Question about 2002 Mercedes-Benz C-Class

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2002 Mercedes C320 very poor fuel economy ~8 mpg, no engine codes or faults present

I drive about 3 miles per day, 15 miles per week. The car has no engine codes or faults present when plugged into OBDII device. Changed spark plugs, wires, MAF sensor, and fuel filter but still get about 8 mpg. I use 93 octane fuel. What could be the cause of such dismal fuel economy? The car has around 60K miles on it and I am the original owner. I use to get around 20-23 mpg during the first 5 years or so. Except for the bad mpg, everything else seems to work fine - good starts, idle, acceleration, etc. 2002 Mercedes C320 very poor fuel economy ~8 mpg, no engine codes or faults present

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  • john wongvipat Jan 01, 2013

    93 Octane available in NY but 91 octane isn't. Can't use below 91 according to manual.

  • john wongvipat Jan 01, 2013

    Thanks everyone for your comments.

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  • Contributor
  • 35 Answers

I'm not sure what the problem is specifically, but I can assure you this--you're basically throwing money way (and possibly exacerbating the issue) by using 93 octane fuel. Your car is timed and tuned to run most economically and with best performance with 87 octane fuel. The higher the octane, the slower the fuel burns. Longer burn time can equate to more power, but ONLY if your engine is designed and tuned for this application.
Couple of suggestions..checkto make sure your exhaust is "free". A plugged catalytic converter can really rob mileage. Tire pressure and air filter are worth mentioning as well.

Posted on Jan 01, 2013

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Posted on Jan 02, 2017

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stormbrewin
  • 426 Answers

SOURCE: 1997 mercedes benz E320 acceleration problem

You may also have issues with your air flow meter.Generaly though this symptom is usualy a fuel pressure problem.This test may or may not work depending on wether the fuel rail is the problem or the pump.Squeeze the fuel return line at the back of the fuel rail and if engine improves the fuel pressure regulator on the fuel rail may be faulty.If no improvement its likely the pump.The best and most accurate test would be to use an inline fuel pressure tester.Can you hear the pump pumping up to pressure when you turn the ignition on?Usualy though the pumps fail but can be heard running but unable to maintain pressure.

Posted on Nov 29, 2008

jasperoni
  • 203 Answers

SOURCE: My 1995 S500 Mercedes Benz is idling very rough.

before you spend any more money on your vehicle run a cylinder compression test. I know it seems unlikley with less than 100,000 miles but 119 engines do like to burn valves. the LH fuel injection system was only used from 93-95. LH is a germen abreviation for hot wire mass airflow. The later systems use a hot film. Your vehicle has electronic fuel injection so why did you have the fuel injecters pressure cleaned. unless you have the cis system which means your car is not a 95. Motor mounts are also a very common failure on that vehicle. In any event rule out the worst case and perform a compression test because it really sucks to spend alot on an engine and find out it needs a valve job. I'm assuming that the check engine light is not on. although wireharness issues are another common issue. these early C.A.N. cars are very difficult to troubleshoot electronically and the information provided by the factory is difficult to follow.

Posted on May 17, 2009

george460
  • 1 Answer

SOURCE: my mercedes e300 (1989) starts and runs ok but then cuts out.

I had a similar problem with my 1986 300e , which got progressively worse until the car was no longer driveable, I changed out the fuel pump relay and the problem went away.

Posted on Jun 28, 2009

michael4wgv
  • 166 Answers

SOURCE: I have a 1995 Mercedes SL500 with 114,000 miles.

your fuel pressure between 30-35psi is showing good at the moment. If you due suspect bad fuel pumps try and drive the vehicle with the fuel pressure gauge attached to monitor if it does drop when driving. Also make sure you have spark at all the spark plugs as a bad coil or a bad spark plug connector could be bad. They are available separately. You can also confirm this by doing a resistance check across the ignition wires. The ohm value should be printed on the spark plug connector. Generally they are about 2k ohms. No spark at one cylinder could cause the same symptoms but usually sets a code. The fuel pump will usually sound louder then normal when they are about to fail. Since there are two fuel pumps for the vehicle it is possible one of them is starting to fail. The throttle actuator can also cause drive ability problems but will generally cause the ASR light to come on. I would also look at the distributor caps and rotors as a potential cause as they can cause your symptoms with no check engine light. If possible drive the car with the fuel pressure gauge attached to monitor fuel pressure and with the engine at idle start pulling the spark plug connectors off and on to make sure the engine stumbles every time. Let me know what results you get and I will try to help further diagnose the issue.

Posted on Nov 17, 2010

  • 1796 Answers

SOURCE: I have a Mercedes s500

Hi!!
What all this codes have in common is that every single one of them can be caused by a vacuum leak, so carefully check for cracked, loose or disconnected vacuum hoses, wiring to the coils, fuel pressure regulator, fuel injectors, specially on cylinder 2.

  • PO100 - Possible causes are wiring harness failure, air leak or defective hot film MAF sensor
  • PO130 - Vacuum leak
  • PO170 - PO173 - Possible causes are air ingress (leak), fuel injector failure, pressure regulator failure or mechanical wear of engine. Inspect and repair as necessary.
  • PO300 - possible causes are vacuum leak, wiring harness failure or ignition coil defective.
  • PO302 - If limit value for misfire "harmful to TWC" is exceeded, the MIL flashes immediately. If too many combustion misfires occur in one cylinder, the cylinder is switched off (cylinder selective fuel shut off). After the affected cylinders are shut off, the MIL changes from flashing to continuously lit until next time the engine is started. If combustion misfires are recognized, the fault code P0460 or P0462 is set if fuel tank level is too low (fuel reserve indicator light is on). Combustion misfires due to a shortage of fuel are recognized by means of this additional information.

NOTE:After cylinder cut-out system is turned off, the system monitors (through misfire detection) if all intake and exhaust valves are open again.
NOTE:Misfiring may be caused by many faults in the fuel injection system. Usually a misfiring fault is stored with faults pertaining to other components. An engine mechanical fault could also cause a misfire condition.
Good Luck!! A HELPFUL - 4 THUMBS - rating for this solution would be greatly appreciated. Thank you for using FixYa.

Posted on Dec 03, 2010

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