Cylinder leak down pressure test gauges

Cylinder leak down pressure test gauges

These are a useful diagnostic tool in the workshop.
They can tell you a bit more than a compression gauge can.
But a bit more effort is required to use them.

First get the engine warmed up to normal operating temp.

You get the cylinder to TDC (top dead center) of the compression stroke, you then screw the appropriate adapter onto the compression hose of the tester (it's the short hose in the kit) then screw the compression hose into the spark plug hole. It only needs to be finger tight.

Next you need to calibrate the gauge unit, you need to turn the large black regulator knob of the all the way counter clock wise. If you cant turn the knob either way it's because the regulator knob has a locking mechanism which needs to be unlocked. Pull the knob to unlock it, press the knob when you need to lock it Now connect the air hose from you compressor (you do have an air compressor don't you!) to the gauge unit, calbrate the gauge unit by turning the regulator knob clockwise unit the needle of leakdown gauge goes all the way to zero and press the regulator knob in to lock it (that's the second gauge of the two. Yes the one with the pretty colours on it's face)

Now connect the (long) hose of the gauge unit to the (short) compression hose that you screwed into the spark plug hole earlier.

Now watch the leakdown gauge a leakage rate of:
* 10% - 15% is OK
* 15% - 20% is borderline
* Over 20% and you have problems.

Listen to hear where the air is leaking from.
* Remove the radiator cap a look for bubbles in the coolant, they will indicate a blown head gasket or a cracked head.
* Remove the oil filler cap and if you can hear or feel air escaping from there it could be broken/worn piston rings, a holed piston or a cracked liner.
* If you can hear air escaping from the exhaust tail pipe, it could be a burnt/broken/stuck exhaust valve, insufficient valve clearance, or the cam timing my be out (a possibility to be kept in mind for VVC engines)
* Remove the air intake from the throttle body and listen/feel for air escaping from the induction system whist opening and closing the throttle plate/butterfly, air escaping here would indicate problems with the inlet valves the same as the ones mentioned for the exhaust.
* If air is escaping from the side of the engine where the head gasket is, well that's obvious (not at all likely on our cars but a possibility on simple engines such as some pushrod over head valve or side valve designs as found on lawnmowers and older cars.)

Now remove the lot, then repeat the procedure on the next cylinder and so on until you've done them all.