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Old 06-16-2018, 07:20 PM   #1
redrexmeister
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Default compression test clarifications needed

Doing spark plugs on ej257 and curious to do a compression test. Needs some clarifications/tips:

1. The test is to be done on a warm engine. So I will run the engine b4 the test to bring it to operational temperature, then remove coils and plugs. Any concerns with removing spark plugs from a hot engine?

2. All four plugs must be removed from the engine before you start testing each individual cylinder, right?

3. Throttle must be prompted open. If I depress the accelerator pedal, will that guarantee the desired result? Or should I remove the intercooler and use some sort of a wedge to keep the throttle open?

4. Before the test I need to disconnect fuel pump and ignition fuses, correct? i.e. I only use starter to let the engine turn but no fuel delivery and spark.

5. The compression numbers from the spec range are for dry test, right? Is there utility to run wet compression test (i.e. when you skirt oil in the cylinder) on boxer engine?

Thank you!
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Old 06-16-2018, 08:18 PM   #2
Cobrakai
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Quote:
Originally Posted by redrexmeister View Post
Doing spark plugs on ej257 and curious to do a compression test. Needs some clarifications/tips:

1. The test is to be done on a warm engine. So I will run the engine b4 the test to bring it to operational temperature, then remove coils and plugs. Any concerns with removing spark plugs from a hot engine?

Warm doesn't have to be operating temp

2. All four plugs must be removed from the engine before you start testing each individual cylinder, right?

Correct

3. Throttle must be prompted open. If I depress the accelerator pedal, will that guarantee the desired result? Or should I remove the intercooler and use some sort of a wedge to keep the throttle open?

Hold the throttle 100% open, crank the engine ~7 times, close throttle and read the compression gauge

4. Before the test I need to disconnect fuel pump and ignition fuses, correct? i.e. I only use starter to let the engine turn but no fuel delivery and spark.

I remove the IGN fuse from the in cabin fuse box found behind the coin tray

5. The compression numbers from the spec range are for dry test, right? Is there utility to run wet compression test (i.e. when you skirt oil in the cylinder) on boxer engine?

If your numbers are low you can squirt oil into the questionable cylinder(s) and retest. If the compression numbers are higher after squirting oil into the cylinder you may have a ringland issue on your hands

Thank you!

You're welcome

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Old 06-16-2018, 08:50 PM   #3
redrexmeister
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Great. Thanks for comprehensive response.

Just one more clarification re "Hold the throttle 100% open..."

Do you mean physically keep it open with the help of channel locks, pliers, wedge or some other contraption?

The above would imply that I remove the intercooler to gain access to the throttle plate to keep it open, right?

Last edited by redrexmeister; 06-16-2018 at 08:57 PM.
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Old 06-16-2018, 10:27 PM   #4
Cobrakai
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Quote:
Originally Posted by redrexmeister View Post
Great. Thanks for comprehensive response.

Just one more clarification re "Hold the throttle 100% open..."

Do you mean physically keep it open with the help of channel locks, pliers, wedge or some other contraption?

The above would imply that I remove the intercooler to gain access to the throttle plate to keep it open, right?


Sorry I meant: push and hold the gas pedal to the floor while you're cranking the engine ~7 times.

You don't have to remove the intercooler, just need to gain access to the spark plugs.

This video might help:

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Old 06-16-2018, 11:15 PM   #5
redrexmeister
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Awesome!
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Old 06-16-2018, 11:57 PM   #6
Charlie-III
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Cable throttle, foot to the floor to hold the throttle plate open.
A DBW, some work when cranking, some require you to prop the plate open.

Fully charged battery, battery on a charger may help.
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Old 06-18-2018, 09:51 PM   #7
redrexmeister
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Default results

well, I am not sure if I did the test correctly but here is what I got so far:

#1 - 134
#3 - 133

#2 - 124
#4 - 125

I ran the engine to bring it to operating temperature, then disconnected fuel pump relay, and unplugged the coils. I initially measured #1 and #3 on the passenger side. The engine was fairly warm, almost impossible to touch by hand. My car is DBW, so I just held the accelerator down while I was cranking 7 starter cycles.

