Did a compression test, not sure if I did it right
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From: AZ-CA-NV-24/7
Did a compression test, not sure if I did it right
So I've been having some misfire issues and after whacking the map sensor and checking the plugs it was still missing. I did a compression test but honestly I'm not sure if I did it right. Does this sound right?
1. Pulled all plugs
2. Pulled fuel fuse
3. Threaded tester into cyl closest to front
4. Cranked motor until gauge stopped moving
5. Repeated other cyls.
Was this the correct way? My # came up a little higher than I've seen posted up here.
cyl 1 (closest to front of car) was 235
cyl 2 was 225
cyl 3 was 225
cyl 3 was 235
Do these # seem too high or did I just not do it right?
1. Pulled all plugs
2. Pulled fuel fuse
3. Threaded tester into cyl closest to front
4. Cranked motor until gauge stopped moving
5. Repeated other cyls.
Was this the correct way? My # came up a little higher than I've seen posted up here.
cyl 1 (closest to front of car) was 235
cyl 2 was 225
cyl 3 was 225
cyl 3 was 235
Do these # seem too high or did I just not do it right?
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From: AZ-CA-NV-24/7
Thanks for the input. I thought that anything under 10% difference between the cyls was ok? After reading Random1's post, I'm thinking that it might be injectors. I'm on the road alot and haven't always been able to use the best gas and maybe that has started to take its toll.
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From: Houston, Texas
I believe you did the compression test correctly.
Keep in mind that every gauge will read slightly different. What kind of gauge was it? Especially if it was a cheap one, I wouldn't worry about it. The compression numbers look pretty good.
Keep in mind that every gauge will read slightly different. What kind of gauge was it? Especially if it was a cheap one, I wouldn't worry about it. The compression numbers look pretty good.
Joined: May 2004
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From: DFW, TX
Numbers look great, I wouldn't be worried about the numbers. And DEFINITLY NOT worried about the 10psi difference. That is entirely fine, especially at 160k miles. I'd say your motor is running very strong.
Another common thing to cause a misfire is a clogged cat. It will build up back pressure in the exhaust system and cause misfires. Its very possible that this is all you have.
Another common thing to cause a misfire is a clogged cat. It will build up back pressure in the exhaust system and cause misfires. Its very possible that this is all you have.
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you did it wrong actuially...
you should do this...
1 pull the fuel fuse,
2 start the car (or try to) and bleed out all the fuel pressure in the lines (which is why #1 was high)
3 remove one plug at a time (its easier to "count cranks" cause the motor wont just spin free)
4 install compression tester
5 hold the torottle wide open with clutch enguaged, wheel chock and an open area to run incase something catastrophic happens,
crank the motor a designated number of times (if you can get a clean count of like 9 or 10 or wahtever just crank it for a minute untill the gauge stops clmbing)
6 read and write down compression,
7 pour a rollop of oil down the sparkplug hole and retest that cylinder
8 record numbers and compare.
9 repeat for all cylinders.
EDIT: sorryt i read a little of your post wrong,
the middle two cylanders are normally lower because they have another cylinder on either side of them, they tend to wear out first just due to heat and what not. thats normal,
i would look to ahve a valve adjustment done and then retest. that difference of 10psi just looks like a valve lash adjustment is needed.
a higher "wet" compression test just means that your ruings are sealing better due to the oil. if there is a drastic change in numbers (more than about 25psi) then start looking at your rungs and ahve a leak down check performed. if ponly a small change (5-10) you;re fine.
a variance of 10PSI is nothing. id start worrying about a 20-35 change.
and like i said, it was because you ahd a little fuel in that cylander from not running the car without the fuel pump fuse removed
enjoy
you should do this...
1 pull the fuel fuse,
2 start the car (or try to) and bleed out all the fuel pressure in the lines (which is why #1 was high)
3 remove one plug at a time (its easier to "count cranks" cause the motor wont just spin free)
4 install compression tester
5 hold the torottle wide open with clutch enguaged, wheel chock and an open area to run incase something catastrophic happens,
crank the motor a designated number of times (if you can get a clean count of like 9 or 10 or wahtever just crank it for a minute untill the gauge stops clmbing)
6 read and write down compression,
7 pour a rollop of oil down the sparkplug hole and retest that cylinder
8 record numbers and compare.
9 repeat for all cylinders.
