Compression Leakdown Test
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Elder User
Joined: Jul 2004
Posts: 620
Likes: 1
From: Toronto, ON
Compression Leakdown Test
Hey,
Everytime I change my oil, I notice that I smell gas in the oil. My truck runs really good (I think), smooth idle and no hesitation. No lean or rich codes at all. I do get horrendous mileage though for how easy I drive it (10-12mpg no matter highway, city, driving it hard as hell, or as easy as a grandma with shifting at no more than 2000rpm).
I was thinking that maybe I should check out my injectors and also do a compression leakdown test.
This is how I think a compression leakdown test should be done (just from bad memory of scanned over posts here, never done it or seen it done):
- take out spark plugs
- connect gauge to cylinder
- turn motor over using rachet connected to crank bolt (on the fan clutch i guess?)
- record reading, connect to next cylinder
Is it really that easy? Can I do any damage or anything somehow?
I once saw a really awesome how-to with pictures on how to service injectors yourself, but I can't find it. I suppose connecting leads from the battery to each injector and seeing if it opens can tell me if I have a stuck injector or not.
Everytime I change my oil, I notice that I smell gas in the oil. My truck runs really good (I think), smooth idle and no hesitation. No lean or rich codes at all. I do get horrendous mileage though for how easy I drive it (10-12mpg no matter highway, city, driving it hard as hell, or as easy as a grandma with shifting at no more than 2000rpm).
I was thinking that maybe I should check out my injectors and also do a compression leakdown test.
This is how I think a compression leakdown test should be done (just from bad memory of scanned over posts here, never done it or seen it done):
- take out spark plugs
- connect gauge to cylinder
- turn motor over using rachet connected to crank bolt (on the fan clutch i guess?)
- record reading, connect to next cylinder
Is it really that easy? Can I do any damage or anything somehow?
I once saw a really awesome how-to with pictures on how to service injectors yourself, but I can't find it. I suppose connecting leads from the battery to each injector and seeing if it opens can tell me if I have a stuck injector or not.
Elder User
Joined: Apr 2004
Posts: 970
Likes: 3
Leakdown tests are taken by turning the engine until the cylinder being tested is
at TDC (they make a whistle which is attached to the test hose) to tell you when you are coming up on compression. We would divide the balancer up into as many degrees as seperated the cylinders (120 for a six 90 for an eight) from the TDC mark on the balancer and turnit to the mark by hand. Now you had to zero the gauge with the air source and then it was attached to that cylinder and the % of leakage read. You also can listen at the various sources of leakage (headgasket intake, exhaust and crankcase and injectors. Far more accurate than the normal compression test also slower to accomplish. ONE important thing don't let the wrench on the crank because
the engines do kick off TDC if it isn't zeroed correctly.
at TDC (they make a whistle which is attached to the test hose) to tell you when you are coming up on compression. We would divide the balancer up into as many degrees as seperated the cylinders (120 for a six 90 for an eight) from the TDC mark on the balancer and turnit to the mark by hand. Now you had to zero the gauge with the air source and then it was attached to that cylinder and the % of leakage read. You also can listen at the various sources of leakage (headgasket intake, exhaust and crankcase and injectors. Far more accurate than the normal compression test also slower to accomplish. ONE important thing don't let the wrench on the crank because
the engines do kick off TDC if it isn't zeroed correctly.
FTE Chapter Leader
Joined: May 2002
Posts: 42,571
Likes: 3,121
From: Fraziers Bottom, WV
As said in kotzy post each cylinder must be on TDC with the valves closed. The engine must be a operatine temp or you will get a false reading. If the engine has over 100,000 miles decrease the operating pressure by 1/2 or you may blow seals out.
listen to the following places:
Exhaust pipe - bad exhaust valve
Intake - Bad intake valve
Oil Fill Cap - Bad rings
Note: you are looking for the loudest noise because you may/will hear hissing from all areas!
listen to the following places:
Exhaust pipe - bad exhaust valve
Intake - Bad intake valve
Oil Fill Cap - Bad rings
Note: you are looking for the loudest noise because you may/will hear hissing from all areas!
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