Power braking can be dangerous, so use caution when doing this test. Do it in an open area away from things you can run into. You can only do this test with an automatic transmission; you really can't do this with a manual transmission. The test is simple enough and only takes a few seconds.
- First, start the engine and activate the parking brake.
- Next, put the transmission in drive or reverse, it really doesn't matter. I often put it into reverse if I'm facing a wall; that way, if the brakes fail or some other issue happens, I can recover before I hit something. I've never had to deal with that situation when doing the test, but I'd rather be safe than sorry.
- Next, put your foot on the brake and floor the gas pedal. You only need to do this for a few seconds. Don't continue to do it for long periods of time, as you can overheat the engine.
- Keep an eye on the tachometer if you have one, as this information can be helpful. Note when the RPMs no longer go up and at what RPM that happens.
This test will tell you two things. The first is the stall speed of the torque converter. The RPM reading you took when the engine peaked is the stall speed of the converter. This information is really secondary to what you're looking for. You want the problem you're having to manifest. If it does manifest while you do the test, then the problem is likely with the engine. If the problem does not occur when you do this test, your problem might be with some other system, such as the transmission or another drive line component. Like I said, this is a quick test to determine if your performance issue is the result of an engine problem or something else. The test puts your engine under full load, so if there is an issue with engine performance, it will often show up during the test. Because you're running the engine under full load, it can overheat it. As I said, you don't want to do the test for too long; just do it long enough to put the engine under full load and check for a problem.