had all scheduled service performed by a MB dealer, including between the June and August trips. My fuel mileage has stayed about the same and I am using zero oil between changes. I have a Repair Manual ordered (where have I heard that before?

) But would like to know if this behavior has happened to anyone else. The computer has recorded no failures or bad events. Any experience, ideas, theories?? The techs at my dealer are baffled.

SpinnerBait_Nut · Aug 11, 2003

Re: Any Mercedes Benz Techs out there?

JB I don't know if this place can answer your problem, but it might be worth a shot. http://www.allexperts.com/searchcat.asp

JB · Aug 11, 2003

Re: Any Mercedes Benz Techs out there?

Thanks, SBN. Been there. No luck.

mattttt25 · Aug 11, 2003

Re: Any Mercedes Benz Techs out there?

never heard of messing with fuel that much. i always run the cheap 87 in my new toyota without a hitch. may be way off, but your tranny? cruise control at 80 on inclines? blew my jeep doing the same in nevada.

NOSLEEP · Aug 11, 2003

Re: Any Mercedes Benz Techs out there?

The grade of incline on the road could cause your transmission to shift down to try and maintain road speed. If you had your cruise control on. Your cruise may even cut out completely on its own in this type of condition.

Skinnywater · Aug 11, 2003

Re: Any Mercedes Benz Techs out there?

OK JB, First I'm dang certain that octane isn't the issue. For more then one reason. 1. The need for a higher octane deminishes substantially at higher altitudes. 2. How the M112 motor electronics (ME2.0)cope with pre detonation is subtle. While it can be noticeable it isn't abrupt. You wouldn't even know that a ping was happening as soon as the knock sensor would. At that point, only a gradual retard of the timing would occur. This can be sequential and only on the threshold of non predetonation. The actual feel you would get is a lack of power. It would be minute to moderate. Anything more severe, as in constant predetonation along with a severe lack of power will set a DTC (Diagnostic Trouble Code)and a Check Engine light. Now, the 163 chassis is kind of a pet with me. I've been all over it and have been heavily involved with the ML. Without getting involved in the reasons your techs have been baffled, I'll go exactly to the area that is likely the source of your problem. Your techs need to access with the HHT (Hand Held Tester) or StarDiagnosis to menu ETC.6 (Electronic Transmission Control 722.6), read stored (not current)DTC's, read adaptations. Read ATF condition. Certainly, if it wasn't previously ignored and erased, A DTC of several A/T overheats will be stored. In addition, and most definately, adaptations will be at outside limits, therefore out of parameters. This doesn't mean problems. It's more a condition and it likely to have a simple cure. Depending on the read. However, my experience and qualified guess/recommendations are. 1. Clean the bugs and debris from your radiator. 2. Have the fan clutch checked for proper viscous coupling. 3. Check fuse F44, axillary fan. Almost certainly it's blown. It will be blown from thermal stresses, not a short. 4. Change ATF and filter. You must use MB ATF. 5. It is absolutely neccesary that a complete and thourough ETC adaptation reset be performed. This consists of a lengthy roadtest, up to an hour. 6. Probably the most important. The hot ATF level must not exceed maximum level. 7. Have a MBnet performed to check for service campaign regarding ETC module with upgraded software. JB this is the best I can do with the info you've given so far. Without a doubt, there are/were fuel pump issues with the '98/'99's. However, your described symptoms don't take me there. If you'd rather, bachelor@stormnet.com and I'm glad to help.

Skinnywater · Aug 11, 2003

Re: Any Mercedes Benz Techs out there?

BTW, bugs and debris accumulate heavily in between the condensor and radiator, so gain access to see that area. Don't use extreme water pressure against the fins, it will bend them closed.

SeaMasterZ@aol.com · Aug 11, 2003

Re: Any Mercedes Benz Techs out there?