Unfortunately, the compression tool plug was stuck in the cylinder #3, and I spent significant amount of time trying to remove it. By the time I started measuring driver side #2 and #4 the engine was luke warm.

I am wondering if ten psi lower results on the driver side are because of the lower engine temperature (from the thermodynamic view point, higher temperature causes higher pressure). Perhaps, I can measure compression results tomorrow on the cold engine to see if the values 1/3 and 2/4 equalize.

I am also wondering if I should be worried about rebuilding the engine, since the above results are below specification range of 142-171 psi for turbo engines?

Last edited by redrexmeister; 06-18-2018 at 10:01 PM.
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Old 06-19-2018, 12:31 AM   #8
Charlie-III
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I you retest, get dry numbers, then shoot some oil into the cylinders and see if the numbers come up.
If they do, likely have at least weak rings.
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Old 06-19-2018, 11:56 AM   #9
redrexmeister
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Default retest results

I retested dry compression with the engine cold. The air temp in my garage was balmy 82F. The retest results were essentially identical to psi values obtained yesterday with the warm engine. Thus, the engine temp had no significant impact on the compression test results.

I proceeded with the wet test, adding 1 tbsp of engine oil to each cylinder and repeating the compression test:

#2 - 148 #1 - 152
#4 - 146 #3 - 151

Oil definitely helped to seal compression bringing everything to about 150psi, which is in acceptable range.

In addition, I had head gasket test done with an indicator fluid to look for exhaust gas in the coolant, which came negative. From prior history, the engine was rebuilt few years ago and at the time they replaced all warn out / bent valves. Thus, as the above poster commented it seems that the engine has worn out pistons/rings resulting in low compression, more so on the driver's side.

So the question now is what should I do about it?

The engine runs smooth, good idle, no smoke in the exhaust, no excessive oil consumption, no CEL. It is currently at the stock power level, the car is used as a daily. Is it still save to add turboback and Stage 2 tune, while using thicker oil like Shell Rotella 5w-40?

Or should I not risk it and drive as is. If the problem worsens, start planning on short block replacement?

Thanks for your thoughts.

Last edited by redrexmeister; 06-19-2018 at 03:49 PM.
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Old 06-19-2018, 08:32 PM   #10
Cobrakai
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How many miles on the engine?

IIRC the rule of thumb is: The difference in cylinder pressure should be no greater than 10% across the board.

A friend of mine was hovering around 135 PSI on his EJ257 and it runs like a top with over 100k miles on the clock. Car was protuned aggressively 15k miles ago with a Stage 2 set up.

You should definitely be running something thicker than 5W30, the Brotella, I mean Shell Rotella T6 works well for our engines.

The fact that your engine idles smoothly, doesn't misfire or consume oil would give me peace of mind.

Also worth mentioning my EJ207 had lower compression than the numbers provided by the importer, guess they forgot to mention that they squirt oil in the cylinders.

Last edited by Cobrakai; 06-19-2018 at 08:46 PM.
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Old 06-19-2018, 09:18 PM   #11
redrexmeister
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The previous owner indicated that the engine was rebuild about 6 years ago. So I would estimate it is about 75k on the engine.

I was also wondering if the rebuilt engine would have lower compression by default, the short block was likely bored to 99.75 and the piston rings changed ?

Last edited by redrexmeister; 06-20-2018 at 07:38 AM.
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Old 06-20-2018, 08:48 AM   #12
Charlie-III
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Quote:
Originally Posted by redrexmeister View Post
The previous owner indicated that the engine was rebuild about 6 years ago. So I would estimate it is about 75k on the engine.

I was also wondering if the rebuilt engine would have lower compression by default, the short block was likely bored to 99.75 and the piston rings changed ?
Actually, if the bore is bigger but using the same combustion chamber, the numbers should be higher..........a little more air squeezed into the same final space.

I would leave it for now until you start going through oil (1 quart oil/1000 miles) or have other piston ring related issues.

Bad rings won't dump combustion gas into the coolant, leaking head gaskets will.

BTW, next time you list before/after numbers, list them in the same order to make it easier to read across posts.
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