compression test results
08-27-2010, 12:14 PM
#1
2nd Gear Member
Thread Starter
Join Date: May 2010
Location: mississippi
Posts: 386
compression test results
well i decided to do a compression test because i have been getting a knocking sound coming from the motor when it sits for a long peroid of time and does it for the first 3 mins or so of running. not really a loud knock but you can hear it with the windows down.
Drivers side
175
170
175
175
All good right, this is untill
passenger side
150
70
180
150
Spark plugs look great
no smoke or anything car does have 130,000+miles
If the compression was that bad wouldnt it run like crap and not idle worth a crap
It runs good beside the knock early in the morining and has plenty of power What do you guys think. also I get 25mpg average with every tank and thats with 4.10 gears.
The way I did the test was after I got home from work I let it sit for about 45min, took out all sparkplugs, discconected coil packs, held throttle wide open and let it crank about 8 times each cylinder. I had the air intake of if that matters because its hard to get to that side of plugs with the intake in.
Drivers side
175
170
175
175
All good right, this is untill
passenger side
150
70
180
150
Spark plugs look great
no smoke or anything car does have 130,000+miles
If the compression was that bad wouldnt it run like crap and not idle worth a crap
It runs good beside the knock early in the morining and has plenty of power What do you guys think. also I get 25mpg average with every tank and thats with 4.10 gears.
The way I did the test was after I got home from work I let it sit for about 45min, took out all sparkplugs, discconected coil packs, held throttle wide open and let it crank about 8 times each cylinder. I had the air intake of if that matters because its hard to get to that side of plugs with the intake in.
Last edited by 96meangreengt; 08-27-2010 at 12:40 PM.
08-27-2010, 02:48 PM
#2
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
I assume you double/triple/quadruple tested that cylinder?
If the compression really is that low, and there's no smoke/steam from the exhaust, then I'd start looking at the valves for that hole.
Connect a vacuum meter and examine the vacuum at idle with the engine hot. It should be 18 to 22inHg and steady--if not here's a document explaining how to interpret the readings.
If the compression really is that low, and there's no smoke/steam from the exhaust, then I'd start looking at the valves for that hole.
Connect a vacuum meter and examine the vacuum at idle with the engine hot. It should be 18 to 22inHg and steady--if not here's a document explaining how to interpret the readings.
08-27-2010, 03:01 PM
#3
2nd Gear Member
Thread Starter
Join Date: May 2010
Location: mississippi
Posts: 386
I assume you double/triple/quadruple tested that cylinder?
If the compression really is that low, and there's no smoke/steam from the exhaust, then I'd start looking at the valves for that hole.
Connect a vacuum meter and examine the vacuum at idle with the engine hot. It should be 18 to 22inHg and steady--if not here's a document explaining how to interpret the readings.
If the compression really is that low, and there's no smoke/steam from the exhaust, then I'd start looking at the valves for that hole.
Connect a vacuum meter and examine the vacuum at idle with the engine hot. It should be 18 to 22inHg and steady--if not here's a document explaining how to interpret the readings.
Im just baffled because like it said it idles fine and pulls hard and doesnt smoke, all sparkplugs looks exacty the same sorts grayish, does burn a lil oil though probly 1 quart between changes
I would think it would run like crap with that one being that low and not to mention the other 2 being pretty low. 15% difference than the rest
08-27-2010, 03:15 PM
#4
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
I have seen stranger things over the years--you might want to run a "wet" compression check, put a couple teaspoons of motor oil in the cylinder then perform the check letting it crank 5 or 6 full turns.
If the compression goes up that's an indicator of worn or broken rings...
If the compression goes up that's an indicator of worn or broken rings...
08-27-2010, 03:26 PM
#5
2nd Gear Member
Thread Starter
Join Date: May 2010
Location: mississippi
Posts: 386
I have seen stranger things over the years--you might want to run a "wet" compression check, put a couple teaspoons of motor oil in the cylinder then perform the check letting it crank 5 or 6 full turns.
If the compression goes up that's an indicator of worn or broken rings...
If the compression goes up that's an indicator of worn or broken rings...
I was planning on put a new motor in the winter anyway just wanted to be able to drive it untill then.
08-27-2010, 07:55 PM
#6
2nd Gear Member
Thread Starter
Join Date: May 2010
Location: mississippi
Posts: 386
I assume you double/triple/quadruple tested that cylinder?
