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Old 09-15-2007, 10:47 PM   #1
justinflo200
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Default Engine Compression Testing

First, where can I find a compression gauge? I'm assuming they will sell them at my local parts store. Second, exactly how do I perform the test? I have the Haynes manual. I did a search and didn't find a how-to. It seems pretty easy, but is there anything else I should be aware of besides whats in the manual? Thank you.
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Old 09-15-2007, 11:09 PM   #2
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Default Re: Engine Compression Testing

Yes it's easy.

Remove all the spark plugs, screw in the compression tester (in place of one of the plugs). Then crank the engine with the gas petal to the floor (this disables the injectors so they don't spray fuel). Then go check it, write down the cylinder number and the compression. Release the pressure and unscrew the tester. Then repeate for all the cylinders. #1 cylinder is on the passenger side, #4 is on the drivers side.

You can get a tester almost anywhere you can get automotive tools. Kragen, Autozone, Pepboys, Sears ...
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Old 09-16-2007, 08:12 AM   #3
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Default Re: Engine Compression Testing

What he ^ said.

You can also add a little oil to the cylinder after the first test and see if the pressure goes up. If it does it indicates that the rings aren't sealing 100%. If it's still low it means the air is leaking out the valves. You can also do a leakdown test to see how well the cylinders maintain pressure over time
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Old 09-16-2007, 09:08 AM   #4
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Default Re: Engine Compression Testing

Yes, a compression gauge will be available at any parts store and most tool places.

This site has an excellent How-To section. I really do wish more people would use it. You can get there off the home page or use the forum jump at the bottom of the page. This thread in the How-To Library will tell you the best way to perform the test.
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Old 09-16-2007, 04:40 PM   #5
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Default Re: Engine Compression Testing

Harbor Freight has compression gauges for cheap.
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Old 09-16-2007, 10:14 PM   #6
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Default Re: Engine Compression Testing

One thing that was left out was to do the test with the engine hot. Operating temp, preferably. Pull it in, yank the plugs, and do the test. You should only crank 6-10 times. More or less can give erroneous readings. It should be hot so all rings and valves have expanded and will give the truest readings. Refer to the manual for compression specs. If it's below the service limit, then it's time for a rebuild.
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Old 09-17-2007, 03:02 PM   #7
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Default Re: Engine Compression Testing

Hey again, I just wanted to show my results from the testing I did this afternoon. Cylinders 1 & 2 both showed 210. Cylinder 3 showed between 200-205. However, cylinder 4 was the problem cylinder which I expected from the first place because everytime I took out the spark plugs, #4 was really sooty and worn. Anyways It first had a reading of 195. Then I added a tad of oil and it shot all the way up to 215. So from what I understand, that is worn piston rings? Thanks for your replies in helping me out.
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Old 09-17-2007, 06:57 PM   #8
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Default Re: Engine Compression Testing

Why were you testing the compression? Those readings don't seem too bad... that indicates that your rings are worn but definitely not shot...
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Old 09-17-2007, 11:46 PM   #9
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Default Re: Engine Compression Testing

Why, am I not supposed to? I wanted to see how bad the engine was to see if it would be worth it to do a rebuild or just live with it.
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Old 09-18-2007, 01:27 AM   #10
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Default Re: Engine Compression Testing

Quote:
Originally Posted by justinflo200 View Post
Why, am I not supposed to? I wanted to see how bad the engine was to see if it would be worth it to do a rebuild or just live with it.
You're saying this was just out of curiosity? Usually people check compression because the engine is giving them a reason to do it. That's what I was asking about.
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Old 09-18-2007, 04:10 AM   #11
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Default Re: Engine Compression Testing

Quote:
Originally Posted by justinflo200 View Post
I wanted to see how bad the engine was to see if it would be worth it to do a rebuild or just live with it.
Your engine does not need a rebuild. Those numbers are good. The fact that adding oil to #4 boosted the compression means that you have good valves.

