Compression Check Write up
By: KoolerSL2
First off lets start with this. Almost every Saturn out there is going to be compression checked sometime or another in its lifetime. This write up is for All S-Series DOHC motors. This write up was done on my 02 SL2.
SAFETY FIRST!
Always wear safety glasses and gloves, some surfaces can be hot! Make sure the car is parked well and e brake is engaged. Now pop your hood and lets start.
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This is what my most engine bays look like less the different intake manifold and valve cover. This is your starting point. Go ahead and start the engine and let idle for approximately 3-4 minutes to get warm. After this shut it off. Go to your interior fuse panel and find the fuel pump fuse.
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Itâs a 10A fuse. Go ahead and pull it out, probably have to use some small needle nose pliers to get it. Next start the car, it should start then die almost immediately. The next step is to go under hood and find the injector fuse.
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Go ahead and pull it out. This prevents the injectors from cycling with out fuel as not to damage the injectors. Your next step is to find the harness plug on the ignition module.
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There is a little clip underneath that needs to be unclipped.
Once unclipped it should pull off, but be gentle I have seen an older S series harness plugs break off.
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Once pulled off lay it to the side out of the way. Now the next step has 2 ways of being done. 1st way is to do 1 cyl at a time with leaving the other 3 plugs in place as so.
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The 2nd way is to pull out all the plugs and test as so.
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Either way works but this way sometimes you forget what wire goes where (its happened even to the best of us) thatâs where wire markers can come in very handy.
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Most aftermarket wires come with these. If you still have stock wires just some masking tape and a marker will work to mark the wire to cyl locations.
No comes the fun part. Now its best to have a helper in this process because it can become difficult just by yourself. Now get a pen and paper and write down cyl 1-4 so u can write down the compression numbers.
With the compression tester in place have your helper get in, hold the throttle wide open, and start the car.
Let it cycle at least 7-10 times. Write down the compression psi . repeat for other 3 cyls.
Now compare your numbers. According to FSM and other sources, compression should be between 180 PSI to 210 PSI. anything below 180PSI indicates a problem. Could be any number of things. If you get any reading below this, it maybe time to plan going more in-depth diagnosis and repairs.
Now when I did mine the tester showed the needle jumping from 180 to 210 PSI. I spoke to my local Saturn tech and because of the tester I used this was normal. He even checked behind me with the same tester then brought out his snap-on tester. His tester showed steady 210 PSI. Now remember these PSI readings are for stock compression S series DOHC Engines. The tester I used was the loan-a-tool from Autozone. $35.00 + Tax. Now this is also a good time to check your plugs. Mine didnât look to hot.
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So I went ahead and replace them with some NGK V powerâs.(Part # BKR5E-11 )
Always when in doubt on your plugs, go ahead and replace them. Make sure Gap is it 0.040 for all S-Series DOHC engines. Always remember when in either re-installing your old plugs and installing new plugs give them a coating of Anit-Sieze to prevent possible thread stripping and for ease of removal. Of course replace your wires to their proper cyls.
Then replace the control module harness plug.
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Reinstall the injector fuse.
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Then reinstall your fuel pump fuse in the interior fuse panel.
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Reinstall all your fuse panel covers before you go any further. Once your done with all that get in turn your key on to the IGN position you should hear your fuel pump kick on. Once it shuts off turn the key off. Then again turn the key to the IGN position and let the fuel pump turn on the cut off. Finally restart your car and let it idle for about 5 mins to let the plugs settle in.
After that cut the car off, double check everything if your check is good, your done! Go clean up, have a drink and relax. And of course always enjoy your Saturn.
KoolerSL2 (Chris)
Glossary
IGN: Ignition
PSI: Pounds per Square Inch
CYL: Cylinder
DOHC: Dual Over Head Cam
How-To: S-Series Compression Check 
Linear Mode
