Performing A Compression Test

[salemf]

Hi guys can anyone confirm for me this is the right way to do a compression test on a 1999 Nissan Silva JDM s15.

1: Remove Sparkplugs

2: Remove Coilpacks(ignition system)

3: Put in the Hand gauge

4: Hold throttle open to full and keep turning the key until the value on the meter doesnt go up

5: This is your reading

Quick Question though:

1: Does the battery Need to be removed?

2: Do you need to remove anything to do with the fuel etc?

It should read +/- 10% of 170 does all this sound right guys?

[blind_elk]

Hi guys can anyone confirm for me this is the right way to do a compression test on a 1999 Nissan Silva JDM s15.

1: Remove Sparkplugs

2: Remove Coilpacks(ignition system)

3: Put in the Hand gauge

4: Hold throttle open to full and keep turning the key until the value on the meter doesnt go up

5: This is your reading

Pretty much.

Quick Question though:

1: Does the battery Need to be removed?

No. (how are you going to crank the engine otherwise?)

2: Do you need to remove anything to do with the fuel etc?

No

It should read +/- 10% of 170 does all this sound right guys?

It should be consistent across all cylinders with +/-10% variation (not necessarily 10% of 170)

[salemf]

Pretty much.

No. (how are you going to crank the engine otherwise?)

No

It should be consistent across all cylinders with +/-10% variation (not necessarily 10% of 170)

cheers mate appreciate it alot! is it worth putting some oil in teh cylinder after doign the comrpession test and seeing the results afterwards?

[SECURITY]

yes you do need to unplug something else - you need to unplug either the CAS or the injector loom. i usually unplug them both for good practice.

after you do the compression test it would be good to see the variance in compression with oil in the cylinders (wet test), a cap full is plenty.

for example if you've got 140psi dry and 160 wet then you know youve got a compression ring problem but if you've got 140 wet and 145-150 dry then its not a huge problem.

[salemf]

yes you do need to unplug something else - you need to unplug either the CAS or the injector loom. i usually unplug them both for good practice.

after you do the compression test it would be good to see the variance in compression with oil in the cylinders (wet test), a cap full is plenty.

for example if you've got 140psi dry and 160 wet then you know youve got a compression ring problem but if you've got 140 wet and 145-150 dry then its not a huge problem.

Ok cheers mate so for a healthy engine so absically a used car worth buying what results for the dry and wet test would you say would be acceptable mate?

btw Happy Easter

[SECURITY]

Ok cheers mate so for a healthy engine so absically a used car worth buying what results for the dry and wet test would you say would be acceptable mate?

btw Happy Easter

155 and above is average for a healthy engine. too high is no good. anything above the 175 mark COULD mean cracked ring/land but you would know from the colour of the plugs.

good plugs are usually brownish. black and you're running rich, glazed black and its usually cracked ring, white and its usually turbo oil seal or worn rings.

for buying a car you would want to do a leak down test too. anything 5% and below is good.

and happy easter bud.

Edited April 4, 2010 by SECURITY

[salemf]

155 and above is average for a healthy engine. too high is no good. anything above the 175 mark COULD mean cracked ring/land but you would know from the colour of the plugs.

good plugs are usually brownish. black and you're running rich, glazed black and its usually cracked ring, white and its usually turbo oil seal or worn rings.

for buying a car you would want to do a leak down test too. anything 5% and below is good.

and happy easter bud.

Ok cheers security...so both the dry and wet tests should be above 155 got it!

Can a leak down test be done by myself as well? any additional tools required?

And while im at it besides the usual oil leaks,clutch,suspension etc any other things i should look out for with a s15?

[SECURITY]

Ok cheers security...so both the dry and wet tests should be above 155 got it!

Can a leak down test be done by myself as well? any additional tools required?

And while im at it besides the usual oil leaks,clutch,suspension etc any other things i should look out for with a s15?

you'd need a leak down tester. ive never used one so ive got no info on it, sorry mate.

s15's have mostly been in front enders.. here is my checklist:

- make sure all panels line up perfectly, each panel should have the exact same space between them. if for example the left side of the bonnet doesnt line up with the right side, then its been removed/replaced at some point. same with the back and sides (boot, guards, doors). look for the usual excessive welds around the strut brace and in the boot, remove the boot carpet to check for this.