Try an MMO piston soak, or a Seafoam piston soak or both a couple of times each and see if it makes any difference if you feel like messing around, but you definitely don't need a rebuild.

What I'd like to know is what eactly would you be living with? Are there any performance problems with your engine?
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Old 09-18-2007, 10:02 AM   #12
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Default Re: Engine Compression Testing

Its a five speed, but it seems really slow on acceleration. Brand new plugs and wires and it still seems sluggish. Even if I put the pedal to the floor it doesn't accelerate any faster. Do you think a new air intake will help this. Also with the oil burning at about every couple stoplights when I'm at a dead stop, then when I take off it smokes out of the exhaust through third gear and usually quite a bit.
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Old 09-18-2007, 10:12 AM   #13
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Default Re: Engine Compression Testing

What are the RPM's when you are accelerating?
If it's winding up fairly high, but still no get up and go, then I'd look into the catalytic converter.
Remove the oxygen sensor (temporarily), and see if it's any better.
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Old 09-18-2007, 10:14 AM   #14
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Default Re: Engine Compression Testing

Quote:
Originally Posted by justinflo200 View Post
Its a five speed, but it seems really slow on acceleration. Brand new plugs and wires and it still seems sluggish. Even if I put the pedal to the floor it doesn't accelerate any faster. Do you think a new air intake will help this. Also with the oil burning at about every couple stoplights when I'm at a dead stop, then when I take off it smokes out of the exhaust through third gear and usually quite a bit.
Classic symptoms, of.......


Oh no I'm gonna say it.....


ECTS (Engine Coolant Temperature Sensor)

A bad sensor will make the engine run too rich and cause the exact problems you've described.
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Old 09-18-2007, 10:45 AM   #15
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Default Re: Engine Compression Testing

Found in another post he replaced his ECTS.
However, don't know if the connector is bad.

Questions -
Does it run bad when it is cold?
What plugs did you use?
What RPM do you shift at?
(If you are used to a V6, you need to rev these little babies much higher)
Try running up to 4500 RPM before shifting, espically in second gear. Third is really a big jump for a SOHC.
It should be pulling pretty good above 3k, well, as good as you can with 100 hp at redline....
Drop a quart of MMO in the oil and run it for 400 miles before changing to help with oil burning.
Take the throttle body off and clean it really good.
How old is the air filter?
Al.
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Old 09-18-2007, 12:33 PM   #16
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Default Re: Engine Compression Testing

First, thanks for all the suggestions. Second, I bought the NGK plugs at a Saturn dealer, so no problem there. I usually shift around 2200-2300, maybe a little quicker in the lower gears because it seems the engine loses power if I go any higher. I changed the oil and the oil filter about two months ago. Also mine is a DOHC, don't know if that makes a difference to shift rpms.

I do have a feeling it is the throttle body because no matter how much I press on the gas it doesn't seem to go any faster. It's like no extra air is getting into the manifold no matter if I'm barely on the throttle or if I'm wide open. And yes I did change the ECTS a couple weeks ago and it is a possibility that the connectors are bad.
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Old 09-18-2007, 12:59 PM   #17
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Default Re: Engine Compression Testing

DOHC has more power at the higher end. I shift mine at or above 4500 at times, and it really get's up and goes at that RPM in first and second gear.

If you're loosing power above 2500 RPM you either have a clogged CAT, or a fuel supply problem. Maybe a new fuel filter. It might also not be getting enough air, so you might try a new air filter too.

More than likely it's the fuel supply, except that doesn't explain smoke.

Check the ECTS connector. Make sure you can see around 5v across the two pins when the key is in the run position.
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Old 09-18-2007, 01:13 PM   #18
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Default Re: Engine Compression Testing

Before investing in a fuel filter, since they are rather expensive, I would pull the front O2 sensor. Take it for a loud drive around the block. Rev her up and shift at 5k. If it has tons of get up, then you definately have a clogged cat. If there is no difference, then go the fuel filter route. Maybe someone here can advise of an inexpensive way to monitor the fuel pressure.
(this is provided that it isn't an ects connector issue.)

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