Yesterday, the 'Check Engine' message came up in the dash computer of my 2005 Mercedes C230 Kompressor during hard acceleration. I immediatly thought a line might be pinched in the EGR system, but then the engine sputtered and hesitated. I pulled over, turned off the engine for a couple minutes, then restarted. The engine seemed to run smoothly, but I babyed it straight to the dealer and left it with them to check it out. The service manager called to say he would have to keep it over night because he had to order injectors. Injectors! The car only has 8200 miles on it!

Now here's what he says that I'm unsure about. He questioned the quality of the fuel I'd been using. I told him that I had only ever used 1 type of gasoline in the car: BP 93 octane (BP now sells Amoco Fuels, which I have heard is some of the cleanest gas you can buy). He then said that I should be using a lower octane fuel. Like 87 octane or 'regular' unleaded. This is in direct contradiction with the owners' manual. He said that the fuel in the US is so much purer than the fuel in Europe that we don't always need the highest octane, especially in the warmer areas of the country. He said that the high-octane gas is burning too quickly and a residue is building up on my injectors (especially the #4 injector).

OK, I thought higher octane made the gas burn slower to prevent knocking in the colder weather, not faster. And what about his recommendation vis-a-vis my warranty. Manual says 91 Octane and above, he says 87 is OK. He said something about a service bulletin on this topic, which I will ask for a copy of, but what do you guys think? Does thic sound right to you?

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--Craig.

"When you see a fork in the road, take it!"
(Yogi Berra)

That mechanic is an ass. All MB's produced now require Super or 92+ Octane fuel due to the higher compression ratio of most of there engines. The C230K is a Supercharged engine and does require the 92+ Octane fuel. If you use lower octane the engine will Ping and then the ECU will retard the timing! Thus losing power to save the engine. Pinging is never a good thing and the ECU has to detect it first to retard timing, thus meaning that there is a risk to the engine in the long term due to excessive pinging. I would follow what the MB Engineers and Designers suggest not some Mechanic who obviously would like to tell you something diferent than the guy who actually designed and built the damn engines! The M271 engine is pumping 11psi of boost from the factory, not exactly low boost for that 1.8 L engine. Follow what the Boys and Girls in Stutggart suggest!

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~Jamie
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2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....

I would suggest your mechanic is fibbing.

Higher octane fuel does not burn faster or slower than lower octance fuel. The octane rating is simply a number that shows how reistant the gas is to burning upon compression. A "93 octane" fuel has the same properties as far as resisting detonation as a mixture of 93% octane and 7% heptane. Octane is much more resistant to detonation and therefore a higher octane number means higher detonation resistance. And why would how fast the fuel burns leave residue on the injectors? This mechanic does have previous experience with motor vehicles, does he?

Follow the owner's manual and find a new mechanic.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record

The guy is clueless! You probably can use lower octane, but the detonation sensor will retard timing (or maybe even boost) and the car will not feel as peppy. The best course of action is to continue using premium.

I would also question his diagnosis. What engine code was in memory and what does it mean? This is a very important question. What's the basis for changing the injectors. (I'm assuming the car is on warranty.)

You should either go to another dealer service department or ask for a meeting with the Mercedes dealer service rep and ask him to do a proper diagnosis, and then repair whatever is the problem, if their is a problem.

Duke

Yep......he's right, there was a bulliten concerning fuel quality but it was very specific that you must use PREMIUM FUEL in all current vehicles. So you are fine with the fuel you are using.

Ask which cylinder it was if it ever does it again. Cylinder 4 are known for either a problem with the valve seats or carboning up on that cylinder. Also ask them if they checked the fuel pump current draw (7-10amps from memory). If the current draw at idle gets out of that range then you have a fuel pump problem (common).

I'm presuming they are changing injectors because of a fuel starvation/lean running fault code. The fuel pump will do that.

Also ask if they took a fuel sample. This is a very early steep in diagnosing a misfire on these engines (water/contaminents in the fuel).

Sometimes the smooth running sensitivity is too low and needs to reset to the lowest sensitivity to avoid unnecessary cylinder shutoff.

