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Low Compression And Leakage...


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#21 james4563

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Posted 13 May 2018 - 10:31 AM

It runs okay, minus the issue I've had for a long time where building boost under load, e.g up a hill in 4th sometimes 3rd, results in terrible turbo stalling and flutter, which is the issue the garage were investigating yesterday. 

 

Full health check and the only issue they found was rusty plugs which I knew about and were not causing any running issues. Made no difference when they changed them, I did tell them it wouldn't. The other issue was the leakage/low compression.

I had wondered if they did the test on a cold engine, does that have much of an impact to the figures? It was sat for about an hour or more before they took it into the workshop and then probably another hours work before they did the compression test, no idea if they warmed it up at all in this time.

 

I was shocked when they told me the figured because as mentioned above it's a new(ish) bottom end from vaux, I have the paper work. If its just general wear I would be surprised to pick up that amount of wear in only 20k miles since the bottom end was fitted. I have no idea of how the engine was run in other than the previous owner telling me he'd run it in for 5k before it went to Courtney for the stage4 mods. I would imagine it would have been run in properly as he would have been advised by back on track I would have thought.

 

I will test the compression myself at some point to see if I get the same figures with engine fully warmed, not had a chance yet to do it.



#22 NOSBandit

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Posted 13 May 2018 - 11:08 AM

If it runs ok and you're not burning loads of oil I wouldn't worry. As long as the results are similar across all cylinders, if one was completely out then I'd worry. Sent from my SM-G935F using Tapatalk

#23 siztenboots

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Posted 13 May 2018 - 11:28 AM

are you getting masses of blowby from the PCV pipe?



#24 james4563

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Posted 13 May 2018 - 03:06 PM

Just tested it all myself, when fully warm.

 

Whats happening on all four cylinders is they reach about 160-170psi and as soon as you stop cranking the pressure drops down gradually to about 130-140psi on my gauge and then holds at that level.

 

Something is obviously leaking, seems a little strange that they all do exactly the same thing.

 

It doesn't seem like there is excessive blowby from PCV....

 



#25 gaffer1986

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Posted 13 May 2018 - 04:49 PM

I think the compression sounds fine.

#26 vocky

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Posted 13 May 2018 - 06:32 PM

160-170 psi is about right for a z20let engine



#27 james4563

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Posted 13 May 2018 - 06:56 PM

From reading online I wonder if my gauge is damaged. It says that compression gauges are supposed to just hold the peak figure that they get while you crank it. Because of course they have a one way valve in the end.

 

Probably the reason that the garage had lower readings is because they tested it while it was completely cold.

 

And yeah, 160-170 is the expected values. 130 is on the low side as mentioned in this thread, but because they are all the same it doesn't provide such a concern as if one piston was say 50psi and the rest 130psi.

 

I was just a bit surprised by the results from teh garage because the bottom end is new standard internals from vauxhall under 20k miles ago. So I would expect the compression to be OEM (~160psi) and not really worn at that stage of it's life. Given that most of those miles are me driving 60 miles a day to work and back.

 


Edited by james4563, 13 May 2018 - 06:59 PM.


#28 gaffer1986

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Posted 13 May 2018 - 09:20 PM

Mine holds it's peak figure. Same as my tyre gauge until a press a button to release the pressure.

#29 Nev

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Posted 14 May 2018 - 06:36 AM

You have PM James.

#30 james4563

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Posted 14 May 2018 - 08:55 PM

I tested with a brand new gauge today. Engine fully warmed up. 180, 180, 175, 180. I let it crank over like 4/5 times. What a fcuking joke garage. How have they managed to get 130psi.

#31 Nev

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Posted 15 May 2018 - 06:57 AM

I tested with a brand new gauge today. Engine fully warmed up.

180, 180, 175, 180. I let it crank over like 4/5 times.

What a fcuking joke garage. How have they managed to get 130psi.

Great. This is precisely why I asked you get answers to those questions I raised - to find out what they actually did.

 

Really glad you've discovered that and can rule it out for certain. Misdiagnosed faults probably contribute a big % to garage's profits you see, it can be in their interest to lead you astray, either deliberately or negligently.


Edited by Nev, 15 May 2018 - 07:15 AM.


#32 gaffer1986

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Posted 15 May 2018 - 07:23 AM

Glad it's OK. What do you think the problem is?

#33 james_ly

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Posted 15 May 2018 - 08:39 AM

Out of interest why did they do a compression test, presumably you had symptoms to trigger that?



#34 james4563

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Posted 15 May 2018 - 09:58 AM

Out of interest why did they do a compression test, presumably you had symptoms to trigger that?

I have long time issue with turbo surge/flutter under load mostly. Eg uphill high gears. I wanted the garage to take a look and their first point of call was to health check the engine to get an idea of condition. It makes sense. They didn't find any issues other than low compression and some leakage showing up on leakdown test. Presumably because they did it wrong or have bad equipment. All I ended up with was a worry my engine was knackered and few hundred pound bill to find when I drove home it was the same. 😂 Writing them a letter today.

Edited by james4563, 15 May 2018 - 10:00 AM.


#35 gaffer1986

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Posted 15 May 2018 - 11:30 AM

That really sucks, any idea what could be causing your issue now?

 



#36 james4563

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Posted 24 May 2018 - 09:48 AM

I have no idea what the issue is, but upon speaking with the garage and asking why I am getting such a different compression reading to them they have told me:

 

The car was running badly, because my spark plugs were rusty from water ingress, now that it's running better because of their service the compression level has come back up and the engine has basically healed itself. 

 

:glare:  :glare:  :glare:  :glare:  :glare:  :glare:  :glare:  :glare:  :glare:  :glare:

 

I have to be honest, that sounds like BS to me. It makes sense if the car is sat a long time the rings might seize up a bit and not seal very well, but I drive mine every day and it wasn't suffering from any other running issues minus the fluttering that I'd asked them to investigate.


Edited by james4563, 24 May 2018 - 09:50 AM.


#37 Pidgeon

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Posted 24 May 2018 - 12:07 PM

It sounds like BS to you, because it is BS.



#38 gaffer1986

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Posted 24 May 2018 - 12:09 PM

Rusty spark plugs :D yeah that's the first reason you may have a lack of compression :D

#39 gaffer1986

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Posted 24 May 2018 - 12:10 PM

Have you found the cause of your fluttering turbo issue? I wouldn't think more about the compression if I was you.

#40 fezzasus

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Posted 27 May 2018 - 07:35 AM

As a general rule if the compression test shows you're down on all cylinders, it's probably not the piston rings/cylinder bores as they don't wear/stick at the same rate.

 

If it's a turbo issue, why don't you look at the turbo? It sounds like you may have an air (either vacuum affecting the wastegate or boosted air post turbocharger) leak if it's only showing issues under high load.






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