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Compression test reliability

2010 Ford Fusion. 2.5 L. Variable valve timing , electronic throttle, auto trans. 89,000 miles.
My daughter just had this used engine installed by a shop I or she knows nothing about. She came to town, so I made necessary repairs to the car because she’s temporarily moving out of state. I did a compression test but did not open throttle because it’s electronic. Was just going to get a rough idea of engine integrity. Cyl. 1,2,3 got 180 lbs. Dry. Cyl. 4 got 60 dry, 64 wet. I told her to bring it back to the shop with these concerns. They did a power balance test at idle and 1900 rpm and it passed and they said no problem with engine. I called him about my concerns about cyl. 4. He said that because I didn’t open throttle plate and that it is VVT my compression test is invalid. I then asked him about a leak down test and he said that would be invalid also. The engine runs good. I can feel a very small vibration with my hand on the engine but barely noticeable past motor mounts. No codes. Did not notice any sloppy work. He told me verbally that there is a six month warranty on parts and labor if engine fails or if a second opinion by a Ford dealer contradicts his diagnosis. This seems good enough for me if I can get the warranty in writing, so I have no problem with this arrangement. My question is: Am I nuts for still being extremely concerned with my compression test? A power balance test only tells me that the cylinders are performing satisfactory at idle and 1900 rpm. It’s mostly for my own education.

That would be wrong. Pressure is being introduced into the cylinder and leak rate measured.

If you got 180 psi readings on 1,2 and 3 and 60-ish wet and dry, even with the throttle closed, #4 may very well have a burned or stuck valve.

I would really doubt his honesty regarding power balance tests.

So far that’s what I’m thinking, but my daughter sent kinda fuzzy pictures of the power balance test as follows:
21267 21266

Maybe the solution if the daughter can handle it is to plan on replacing this vehicle before the 6 month warranty expires.

The engine has a valve problem in the cylinder head. If they say that 60 is fine then they’re full of crap no matter the throttle plate position or the power balance.

The vibration you feel is the low cylinder. I can guarantee you that the engine is not running as well as you think and the shop says it is. The shop claims the test is invalid because of the alleged throttle plate issue. How does he explain the good readings on 1.2, and 3 if that’s the case? They have a vested interest in blowing this off.

Leak down tests are used everyday on reciprocating aircraft engines. Yes, they ARE reliable.

I’ll trust a leak down test way more than a compression test as it is much easier to manipulate a comp. test if you want to. Also, you get a much more precise picture of where the problem is.

If anything, it would indicate that the VVT system is malfunctioning. Otherwise - pure nonsens.

Who performed a leak down test? You didn’t say that you performed one.

Anything below 120 PSI reading for a compression test on a cylinder will result in a misfire or weak performance at idle and the PCM will pick that up and turn on the check engine light.

With 60 PSI that cylinder would be dead, I think you had some dirt in the check valve on the gauge or a poor seal with the hose to the cylinder head.

There was no leak down test made. I asked the mechanic if he would do it. He said it would be a useless test with VVT. When I got 60 on #4 I inspected opening. It is spotless retested: same. Got another type tester that you have to press down on to seal: 60 lbs. Confirmed.

What fault codes and symptoms are you having and what kind of problem are you trying to solve? If in fact a cylinder has lost compression there are far less intrusive ways to determine the cause.

The engine runs good. I can feel a very small vibration with my hand on the engine but barely noticeable past motor mounts. No codes.

  1. Was trying to determine if I should request warranty work, but I believe that issue is resolved.
  2. I was wondering if this mechanic has a valid point in saying that I can not trust a compression test on these types of vehicles. I firmly don’t believe his leak down test beliefs.

The mechanic is going to tell you what ever he wants to get you off the phone. If there was only 60 PSI in that cylinder it would be misfiring and towed to the shop, can’t drive reasonably on 3 cylinders.

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We were always advised to hold open the throttle when doing a compression test - as if the gas pedal is floored. Is that safe to do with electronically controlled throttle plates - can you just move the plate open and hold it open with something? Or will that mess up something?

If you move the throttle by hand, you can unlearn the ECMs readings on the throttle positions. This may lead to a relearn procedure to be done. On some cars, it is done automatically when the ignition is turned on. Some cars you need to do a procedure. Some can only be relearned with a scan tool. Some recommend never to move by hand or damage may a occur to sensor.

So, could a mechanic turn the ignition on, jam the gas pedal to the floor to open the throttle, then do the compression test - making sure to disable the ignition signal to the spark plugs?

A 2nd tech can hold throttle with gas pedal
Or a close throttle will result in slightly lower numbers for ALL cyls.
Which is not the case

Yeah, I would think that even without holding the throttle plate open, the vacuum created by the engine would pull in air through the smallest gap, or fluctuation, of the throttle plate - and that slightly lower numbers for all cylinders could be expected.

If someone is holding the gas pedal down with an electronic throttle, will that work even with the ignition switch (OK, I am showing my age) completely off? I suppose the answer is to try it on the car and see what happens.

If the engine runs well and there is no misfire and no fault codes then the compression is acceptable. If in fact you had one cylinder with 60psi compression the car would hardly be driveable.

Mechanics use electronic means for engine diagnosis these days, it appears you were sent a screen shot of a cylinder contribution test or a power balance test. If that testing shows no abnormalities there is no reason to go further.

I suspect what you are feeling is a vibration related to a worn motor mount.

More inadvertently withheld detailed information: When I tested #4, the first time I heard what could have been a leak past the testers o-ring. It was then that I inspected the spark plug opening and it was shiny clean. I retested with same gage and still got 60 lbs. Still suspecting leaking gage, I put another type gage on it. Still 60 lbs. I heard no leakage 60 Lbs.Then a wet test at 64. That convinced me of a good reading. I don’t know at what point a cylinder starts misfiring, But I’m starting to lean towards @Nevada_545 that it was a faulty reading on my part due to something obstructing both gage seals, even though it visually looked extremely clean. But these are also down in a well, so I suppose it is possible that there could have been a burr that I could not see. This reply was actually for @Nevada_545

I presume you have the 2.5L 4 banger engine. Suggest to ask the shop to do its own compression check. The service data I’m seeing says it’s possible to do, takes about an hour, and simply to open the throttle plate and do the test with a compression gauge, as it is normally done. I presume by “open the throttle plate” they mean to use the Ford scan tool to command the throttle plate to open. If 180 psi is measured for the highest cylinder, the lowest acceptable compression for the lowest cylinder is 135 psi from what I’m seeing.

On this vehicle compression testing is done on a warm engine, all spark plugs removed. The starter should be turned on with an aux starting switch, not using the ignition switch, while noting the highest compression for the cylinder during 5 compression strokes. If one cylinder is low then squirt a little oil into the cylinder and repeat the test to determine if it is a ring or valve problem.

The service data indicates a leak down test is also possible on this engine.

Since you got the low compression on cylinder 4, one theory that could account for that is you did the test with the ignition key, so the injectors were still squirting gasoline. The fourth cylinder would have got a lot of gasoline in it from the first 3 tests, so that gasoline may have messed up the test for the fourth cylinder.