Compression Test Results

[ozclio03]

Hey Guys

Wondering if anyone can help me determine if there is something wrong with my clio, the back of the car is always heavily covered in black smoke marks(looks like Turbo Cards rear end) Doesnt seem oily I hoped it is simply fuel. Had a couple of mechanics look at it but they got no idea. I thought it was simply an issue with the custom RS Tuner Map / JMS RS2 Manifold

As the car doesnt burn oil, (oil level fine) never seen black smoke, piece of paper test all good! Fuel Usage lil high then standard but nothing crazy

Compression test was done after driving so car was 'up to temp'

I simply removed plugs one by one (and coil pack plug)

1 - 160
2 - 150
3 - 152
4 - 148

Gave it about 4 - 5 cranks and the car has 150,000km

Any ideas what the F is going on, are the figures low?

 

[Fred@BTM]

yes that's low, a "good" one is up around 190psi across the board, but saying that yours are all not that far apart, have you checked the cam timing as if that's out significantly it can affect a compression test

 

[ozclio03]

was last done by a reputable renault workshop, it is due again in the next couple of months, once its set corretly it cant change can it? even if the Harmonic Balancer is screwed?

 

[Chip-mk1]

You mean dephasor, and not that wont effect the values on cranking.

Did you have the throttle open when cranking, like fred says normally if its screwed you would expect more discrepancy between values, but it could be that all 4 are just really worn out.

 

[ozclio03]

didnt touch the throttle,should i have?

 

[Chip-mk1]

Yes you should have it fully open so the engine car breathe as easily as possible during the test.

Also you need to either do all tests with only one plug our or all with all 4 plugs out, not take one plug out at a time as you test and not put back in before the next (or the engine turns over at different speeds for the tests)
Personally I do with all plugs out normally, its less strain on the starter and battery that way. (but either are valid)


Also you should unplug the injectors during the test. (fuel can effect the seal and hence the readings)

 

[MartinR]

Mine ran 190 across all four.

 

[Chip-mk1]

Mine ran 190 across all four.

190-200 is about right for a healthy 172 IME but I dont take too much notice of specific values as Ive got 2 gunson gauges that read 10psi differently anyway, so clearly they arent all mega accurate, the key thing is normally if one or more cylinders vary a lot on the same tester on the same engine.

A leakdown test is more reliable TBH, but compression test is better than nothing!

 

[ozclio03]

ok I simply removed one plug, screwed in gauge ran test, re installed plug moved onto the next.

I will remove all the plugs tomorrow and un plug injectors (I can still leave injectors in right)

keep foot flat to the floor when re running the test.

Heres hoping it reads a lot higher.

Thanks Heaps Chip and Fred - Love reading all your posts and only wish I lived over there and either of you could look after my car!

 

[Chip-mk1]

Its fine to refit the plugs like you did, so long as you do it each time, but all 4 out will let it spin easier.

Yes to all the other points, let us know how you get on.

 

[MartinR]

Chip bit of a stupid question but would incorrect timing affect the compression figures by much? As in alot lower?

 

[Chip-mk1]

Chip bit of a stupid question but would incorrect timing affect the compression figures by much? As in alot lower?

Yes mate it can do, as what you are measuring isnt the compression ratio explicitly its the amount of compression achieved, which means that if the cylinder hasnt filled as much in the first place, or has been allowed to empty a bit (by valves not opening until later on the intake stroke or shutting after the compression stroke has finished) then it will effect results.

If you have a very big duration cam its not uncommon to see a big drop in compression tester figures.

 

[MartinR]

Thanks Chip you are a star!! Just put a few demons to bed now

 

[ozclio03]

Thanks Chip you are a star!! Just put a few demons to bed now

I second that - Your are a star!

 

[Chip-mk1]

No problem mate, cam timing is something very few people really get properly.

Its easy to think as the valves as opening at the top and closing at the bottom for the inlet and opening at the bottom and closing at the top for the exhaust, but in reality its quite a long way from that.

This is why when you advance or r****d the cams it makes a difference to power, you are changing which parts of the stroke the valves are open for.


Easiest one to think about is the point the inlet valve should shut.

At low rpm the cylinder has a lot of time to fill, so by the bottom of the stroke its almost full, so if you hold the valve open for much of the compression stroke it will leak air back out, but at high rpm when the cylinder hasnt had enough time to fill in the first place, if you keep it open for a portion of the compression stroke, air continues to poor in even though the piston is going up, the sweet spot is when the valve shuts just as the pressure in the cylinder equalises with the pressure outside.

Thats why a long duration cam that works well at high rpm loses you power at low rpm, and hence is why Vtec is the best thing since sliced bread unless you have an engine with pneumatic valves that can be programmed instead of operated by a cam, as vtec allows you to have two different profiles.

 

[ourboy]

chip you should get your membership for free because of the amount of knowledge you share

every days a school day on here :approve:

 

[Chip-mk1]

chip you should get your membership for free because of the amount of knowledge you share

Flol, thanks for that mate, but im happy to support the club by paying a membership anyway and would always encourage others too as well.

