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Compression check problem

  
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Compression check problem

 
lit549 lit549
V-6 Camaros rule! | Posts: 35 | Joined: 06/13
Posted: 07/01/13
07:29 AM

Well,in the endless search for my vibration I went and bought a leak down tester and compression gauge to check it since number 7 is oil fouled.When I do the leak down test with the pos gauge from harbor freight,it holds pretty good at tdc showing about 30 percent loss.Plug in compression gauge,do the test and it shows 150-160 on them but it does not hold,it comes right back to 0 psi..What is my issue? Leak down tester just plain scrappy? Or valves to tight cause it to not hold cylinder pressure? Number 7 wont hold any at all and plug is oil fouled.I'm getting about 5 mpg and a quart of oil every 200 mi!  

waynep712222 waynep712222
V-6 Camaros rule! | Posts: 122 | Joined: 03/13
Posted: 07/01/13
08:04 AM

ok...

the compression tester...

this should HOLD pressure once its pumped up...  if you are loosing pressure inside the compression tester... use a tire valve core tool and snug the schrader cores slightly...  warning compression testers use schrader cores/ valve cores that are different than tire valve cores.. the compression tester cores open at 4 to 6 psi.. where tire cores open at 15 psi or so.. this give you the best reading..

if the compression tester is leaking down.. then there is a leak someplace in it..


the cylinder leak down tester.. DOES NOT have any valve cores in the end of the hoses..

you set this up with the shop air hose hooked up..  the hose to the spark plug hole disconnected from the main tool connector.. turn the regulator knob to bring the needle to 100%... when you hook up the hose without it being screwed into the motor.. the gauge should drop to ZERO..  there is a calibrated opening inside the end of the leak down tester hose.

there are uses for both tools in most tool boxes... compression tester is always first..   please invest in a remote starter button..  it will make your life simple when running either of these tests.. and a hint... if using a button type.. turn it button down in your hand..  and bump it on the engine or inner fender  this gives you the ability to move the engine in tiny fractions of a turn..


want a tip...
set up the compression tester hoses with an pair of quick connects to hook directly to the shop air hose quick connect..  take the valve core out and store it carefully..  screw the compression tester hose into the spark plug hole.. bump the engine around with the remote button.. with the radiator cap off and the radiator filled to the top or using a radiator cap test adaptor with clear vinyl hose on it.. and part way filled with coolant, then hung up on the hood latch..  so you can see any changes in the cooling system level...

when you hook up the shop air hose... if you get bubbles or movement in the radiator coolant level.. you have just proven that you have either a cracked head or a blown head gasket..    yes .. the engine will spin sometimes.. it only takes seconds to reset..  this has proven a lot of head gaskets were bad causing overheating...

its dead simple. and ends all the questions from the customer as they can see.. air into the cylinder.. should not come out the radiator..

hint.. the leak down tester hose has that restriction that will limit the amount of air and reduce the test ...

please stay clear of rotating components.. the engine can turn when charging the cylinders with air...  

lit549 lit549
V-6 Camaros rule! | Posts: 35 | Joined: 06/13
Posted: 07/01/13
01:55 PM

Ok,you was right.Gauge was leaking,tightened Schrader valve and now all of them were around 185 psi on passenger side,drivers side they were 165 psi,which tells me there a problem with that big of a difference.and leak down was all around 15%…BUT,that's with this junky Harbor Freight tester,it only goes to 15 psi to get % gauge to 0, so I'm thinking to either add another psi gauge in place of % gauge so I can test them at 80 psi minimum..Maybe a different result I do? Also #7 is oil fouling ,but it does it worse when I run the truck at high rpm..It had about 190 psi compression..All I know is it still sucks the gas and oil..Pvc hose to intake outlet on carb is dry so pvc is working ..Truck doesn't smoke either..How about Bon-ami treatment??  

