W124 E220 down on power, mpg

Discussion in 'Engine' started by Dickie14, Jan 3, 2019.

  1. Dickie14

    Dickie14 New Member

    Messages:
    19
    Joined:
    Apr 6, 2014
    Car:
    W124 E220 Coupe
    Recently acquired a '96 E220 coupe but it is noticeably down on power compared to the one I owned until recently (same age, similar mileage). I'm also getting worse fuel economy - 28mpg if I'm lucky on a motorway run when my previous one would consistently return 30-32mpg.

    Anything I should I be looking at?

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  2. grober

    grober MB Master

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    The obvious one would be a fault on the HT circuitry causing a cylinder misfire, altho that should probably be detectable as a certain engine roughness. The inlet camshaft is variable so a cam adjuster failure to alter cam timing would noticeably alter engine power/ response. Other possibility might be transmission loss or the quite simple throttle plate/ throttle cable adjustment not permitting full throttle opening. Fuel rail pressure should be checked and weak running /combustion problems might be revealed by examining the spark plugs
     
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  3. OP
    OP
    Dickie14

    Dickie14 New Member

    Messages:
    19
    Joined:
    Apr 6, 2014
    Car:
    W124 E220 Coupe
    Cheers for the swift, detailed response! In terms of s misfire how rough are we talking? The engine does sound coarser than my old one but it's not lumpy.

    Going to get the garage to look at the throttle adjustment and cam adjuster in a couple of weeks

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  4. grober

    grober MB Master

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    With the E220 HT breakdown is normally down to faults with one of the 2 coils located under the inlet manifold- its a lost spark system - each coil fires two plugs simultaneously 1+4 or 2+3 but one cylinder is on the compression stroke and one on the exhaust. If not the coils then possibly the low tension wiring or dodgy HT wiring/plug connectors. Easiest diagnostic is to check all the plugs for any sooting up indicating its not always firing correctly.
    This video on a M104 engine [ same family] demonstrates a rough test for the camshaft adjuster solenoid operation- you will note he limits the current supply!- altho much better to test its operation by checking with a fault code reader. It should also be noted that cars of this vintage are plagued with dodgy engine wiring looms- the insulation cracks leading to shorts/ mysterious symptoms- any signs of cracked or flaked insulation means a new/ rebuilt wiring loom!
     
    Last edited: Jan 4, 2019
  5. coupe addict

    coupe addict Active Member

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    Odd faults can arise from partial failure of the wiring to the MAF sensor at the point where it clips to the back of the head. Generally the engine bay wiring loom isn't as fallible as on the M104 engine, but this particular location is is weakest spot. Splitting the outer case of the wiring will quickly confirm or deny the fault: if the insulation is cracked or crumbling a local repair is very easy.
    Steve
     
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  6. Vlad

    Vlad MB Enthusiast

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    I would also suspect a failing Air Flow Sensor
     
  7. OP
    OP
    Dickie14

    Dickie14 New Member

    Messages:
    19
    Joined:
    Apr 6, 2014
    Car:
    W124 E220 Coupe
    Finally got the garage to have a look into this. They immediately noted the throttle cable was a bit slack and tightened it up correctly and wow, what a difference! Feels like a different car! It now drives as perkily as my old one so I'm very happy. Doesn't explain the mpg but I'll keep an eye on that.
     
  8. jpwilliams

    jpwilliams Active Member

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    Wirral /Axarqia,Spain
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    W210 DIESEL AUTO EST,LEXUS GS 450h

    Colder weather might explain the increased fuel consumption ?
     

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