I get a lot of useful info here myself too, I know obviously a lot about engines so tend not to learn anything on that front as TBH there doesnt really seem on this particular forum to be anyone I can really learn from in that context, but in terms of clio specific knowledge this forum teaches me things, the first thing I found on this forum that helped me for example was a guide to how to fix the problem with the plastic female spline going over the climate control motors by putting a cable tie or jubilee around it, that saved me stripping the dash out and is still working now 2 years later, so while I might be the teacher in some threads in the student in others.

 

[Andyman]

Yes you should have it fully open so the engine car breathe as easily as possible during the test.

Also you need to either do all tests with only one plug our or all with all 4 plugs out, not take one plug out at a time as you test and not put back in before the next (or the engine turns over at different speeds for the tests)
Personally I do with all plugs out normally, its less strain on the starter and battery that way. (but either are valid)


Also you should unplug the injectors during the test. (fuel can effect the seal and hence the readings)

Just to pick up on the throttle open thing. I'm guessing you bolt your plenum chamber / upper inlet back down between tests?

Also going by the other compression thread is it right you unplug your injectors ?


Any time iv done a comp test or seen it done theyve never touched the injectors and the plenum has just been propped up out the way

 

[Chip-mk1]

Just to pick up on the throttle open thing. I'm guessing you bolt your plenum chamber / upper inlet back down between tests?

Sorry mate, if its a standard inlet manifold you dont need to open the throttle as its not there anyway, so by definition its an open pathway to the head.

Also going by the other compression thread is it right you unplug your injectors ?

Yes or fuel will effect the results.

Any time iv done a comp test or seen it done theyve never touched the injectors and the plenum has just been propped up out the way

Out the way = not restrictive, so not an issue, its if you are on bodies or an RS2 or a 197 inlet or other that allows you to compression test with the inlet still in place that you need to open it.
So for example all 3 of my current clios I can do it without removing the inlet.

as the mk1 is on a custom inlet that is forward of the engine:

the ph1 has a 197 inlet which allows access to the plugs anyway:

And the ph2 has an RS2 on it:

Apologies I should have been clearer that its only if you have a throttle body on the car still during the test that it needs to be open.


Also instead of unplugging the injectors, another option is to unplug the fuel pump or the ECU on most cars (so long as the ecu doesnt control the starter).

 

[Andyman]

Thanks for the info Chip

I'll know in future the proper procedure for this lol

 

[Fred@BTM]

Did you have the throttle open when cranking, like fred says normally if its screwed you would expect more discrepancy between values, but it could be that all 4 are just really worn out.

Chip you do however get r****d post of the day, why do you have to hold the throttle open when compression testing?? i'd hope you'd have removed the plenum to get the plugs out

 

[Chip-mk1]

Hey Guys

Wondering if anyone can help me determine if there is something wrong with my clio, the back of the car is always heavily covered in black smoke marks(looks like Turbo Cards rear end) Doesnt seem oily I hoped it is simply fuel. Had a couple of mechanics look at it but they got no idea. I thought it was simply an issue with the custom RS Tuner Map / JMS RS2 Manifold

As the car doesnt burn oil, (oil level fine) never seen black smoke, piece of paper test all good! Fuel Usage lil high then standard but nothing crazy

Compression test was done after driving so car was 'up to temp'

I simply removed plugs one by one (and coil pack plug)

1 - 160
2 - 150
3 - 152
4 - 148

Gave it about 4 - 5 cranks and the car has 150,000km

Any ideas what the F is going on, are the figures low?

Chip you do however get r****d post of the day, why do you have to hold the throttle open when compression testing?? i'd hope you'd have removed the plenum to get the plugs out

As per my replies above mate, IF there is a throttle or set of throttles in place, you need to hold it open, if its a standard 172/182 then obviously by definition its removed and hence no restriction to need to hold open, but as the person in this thread said they have an RS2, they wont have removed the plenum now will they freddy boy?

So I think its you winning r****d post of the day

 

[Fred@BTM]

thought you'd found a way to remove plugs without taking off the plenum

 

[Chip-mk1]

thought you'd found a way to remove plugs without taking off the plenum

I have found a way mate, so has the person this thread is about, as you can see on the pic of my mrs car:

See the red wires with the black ends on them going into the engine? The plugs are just under there mate, no need to remove the RS2 inlet plenum at all

 

[Fred@BTM]

t**t!

 

[BIGASH]

Lol

 

[Chip-mk1]

tw*t!

