Hello, I am new to Honda and I have a 98 civic with the base d16y7 I am wondering what normally will cause a cylinder to lose compression. cylinder one, two, and four are reading 150 but cylinder three isn't even hitting 20. there is no bottom end knock nor top end noise in addition there is no metal shavings in the oil. I took the cam gear cover off to see if someone had replaced the timing belt and set it off a tooth the belt is old and warn. I then pulled the valve cover and neither the intake or exhaust valves on cylinder three are stuck. what would be everyone's next step be?

 

Do a leak down test. Check the coolant for exhaust gases with a block tester.

 

what is the process of a leakdown test?

 

basically injecting air into a cylinder and seeing where it leaks from. IE valves, head gasket, oil jacket.

 

ok is bad head gasket most common?

 

Many possible causes - do the leakdown test and check whether the fuel injector #3 is stuck open.

 

ok I did the leak down test. got cylinder 3 at tdc applied air to the cylinder no air came out of the throttle body no air came out of the radiator no air came out of the dipstick tube nor did it come out of the exhaust. however air was releasing slightly out of cylinder one and a bit more out of cylinder 2 spark plug holes. would bad timing cause this? as I said before the timing belt doesn't look "new" but you can still read the writing on it and the rest of the belts (serp belt, ac belt, power steering belt) all look the same age as the timing belt but u can still read the part number on all belt. maybe previous owner did timing belt and it off a tooth?

 

Have you checked the mechanical timing to see if it's off by a tooth or two?

 

I have the top belt cover off the they all seem to be right on mark but I do not have the bottom cover off to the the bottom marks.

 

You don't need to remove the lower cover. Just check whether the pointer on the lower cover aligns with the white TDC1 mark on the crank pulley when the cam is set at TDC1.

 

tdc1 means the normal cylinder #1 at top dead center correct

 

I was not aware of the third mark for the crank I will go check that now. if they are lined up as they should what do u think the problem could then be?

 

Yes

 

We'll get there if we get there.....

 

ok so I got tdc1 and all marks on cam and crank match up perfectly! im stumped I did a leak down double check and this time cylinder one was fine cylinder two couldn't hold the pressure and took it off tdc and leaked out the intake cylinder three held the pressure and leaked out cylinder one and two and cylinder 4 couldn't hold the pressure and leaked out the intake... warped head...?

 

Are you removing the hood 15A ECU fuse to prevent spark and fuel and holding the throttle at WOT during the compression tests?

 

****... I did not hold WOT but I unhooked the injectors to stop fuel so it wouldn't fire. could this be the confusion whats the reason behind WOT? I feel like a dumb *** now haha.

 

Redo the compression tests.

 

there is no oil in the motor right now I will do it at a later time and get back to you please keep an eye on this thread thank you for all your help

 

not doing WOT could potentially make a single cylinder drop that much compared to the other three

 

When you do leak down test, if #1 @ TDC compression stroke , then intake & exhaust valves should be closed for that cylinder. Other cylinders will have either exhaust or intake open some amount based on the firing order. Leakdown for each cylinder is done by putting the tested cylinder @ it's TDC compression stroke.

 

I had each cylinder on tdc compression stroke for the test.

 

I did another compression test with WOT this time the numbers were higher towards the 180's but cylinder three was significantly lower at a high of 60

 

These^ are obviously spurious results. Install spark plugs in all but cylinder 3 and redo the leakdown test for cylinder 3.

 

Ensure proper engine oil level, remove ecu fuse from engine bay fusebox, only remove the spark plug for the cylinder you're doing the compression test on, screw in compression tester, step on gas pedal and crank car.