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Low Compression Test Results

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Low Compression Test Results

 
Old 09-09-2018, 02:48 PM
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Question Low Compression Test Results

I just finished doing a compression test and the results are relatively consistent but very low.
Cylinder #1: ~160psi
Cylinder #2: ~150psi
Cylinder #3: ~147psi
Cylinder #4: ~156psi


Cylinder #1

Cylinder #2

Cylinder #3

Cylinder #4

I read in a few posts here that you should expect the range to be around 200-240psi but that consistency was more important. Is there any kind of leak that would lower overall pressure? Should I be concerned? I have the tools to do a leak-down test as well and will likely be doing that this upcoming Tuesday if the weather permits.

Additionally, I bought this car used a few years ago and just recently decided to start fixing everything wrong with it. I've done regular maintenance to it, but there are some issues I've known about but was not in a position to either fix myself or have fixed professionally. With that said, I just recently noticed this:

Engine
It looks like there is a leak coming from the bolt that holds the idle gear. I'm going to order the O-Ring to replace and tighten it to 36ft./lb., but in the meantime do you think that may be a cause for the low pressure? I also noticed that the oil drain valve is leaking (not sure when that started) so I'm going to tighten that as well (I assume to 29ft./lb. like the OEM drain bolt?). The MAP sensor likely needs to be replaced as well (whacking was not effective, but I'm going to clean the IAC valve first to make sure), would that cause issues with pressure?

Lastly, as I did the test I noticed that while the engine was cranking, there was a rather loud noise and smoke/vapor coming from the engine... is this normal? I would assume that it is not.

Thanks for the help.
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Old 09-09-2018, 03:30 PM
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You should have also read on here not to use a Harbor Freight compression tester. They just don't work. At least not for high compression engines like ours.

I like HF. I buy a lot of tools there. Most of their stuff is decent. Some of it is excellent. Some of it is total junk. Their compression tester is at or near the junk category.

Rent a gauge from a place like Autozone. Make sure motor is warm. All plugs out. Throttle wide open. Fuel pump fuse removed.
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Old 09-09-2018, 03:38 PM
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Originally Posted by Car Analogy View Post
You should have also read on here not to use a Harbor Freight compression tester. They just don't work. At least not for high compression engines like ours.

I like HF. I buy a lot of tools there. Most of their stuff is decent. Some of it is excellent. Some of it is total junk. Their compression tester is at or near the junk category.

Rent a gauge from a place like Autozone. Make sure motor is warm. All plugs out. Throttle wide open. Fuel pump fuse removed.
I see. I mostly followed Rob Robinette's guide that was linked on here as well as the faddis2k's guide. In Rob's guide he used a Harbour Freight tester. I'll go ahead and return it and try to see if the O'Reilly or Napa near my house has something better I can use. Thanks for the tip! Do you recommend the same thing for Harbour Freight's leak-down tester too?
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Old 09-09-2018, 03:45 PM
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The important thing if using a questionable gauge (or technique) is that all the readings are somewhat similar. If one stands out that is an indication of a problem.
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Old 09-09-2018, 04:09 PM
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I had almost those exact readings when I did my test with that same HF tester. Read through the threads and saw the warning about the readings being low with the HF tester. I took it back and picked up one from Advanced Auto for a little more. It has the valve at the bottom instead of near the gauge. Redid the test and have the 230/240 that we are looking for. Those numbers are solid but if you’re like me, who wanted to know for sure, get a different tester.
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Old 09-09-2018, 04:14 PM
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Originally Posted by Birdybog View Post
I had almost those exact readings when I did my test with that same HF tester. Read through the threads and saw the warning about the readings being low with the HF tester. I took it back and picked up one from Advanced Auto for a little more. It has the valve at the bottom instead of near the gauge. Redid the test and have the 230/240 that we are looking for. Those numbers are solid but if you’re like me, who wanted to know for sure, get a different tester.
Glad to hear, the engine pulls hard and feels really good so it seemed odd to see such low numbers. Because of the solid results, did you bother with the leak-down test?
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Old 09-09-2018, 04:19 PM
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Originally Posted by tohlenforst View Post
Glad to hear, the engine pulls hard and feels really good so it seemed odd to see such low numbers. Because of the solid results, did you bother with the leak-down test?
No, I have not done a leak-down test.
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Old 09-09-2018, 05:18 PM
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Hard to tell from the one photo, but the accessory belt looks to have a sheen on the surface. When was the last time you changed it?

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Old 09-09-2018, 05:30 PM
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I tested with the same tester as you and got similar results, it lead me down a paranoid path thinking I'd be shopping for a new motor soon. Long story short, everything is fine and the car tested at leakdown numbers below like 5% and tested normal compression numbers on a different gauge.
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Old 09-09-2018, 05:31 PM
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Originally Posted by windhund116 View Post
Hard to tell from the one photo, but the accessory belt looks to have a sheen on the surface. When was the last time you changed it?

I'm going to be completely honest and say I have no idea when it was last changed. You're referring to the serpentine belt, right (are those the same thing?)? What exactly do you mean by a sheen? I can post some more photos tomorrow.
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