Compression Test - Am I doing this right?

[bobski1]

08 VW mk5 GTI

VCDS states I have a various misfires but repeating on cylinder 3 so I decided to investigate the cause before I start to strip the engine to do the cam chain.

I swapped coil pack 3 to 4, issue remained on cylinder 3
I swapped the plug 3 to 4, issue remained on cylinder 3

Next step was to do the compression test. I borrowed the tested from a friend and screwed into cylinder 1 (M14 thread adaptor), removed 15A fuse F27 from passenger side box which I believe to be the fuel pump? I cranked it 5 times and each time it made an awful squeak/screach like the air was escaping out and read 0bar. Wasn't sure what was going on so moved onto the rest of the cylinders and they all did the same sound and all ready very poorly. I am unsure if its a dodgy tester, user error or if the engine is truly goosed.

Cylinder 1 - 0 bar
Cylinder 2 - 2 bar
Cylinder 3 - 4 bar
Cylinder 4 - 4 bar

Each time I cranked the tested would pulse up but would immediately loose all the pressure but I cannot say how much as it was quite dark and visibility of the gauge wasn't the best, anyway any help or tips would be most welcome?

[GreenV8S]

Those readings are not plausible - you probably didn't get a good seal in the spark plug hole.

Also, you should have had the throttle wide open and cranked it until the reading maxed out.

[E-bmw]

GreenV8S said:

Those readings are not plausible - you probably didn't get a good seal in the spark plug hole.

Also, you should have had the throttle wide open and cranked it until the reading maxed out.

^^^^ Wot 'e said.

There is normally an o-ring to prevent leakage at the plug hole & any other connections, make sure they are all there and the hose isn't perished.

[davidexige]

bobski1 said:

08 VW mk5 GTI

Each time I cranked the tested would pulse up but would immediately loose all the pressure but I cannot say how much as it was quite dark and visibility of the gauge wasn't the best, anyway any help or tips would be most welcome?

If I'm reading this correctly, your saying the gauge registered a pressure but dropped off once you stopped cranking? If so two things spring to mind, though first I'll say its quite a few years since I've done a compression test, the testers I used would trap the pressure within the gauge as you cranked the engine, you could then read the max pressure reached, there would then be a pressure release screw/button on the side of the gauge that you had to operate to release this trapped pressure, does your tester have this, if not is it just a gauge on the end of a pipe? if so you will need to someone to crank the engine while you monitor the gauge.

[bobski1]

It has an o-ring on the end of the brass fitting and looked in good condition, I put in the rubber hope till it was as right as I couldn't.

Yes the gauge does have a pressure release valve button which you press in to release and reset the gauge back to 0. The needle was pumping with each crank but it seems to be leaking straight back out which could be where the squeak/noise was coming from.

Going to get a 2nd tester and try again tonight, hoping it is just the gauge but if not sounds very goosed.

[Super Josh]

Did you have your foot flat on the throttle so that you weren't chocking the engine?

[Doofus]

You say you screwed the gauge in. Is it the right thread?

[Lincsls1]

Doofus said:

You say you screwed the gauge in. Is it the right thread?

[bobski1]

So confirm it was a bad tester. I got a different one and it ran perfectly, 180PSI in each cylinder after 5 cranks. All good on the head and likely just a bad injector, new repair kit, inlet manifold gasket and injector on order and will fix along with the other bits on the list.

Pays to have the right tool, of the right quality when doing these bits