To perform a VE test, all you need is:
- A vehicle with a MAF sensor
- A VE calculator
- A Scan Tool displaying the following PIDs
- MAF in grams/second or pounds/minute
- IAT (air temperature affects density)
- Barometric value (or check online for current atmospheric pressure)
Volumetric Efficiency (VE) Test Procedure
While graphing the PIDs, accelerate at wide-open-throttle (WOT) to near redline in first or second gear. Capture the movie or screen on the Scan Tool and return to the shop to enter the peak RPM and MAF values into the VE calculator along with intake air temperature, altitude, and engine displacement. The VE calculator will let you know the engine’s breathing efficiency.
Interpreting Test Results
The table below shows approximate ranges for the test. As you can see, sometimes the results aren’t clear because some engines are naturally more or less efficient. For example, a 2-valve pushrod V8 from GM doesn’t breathe very efficiently even when new, and 80% is a decent result. On the other hand, a 4-valve Hyundai with variable valve timing and intake tuning should get to 95%. Therefore an 80% result on a 5.3L Yukon V8 is a pass, but on a 2.4L Sonata it’s a fail.
The good news is that the results are often very obvious, so don’t worry about the ‘fuzzy’ result range unless you have to. Even then, you can often reason your way through a result. For example, if our hypothetical Sonata barely runs, our ‘failed’ 80% result does indicate a fault, but isn’t bad enough to explain the barely running engine. Look for something else. On the other hand, if the complaint is ‘it seems like it doesn’t have as much power’, the 80% result completely explains that symptom.
|90% or More||No breathing faults are present, or at least they are so minor that they will not cause a code to set or a customer to report a symptom. Note that non-turbo engines with very clever engine and intake designs may exceed 100%.|
|76-89%||The ‘fuzzy’ zone. Consider the engine design (e.g. number of valves, number of cams, use of VVT, use of variable intake). Also consider whether the vehicle is designed for performance, economy, or workload when calibrating your expectations for this test. The higher the result in this range, the less obvious the symptom, so consider the severity of the fault you are diagnosing before jumping to conclusions.|
|56-75%||This range clearly indicates a breathing problem. Use Fuel Trim to determine if this is a real breathing fault or just a sensed breathing fault.|
|55% and less||Very few engines will even run if the actual breathing is under 55%. However, if it’s a ‘fake’ breathing fault, then Short Term & Long Term Fuel Trim may be able to add enough fuel (often over 50% combined) to keep the engine running. Therefore, if your results are in this range and the engine runs, verify high Fuel Trim and then diagnose|