Engine Mechanical Testing Tech Tip
Hi, everyone. This is Michael Eilbracht with Diesel Laptops. Today's Tech Tip video, we are going to go over some more engine testing techniques. Just some quick easy tests that you can do to help rule out engine mechanical issues. In one of my prior videos that I did, I showed you how to do relative compression with a current clamp and looking at the current. Well, what if after you do the test with your sync and you find a cylinder that's a low contributor?
Well, what could be going on? Could you have a problem with your valves not sealing? Could you have leaking rings? A hole in the piston? Things like that. Here in this video, I'm going to show you how to do some quick tests to help rule out where the fault lies. Is it in the valve train? The valves? Are you getting excessive pressure into the crank case? Do you have bad rings? Things like that. We're just going to do a quick test here, and I'm going to show you what to look for.
As you can see here, I've already got my scope running. Channel number one in yellow is going to be my injector current. Number one, I'm going to use that as my sync. Channel number two is a piezo sensor. It's a two-wire sensor that changes in voltage relative to change in pressure. It's basically a first look sensor. Channel three, I'm using an inches of water sensor. It's actually a very good sensor. They're very sensitive. I've got that in the intake. And then, channel two, the red trace, I have that piezo sensor in the oil fill tube with a rag wrapped around it to help secure the pulses, so I can get good pulses.
Then, on channel four, the blue, that is a 300 PSI transducer that I have teed into the exhaust gas. It's a pressure sensor that, on this PACCAR, it's the one exhaust gas pressure sensor that is before the turbine of the turbo. All right. It's going off of that pipe that's right on a centralized location of the exhaust manifold. That's how I'm going to look at my exhaust pulses. So I've got that hooked up. And then, I have a current clamp around the battery cable, so I can look at the starter current as well.
All right. This test, what we're going to do first is we're just going to do a cranking test. And then, I'm going to go through the waveforms and show them to you. I'm going to go ahead and crank over the engine for a little bit. Then, I'll stop the capture. And then, I'll explain it to you. As you can see here, the white trace, that's the current from the starter motor. Now, what we're going to do is, we're going to zoom in on the area of the injection.
I'm just going to show some things here to you real quick and we'll do bit by bit. Now, if you look at my green trace here ... I'm just going to shut off the other channels here, so you can see this better. My green trace is the inches of water sensor that's in the intake manifold. What we can do here to figure out what intake pulse is what, we can go here to our cursors. I'm just going to line this up with the main injection event here. Then, I'm going to go to Mark Cylinders. Firing order is 1-5-3-6-2-4. I'm going to select Intake Events. I'm going to hit Enter.
And if I take my cursor and drag this down ... On the green trace, this is the intake pole. The negative pole that you see here, that is the maximum amount of air that's being pulled in from the intake valve. If you notice, all of them look relatively even. All of the negative poles look pretty good. You don't see anything extremely abnormal. This is how you'd tell if your intake events are working properly. Also, what's nice about the inches of water sensor is since it measures the amount, it's showing here that it's measuring about minus two inches of water.
Well, if you convert that, you could put it into a vacuum reading if you wanted to and you could actually have a measurement for the vacuum while it's cranking over. Now, granted on a diesel engine, you don't have much vacuum in there. My point is this sensor is sensitive enough it can see that. This is how you look at intake events. These all look pretty good. Look in decent shape. Now, if I turn off this ... I'm going to zoom back out to full and I'm going to turn on the red trace now.
The red trace is coming from the crank case. I've got it in the oil fill tube right now. All right. I'm just going to hit Process Data here. I'm just going to make this just a little bit bigger. Now, if you look at the red trace here, you see that there's a little rise here at every little pulse. Well, that's your pressure in the crank case, but I'm using the piezo sensor on this. So I'm just looking for a relative change. If you look at this, they all look pretty relatively even. They look decent. With this, this would basically tell me I don't have any one of these cylinders that has an excessive leak, but that's relatively speaking.
Now, if I wanted to know exactly the exact amount of pressure I had, then I would use my inches of water sensor, and then measure it. If I had another inches of water sensor, I would be using that too, because it gives me an exact measurement. That's what I prefer. Because then, I know how much pressure I have. All right. I'm just showing you this way, so you have an idea of what to look for. All right. I'm just going to multiply this just a little bit more. And then, I'm going to move this up. Now, as you can see here, I've got more distinguished humps right here.
Let me just scroll down just a little bit. And I'm going to smooth that out just a little bit more. There we go. Now, I'm just putting a filter to this. If you look at the red trace here, this is showing the crank case pressure. And if you look at my starter current here, which is the relative compression ... If you notice, if I take my cursors here, you have top dead center compression. Then, the cylinder fires. And then, you get a peak pressure from the crank case. And if you look at where it's at in relationship to the starter current here, that is showing you that is happening on your power stroke.
Because on the power stroke, you've got pressure pushing down on the piston. Any pressure that leaks by the rings or past the cylinder wall, it's going to show up as that. That just proves to everyone that that's showing the crank case pressure. That's how you look at the crank case pressure, and then see how they all look. The level isn't too high. The pressure on this, they all look pretty good. My intake events look good as well. Now, the last thing I'm going to show here is the exhaust events. I'm going to multiply that. Now, we have our exhaust events.
Now, what I'm going to do is ... To ID exhaust events, I'm just going to line up this cursor there and there. I'm going to hit Mark Cylinders. I want to look at exhaust. Now, we're looking at all our exhaust events here. This is exhaust event 2-4-1-5-3-6. Now, you can get different software where you can get overlays to tell you what piston event you have. I'm just using this one because it's on the software. But anyway, this is your peak exhaust right here. Basically, at top dead center, exhaust 360.
And then, another thing is on a six-cylinder engine, all of your events, exhaust events, intake events ... Doesn't matter. When you're looking at it this way, each one is going to be 120 degrees apart. If you look at the top here, it says 120 degrees right by my calculator right there. These are my exhaust events. As you notice, they all look pretty good. Decent shape. Not only that, I can measure how much exhaust I have in there with the pressure transducer. This is how you would go about doing a cranky mechanical test.
In the next video that I do, I'll do another one where I show you how to check it while it's running. Some of the things that you need to be aware of. But this in a nutshell is how you check the rest of the engine mechanical to figure out where exactly your problem lies. That's about it for today. If you have any questions, just give me a shout-out. Or go to our website, training.diesellaptops.com. I would love to hear from you. Okay? Everyone have a good afternoon and take care. Thank you.