Performing a leak-off test on a car engine

Speaker 1: Jake, I've had a customer come in and he thinks there's a problem with the exhaust emissions, so if you could do a leak-off test on it to prove that it is from the cylinders and not a major part of the engine.

I've downloaded the manual, Jake, so we know exactly what it should be.

You know where the leak-off test kit is, so if you could get started, alright?

Speaker 2: Yeah. (TO AUDIENCE) The boss has asked me to perform a leak-off test.

This checks the amount of fuel literally leaking off the cylinders is at an acceptable amount.

The fluid is measured in millilitres, so I have to work out how many millilitres over the acceptable amount this car leaked, if at all.

I then need to work this out as a percentage.

That will give my customer a better understanding of how well or badly the cylinders are performing.

Speaker: Right, so here's the manual.

It shows the maximum allowable leak that this car can have is 5 millilitres.

So I need to see how many, if any, millilitres over the accepted amount this car leaks.

Right, so first of all, I'll attach all of these to the cylinders here.

Now I need to run the car for 30 seconds to see how much fuel leaks.

One and two were OK, within the working parameters.

I'll need to work on three and four.

I will start with the one that's leaked the most.

That's cylinder four, looks like it's just over 8 millilitres.

We'll call that 8 millilitres. And number three is 7 millilitres.

So cylinder three is 2 millilitres over, and cylinder four is 3 millilitres over the maximum allowable amount.

Next, I'll work these figures out as a percentage.

Speaker 1: (TO AUDIENCE) So if I start with cylinder four, this one was 8 millilitres, 3 millilitres over the recommended amount.

So what I have to work out is what 3 millilitres as a percentage of 5 millilitres is.

This will give me the lack of efficiency as a percentage.

So I divide 3 by 5… equals 0.6.

Now I multiply that by 100 to get the percentage.

So there is 60% more fuel leaking from this cylinder than the maximum amount allowed.

Wow, that's really underperforming. Right, to cylinder three, this is the same formula.

This time it's only 2 millilitres over.

I wonder if I can work this out in my head?

If 3 millilitres is 60%, that means that 1 millilitre is equivalent to 20%, so 2 millilitres is going to be 40%.

So this one is leaking 40% more than it should.

So these two cylinders will have to be replaced.

Speaker 2: (TO OTHER PEOPLE) Alright Jake?

Speaker 1: Yeah, not great news unfortunately.

Cylinder three and four aren't operating correctly. Cylinder four is 8 mil.

Speaker 2: Yep.

Speaker 1: Which is 3 mil over the recommended, which is 60%.

Cylinder three is 7 mil, 2 mil over the recommended amount and 40%.

Speaker 2: If you could just let the customer know how much it's gonna be and we'll go from there.

Speaker 1: No worries.