How can we get to know that the valves of a car engine(for both petrol & CNG use car as fuels) r leaked n weak?

Question

how can we get to know that the valves of a car engine esp. petrol engine in which car uses CNG as a fuel and petrol as a fuel r leaked n weak.

what could be the possible symptoms ?

thanks

Additional Details

rough idling or rough running on idle
means " car' engine is start, but the car is not in gear and at this time giving too much race (while the car is at rest, its engine is start and giving too much race to it) am i right ?

Answer 1

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actually, you have to run a wet and dry compression check.just search for the how to, its long.variation should be less than 10 # or so from dry to wet.any cylinder under 10% of the others is a high wear situation.anyway if tested dry it runs 92, and wet it runs 135, its rings.if the wet number is equivalent to the dry+- a few pounds, youve got cruddy valves.
does it run fine on 1 fuel or the other?and are you positive both fuels arent running, causing a rich condition?

Source(s):

you can also t fit a vacumm guage to your intake port(where vac line hooks up) and read the guage. a fluctuating guage is most definately a valve problem.

Answer 2

The only way to be exact and to locate which cylinder is bad is by using a compression tester to see if they all read within spec. Otherwise your only clue would be losing power, burning oil, ect....

Answer 3

Symptoms---rough idling & loss of power (acceleration)---increase in fuel consumption.
Assuming you have no pressure gauge specially designed for measuring compression pressure----there is one simple & quite accurate way---pull out the high tension spark plug cable one by one & replacing back one by one while the engine is idling---notice the dropping of RPM. For "good" cylinder, the drop of RPM is a lot more compared to one which is already leaking. In the extreme case, there is hardly any drop in RPM when you pull out that particular cylinder cable.Chance is that normally there is only one cylinder that is bad, so you can deduce which one is the bad one easily.

Answer 4

Pressurize one cylinder at a time and listen.
It's simple really.
First position the engine so the cylinder you want to test is at the top of the compression stroke (piston at top, both valves closed).
Then remove the spark plug and insert a fitting to allow you to put pressurized air in that cylinder (use a regulator set at 20-30 lbs).
Now you listen at three places... intake, exhaust, oil filler.
If you hear hissing at the carb (or throttle body) you have a bad intake valve. If at the exhaust, a bad exhaust valve and if you hear hissing at the oil fill opening then your looking at weak rings.
Happy hunting!

Answer 5

Rough running on idle, lack of power. The valves normally burn when you give the thing a thrashing over long periods. You have been to heavy with your right foot, not giving the valves time to cool.

Source(s):

saw a big V8 streached limo with this problem recently