68scott385 68scott385
I have an SS396 tatoo | Posts: 325 | Joined: 07/09
Posted: 07/01/13
06:21 PM

Now that you've done the leak-down test, where is that 30% air volume going? Into the cooling system, out the exhaust system, back up through the intake manifold, or into the oil pan out the valve cover breather.  
68scott385 68scott385 68scott385

lit549 lit549
V-6 Camaros rule! | Posts: 35 | Joined: 06/13
Posted: 07/01/13
08:29 PM

It's hard to say Scott,at only 15 psi I can't hear it.I can dial it up to 80-90 psi and I hear it in the crank case..Getting a better leakdown tester tomorrow and try it again.When I first bought this engine,(was New supposedly) I put 3k on it and it was burning oil real bad and ran bad.So after leakdown test revealed thing rings not seating,we pulled it and my mech friend rehoned the cylinders saying that they didn't do it right the first time.Put it all back with iron rings and it has been a lot better,but still uses oil..I should've just had it bored at the time,but at the time after just shelling out for the engine,I was broke so he swore that's all it was.NOW its my daily driver so I'm actually driving it enough that im seeing all the issues..Can't get it to idle smooth for anything either,it's close but still has that miss at idle.Also every time I pull the plugs 3-4 of the have oil on the threads..Wish I could do something to seat the rings a little better, I'll see for sure with better leakdown tomorrow..Frustrated!  

waynep712222 waynep712222
V-6 Camaros rule! | Posts: 122 | Joined: 03/13
Posted: 07/01/13
11:05 PM

use the compression tester hose without the valve core..

the cylinder leak down tester might be accurate.. its only a small amount of air needed to get to the proper percentage..of leak down...

if you blow a hurricane into the cylinder.. you will never get an accurate reading of leak down..

next.. you might .. if you have a deep wallet.. invest in the almost 200 buck harbor freight video camera..

Image 19657

High Resolution Digital Inspection Camera With Recorder
Cen-Tech - Item#67980
With vivid 640 x 480 images and a tempered glass lens, this high-resolution digital inspection camera allows you to inspect engine parts, home appliances and other tight spaces with precise clarity. The inspection camera also features a recorder that enables you to hook up the camera to your computer for review. And then, save those images on internal flash memory or SD card (cable, SD card not included).
8.5mm probe fits most spark plug holes
38" watertight flex shaft with CMOS imager

just an idea...

run the high pressure test with the valve core out of the cylinder...   see where the air is coming out of...   breather.. exhaust, carb, radiator...  

68scott385 68scott385
I have an SS396 tatoo | Posts: 325 | Joined: 07/09
Posted: 07/02/13
08:32 AM

I have done what Wayne has suggested; run air from compressor into cylinder, you'll find the leak then. My compression tester has two hoses that the gauge connects to via air hose fittings. I matched that fitting and made an adapter to plug the air hose from the air compressor to the compression tester and filled the cylinder. Odds are it's going to turn the motor over in one direction or the other unless you are at absolute tdc or bdc.


I hope that made sense.Tongue  
68scott385 68scott385 68scott385

lit549 lit549
V-6 Camaros rule! | Posts: 35 | Joined: 06/13
Posted: 07/02/13
03:21 PM

ok,i just blew straight air in and they all held good..I did it with the engine warm so im pretty confident that my rings are ok..With that being said,the oil that was caked up on #7 is a mystery to me cause its never done it that bad,im thinking when i took it out and romped it for awhile it leaked some oil there? My oil consumption has to be going somewhere! One very strange thing it did today when i did the leak down test again was,when i went to start it,the lifters rattled pretty good..It never does that..Blowing air inthere must have blown the oil away from rockers? Hell idk,pretty weird..Only things i know to look for is stem seals and intake gasket leaking,pulling oil through manifold? Again,my pvc is working good and no oil getting sucked up..No smoke out exhaust,starting or running down the road..Hey,,thanks for the help too everybody!