Low Compression?

Discussion in 'VW Mk4 Jetta, Golf, New Beetle, Passat TDI forum' started by Riccogolf, Mar 19, 2017.

  1. Riccogolf

    Riccogolf New Member

    Joined:
    Nov 12, 2016
    Messages:
    9
    Car:
    VW, Golf Mk4 pd150 ARL, 2003
    Location:
    Chichester, uk
    Hi,
    On a 2003 pd engine (1.9 ARL on 104k mi) with compression on all 4 cylinders around the 280psi/ 19bar mark what starting characteristics would members expect to see?

    1. Never start, 2. lots of turnover but catch eventually, 3. difficult on cold engine but fine with warm, 4. No real problem or 5. other

    Any comments, or number, grateful received,

    Many thanks in advance

    PS No test! I'm just curious to know the starting characteristics of such an engine as mine been diagnosed with this compression but in my inexperienced opinion, starts better than I'd expect.
     
    Last edited: Mar 22, 2017
  2. Riccogolf

    Riccogolf New Member

    Joined:
    Nov 12, 2016
    Messages:
    9
    Car:
    VW, Golf Mk4 pd150 ARL, 2003
    Location:
    Chichester, uk
    so an update after work has been carried out, more below, will try to be brief and still interested to hear of any similar experiences or possible reasons....as I'm not convinced there has been complete resolution.

    As a background, recently had a new head and turbo fitted because of cam failures. Car computer showing 37mpg for secondary road driving, worse than before original cam got replaced....But car basically running well, had great acceleration, plenty of power and steady idle. Warm start was never an issue, only in the mornings, from cold (0-5c), although it catched quickly it would then hesitate and splutter for 3-5 seconds, quite a lot of white smoke, then settle down and run fine, except on pulling away immediately (when cold), it would loose acceleration for a few seconds before re-establishing normal good driving with exception of higher than expected fuel use. This only ever happened very soon after starting from cold.

    Compression was found to be 19bar/ 275psi on all 4 cylinders....diagnosis, although the piston rings were replaced with specced replacements when the new head went on, the machined top groove on the original piston heads was too large for the replacement rings allowing movement. Apparently there has only ever been one size for these, but the loose fitting top rings giving the poor compression reading.

    New pistons have been fitted, compression improved to 23-24bar/ 340psi, and although there has been an initial improvement, including mpg to around 40mpg, there is still a hesitation immediately after cold start, though better, still smoky (and getting worse?), and had another episode of lack of acceleration from cold yesterday.

    Anyway, going to keep driving, monitor everything as much as possible, and compare computer mpg with filling tank. Fuel system has been looked at but no obvious fault found.

    If any of this sounds familiar with anyone would be interested to hear.

    Many thanks
     
  3. Riccogolf

    Riccogolf New Member

    Joined:
    Nov 12, 2016
    Messages:
    9
    Car:
    VW, Golf Mk4 pd150 ARL, 2003
    Location:
    Chichester, uk
    So, just filled tank to get an average mpg number to compare with ecu dash computer reading.

    Over 480 miles, ECU gave an average (mainly shortish cold start drives and some motorway) of only 40.6mpg. Filling the tank showed an average 46.4mpg, a 14% better number, though still down on the 50-52mpg I used to get (if the ecu to be believed)

    I've no idea why such a big discrepancy...even comparing and taking l/h readings from VCDS and comparing directly with the dash readout gives a 4-5% better reading (than the dash computer av mpg).

    I've read plenty of stories where mpg worsened after a camshaft job, but never saw any reasons or solutions.

    Mind boggling.
     
  4. crsmp5

    crsmp5 Well-Known Member

    Joined:
    Feb 14, 2012
    Messages:
    1,432
    Car:
    85 kubvan
    how many miles since new rings?? till ya get to 10,000 or so.. with non synthetic oil... that will slow break in of rings big time... the compression will be "low" you concern is how even they are.. with in 10% type thing.. as it breaks in the compression will go up.. so fuel milage, cold start, smoke on start up will go away and improve
     
  5. Riccogolf

    Riccogolf New Member

    Joined:
    Nov 12, 2016
    Messages:
    9
    Car:
    VW, Golf Mk4 pd150 ARL, 2003
    Location:
    Chichester, uk
    Thanks for the input. 10k? Really. Okay, very early days then, the car's barely left the workshop. Will keep driving, enjoy it and monitor every so often..
    ...
    Regards
     

Share This Page