Results bad compression. Move forward with leak test?

Discussion in 'VW Mk3 Jetta, Passat TDI and other/older diesels' started by fleck, Jul 14, 2016.

  1. fleck

    fleck New Member

    Joined:
    May 23, 2016
    Messages:
    11
    Car:
    98 Jetta tdi
    Location:
    Alaska
    I been intermittently noticing some "slap" when driving slowly but it is becoming more constant. I have done 2 purges, removed brand 5w40 I recently used which was VW compliant and splurged for Liqui Moly 5w40, replaced air, fuel and oil filters which I believe has made the sound more clear and bright. I have also replaced power steering belt, serpentine belt, tensioner pulley and pulley tensioner, disassembled and cleaned EGR to turbo. I was considering replacing the camshaft and lifters, but decided to buy a inexpensive diesel compression tester and check compression before moving forward. It appears that I have issues with cylinder 2 and overall low compression in the mid to low 300's but within spec except #2.

    I have only had the car for a few months but really love it, it was cheap, its a little rocket and I am getting 34 to 37 mpg, I bought it to work on and learn.

    Will a leak down test help me to understand if it is a blown head gasket issue vs a bad cylinder? I am planning to replace the timing belt and now want to replace camshaft, lifters and head gasket but maybe I'm done and I should just watch the fluids and drive.

    This a hobby for me so I may be way off in assesment of problem and using the tool incorrectly, any advice is much appreciated. Thanks-Mike

    Attached a link to #1 which 3 & 4 were about the same and #2 the bad cylinder.

    #1

    Bad Cylinder#2
     
    login to remove this ad
  2. chittychittybangbang

    chittychittybangbang Administrator

    Joined:
    May 23, 2007
    Messages:
    23,721
    Car:
    2006 Jetta TDI
    Location:
    CT
    Your compression tester is leaking somewhere. The pressure should build up and then level off. On TDI, you read the peak when it stops going up vs. gas engines where you crank 3-4 times. So you may have to crank 7-8 times and then the needle stays there until you press the button to release pressure. So I would say the videos are inconclusive. Make sure all the unions are not leaking.
     
    Magnus likes this.
  3. fleck

    fleck New Member

    Joined:
    May 23, 2016
    Messages:
    11
    Car:
    98 Jetta tdi
    Location:
    Alaska
    Thanks, I will replace the bulky connector with something else and re-test. I was very mindful of the atypical angles and not cross-threading. I did not use a rubber grommet on the shoulder of the adapter fitting, I will get one.
    I have read in some articles to floor the gas pedal when compression testing, I did not and would assume if it is drive by wire/ecu this would not make a difference. Thanks-Mike
     
  4. Keithuk

    Keithuk Super Moderator

    Joined:
    Aug 29, 2010
    Messages:
    6,771
    Car:
    2010 Golf GTD (170) CBBB
    Location:
    Stoke on Trent, England
    You only floor the accelerator pedal on gas/petrol engines to remove the vacuum from the inlet manifold and to get a full charge of air. Diesels don't do the same as they have an exhauster (vacuum pump) to supply vacuum for the brake servo. It doesn't hurt anything if you give it full throttle.

    I've watched the video's and I agree with Chitty you have a leak on the connection somewhere as it goes up then down it doesn't hold the pressure. I good quality Compression Ignition (CI diesel engine) compression gauge is needed.

    When you do a compression test to test it dry first and note the reading. Then you get an oil can and squirt some oil in the cylinder and crank it for a second or two to remove the excess. This makes a temporary seal around the piston rings. Check compressions again to see if it increases.
     
    fleck likes this.
  5. fleck

    fleck New Member

    Joined:
    May 23, 2016
    Messages:
    11
    Car:
    98 Jetta tdi
    Location:
    Alaska
    Thanks,
    I am going to work today, I will hook the tester up to my air compressor. I wanted to do a second test with oil test also but was concerned about my battery charge, need to get some kind of backup together. Thanks again -Mike
     
  6. fleck

    fleck New Member

    Joined:
    May 23, 2016
    Messages:
    11
    Car:
    98 Jetta tdi
    Location:
    Alaska
    Tester functions properly when hooked to airline and a ball valve between two to stop flow. I must have done something incorrect repeatedly. I am going to look for a longer less bulky glow plug adapter, or bite the bullet and pull the injectors. Thanks again
     
  7. ALT 10000'

    ALT 10000' New Member

    Joined:
    Apr 14, 2014
    Messages:
    21
    Car:
    VW, Jetta,'04 BEW
    Location:
    Colorado
    Mods:
    Chipped
    Since you mentioned its a hobby. Preform the leak down test for a piece of mind. This could show a valve that is not closing completely/cracked or even needing a adjustment.
     
  8. Tom MacDonald

    Tom MacDonald Member

    Joined:
    Nov 1, 2015
    Messages:
    52
    Car:
    2004 Jetta TDI Station Wagon (North American)
    Location:
    Halifax, Nova Scotia
    Any updates on this?
     
  9. crsmp5

    crsmp5 Well-Known Member

    Joined:
    Feb 14, 2012
    Messages:
    1,234
    Car:
    85 kubvan
    ahhh bad way to test it.. cause a ball valve will not let the air outta the line like when a valve opens and looses compression due to open vent... imo the check valve in the tester is stuck open... think tire shrader valve in valvesteam.. its built into the adapter that goes into the glow plug hole...

    never seen a worn cam in one of these and once in a while you will find a bad lifter.. but its not common either unless t belt broke... so vs pissing $ away on stuff you do not need.. buy a good tool!! as i expect you half assed what ever glow plug adapter you have.. mine is nice like glowplug... nothing bulky
     
    Last edited: Jan 15, 2017 at 6:20 PM

Share This Page