Tools Maintenance

Resurrecting the emissions analyzer

Order Reprints
Resurrecting the emissions analyzer


Alex Portillo is the head technician of Car Clinic, a state-of-the-art automotive repair facility in Mahopac, N.Y. He is a protégé of Jerry Truglia and has been trained by Automotive Technician Training Service and is TST certified. Alex’s real-world, in-depth diagnostic articles will appear in Auto Service Professional on a regular basis.

Emission analyzers have been under-utilized pieces of equipment in our industry for years. Many shop owners and technicians think that the emission analyzer is only used for vehicle inspections rather than using it for diagnosing vehicle drivability problems. Their short-sightedness is preventing them from diagnosing many vehicle problems in a shorter period of time.

In this article I’ll explore the different ways that the five-gas analyzer can make your job easier and more profitable.

The old Sun diagnostic saying “Test Not Guess,” is what you will be doing when you use a five-gas analyzer in your diagnostic routine. Keep in mind that the five-gas can be used both on old and new vehicles, for all different systems from cooling to EVAP and a bunch more in between.

We should first do a quick review on what the five gases are so we understand what we are looking at and for. For seasoned techs this will be a simple review. For the newer techs, or for those that have not worked in a shop with a four- or five-gas analyzer, this will serve as an eye-opener.

You will be happy to know that I am not going to get into a lengthy explanation of the molecules, but rather just what you need to know.

Let’s start with the main ingredient HC that makes it all happen along with air. HC is the abbreviation for hydrocarbons, which is unburned fuel. Our next ingredient is O2 (oxygen), which is what we breath and what the engine needs to burn the HC. As a result of the burn/combustion, CO (carbon monoxide) is produced that is a by-product of incomplete combustion.

Now with three down and two to go, it’s NOx up next, which stands for oxides of nitrogen which are formed in the combustion chamber when temperature exceeds 2,500º Fahrenheit — you know, the pinging sound. Engine manufacturers have installed EGR (exhaust gas recirculation) valves on engines for years but they have a tendency to cause problems from stalling to no starts. So they came up with VANOS (Valvetronic Variable Valve Lift System), first used by German manufacturers, eliminating the use of an EGR valve while still lowering NOx emissions.

The fifth, CO2 (carbon dioxide), is the final one which I like using as a diagnostic tool that helps me decide if the engine is running to it optimum efficiency. Keep in mind that CO2 is an indicator of combustion and catalytic converter efficiency.

So there you have a painless review of the five gases. Now it’s time to move on and explore what the information can be used for in the shop bays.

I am going to start with inserting the five-gas probe into the tailpipe of a vehicle and use the readings as a diagnostic tool. The results of how efficient the engine and catalytic converter are will appear right on the screen in seconds.

Take a look at the following reading and see if you can diagnose what the problem may be on this hypothetical vehicle’s emission readings:

HC 350 PPM (idle), 310 PPM (2,000 rpm), CO 3.5% (idle or 2,000 rpm), CO2 = 8-10% (idle or 2,000 rpm), O2 0.2% (idle or 2,000 rpm), Lambda 0.97.


The first thing I like to look at is Lambda, which is the air-fuel measurement, so let’s start there. Perfect Lambda is 1.0, which equals 14.7 parts of air per part of fuel. Lambda below 1 indicates the engine is rich and Lambda above 1 indicates the engine is lean. Being armed with this information you are now able to diagnose the engine condition as running rich.

The causes for a rich running engine can be many things, air restriction, high fuel pressure, vacuum leak to MAP sensor, faulty MAF, fuel injectors leaking, O2 and AF sensor problems, to name a few. The symptoms may include an illuminated MIL, DTCs, surge/hesitation, foul/sulfur odor, black smoke, etc. Using the five-gas you can locate misfires that sometime may not set a DTC, but elevate Mode 6 misfire cylinder counters. We have all come across a vehicle where the engine seems to have a roll or misfire but no DTCs are present. The next time you come across this type of problem, blow the dust off your gas analyzer and take a look at Lambda (should be about 1). CO2 (should be about 14.5) and O2 (should be less than 0.5%).

For example, any cylinder that is misfiring can mask the HC and CO readings due to the efficiency of the catalytic converter, but will not affect the O2 readings as much. The converter will use the O2 in the process of cleaning up emissions and release any extra that is not utilized, while providing you with a clue of an engine misfire. Remember that the air we breathe is 78% nitrogen, 19% to 21% oxygen and the rest are other gases. The O2 reading at the tailpipe can be very helpful to our diagnosis.

