[.1135058]

Thought I'd share my compression results today at 8273 miles.

#1 (PS) 144
#2 145
#3 144
#4 147

Engine hot. You'll need a 12mm plug thread adapter and extension. My gauge is good quality (ANSI-B40.1), but it is not certified. What's important is the numbers are close.

I like to do various tests when the engine is new to establish a base reference.

Here are pics of the plugs:

 

[.1135058]

I should have pointed out you need to disable the fuel pump and ignition coils.

My Sonata has a 20 amp fuse for the electric fuel pump. Just let the engine idle and pull the fuse - the engine will stall when pressure drops to zero.

There is another 20 amp fuse for the coil primaries. Pull that as well and you'll get no power to coil plugs.

Since the throttle is drive-by-wire I found that just applying the brake and pushing the start button will give enough air flow for test.

 

[SGR]

To the OP:
are you happy with numbers you have received?

 

[.1135058]

are you happy with numbers you have received?

Don't know, I've nothing to compare it to in a 2.4 Sonata. My 1995 Camry 2.2 gives me about 170 psi with 235k miles.

One of the reasons I posted was if others do the same then that gives comparisons. I don't have any factory specs on compression.

 

[wongpfh]

Don't know, I've nothing to compare it to in a 2.4 Sonata. My 1995 Camry 2.2 gives me about 170 psi with 235k miles.

One of the reasons I posted was if others do the same then that gives comparisons. I don't have any factory specs on compression.

Compression Pressure Inspection info attached, hope this helps!

 

[.1135058]

hope this helps!

Not really, but appreciate the try. Going by those generic numbers my engine is shot. My 2003 Ford Ranger 3.0 has about 190 psi.

The car doesn't drive like low compression - plenty of power. I wonder if anyone else has done a compression check.

 

[Airforce1]

Don't know, I've nothing to compare it to in a 2.4 Sonata. My 1995 Camry 2.2 gives me about 170 psi with 235k miles.

One of the reasons I posted was if others do the same then that gives comparisons. I don't have any factory specs on compression.

Should be pretty easy to find.I am sure SBR will know or could easily provide the numbers.

 

[dtech]

Not really, but appreciate the try. Going by those generic numbers my engine is shot. My 2003 Ford Ranger 3.0 has about 190 psi.

The car doesn't drive like low compression - plenty of power. I wonder if anyone else has done a compression check.

Was yer throttle plate open ?

 

[Airforce1]

That pdf in post #5 states a minimum of 171 psi for a 2013 Sonata 2.4L.

 

[.1135058]

Was yer throttle plate open ?

Yes, well maybe. I've never worked on a drive-by-wire throttle. At first I held the throttle open with my fingers while the engine was cranked - foot on brake only. It stayed open for short bit then seemed to push shut against my fingers. The return spring is quite strong. Holding the gas pedal to the floor had no effect on the throttle plate. After that I just left it. The gauge kept rising as the engine cranked, so air must have been entering.

I have been thinking about also disconnecting the throttle plate connector and wedging the throttle plate open with something. I didn't want to use a screwdriver so as not the mar the plate and throttle body.

 

[.1135058]

That pdf in post #5 states a minimum of 171 psi for a 2013 Sonata 2.4L.

Yes, now I see the top of the PDF. Didn't catch that at first.

 

[Grady Wilson]

Wouldn't an accurate reading need the throttle butterfly to be open all the way?
That pressure does seem low.

 

[AUTOSPARK]

Wouldn't an accurate reading need the throttle butterfly to be open all the way?

Yes.

 

[wongpfh]

Yes, well maybe. I've never worked on a drive-by-wire throttle. At first I held the throttle open with my fingers while the engine was cranked - foot on brake only. It stayed open for short bit then seemed to push shut against my fingers. The return spring is quite strong. Holding the gas pedal to the floor had no effect on the throttle plate. After that I just left it. The gauge kept rising as the engine cranked, so air must have been entering.

I have been thinking about also disconnecting the throttle plate connector and wedging the throttle plate open with something. I didn't want to use a screwdriver so as not the mar the plate and throttle body.

Check the PDF again, page 2/7, step(2) FULLY OPEN THE THROTTLE!

 

[.1135058]

Wouldn't an accurate reading need the throttle butterfly to be open all the way?

You need air flow into the cylinders, but having the throttle open all the way as opposed to a little bit means you get to max pressure sooner, it just takes more rpms. The gauge Schrader valve holds the previous pressure.

I'll redo the test with the throttle plate electrical connector disconnected and use a rubber hose to hold the plate open.

 

[.1135058]

Check the PDF again, page 2/7, step(2) FULLY OPEN THE THROTTLE!

Yes, but it doesn't say how to do that. I have no idea how the ECU is operating the throttle plate and I don't want to damage it. As I said when I was holding the plate open with my fingers it pushed back to close the plate. I'm not sure if there is an IAC and the computer just uses the throttle plate to achieve idle.

Cable connected throttles are no problem to jam open.

I'll redo test with electrical connector disconnected and hold the plate open with a rubber hose.

 

[dtech]

You need air flow into the cylinders, but having the throttle open all the way as opposed to a little bit means you get to max pressure sooner, it just takes more rpms. The gauge Schrader valve holds the previous pressure.

I'll redo the test with the throttle plate electrical connector disconnected and use a rubber hose to hold the plate open.

You need a certain amount of intake air to get an accurate max pressure reading, if throttle body isn't open enough you get a partial vacuum condition and can crank all day and never get a true reading, the cylinder relieves pressure every time the exhaust valve opens, so the tb plate needs to be open.

 

[.1135058]

You need a certain amount of intake air to get an accurate max pressure reading, if throttle body isn't open enough you get a partial vacuum condition and can crank all day and never get a true reading

There's always vacuum in the intake. The engine is just in start rpm mode so as long as there's enough air to fill the chamber it should compress enough - it always takes a number of rpms to get to full pressure as the gauge holds each pressure as the engine rotates. Max pressure is that psi where the pressure differential is high enough to produce leakage.

OK, so I just finished a second test with the throttle plate connector disconnected and a 1/2" rubber hose holding the plate open - lots of air flow.

Same numbers. Something is going on I'm not understanding as there can't be anything wrong with an engine with about 8k miles. This is the same gauge I've used for years and has given me 170 (factory spec) psi on my Camry and 190 psi on my Ranger, also factory spec.

How are the valves opened on these engines - hydraulic pressure?

 

[FrancescoJr]

With the variable valve timing I believe the valve timing can change enough at cranking to prevent the valves from closing early thus allowing easier cranking with less compression. I had a 2009 Nissan that if I let the car sit unused for 2 weeks the fuel pressure bled down too low to prevent it from starting immediately and I also believe the variable valve timing moved enough so the starter would spin the engine for a few seconds as if the plugs were out due to low compression.


Frank 2017 Sonata SE with 16K miles

 

[.1135058]

With the variable valve timing I believe the valve timing can change enough at cranking to prevent the valves from closing early thus allowing easier cranking with less compression.

Yes, I think it's something like that. If a few others here also did compression checks we could compare numbers.