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  #1 (permalink)  
Old 30 Aug 2013, 11:53 am
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Default Compression

How much compression should 2002 pt cruiser should have
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Old 30 Aug 2013, 01:26 pm
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Default Re: Compression

The maximum even compression should be tested to read between 145-160psi

This should be taken with the engine cold and the TB wide open. You need to also make sure that the same engine rotation count 4 or five is done on each cylinder when checking the compression. Then you compare the results. The highest cylinder would be your guide and all other should not be more then about 10%max. or a cylinder leak down is the next step in testing.
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Old 30 Aug 2013, 01:48 pm
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Default Re: Compression

nitro, just curious where those numbers came from and why alldata has these instead.

i looked on alldata pro at 5 different pt's, turbo and non turbo and they all had these numbers. just wondering if you were getting exact numbers somewhere and alldata has a generic standard number in there or something. I looked at several other vehicle manufacturer numbers and the numbers, ranges, and testing instructions seemed to vary widely. 93 ford mustang had a chart, 97 corvette had a minimum and a variance range formula, the prowler simply says all should be over 100psi, but pt's all come up with this:

just wondering if you know something about this that i dont. just curious is all.

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Old 30 Aug 2013, 02:22 pm
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Default Re: Compression

Not taking sides but just checked Haynes and Chilton and they agree with Rob, 170-225 psi.....but Haynes has known to be wrong.
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Old 30 Aug 2013, 09:05 pm
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Default Re: Compression

140-160 is low, but he's prolly doing it so someone doesn't condemn their engine for no reason other than a few miles or a retarded gauge.

Just don't take compression- BAD, BAD thing to do. If it's running acceptably and oil consumption is acceptable, just let it go.

Say you take compression and it's 175, 170, 125, 165 and alls well. That 125 will nag at you- you'd be better off not knowing.
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Old 30 Aug 2013, 09:10 pm
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Default Re: Compression

Quote:
Originally Posted by UptownSport View Post
1

Say you take compression and it's 175, 170, 125, 165 and alls well. That 125 will nag at you- you'd be better off not knowing.

But wouldn't cylinder #3 being that low give you a P0303 fault code ??
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Old 31 Aug 2013, 03:13 am
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Default Re: Compression

CREWZIN; I don't think the 125 psi cyl would throw a code [speculation] ; but when the pressure drops to a level that causes missfire or incomplete combustion, the o2 sensor would 'confuse' the computer into doing strange things. One low cylinder is a predicter of things to come. All bad.

2006 PT: 170-225 psi. The turbo and nonturbo ARE listed as the same, even though they have different compression ratios!!!!

Last edited by CREWZIN; 31 Aug 2013 at 07:54 am.
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Old 31 Aug 2013, 10:25 am
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Default Re: Compression

Quote:
Originally Posted by NitroPT View Post
The maximum even compression should be tested to read between 145-160psi

This accounts for an overall average miles on a PT Cruiser of 85k miles. I did not say maximum normal of a new and worn in street engine of about 5k miles?A factory engine properly run in may make between a Service manual compression range of between 170-225 with a maximum 25% variation between cylinders. But it also shows 10.5: compression Ration. This means as the technician you actually have a greater testing variance and more realistic of between 145-160 psi cold WOT and an average ambient testing of 70F with a 10% variance for possible further engine condition checking.

This should be taken with the engine cold and the TB wide open. You need to also make sure that the same engine rotation count 4 or five is done on each cylinder when checking the compression. Then you compare the results. The highest cylinder would be your guide and all other should not be more then about 10%max. or a cylinder leak down is the next step in testing.
This test is done with a cold engine (not hot not warm) as ambient tempretures as well as altitude can effect the test.

Many DIYrs do not do compression tests correctly and there is a wide variance of results from them. So when I post information I take that under considerations and as Ted commented it eases the physiological pain of thinking something is seriously wrong with your engine if you test and have a seemingly low compression tested in the range of 145 psi.

The PCM may indicate a code if the a single cylinder gets around 100 psi or lower or a combination of anomalous inputs from all the engine operating sensors? The Chrysler PCM is not that sophisticated to detect minor psi changes between cylinder in the engine maybe even as lower as 90 psi variance? Spark can still ignite fuel at this low cylinder psi. Now this is not to say that the knock sensor may pick up pre-ignition sounds from the low cylinder which may show a code.

So if you all went by the book here is what one example would be. I properly tested my engines compression @ 52K 160,165 165 165. A dyno run with properly set Delta's shows a 223whp@5300rpm. So by factory information manual I would be on the low side? Hmm... 2whp off from advertised power output?
When I check my compression after a warm up and the engine temperatures are showing 140-160F measured off the valve cover my test compression readings are now 214 -220 psi closed throttle plate.

If I were not cleaning the combustion chambers with water every 5k miles I may even have some carbon build up in the combustion chamber which might even raise my CR another 5%. There I got the 225psi mark!
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Old 31 Aug 2013, 10:41 am
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Default Re: Compression

that answers my question -thank you
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Old 31 Aug 2013, 12:52 pm
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Default Re: Compression

Yes- to cause misfire (misfire is just that, misfire, not 'different output') compression would have to be in the low double digits.

And a really good overheat could score a cylinder.
It won't get any worse so reject a low cylinder is immenent problems.

Also note compression readings will drop as you advance cylinders; the battery wears down and engine doesn't crank as fast
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