1999 Kia Sportage 40psi compression in all cylinders

LJRIX1

MEMBER
1999 KIA SPORTAGE
4 CYL
2WD
AUTOMATIC
81,000 MILES

Regular driving. Car began to run rough, sputter, cut-out. Got check eng, power, and hold lights. Car died. Obd reader codes as follows: throttle pos. Sensor and engine temp sensor bad. Replaced. During troubleshooting noticed no fuel pressure. Replaced fuel pump. Now pressure, but no joy for starting. Car has not started since and no longer has codes. No water in oil or visa versa. However cylinder pressure in all 4 cyl.'S is approx. 40 psi. Instead of the 140-160 it should be. What would cause all four cyl's. To read so low? Have fire, have fuel. Timing belt jump poss? If so did I ruin engine and is there anyway else to trouble shoot without pulling whole engine apart? Thank you very much for your help

1 Reply

RASMATAZ

MECHANIC
75,992 POSTS

Do a cylinder leakdown test to get to what caused the low cyls.

A leak down test requires the removal of all the spark plugs. The crankshaft is then turned so that each piston is at top dead center (both valves closed) when each cylinder is tested. Most people start with cylinder number one and follow the engine's firing order.

A threaded coupling attached to a leakage gauge is screwed into a spark plug hole. Compressed air (80 to 90 psi) is then fed into the cylinder.

An engine is great condition should generally show only 5 to 10% leakage. An engine that's still in pretty good condition may show up to 20% leakage. But more than 30% leakage indicates trouble.

The neat thing about a leakage test (as opposed to a compression test) is that it's faster and easier to figure out where the pressure is going. If you hear air coming out of the tailpipe, it indicates a leaky exhaust valve. Air coming out of the throttle body or carburetor would point to a leaky intake valve. Air coming out of the breather vent or PCV valve fitting would tell you the rings and/or cylinders are worn.

A leakage test can also be used in conjunction with a compression test to diagnose other kinds of problems.

A cylinder that has poor compression but minimal leakage usually has a valvetrain problem such as a worn cam lobe, broken valve spring, collapsed lifter, bent push rod, etc.

If all the cylinders have low compression but show minimal leakage, the most likely cause is incorrect valve timing. The timing belt or chain may be off a notch or two.

If compression is good and leakage is minimal, but a cylinder is misfiring or shows up weak in a power balance test, it indicates a fuel delivery (bad injector) or ignition problem (fouled spark plug or bad plug wire).