Compression test procedure?

[Spenser281]

I'd like to do a compression on my '10 SHO.  I have some questions first.

How do I disable the fuel system?  I'm assuming there is a fuel pump relay for the in tank pump, but is there anything I need to do about the high pressure pump?  Do I need to purge the lines and the high pressure pump after removing the relay or will it even hurt anything?

What about disabling the ignition system?  Is there an ignition relay that will disable the coils but still allow me to use the push button start and engage the starter?

Once I push the button to turn the engine over, how do I get the starter to quit cranking?  Push the start button again?

Any help would be much appreciated.

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[sholxgt]

I have a tiny bit of info to provide and this will need testing. My understanding is that you can floor the throttle first and then push the start button and the car will only crank. Release start button before releasing throttle. Good luck!

[SHOdded]

sholxgt's suggested method should work.  Making sure power was cut off to the fuel pump is more than just pulling the fuel pump relay on these cars though, IIRC.  A few people, including polskifacet, have recently done compression tests, hope they chime in.

[ZSHO]

I will try to get some Info from WSM for ya by lunchtime....short or long version prefered,need to reference it(between three large books)LOL.  Z

[ZSHO]

Here it is as promised earlier hope it help's any.  Z        Compression Test
1)Make sure the oil in the crankcase is of the correct viscosity and at the correct level and that the battery is correctly charged. Operate the vehicle until the engine is at normal operating temperature. Turn the ignition switch to the OFF position, then remove all the spark plugs.
2)Set the throttle plates in the wide-open position.
3)Install a compression gauge in the No. 1 cylinder.
4)Install an auxiliary starter switch in the starting circuit. With the ignition switch in the OFF position, and using the auxiliary starter switch, crank the engine a minimum of 5 compression strokes and record the highest reading. Note the approximate number of compression strokes necessary to obtain the highest reading.
5)Repeat the test on each cylinder, cranking the engine approximately the same number of compression strokes.
Compression Test — 3.5L Engine Test Results
The indicated compression pressures are considered within specification if the lowest reading cylinder is at least 75% of the highest reading. Refer to the Compression Pressure Limit Chart. 

If one or more cylinders reads low, squirt approximately one tablespoon of engine oil meeting Ford specification on top of the pistons in the low-reading cylinders. Repeat the compression pressure check on these cylinders.
Compression Test — 3.5L Gasoline Turbocharged Direct Injection (GTDI) Engine Test Results
The indicated compression pressures are considered within specification if the lowest reading cylinder is at least 75% of the highest reading. Refer to the Compression Pressure Limit Chart. 

If one or more cylinders reads low, squirt approximately one tablespoon of engine oil meeting Ford specification on top of the pistons in the low-reading cylinders. Repeat the compression pressure check on these cylinders.
Compression Test — Interpreting Compression Readings
If compression improves considerably, piston rings are worn or damaged.
If compression does not improve, valves are sticking or not seating correctly.
If 2 adjacent cylinders indicate low compression pressures and squirting oil on each piston does not increase compression, the head gasket may be leaking between cylinders. Engine oil or coolant in cylinders could result from this condition.
Use the Compression Pressure Limit Chart when checking cylinder compression so that the lowest reading is within 75% of the highest reading.
Cylinder Leakage Detection
When a cylinder produces a low reading, use of a cylinder leakage tester will be helpful in pinpointing the exact cause.
The leakage tester is inserted in the spark plug hole, the piston is brought up to Top Dead Center (TDC) on the compression stroke, and compressed air is admitted.
Once the combustion chamber is pressurized, the leakage tester gauge will read the percentage of leakage. Leakage exceeding 20% is excessive.
While the air pressure is retained in the cylinder, listen for the hiss of escaping air. A leak at the intake valve will be heard in the Throttle Body (TB) . A leak at the exhaust valve can be heard at the tailpipe. Leakage past the piston rings will be audible at the PCV connection. If air is passing through a blown head gasket to an adjacent cylinder, the noise will be evident at the spark plug hole of the cylinder into which the air is leaking. Cracks in the cylinder block or gasket leakage into the cooling system may be detected by a stream of bubbles in the radiator.

[Spenser281]

Perfect!  I'll be getting this taken care of this weekend.  Just so it is clear, the foot on the brake and accelerator pedal held to the floor during start up does indeed keep the vehicle from starting.  We will see what the results are once I'm done.  Hopefully it will give me some insight to this rough idle.

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[Spenser281]

Thanks for the info and help everyone!

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[glock-coma]

I'm not sure I would trust not disabling the fuel system. If someone's foot happens to slip off....boom hydro lock.

