LQ9 cranking compression
11-23-2014, 01:40 PM
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LQ9 cranking compression Got a 2005 LQ9 with 110,00 miles from LKQ to start my conversion project. Threw it on engine stand and did a cranking compression test. 270 - 300 psi. WTH!!! I was expecting 190-210. My first thought is user error, but how could i screw up a cranking compression test? Is there something wrong with this engine? I am tempted to return it now. I don't want to install it and have it not work. Any thoughts?
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Thanks
11-23-2014, 04:39 PM
#2
try a different gauge.
11-23-2014, 07:29 PM
#4
Hydraulic lifters work with oil. If an engine has not run in a while and has been rotated a lot you can squeeze the oil out of the lifters. If the lifters are bled down, you will have an earlier intake valve close which increases dynamic compression.
12-02-2014, 12:40 PM
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Sorry it took so long to retest the motor, but here are the results.
I first hooked up a mechanical oil pressure gauge. Spun the motor and no oil pressure. I did put oil in filter prior to screwing it on. So I spun the motor for 20 seconds four times and got 30 psi pressure while cranking. I then repeated the compression test and found 230-250 psi on all but number 8 which was 210. I did get another compression gauge and it read about the same as mine. I guess there was something to the theory of lifter leak down and higher dynamic compression as the compression is now down to what is expected.
I made a leak down tester (using a dampener plug 0.25"x0.040") and got 93-98% all cylinders but 7 and 8. They were 90%. Sounds reasonable right? I used a HF inspection camera to inspect the piston tops ( actually I was using it to ID TDC). and saw the apparent marks in the tops of pistons 7 and 8. Is that my imagination or does that look like the valves kissed the piston?
The leak down and compression tests are ok so should I be concerned? I know that this is a salvage yard motor with 110K miles. I don't want to take it back to LKQ and ask for a different motor unless needed. I most likely won't be able to start the motor til spring to see how well it runs.
Thoughts?
I first hooked up a mechanical oil pressure gauge. Spun the motor and no oil pressure. I did put oil in filter prior to screwing it on. So I spun the motor for 20 seconds four times and got 30 psi pressure while cranking. I then repeated the compression test and found 230-250 psi on all but number 8 which was 210. I did get another compression gauge and it read about the same as mine. I guess there was something to the theory of lifter leak down and higher dynamic compression as the compression is now down to what is expected.
I made a leak down tester (using a dampener plug 0.25"x0.040") and got 93-98% all cylinders but 7 and 8. They were 90%. Sounds reasonable right? I used a HF inspection camera to inspect the piston tops ( actually I was using it to ID TDC). and saw the apparent marks in the tops of pistons 7 and 8. Is that my imagination or does that look like the valves kissed the piston?
The leak down and compression tests are ok so should I be concerned? I know that this is a salvage yard motor with 110K miles. I don't want to take it back to LKQ and ask for a different motor unless needed. I most likely won't be able to start the motor til spring to see how well it runs.
Thoughts?