Varied uses of the five-gas analyzer

Let’s take a look at what else the five-gas can do for us on other systems or mixed problems. We can pitch a tent over the radiator while the probe is held high capturing emission gas readings only. WARNING: Make sure that the five-gas probe does not contact any liquid, or the analyzer will be toast. Many techs use the blue dye in the tube with the suction bulb or try other methods, but if you really want to locate a head gasket problem try the five-gas. You won’t just be looking for HC readings, but rather CO, since the only way you get CO is from combustion. If we have a leaking head gasket, cracked cylinder or block problem, the gas reading I look at is CO first, followed by HC. Don’t forget to baseline your analyzer away from the vehicle, followed by an under-the-hood baseline, so you get a true start point reading. There are many things under the hood that can cause elevated readings such as leaking fuel injectors or pressure regulators, vapors from an EVAP system or leaky exhaust, to name a few.

I had a 2002 Chevy Blazer with a 4.3LW that came in with an overheating problem. The intake manifold gaskets were replaced along with a new thermostat on this engine due to an external leak, but the repair did not solve the problem of overheating in heavy traffic. I used the emission analyzer along with a coolant funnel to fabricate a tent as I mentioned above.

If you don’t have a coolant funnel handy, cut a gallon container to achieve the same results (see Figure 1). The readings that were displayed on the analyzer were 648 HC which is not super high, but enough to be a problem. Keep in mind that this vehicle was not overheating all the time, but only when it was in heavy traffic (see Figure 2).

Using the five-gas on EVAP is one of the best tools to use when smoke is not visible. Many times when I smoke an EVAP system I don’t see the smoke right away. Using my Smoke Wizard machine along with CO2 helped me to locate the problem. While looking at the flow ball (0.040, 0.020 or 0.010 leaks) to confirm a leak, I take the five-gas probe, and move it slowly near the top of the fuel tank and the rest of the system. Sometimes the smoke is trapped on the top of the tank or in the charcoal canister, and this is where the five-gas along with CO2 has helped me find the problem.

[PAGEBREAK]Shown on page 20 is an EVAP example on a 2005 GMC Yukon with a PO456 DTC (EVAP small leak detected) problem. I started my diagnosis by checking TSBs, inspecting hoses, activating the purge and vent solenoids and could not find the problem. I then proceeded to smoke the EVAP system, spending a solid 10 minutes trying to locate the leak. I kept looking for smoke but did not see any. I started to smell some fuel odor as I was near the gas but could not see any smoke.

At least I now had a clue that was going to help me find the cause of the P0456. I should mention that the fuel tank was about three-fourths full so it should not be as hard to fill the tank with CO2 and smoke as it would be if there was less fuel. The smoke must have been leaking from the top of the tank but I could not see it, so I decided to pull out the five-gas analyzer. Bingo: I found the leak after moving the probe around for a couple of minutes (see Figure 3).

The reading would have been faster if I used a shorter probe hose on the analyzer. In this case the HC spiked first (see Figure 4), since the smoke machine and the CO2 were pushing the high volume of HC fumes out. In most cases when I use this method I see elevated CO2 readings which lead me to the problem.

Another way to use the five-gas is checking for a leaky injector, both external and internal. We have all seen injector bodies leak where the metal and composite/plastic are bound together, causing an owner complaint of a gas smell. For internal problems you may encounter an illuminated MIL with a PO172 (system too rich) present.

To check for leaky injectors, start by base-lining the analyzer away from the vehicle and again near the vehicle as I described previously. After shutting down the engine, start to remove the spark plugs from each cylinder one at a time and record the HC readings. Look for the cylinder with the highest HC reading and you found the leaky injector.

When dealing with A/C systems (that’s right... A/C systems), you can use the same strategy to find leaks in the system with the refrigerant out of the system.

I fabricated an A/C hose that can be connected either to the high or low side of the system.


Step-by-step use of analyzer

1. Evacuate the entire system.

2. Connect either to the high or low side of the system using the CO2 bottle only.

3. Take the probe of the five-gas and start your search for CO2 readings. Remember to always observe safe working pressures by using a regulator while keeping in the pressure range of the A/C system.

Hopefully by reading this article you now have a different view of the often-ignored emission analyzer.   ‚óŹ

Related Articles

Tool review: Midtronics' DSS-7000 battery analyzer -- A very sophisticated diagnostic tool

Tool review: Disc brake analyzer

The beauty of tools

You must login or register in order to post a comment.