Hmmmm, as a once upon a time mechanic I would hazard a guess that the knock sensor may be at fault ... the sensor "listens" to the engine, and when it "hears" knocking, it retards the spark, so that the engine doesnt hand grenade itself to pieces ... (and it might just be the on board computer trying to maintain harmony, lol, as youll see) of course, and finally a chance to chastise JB ... JB, for SHAME, (think Jim Nabors for a moment,

SHAME SHAME SHAME, where in these United States is it legal to travel at 80???? (montana is getting to be pesky bout that "no limit" thing) now for the flatlanding friends on here, a five percent grade is steep, and out west they tend to be LOOOONGGGGG and ... AND ... at elevations that high, the air gets a bit thin, and stoichometric ratios take a hit,(air density lightens, which affects cylinder charging, which affects spark propagation, etc etc) which the computer had to juggle .. that auto tranny is a wonder of sophistication, and I wouldnt be surprised if it had power to override the engine computer to keep the shock on it lowered, the cruise control is a Nazi, all it knows is to keep the speedo at 80, and it will do that til the gas pedal is flat to the floor, tremendous strain on the engine / drivetrain killing off some engine power is possibly its way of compensation for bad fuel ... maybe this will help, maybe not but I tried JB, I tried!!!

JB · Aug 12, 2003

Re: Any Mercedes Benz Techs out there?

Skinnywater, Thanks. You have given me several avenues to pursue. My brain was locked in on engine behavior; now I will examine the AT. I will also peruse my recent service invoices to see if any of what you recommend was done on my A and B maintenance schedules. I will report any findings or new evidence.

Ray, Driving 80 was a compromise between the law and fellow travelers. If I drove 70-75 vehicles piled up behind me waiting to pass. The Smokies we saw seemed indifferent, so I cooperated with the flow of traffic.

SpinnerBait_Nut · Aug 12, 2003

Re: Any Mercedes Benz Techs out there?

That's right Ray, throw the speed limits out the window anymore. You drive the speed limit and you get run over or called names and get pointed at with that one finger.

Don't know why people are in a hurry, cause where ever their going will be there when they get there. P.S. I get pointed at quit a bit lately.

Skinnywater · Aug 12, 2003

Re: Any Mercedes Benz Techs out there?

And your correct about engine behaviour, as the AT via the CAN (Control Area Network) will effect engine output. In addition, there is specific service information regarding your complaint. Specifically, a stuck kickdown selenoid limiting engine speed via the fuel pump relay. You mentioned your techs were unable to come up with a stored code in the engine management, this along with your description led me to the AT. Keep me posted.

11 footer · Aug 12, 2003

Re: Any Mercedes Benz Techs out there?

Sounds simple to me and I don't know my foot from a Benz

JB was going up a hill, at 80 [you bad boy,you

] the cruise tells the drive train not to go any slower then 80, but when there is a hill it down shifts to stay at that speed. My dads truck does it sometimes, on the highway at will shift down and scream to stay at 80-85, once you get over the hill it shifts back into overdrive........seems simple to me. What am I missing?

DJ · Aug 12, 2003

Re: Any Mercedes Benz Techs out there?

JB, Great advice has been given already. I'll throw my experience in the mix. Do not discount some of the simple things. Fuel filter, O2 sensor. I got involved with a fleet of high perf. cars a while back. They kept losing power at higher highway speeds. They exhibited similar symptoms to yours. The engines just would go a little flat and the trans. would try to make up for it. It turned out the engines were leaning out, yet not to the point that they would throw a code. High octane fuel masked the problem by keeping the knock sensors from going off, too much. It seems that this outfit had completely missed fuel filters in their PM's and didn't even think that an O2 sensor is a "maintenance" or wearing part.

SeaMasterZ@aol.com · Aug 12, 2003

Re: Any Mercedes Benz Techs out there?

Just teasin ya JB, when I went out to Gettysburg in my plumb tuckered out 83 shabby chebby, (which is vastly, overwhelmingly inferior to a safety laden beast such as your M class) the traffic on the Pennsy Pike had me running right around 90 just to keep from being a grease spot ... and coming home with a 67 33 horse Johnson in the trunk, lid open (and bungee'd down) I saw the lid flexing with the downward force of air (trivia point ... in 82 Chevy took a look at the B body cars,(Impala, Caprice) and after dumping a few hundred MILLION dollars into some computer analysis (the laptop Im writing this on was prolly superior!) they added a little flip to the trunk lid, like a spoiler - boy I sure upset THAT apple cart, lol)

JB · Aug 16, 2003

Re: Any Mercedes Benz Techs out there?

Hey Skinnywater. Yes, F-44 was blown and has been replaced. Radiator and heat exchangers cleared (they appeared clear), ATF and filter change pending. The "Repair Manual" I ordered was a waste of money. Makes an aftermarket outboard shop manual look like a library. My Owner's Manual is more help. I need something to show me: 1. Where things are and directions on how to replace or test. 2. How to get access to trouble codes and interpretations of those codes. It is 80 miles to my dealer and their labor rates are killing my retirement fund. They charged me $261 to replace my fuel filter ($220 labor, $41 for the part). Thanks for your advice. Any suggestions on reference documents?