I hope this helps you with your problem. Have comfort knowing that even if you get bs answers from service manager/advisors, the people who work on your car usually know these cars back to front.

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Alex.

MB Tech
Sydney, Australia
Volvo 122S
W201 190D 2.5 manual
W202 C240
W203 C32

I forgot to add that all the loan cars at my dealer are run on the cheapest grade of fuel available in Australia. The C180 (highest compression and lowest boost) is the vehicle that feels the crap fuel the most. Anything over 50% load between 2000-4000rpm is where you can feel the ignition beind retarded. This is a range where the average driver will use often so the old "I don't need performance fuel, I don't drive it hard" doesn't bear relivance anymore.

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Alex.

MB Tech
Sydney, Australia
Volvo 122S
W201 190D 2.5 manual
W202 C240
W203 C32

I see you mentioned that the mechanic in question is an M-B mechanic from a proper licensed M-B dealership, right???

What I have always done in situations like this (when the service manager or a mechanic from the dealer contradicts owner's manual specs), either to justify a work that is NOT needed or to cover for something they don't ACTUALLY KNOW is to have there answer or justification written and handed over to me (preferably using the dealer's stationary) and, of course, signed by all responsible parties.

Then, with this letter, contact your M-B representative or zone offices and inquiere about the issue.

You'll see what there reaction is...

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A. Rosich
CL 500, 1998
S 500 L, 1998
E 320 T, 1995 [Sadly sold ]

Thanks to everyone who offerred their opinions and direct knowledge of my problem! I picked up my car from the dealer yesterday and voiced my concerns (even quoting some of you responders) about the fuel recommendation. This is the only Mercedes dealership in town and I have been extremely satisfied with every department I have dealt with there so far. The service manager is a 20 year veteran at that dealership, a very friendly person and seems to genuinely know what he is talking about. However, he reiterated that MB has told his shop foreman that in certain, isolated cases (where there is carbon buildup on the #4 injector) better results and less buildup can be gained from 87 octane fuel. He says he has had a few cases like mine in the past and this took care of the problem.

He went to the foreman to see if a service bulletin existed that spelled this out, but couldn't find one. He said he knows the instruction was given verbally by phone from MB to his shop foreman. He said I was free to use any fuel I chose, but that he recommended trying the 87 octane fuel. What was done to my car:

Code 8319 Faulty injectors. Performed short test. Performed ME-SFI flash and scn code fuel computer. Replaced all injectors. Replaced ignition coil. Replaced spark plugs. Drained fuel tank, clean air intake system, add BG44K fuel additive to fuel tank.

All work was performed under warranty. Ignition coil was part of the prescribed remedy from MB--service manager didn't feel it was necessary, but followed MB's procedures. Also, injectors were not exact replacements of the stock injectors as the new ones were some sort of upgraded injector. I spoke with a representative from MBUSA's Customer Assurance Center today and told him my story. He was unable to find any written material to support using a lower than 91 octane fuel in this car, nor had he ever heard of such a remedy. He recommended that I continue to follow the fuel guidelines in the owner's manual, so I will. It was suggested to me on one of the forums I posted this issue on to rotate brands of fuel periodically so that I don't always have the same additives in every tankfull and I will try that as well.

Thanks again to everyone who responded to my thread--I really appreciate your collective knowledge!

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--Craig.

"When you see a fork in the road, take it!"
(Yogi Berra)

I could be wrong, but it sounds like the dealer was trying to make some warranty dollars from MBNA.

The "I was told you should use lower octane by phone" excuse sounds fake. They changed all of your injectors and a coil (was this even necessary?) to run up a huge bill with MB. They then blamed the whole thing on fuel.

I guess it's no big deal for you. You have new injectors and a coil. I'd DEFINATELY keep using high octane fuel.. you have a manual printed by experts on what you should use -- don't risk MB denying you a warranty claim in the future based on what some mechanic told you.

This is not an entirely uncommon thing, by the way

Neal

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'83 300SD 335,000km (207k) mi SOLD
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