Solving Automotive Performance Issues
A power balance test helps determine the source of a misfire(s). If you have misfire codes or if you have a rough-running engine, this is a good place to start your diagnosis. No matter how many cylinders you have in your engine, each cylinder is designed to produce the same amount of power. When one or more cylinders aren’t producing their proper power output, you can have a misfire and also a loss of power.
One way you find the offending cylinder(s) is by doing a power balance test. While the engine is running, you cancel each cylinder one at a time and look for a drop in RPM. Each cylinder should produce the same RPM drop. If you get to a cylinder and there is no RPM drop, you’ve found a bad cylinder. Once you’ve found a bad cylinder, focus your diagnosis there to find the source of the issue.
There are a couple of different ways you can go about canceling cylinders. The easiest way is with a scan tool. Some manufacturers have built in the capacity to do a power balance test this way. You need a scanner capable of communicating with your PCM, and the vehicle needs to be capable of doing a self power balance test. If you don’t have the means for that, you can use one of two methods.
- You can cancel the ignition to each cylinder one at a time. If you have a coil-on plug design, meaning you have an ignition coil for each cylinder on the engine, it’s a fairly easy test. Just unplug the coils one at a time and check for the RPM drop.
- If you don’t have a coil-on plug design, you can remove the spark plug boots one at a time. You need to be very careful doing this, as you can get quite a shock if you’re not careful. One way to prevent getting shocked is to use a pair of plastic pliers specifically designed for this task. These are pretty handy for this sort of thing and they help protect you from the high voltage ignition circuit.
There are other ways to disable the ignition for each cylinder. Say you have a coil pack assembly that is easily accessible. You can remove each of the leads going to the coil packs and place a small piece of vacuum line in between the coil and the spark plug lead. Use just enough vacuum line to leave a 1/4-inch gap between the coil tower and ignition lead. Do this for each cylinder and start the engine. Then take a grounded test light and touch each vacuum line one by one. This shorts out the cylinders one by one and is a safer (and sometimes easier) method of disabling the ignition to each of the cylinders.
You don’t have to disable the ignition to do a power balance test. If it’s too difficult to get to or you’re afraid of dealing with the ignition circuit, you can instead disable the fuel injectors one by one with the same result. You can simply unplug each injector one at a time and check for the same RPM drop as you did, disabling the ignition. You get virtually the same information. I often find the injectors hard to get to, so I usually go for the ignition before I look to the injectors. That might not be the case on your vehicle, and disabling the injectors might be a simpler option. Here is a video on power balance testing that will help illustrate how to perform the test and the results you’re looking for.
Another common problem that causes engine performance issues is vacuum leaks. Vacuum leaks are air leaks into the engine that occur after the throttle body and before the intake valves. Any leaks in this area are considered vacuum leaks. Vacuum leaks upset the air/fuel mixture and can cause misfires, a loss of performance, idle issues, or poor fuel mileage. Vacuum leaks are on the top of my list of probable causes for performance issues. The engine likes balance; anything that upsets that balance will cause performance issues. Vacuum leaks are a very common cause of this imbalance.
How do you go about determining if you have a vacuum leak, and how do you determine its location? Some methods are quick and easy, while others are a bit more involved and require special tools. I like easy, so I normally grab a can of carburetor cleaner and spray around the suspected areas while the engine is running to see if there is a change in RPM. If I find an area where I spray and the RPM changes or I can actually hear a gurgling sound as I hit the source of the leak, I know I’ve found a vacuum leak and I’ve got a pretty good idea where my leak is.
I will admit that doing this to a hot engine can get dangerous, as carburetor cleaner is flammable. No worries, because you can also use water in a spray bottle to do pretty much the same thing. It’s not as accurate, but it does get the job done.
One other method is to use smoke. While the engine is off, you can introduce smoke into the intake through one of the vacuum lines and look for where the smoke comes out. If you see smoke coming out, then you’ve found the source of your leak. There are machines that produce smoke, but I’ve seen people do pretty much the same thing using smoke from a cigar.
The method you choose is up to you, but I would suggest including checking for vacuum leaks in your diagnosis. Here’s a video on finding vacuum leaks you may find useful.
Voltage leaks are another common cause of engine performance issues. Voltage leaks are leaks in the ignition system where the spark does not reach the tip of the spark plug. This loss of ignition translates to a misfire on the offending cylinder. Misfires, as we have discussed, can cause a rough-running engine and a loss of performance.
Finding ignition voltage leaks isn’t that hard. Sometimes you can actually hear a voltage leak. Listen for a loud snap that is irregular and might coincide with the miss of the engine. If you don’t hear them right away, don’t worry; this method will help you find any voltage leaks, should you have any. All you need is a spray bottle full of water; if you’re brave, you can turn the lights off during the test. While the engine is running, spray the ignition system with the water. Look for sparks or arching, listen for the snap, or listen for the engine RPM to change in some way as you do this.
Keep in mind that sometimes when doing this you can actually seal a vacuum leak, as mentioned above in the vacuum leak test. Personally I like to look for the light show in the dark, as this makes it easier to see. If you find a voltage leak, replace the parts and recheck for your performance problem. Don’t forget to check the ignition cap and rotor if you have them. If you have a coil-on-plug setup, this method might not work so well. For those, you might remove the coils one by one to inspect them. Look for burned areas or white residue on the coils themselves.
This can indicate a voltage leak. If you find parts in this condition, replace them and recheck for the problem. Here is a video on how to look for voltage leaks.
Video Title: Solving Automotive Idle Problems – EricTheCarGuy Video Description: In this Article, Solving Automotive Performance Issues, Eric looks at what can be the cause of Solving Automotive Performance Issues with your vehicle .Thumbnail: http://www.ericthecarguy.com/images/faq_buttons/Large_FAQ_Images/Performance-and-Driveability-icon-large.png