- s15 6 speed gearboxes are shit and unfortunately most of their owners think they're pro drifters so check for any noises and strange vibrations through the shifter.

- rocker arms usually break on the s15's too. there isnt a way to check for worn/broken ones without opening up the rocker cover but if the thing starts to run rough its usually a broken rocker arm. get some rocker arm stoppers for it.

- its a good idea to get under the car and check for brand new parts, once i saw an s15 with the 2nd hand parts writing all over the rear right hand corner of the car. pretty much all the parts on the rear right hand side of the rear cradle had the chalky writing on it.

other than that, good luck.

[salemf]

you'd need a leak down tester. ive never used one so ive got no info on it, sorry mate.

s15's have mostly been in front enders.. here is my checklist:

- make sure all panels line up perfectly, each panel should have the exact same space between them. if for example the left side of the bonnet doesnt line up with the right side, then its been removed/replaced at some point. same with the back and sides (boot, guards, doors). look for the usual excessive welds around the strut brace and in the boot, remove the boot carpet to check for this.

- s15 6 speed gearboxes are shit and unfortunately most of their owners think they're pro drifters so check for any noises and strange vibrations through the shifter.

- rocker arms usually break on the s15's too. there isnt a way to check for worn/broken ones without opening up the rocker cover but if the thing starts to run rough its usually a broken rocker arm. get some rocker arm stoppers for it.

- its a good idea to get under the car and check for brand new parts, once i saw an s15 with the 2nd hand parts writing all over the rear right hand corner of the car. pretty much all the parts on the rear right hand side of the rear cradle had the chalky writing on it.

other than that, good luck.

legend mate cheers! have a good day

[mad082]

it's not uncommon to have the rocker cover get damaged when a rocker arm breaks. had it happen to a mates sr20 out of a s13. hole in the rocker cover the size of a 50 cent piece, LOL

[aerofocker]

security.are you a mechanic?

Edited April 5, 2010 by aerofocker

[SECURITY]

security.are you a mechanic?

nah mate, why?

[aerofocker]

just wondering why/how +175psi could mean a ringland?

[SECURITY]

When you bust a ringland you can either have it give you 0 compression or it could have oil push past it and sit around the crown of the piston giving you overly high compression. That is usually caused by a small fracture or crack rather than the usual chunk that breaks.

Edited April 6, 2010 by SECURITY

[aerofocker]

well im a mechanic and high compression has never been an indication of a cracked ringland in my expierence, high blow by,increeced knock and uneven idle are the usual indication

[SECURITY]

well im a mechanic and high compression has never been an indication of a cracked ringland in my expierence, high blow by,increeced knock and uneven idle are the usual indication

Those are the usual symptoms, just telling you what I've seen on a motor.

[Peter89]

remove the fuel pump fuse otherwise you ll be pumping in lots of fuel into the engine, without it burning and possibility changing the results.

then, when you start it, you ll hear the backfire OF YOUR LIFE.

trust me, i learnt the hard way.

[salemf]

remove the fuel pump fuse otherwise you ll be pumping in lots of fuel into the engine, without it burning and possibility changing the results.

then, when you start it, you ll hear the backfire OF YOUR LIFE.

trust me, i learnt the hard way.

isnt that why you push your foot all the way to the floor on the accelerator when u crank it? can u just remove the relay to the fuel pump instead?

[**RB2530**]

isnt that why you push your foot all the way to the floor on the accelerator when u crank it? can u just remove the relay to the fuel pump instead?

One reason for WOT during comp test is to allow NTP (lets see who knows what NTP means??) air to into cylinders. If you didn't do this the resultant peak cylinder pressures would be lower as there would be at a vacuum in all cylinders during cranking.

[SECURITY]

i can make up abbreviations and pretend i know stuff too... LOL.

with the throttle closed while you perform a compression test your pistons will try draw air in while the inlet valves are open and cause resistance against the rings (vacuum) while the motor turns. so if the motor begins its compression stroke with -10psi your compression test will show up 10psi lower. pretty much what Paul said but less technical.

NTP is a term they use in physics, here we'd just use "0 vacuum" as the air does not need to be at a 'normal' temperature and the air entering the combustion chamber isnt actually pressurised. it is the chamber that is causing the pressure.