Skinnywater · Aug 16, 2003

Re: Any Mercedes Benz Techs out there?

I know you don't have a dipstick to confirm, however I'm certain your ATF and filter will need changing. As an idea so you can feel better about it, if you know someone with a long dipstick, so as to take a sample. The MB ATF is bright red, you'll find yours to be rusty brown in color, or worse. The repair manuel, if you purchased it from Mercedes, was what is refered to as an Introduction Manuel and is just an overview. The vehicle wireing diagram is is print now, but it's 5-600 dollars. All of our repair information is on WIS, (Workshop Information System), which is dedicated computer software, keyed and licensed and only available to Mercedes dealerships. Almost nothing is in printed form. I can suggest MBCA, Mercedes Benz Club of America. There may be some aftermarket source of information you are looking for. I have a generic OBD2 scan tool here at home that I'm able to access my wifes '98 C230 Kompressor's Fuel system with. It's very limited but gives most of the ME fuel system DTC's. You may look into one at your local discount parts store and decide if it's something you want to get involved with. Also, I'm perfectly happy to answer specific questions or provide repair proceedures. Yeah, the fuel filter is a bit of a pain to get to and it actually has a integral pressure regulator for the injection system. Sounds steep though, they must be a $120 an hour or better. BTW, you'll go though f44 a couple times a year, so check it every oil change.

JB · Aug 17, 2003

Re: Any Mercedes Benz Techs out there?

More thanks, Skinnywater. The "Repair Manual" I bought was pretty badly misrepresented. It was advertized on Ebay as a Mercedes Benz ML320 Repair Manual on CDROM. It turned out to be one cd from a set of 7 by an outfit called Mitchell. It "covers" Audi, BMW, Mercedes Benz, Merkur, Porsche and VW. Not very helpful. Is the Introductory manual you mention directed at the owner who seeks do do some of his own maintenance and understand what to ask of the dealer?? That might be an option. Thanks again for your help.

petryshyn · Aug 17, 2003

Re: Any Mercedes Benz Techs out there?

JB Since the shift pattern has been affected, and the problem is aggravated by fuel quality, I'd be inclined to suspect the "throttle position sensor". By changing the load and/or fuel quality, the position of the "TPS" will be affected. There may be an small "open spot" in the travel of the sensor. This small section of travel might not be noticed when off of cruise because you are constantly pulsing the foot feed, but cruise control is much more steady and likely to reference a spot in the throttle position for longer periods. Connect a voltmeter to the signal lead from the "TPS" and ever so slowly, cycle the throttle from idle to wide open position. If the sensor voltage has any "drop out" or fluctuations (other than a linear rise in voltage)......replace.

Skinnywater · Aug 17, 2003

Re: Any Mercedes Benz Techs out there?

The EA (Electronic Accelorator) doesn't use a TPS. There isn't a direct physical or mechanical link from the pedal to the throttle valve. Resistances are closely matched between the electronic throttle valve actuator and pedal sensor. Any deviation is an automatic permanently stored hard code with MIL illumination, a limp home mode, freeze frame data and potential safety shutdown where the engine will not accelerate higher then idle speed. JB, send your mailing address to bachelor@stormnet.com. I'll send an extra copy of a '98 Model 163 (ML) Inro manuel to you. It's a technical overview of your entire vehicle. I might have a few other ML goodies here to send you as well. I'm not going to have anything with great detail. I can copy WIS doc's if you have a specific inquiery.

DJ · Aug 17, 2003

Re: Any Mercedes Benz Techs out there?

JB, You never mentioned anything about the 02 sensor(s). That is fuel sensitive!

Any Mercedes Benz Techs out there?

Honorary Moderator Emeritus

Honorary Moderator Emeritus

Honorary Moderator Emeritus

Commander

Commander

Commander

Commander

Lieutenant Commander

Honorary Moderator Emeritus

Honorary Moderator Emeritus

Commander

Lieutenant

DJ

Guest

Lieutenant Commander

Honorary Moderator Emeritus

Commander

Honorary Moderator Emeritus

Commander

Commander

DJ

Guest