Compression Test Procedure <WITH RESULTS>

[patkennedy78]

I’m going to give the sedan (92 Loyale) a compression test. I’ve never done this before and it seems like an odd procedure to me. Basically I’m going to disable the spark and fuel from going to the engine so all I’m left with is the pistons moving back and forth creating dry compression, yes?

 

So here is the plan:

 

When the car is cold. Disable the fuel pump by either disconnecting wires at the pump or taking out the fuse. Unplug the hose going to the fuel filter and place a catch bottle. Crank the car over a few times to rid remaining fuel from the line.

 

Remove spark plugs. Take the wire coming from the coil and clip it to the strut tower bolt to complete a ground.

 

Attach compression tester. With gas pedal all the way to the floor crank engine over for 4 cycles and record the highest reading. Repeat this step with other 3 cylinders. Repeat on all cylinders for comparison.

 

Sound Right?

 

Now after this point do I put everything back to normal, get the engine up to normal temperature and repeat the whole process?

 

Another question I have is when or why do I put a few drops of oil into the spark plug holes? Is this just if the reading is low? Then if the reading comes back up after I add the oil is that good or bad or what does that indicate?

 

I think that about covers it for now.

[Jerry DeMoss]

That is one way of doing it which I have never done.

 

This is the way I do it:

-Warm the engine up to operating temp and remove the spark plugs and as you said block off or shut off the fuel supply and spark.Then insert the copression tester in the spark plug hole.Hold the throttle down to the floor to create vacuum and crank.

 

I am sure there are other ways of doing it.This has just always worked for me.

[idosubaru]

sounds like you got it about right.

 

simply put - prop the throttle open, disconnect plug wires, unplug fuel pump, remove plugs and crank the engine over a few times for each test.

 

prop the throttle open and you don't have to hold the gas pedal down. the gas pedal keeps the plate open so air moves freely to the cylinders, otherwise you'll get a slightly lower reading sometimes.

 

remove all the spark plugs (the wires will be remove when you do this so yo'ure done with that). pull the ignition coil wire if you'd like, i never do.

 

unplug the fuel pump and crank the car for a bit. keep it simple, those other steps are unneccessary in my oppinion.

 

test compression.

 

the oil in the cylinders will help seal rings that have blow-by. so if you're compression is low and goes up with some oil then that cylinder has some blow-by. this doesn't work so great in subaru's because of the flat 4 design. in a subaru the oil will pool at the bottom of the cylinder and not evenly disburse around the cylinder walls very well so it's not all that efficient of a test on a subaru. a leak down test would be more appropriate. or just attach your air compressor to the cylinder with an adapter and add air with both valves closed and see where it's escaping. if it's blowing through the oil dipstick and crank case venting areas then the rings are bad. through exhaust or intakes and it's valve related.

[NorthWet]

I agree to keep it simple. The one thing that I would do, if you are using the ignition switch to do the cranking (and not a remote starter switch), is to either disable the coil or ground the coil's secondary wire. If possible, unplugging the ignitor connection or removing the primary wires from one of the coil terminals would be best. If you just unplug spark plug wires the coil will try to develop enough voltage to jump whatever gap exists, risking damage to ignition components.

 

Although I wouldn't worry too much, another thing might be to unplug the injector's connector. The amount of fuel we are talking about is minimal but the SPFI system makes it pretty easy to prevent fuel being injected.

[patkennedy78]

Ok, it looks like I'm on the right track, I feel better.

 

This may be a stupid question, but I'll ask it in fear of being wrong. Does the ignition coil store any charge? Should I be careful when unplugging it? I think the coil is the only part of the igniton system I've never really messed with. I'd rather disconnect it all together then risk giant sparks or damaging the whole system.

[patkennedy78]

I didn't find anything in here about the coil, so I went ahead with the procedure.

 

I grouned the wire from the coil to the strut tower. unplugged the fuel pump fuse, and took out all the plugs. Here are the results:

 

1 - 115

3 - 110

 

2 - 100

4 - 100

 

Needless to say I'm pleased. For now my head gaskets are in tact.

[GeneralDisorder]

Now try the oil squirt step - that will tell you if your low readings are rings (unlikely) or valves.

 

Yeah - those numbers are ok, but a little low IMO. Anything over about 80 or 90 is ok to run, and yours are looking alright in that respect. You may benefit a lot from a valve job. For reference, my Brat pulls 140-150 in each, and my wagon is about 220 on each (I have no idea how it got so high, it's just a stock engine AFAIK). I have yet to test my sedan, but it runs good, and doesn't overheat so I have little reason to..... yet. A newly rebuilt EA series should run in the 175-200 range (after break-in) if it's been done properly. Chrome rings may increase that a bit once they break in. I kinda have a feeling there's already something like that in the wagon's engine - very strange high readings.

 

Oh - and another thing. I've tested engines with bad HG's that ran but overheated, and still got good readings. The gasket was allowing small amounts of compression into the coolant, but once the cooling system was pressurized, the compression readings in the cylinder were normal.

 

GD

[()__1337_CRAYOLA__()>]

my uncle used that restore stuff you put in your oil and his compression went from 120's in all cylinder to 160-170's in all cylinder And i am also using it in my subaru but haven't done a compression test though maybe try that

[GeneralDisorder]

Restore - like most "magic bullet in a can" crap sold to the uninitiated vehicularly impared, contains large quantities of Dupont Teflon - which has shown to decrease friction, and increase compression and power output in the short term. It's long term effects unfortunately are the problem. Among other things, it embeds itself into the bearing material, and causes spalling of the bearing surfaces. It also clogs up oil filters and passages, and just generally wreaks havok within the tightly controlled oil-rich universe of the combustion engine. Dupont recognized these problems, and tried very hard to stop third party companies from purchasing their product for this use. They lost a court case or two on the subject, and now they simply have an official stance that their product (yes - THEIR OWN PRODUCT) has no recognized benifits when used in gasoline engines. Slick 50, Restore, etc tout their claims louder, and have their name on many a race car so you can imagine how well this has worked. When used in a race engine intended to last a season or less, it really doesn't matter, and the money they get from the endorsements would cover the occasional mishap anyhow.

 

Here's a little more detail to chew on:

http://www.msgroup.org/TIP043.html

 

GD

[()__1337_CRAYOLA__()>]

Thats it im never using that stuff Ever Again!