[Spenser281]

What would you recommend, glock?

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[SHOdded]

Here's how the folks at Stratified recommend testing a Focus ST
http://stratifiedauto.com/blog/how-to-perform-a-compression-test-on-a-ford-focus-st/

The Focus ST is a manual, so ignore the part about the clutch in the instructions where the SHO/Flex/X/MKS are concerned.  Pulling the fuel pump relay and/or disconnecting the FP control module connector underneath the rear seat might be a good idea as well.  Though disconnecting the fuel injector electrical connectors might be the most effective way ...

How to perform a compression test on a Ford Focus ST

Posted on June 7, 2014    

Compression tests are a very important tool in assessing your motor's overall health. An especially convenient time to do this is when you are checking your car's spark plugs. It's also good to get a baseline compression test before adding parts or tuning the ST. A weak compression test result is something to be investigated further as it can be an indication of a mechanical failure (worn rings, poorly sealing valves, etc.)

On the Focus ST checking your compression is quite straightforward:

Step One – Prepare for testing:

Preparing your Ford Focus ST for compression testing could not be any easier. First drive the car so that it is decently warm. Park it and carefully pull off the coil packs and remove all four spark plugs.


Step Two – Install the Compression Tester:

You can purchase a number of compression testers and they range in price and quality. Some of the very low quality ones can give poor or erratic readings. So if you get abnormal readings on an engine running well, then it is worth trying another tester. The compression tester simply screws into your spark plug hole. Make sure the O-ring makes contact with the cylinder head in order to prevent a false low compression reading.


Step Three – Test Your Compression:

To do this you simply push both the accelerator and the clutch all the way down. Once the clutch and accelerator are depressed press the start/stop button to begin the cranking process. Wait until you've heard about 15 cranks of the motor then press the start/stop button again to stop the process. Keeping the accelerator down the entire time prevents the injectors from firing while testing compression. If you have a friend helping; have them watch the gauge – ideally you want to crank until the needle stops moving up.

Make sure that you allow the same cranking duration for all four cylinders to allow for consistent readings.


Interpreting the Results:

Compression numbers will vary slightly from motor to motor but for a healthy internally stock ST motor expect around 160-170 psi (~11 bar) at sea level on a mild day.

The altitude and internal engine changes (pistons, cams, etc.) will affect compression readings. With altitude, the higher you go in altitude the lower the compression will read and this is perfectly normal. Multiply sea level numbers by the table below corresponding to your altitude to get what you should expect if you are testing at higher altitudes. For example a healthy ST motor with 160psi compression at sea level will have a compression of (160*0.8617) around 138psi.
1000′ = .9711
2000′ = .9428
3000′ = .9151
4000′ = .8881
5000′ = .8617
6000′ = .8359
7000′ = .8106
8000′ = .7860

Another indicator of a healthy motor is that the compression is fairly even across all cylinders. The rule of thumb is that all cylinders should be within +/-10% of each other.

If you suspect there is a problem and repeated compression tests indicate this, you will likely have other running issues such as oil consumption, fouled plugs, misfiring, etc. The compression test can identify the problem cylinder and you can then investigate further. The next step would be a leakdown test to show you where the compression is escaping (past the rings or past the valves). This requires more equipment so the beauty of the compression test is that it is quick and inexpensive with minimal tools needed.

Record the readings in order and keep the records to track the health of the motor and catch any issues if they show up later down the road.

Happy Testing,

The Stratified Team

[Spenser281]

That's exactly what I was looking for.  Sounds like it's pretty straight forward.  I will probably still pull the fuel pump relay.

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[Spenser281]

Well.....only 90 psi on cylinder 6.  Anyone have a short block for sale?

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[SHOdded]

Ugh, sorry to hear!  What was compression on the other cylinders?

[Spenser281]

160-170.  The car doesn't smoke, doesn't appear to be using any oil, and still runs smooth....except at idle.  I wonder how long it will last?  I imagine the dealership is going to charge an outrageous amount to have a new engine put in.  Even if it is just a short block, I'm sure it will still be way out there.  Anyone had to pay for this on their own, in other words, not under warranty?  Are these engines difficult to remove and replace?

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[Spenser281]

Performed a leak down test today.  Cylinder #6 is leaking air out of the oil filler tube on the valve cover.  Also getting about 60% leakage.  I checked two other cylinders just to verify I was getting it right.  Only showing about 3% leakage on them.  So since the air is coming out of the oil filler tube, that leads me to conclude that it is a broken compression ring.  Ugh.

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