If the compression really is that low, and there's no smoke/steam from the exhaust, then I'd start looking at the valves for that hole.
Connect a vacuum meter and examine the vacuum at idle with the engine hot. It should be 18 to 22inHg and steady--if not here's a document explaining how to interpret the readings.
If the compression really is that low, and there's no smoke/steam from the exhaust, then I'd start looking at the valves for that hole.
Connect a vacuum meter and examine the vacuum at idle with the engine hot. It should be 18 to 22inHg and steady--if not here's a document explaining how to interpret the readings.
Ok went and got a vacuum gauge and at idle it reads a steady 20inHg but when you trottle it real hard and fast it goes past the o into the other side,(i hope thats because its a cheap $25 gauge) then come back up to about 22-23inHg then leverles back down to 20inHg. according to the chart if the needle jumps to 0 when throttled hard it is worn rings. tomorrow im gonna do another compression test and do a wet test to see what i get.
Its just funny if its worn rings surely it would smoke a lil. i have taken it to 5,000rpms several times these past few weeks and it pulls hard and doesnt smoke at all.
08-27-2010, 09:37 PM
#7
2nd Gear Member
Join Date: Oct 2008
Location: massachussets
Posts: 467
Ok went and got a vacuum gauge and at idle it reads a steady 20inHg but when you trottle it real hard and fast it goes past the o into the other side,(i hope thats because its a cheap $25 gauge) then come back up to about 22-23inHg then leverles back down to 20inHg. according to the chart if the needle jumps to 0 when throttled hard it is worn rings. tomorrow im gonna do another compression test and do a wet test to see what i get.
Its just funny if its worn rings surely it would smoke a lil. i have taken it to 5,000rpms several times these past few weeks and it pulls hard and doesnt smoke at all.
Its just funny if its worn rings surely it would smoke a lil. i have taken it to 5,000rpms several times these past few weeks and it pulls hard and doesnt smoke at all.
08-28-2010, 08:32 AM
#8
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
And at the risk of being overly technical, vacuum is highest under closed throttle deceleration...
08-28-2010, 08:47 AM
#9
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
Ok went and got a vacuum gauge and at idle it reads a steady 20inHg but when you trottle it real hard and fast it goes past the o into the other side,(i hope thats because its a cheap $25 gauge) then come back up to about 22-23inHg then leverles back down to 20inHg. according to the chart if the needle jumps to 0 when throttled hard it is worn rings. tomorrow im gonna do another compression test and do a wet test to see what i get.
Its just funny if its worn rings surely it would smoke a lil. i have taken it to 5,000rpms several times these past few weeks and it pulls hard and doesnt smoke at all.
Its just funny if its worn rings surely it would smoke a lil. i have taken it to 5,000rpms several times these past few weeks and it pulls hard and doesnt smoke at all.
I have one from JC Whitney that cost just $10 over 35 years ago--it works fine--that one would be inaccurate is unlikely--it should read 0.0 of course when not connected.
The wet test will tell us a lot, but that the vacuum at idle was steady pretty much rules out a valve problem...
How many miles on the engine?
08-28-2010, 09:28 AM
#10
2nd Gear Member
Thread Starter
Join Date: May 2010
Location: mississippi
Posts: 386
Vacuum gauges are cheap, mostly because they only have 4 moving parts (the Bourdon tube, link, rack and indicator):
I have one from JC Whitney that cost just $10 over 35 years ago--it works fine--that one would be inaccurate is unlikely--it should read 0.0 of course when not connected.
The wet test will tell us a lot, but that the vacuum at idle was steady pretty much rules out a valve problem...
How many miles on the engine?
I have one from JC Whitney that cost just $10 over 35 years ago--it works fine--that one would be inaccurate is unlikely--it should read 0.0 of course when not connected.
The wet test will tell us a lot, but that the vacuum at idle was steady pretty much rules out a valve problem...
How many miles on the engine?
OK just came in from doin the wet test, weird results
drivers side dry Drivers side wet
1. 175 1. 195
2. 185 2. 205
3 185 3. 205
4. 180 4. 195
Passenger side dry passenger side wet
1. 180 1. 180
2. 180 2. 185
3. 170 3. 180
4. 170 4. 175
didnt do anything different than yesterday besides just start it up and let it get warm, got to the O on the water temp gauge and then took everything out, takes like 10mins. I dont see how it could of went up without it being something it did like not having the compression gauge screwed all the way in or something.
On ever cyclinder the first stroke was always above 120psi.