Help with '05 ML500

[Falcon_LS]

Mileage is just over 81,000 km (50,625 miles), all services are up to date following the service intervals set by Mercedes-Benz. Major issue that needs to be addressed.

The engine feels underpowered. When you rev the engine in neutral, it feels heavy and you can have your foot on the floor but it doesn't go over 4,000 rpm. When you're driving, and the accelerator is depressed more than 1/4 of the way, there is a lag before the engine responds.

When I was driving the other day, I needed to floor the gas in the fast lane because the guy behind me was driving like a bat out of h3ll. The moment I did that, the rpm got up to 4,000 and stayed there...no amount of throttle input did anything. I also got an ESP BAS light on the far left of the instrument panel and the engine ran extremely rough. Killed the ignition and restarted the engine, which resolved the problem.

Following the Mercedes maintenance schedule, spark plugs are not due for replacement until 100,000 km. That said, should I go ahead and replace them early? Thanks!

 

[ARCOgraphite]

Sounds like bad fuel or overfilled oil as a simple jump off place assuming nothing is "broken". I dont think a plug change will help (unless the car received leaded fuel or fuel with MMT or octane booster which are plug killers). Maybe the cat converter is plugged by using bad fuel? Does the vehicle have catalytic converters? Also check the air filter for reasonable cleanliness.

 

[Falcon_LS]

I've been told STP Fuel Injector Cleaner was added to the tank. Now I'm thinking if this could be the reason.

 

[ARCOgraphite]

STP is not great but in an of itself woyud not pose this problem. May have gotten bad fuel or somone put bad stuff into the tank. Was the former owner not well liked? Also if the vehicle was driven very conservatively its life, it will be a slow 3 legged dog until you get it "decarboned".

 

[Kestas]

Has the fuel filter been replaced? It's very hard to get at, and it's rare that an owner - even a DIYer - would replace it before 100K.

Ditto to checking the converter. Give it a shake and see if it rattles.

 

[Falcon_LS]

Will take a look at the cats, thanks for pointing that out!

Replaced the fuel filter myself last year, and it was one of the worst jobs I've ever undertaken. The old filter was somewhat clogged, although the new (genuine) one barely has 12,000 km (7,500 miles) on it.

Originally Posted By: ARCOgraphite
STP is not great but in an of itself woyud not pose this problem. May have gotten bad fuel or somone put bad stuff into the tank. Was the former owner not well liked? Also if the vehicle was driven very conservatively its life, it will be a slow 3 legged dog until you get it "decarboned".

Car's been with us for five years now, although it has been driven somewhat gingerly.

 

[NateDN10]

The only thing I can add is that the fact it won't rev over 4000 RPM in neutral isn't necessarily indicative of a problem. Many engines won't let you rev all the way to redline in neutral. However, if it won't redline when in gear, that's a different story...

 

[Trav]

Quote:
ESP BAS light

Did you check for codes?

 

[Falcon_LS]

An update on the issue. The vehicle is on its third tank of fuel since the problem arose, and is running smoothly like before.

The culprit was overdosing the STP Fuel Injector cleaner. My brother's wife used to use ACDelco Fuel Injector Cleaner (Canadian sourced white bottle) every 10,000 km (6,250 miles), which states two bottles should be used to clean the fuel system. She couldn't source the ACDelco stuff this time, and dumped two bottle of STP Fuel Injector Cleaner (1 bottle treats 21 gallons). So she dumped in enough cleaner to treat 42 gallons in about half a tank (9 gallons) of fuel and that must have had quite an affect.

Thankfully, nothing is damaged and the truck runs like before.