Comp testing a V6

[losh1971]

Can anyone tell me how to comp test my V6? Been many years since I have done one and not sure how to go about it on my VR.

 

[vc commodore]

With the fuel relay disconnected, remove one plug at a time...Wind the engine over with the compression tester (preferably a screw in type, rather than push in) about 3 complete revolutions and get the reading...Once that is done, place a bit of oil down the spark plug hole and repeat, noting the reading....Do this with every cylinder.

I am unsure of the compression variations with this engine, dry and wet, so you'll have to research those

 

[shane_3800]

You don't need to only do one plug at a time you can take them all out it's easier on your battery and starter that way. You also don't need to disconnect the fuel just jump the starter relay that way there's no fuel or spark.
Oil in the cylinder is for checking rings and is redundant imo as you should be able to tell the ring condition by blow by and oil consumption and how well it runs ect.

Some people hold the accelerator pedal down but that just speeds up how fast it will hit compression. Just wind it over untill the needle stops increasing.

 

[losh1971]

Thanks VC and Shane. I will try and do it this weekend. I have a screw in comp tester so will be interesting to see if it still works. It's over 30 years old. I'm only going to perform dry test I think.

 

[EYY]

Yep all plugs out and hold throttle wide open.

Do the wet test if you find a suspect cylinder

 

[someguy360]

As above, make sure your fuel pump relay is disconnected and throttle at WOT, I've seen many not do that with hillarious results

 

[gtrboyy]

warm engine up or do it after a drive
remove f/pump fuse or relay...start it up when it stalls good to go.

pop all plugs out,screw tester in then full throttle & crank over to count of 5 revolutions/number whatever..as long as it hits highest reading it can achieve.

write down each bank...if uneven do wet test to see if ring issue or just wet test a few cylinders to see difference for general wear n tear.

cheap shite guages sometimes leak so double check guage if readings all over the place.

 

[Immortality]

When I've had cars tested when purchasing the AA guys have always removed the main DFI plug, pulled all the plugs and held the throttle at WOT and then crank until you get the maximum reading.

No timing pulses from DFI means no injection pulses from the PCM and you're not loading up the coils either.

Pulling the fuel pump relay is not fail safe, on the Commodore The fuel pump is initially powered by the PCM via the relay to prime the fuel system for a few seconds, the fuel pump is also wired via the oil pressure switch so once the engine has oil pressure power is provided to the fuel pump. IF you don't believe me check the wiring diagrams. Practical experience confirms this fact (don't ask how I know).

 

[losh1971]

^^^^^^ This is the thing I needed to know. I was wondering about potential issues with coils and DFI. Last thing I want is to damage the DFI as I don't have a spare anymore.

 

[shane_3800]

Umm my way bypasses all the stuffing around. You give the starter power it spins the engine and the ECU has no power so not input to the DFI or the injectors.
All you have to do is pull the starter relay get a paperclip and jump the relay.