Flol, indeed mate, better luck next time

 

[Fred@BTM]

I like Santa, and planes

 

[davo172]

I have found a way mate, so has the person this thread is about, as you can see on the pic of my mrs car:

See the red wires with the black ends on them going into the engine? The plugs are just under there mate, no need to remove the RS2 inlet plenum at all

FLOL

 

[ozclio03]

test redone 180 -185 across the board, healthy engine right? done 150,000km

 

[Chip-mk1]

With them all being that close its promising, these testers IME vary a bit so the exact values are hard to read too much into (ive got 2 testers that read about 10% different on the same engine)

 

[ripp]

I have done a compression test yesterday, the car is a 182 with standard inlet, the guy just removed the inlet, took off the plugs and then one by one tested each cylinder, but without disconnecting the injectors.
The readings were in bars not psi, he said that a healthy engine should read 11 bars (is this the 11.1:1 compression ratio?).
But I'm a bit confused now as you guys say that it should read about 190 psi which is like 13 bars, so what's the catch?
Anyway the car showed like this:
Cyl no1- 9 bar
Cyl no2 - 8 bar
Cyl no3 - 4 bar!!
Cyl no4 - 11 bar
Needless to say that it drinks 1 liter of oil every 1000 km and that I have to rebuild the engine but what's with those figures? What exactly does 11.1:1 compression ratio refers to?
Thx!

 

[Steven103]

Compression ratio is the engine or cylinder's total volume at bottom dead centre (light green) divided by the clearance volume at top dead centre (grey).

If the intake was 100% efficient (it's not) and there was no valve overlap (there probably is by design) then each cylinder would draw in 2.0 litres / 4 cylinders = 0.5 litres of air. It would then get compressed into approximately-but-not-quite 0.5 / 11.1 = 0.045 litres. Compression ratio is only talking about volume. There is a relationship between pressure and volume but it's too complicated to work out for a real engine.

The gauges are usually really cheap so wouldn't read into the actual number much. Was the engine cold? You will get an extra 0.5 or 1 bar if you do it with the engine hot as the residual oil helps the piston rings form a gas tight seal. The important thing is that something in cylinder 3 is a lot worse than the rest.

Next step I'm afraid is to take it to someone who knows these engines well to confirm the your cylinder 3 results then strip / inspect / replace whatever is causing the issue.

I assume your car feels slow?

 

[JamesBryan]

4bar or nearly 60psi is seriously low. I assume it runs absolutely terrible?

A compression test will only tell you that you have low compression, it doesn't tell you where from. For that you need to do a leakdown test.

That will tell you if it's piston rings or valves.

 

[ripp]

The guy also poured a little bit of oil on top of the pistons and it did the compression test once again. I believe this is called a "wet" test. His conclusion was that oil escapes through rings and valve seals also.
Oddly enough the car runs fine by my standards and also compared to others.
Ot haven't I drove a really healthy 182 yet? Maybe!
The car has 172 k kms on the clock, I'm the second owner, and I bought it back in 2006 when it had 20k km on the clock. Was always careful with service intervals, never thrashed it and changed engine oil yearly or at max 10000 kms interval or less.
So this situation is a bit confusing.. How did it get to these poor results? 🙁

 

[JamesBryan]

If it drives fine then the tester must off because it wouldn't run very well at all with those compression numbers.

 

[ripp]

Should I repeat the test then? Fact is that it drinks 1 liter of oil every 1000km so somth is wrong there

 

[Crazylegs]

The guy also poured a little bit of oil on top of the pistons and it did the compression test once again. I believe this is called a "wet" test. His conclusion was that oil escapes through rings and valve seals also.
Oddly enough the car runs fine by my standards and also compared to others.
Ot haven't I drove a really healthy 182 yet? Maybe!
The car has 172 k kms on the clock, I'm the second owner, and I bought it back in 2006 when it had 20k km on the clock. Was always careful with service intervals, never thrashed it and changed engine oil yearly or at max 10000 kms interval or less.
So this situation is a bit confusing.. How did it get to these poor results? 🙁

It's a diffcult one to say really without knowing prior history of the car. It could have had a hard life previously and not been maintained properly (Poor oil possibly).

I had similar issues with my Integra DC5 last year, the car felt fine and was going well. Had it remapped with a better exhaust, decat manifold etc and it was making 237bhp which I thought was ok. Someone noticed a puff of smoke at low revs, did a compression test and all cylinders were equal but compression was low. Took the head off and all the piston rings were shagged, all bores were badly scored beyond repair and there had been bad piston slap so the engine was knackered basically.

Ended up needing a replacement engine even though it felt fine to me.

 

[ripp]

Well the previous owner had the car for a year in which it did 20 000 km (me being the second owner as I said) so he basically only did one oil change as the car was new (car is 2005 I bought it in 2006) so how bad could it get in only one year?..
Even stranger is that I had a custom remap done in 2017 and the car came out at 182 ps after the remap, it only has an intake and an exhaust so I thought back then it's quite a healthy engine. The oil consumption dates back some 11 years ago but I somehow lived with it until now when I went and did some research into it.
I'm thinking to repeat the test somewhere else and see if the numbers are the same

 

[ripp]

Now I'm trying to understand what happens when you do a compression test.
Following this basic video:

The compression happens at 0:29 and in that case if the rings are bad the air will go between them and the piston wall right? Ok so what if the rings are fine, and you have bad valve seals, how can you tell that as when the compression happens both intake and exhaust valves are closed and if some air will go past them, it will go either in the exhaust manifold or in the intake manifold towards the injectors.
What could possibly force the air to go upwards to the valve seals as there is a much tighter spot for the air to escape rather than the manifolds themselves? How excatly can you diagnose bad valve seals?
Thanks!