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Chevrolet Silverado 2007-2013: How to Find Vacuum Leak

Your car needs a vacuum to run properly. Vacuum leaks will cause an erratic idle and acceleration issues, among other things.

By James Hodgson - August 12, 2015

This article applies to the Chevrolet Silverado (2007-2013).

As you're no doubt aware, your engine requires three things to run: air, fuel, and spark. These three things are measured by your truck's ECU, or brain, to make sure you're producing either maximum power or maximum efficiency. Sadly, we usually can't have both at the same time. In this case, we're talking about the manifold vacuum and not the Venturi vacuum you'd see in a carburetor.

So, why do we need good vacuum? Because the MAF (mass air flow) sensor, which tells your ECU how much air is coming in, is some distance away from the combustion chamber, and there are a few connections in the stream between the MAF and the cylinder. Each one of those connections probably has a gasket or hose that can crack and go bad. If you have a vacuum leak anywhere between the MAF sensor and the combustion chamber, more air is getting in than the MAF knows about, which means the ECU is using bad data to control fuel and spark.

Let's see if we can find any of those pesky vacuum leaks, so your ECU won't think your MAF is a big fat liar anymore.

Materials Needed

  • Carb cleaner (if using dangerous method)
  • Fire extinguisher (if using dangerous method)
  • Smoke machine
  • Light source

Method 1 – Spray smoke machine

Force the problem to visually show itself with a bit of smoke.

The only problem with this method is that you need a smoke machine to do it, and the professional ones aren't cheap. The one in Figure 1 goes for over $800. There are some videos on the internet to build smoke machines out of parts, but you're still going to need an air source of some kind. If you have a powered air pump or an air compressor, this might be just the ticket for you. Those are relatively cheap. There are also "homemade" smoke machines you build to test for leaks. These machines are just party smoke devices and are relatively cheap at around $30 with the fog fluid running at $8 a bottle. Just put a rubber hose on it and then reduce or increase it to the size of the orifice you are testing.

Whatever machine you use, take the outlet nozzle from your smoke machine and hook it up to any of the vacuum lines that go to your intake manifold. Disconnect the breather tube from the MAF sensor and stretch a rubber glove over it to block that end. Begin filling the intake with smoke and use your light to check for any wisps of smoke escaping from anywhere.

If you see smoke coming from anywhere on your engine, you know it came from inside. This lets you know you have a vacuum leak because if smoke can get out, then un-metered air can get in.

Figure 1. Comprehensive vacuum diagnostic tools.

If the smoke machine did not produce any results, try Method 2.

Method 2 – Spray aerosol can

Drastic times call for drastic measures.

Warning

Do this method at your own discretion. If you do, you'll be using a highly flammable aerosolized accelerant near a possible spark source. You could catch your vehicle or yourself on fire.

But if the smoke test is simply not happening within your budget, here's what you would do.

Grab a spray can of carb cleaner, preferably with one of those fancy plastic straws as a nozzle. Spray targeted bursts of the carb cleaner around the intake manifold and other vacuum fittings, while listening for the engine's idle to change. If it changes the idle when you spray a certain spot, you found your leaking area.

The principle here is that you're using accelerant to spot leaks in the system, because the leak will let the carb cleaner seep through and affect the running engine's idle.

  • Figure 2. Consider this $13 well spent, just in case.
  • Figure 3. Use carburetor cleaner to help locate potential leaks by spraying around the gasket surfaces.

Pro Tip

Have a fire extinguisher in your garage at all times, but especially when you're doing things we specifically warned you about. Remind your significant other to use the fire extinguisher to extinguish you before extinguishing the vehicle.

Featured Video: How to Find Vacuum Leak

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