EDIT: sorryt i read a little of your post wrong,
the middle two cylanders are normally lower because they have another cylinder on either side of them, they tend to wear out first just due to heat and what not. thats normal,
i would look to ahve a valve adjustment done and then retest. that difference of 10psi just looks like a valve lash adjustment is needed.
a higher "wet" compression test just means that your ruings are sealing better due to the oil. if there is a drastic change in numbers (more than about 25psi) then start looking at your rungs and ahve a leak down check performed. if ponly a small change (5-10) you;re fine.
a variance of 10PSI is nothing. id start worrying about a 20-35 change.
and like i said, it was because you ahd a little fuel in that cylander from not running the car without the fuel pump fuse removed
enjoy
Joined: May 2004
Posts: 3,403
Likes: 6
From: DFW, TX
Originally Posted by street_ruler,Dec 17 2007, 09:44 AM
you did it wrong actuially...
you should do this...
1 pull the fuel fuse,
2 start the car (or try to) and bleed out all the fuel pressure in the lines (which is why #1 was high)
3 remove one plug at a time (its easier to "count cranks" cause the motor wont just spin free)
4 install compression tester
5 hold the torottle wide open with clutch enguaged, wheel chock and an open area to run incase something catastrophic happens,
crank the motor a designated number of times (if you can get a clean count of like 9 or 10 or wahtever just crank it for a minute untill the gauge stops clmbing)
6 read and write down compression,
7 pour a rollop of oil down the sparkplug hole and retest that cylinder
8 record numbers and compare.
9 repeat for all cylinders.
EDIT: sorryt i read a little of your post wrong,
the middle two cylanders are normally lower because they have another cylinder on either side of them, they tend to wear out first just due to heat and what not. thats normal,
i would look to ahve a valve adjustment done and then retest. that difference of 10psi just looks like a valve lash adjustment is needed.
a higher "wet" compression test just means that your ruings are sealing better due to the oil. if there is a drastic change in numbers (more than about 25psi) then start looking at your rungs and ahve a leak down check performed. if ponly a small change (5-10) you;re fine.
a variance of 10PSI is nothing. id start worrying about a 20-35 change.
and like i said, it was because you ahd a little fuel in that cylander from not running the car without the fuel pump fuse removed
enjoy
you should do this...
1 pull the fuel fuse,
2 start the car (or try to) and bleed out all the fuel pressure in the lines (which is why #1 was high)
3 remove one plug at a time (its easier to "count cranks" cause the motor wont just spin free)
4 install compression tester
5 hold the torottle wide open with clutch enguaged, wheel chock and an open area to run incase something catastrophic happens,
crank the motor a designated number of times (if you can get a clean count of like 9 or 10 or wahtever just crank it for a minute untill the gauge stops clmbing)
6 read and write down compression,
7 pour a rollop of oil down the sparkplug hole and retest that cylinder
8 record numbers and compare.
9 repeat for all cylinders.
EDIT: sorryt i read a little of your post wrong,
the middle two cylanders are normally lower because they have another cylinder on either side of them, they tend to wear out first just due to heat and what not. thats normal,
i would look to ahve a valve adjustment done and then retest. that difference of 10psi just looks like a valve lash adjustment is needed.
a higher "wet" compression test just means that your ruings are sealing better due to the oil. if there is a drastic change in numbers (more than about 25psi) then start looking at your rungs and ahve a leak down check performed. if ponly a small change (5-10) you;re fine.
a variance of 10PSI is nothing. id start worrying about a 20-35 change.
and like i said, it was because you ahd a little fuel in that cylander from not running the car without the fuel pump fuse removed
enjoy
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From: AZ-CA-NV-24/7
Whether to remove all plugs or not is what I was confused about. I pulled all 4 then checked. I bought my compression tester from Harbor Freight tools so it's probably not the most accurate piece of equipment. I have yet to do a valve adj on this car and I think that this also might be contributing to the problem. 
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yah its just easier with only 1 plug out.
and as for accuracy, it doesnt really matter if you ahve a 100,000 dollar gauge or a 10 buck gauge. its all about what that gauge reads. id say the gauge is not the problem
and as for accuracy, it doesnt really matter if you ahve a 100,000 dollar gauge or a 10 buck gauge. its all about what that gauge reads. id say the gauge is not the problem
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[QUOTE=Silver9k,Dec 17 2007, 09:47 AM] I was taught to always pull all the spark plugs, this way if there is a headgasket problem between two cylinders it is likely to show up in a compression test, however.