VCDS (Vag-Com Diagnostic System) offers a powerful way to test diesel injectors using Measuring Blocks 13 and 15. This article delves into interpreting the results, particularly focusing on deviations in fuel quantity and their implications for Pumpe Düse (PD) injectors.
While VCDS data can provide valuable insights into injector performance, it’s crucial to understand the limitations and context of these readings. Simply relying on deviation numbers from Block 13 (idle balance) and Block 15 (fuel usage) might not provide a complete picture, especially for worn injectors.
For PD injectors, significant deviations often indicate the need for replacement. Values exceeding ±2.99 mg/str typically suggest worn injectors. However, before condemning injectors, consider factors like potential cylinder issues or camshaft problems. Swapping injectors between cylinders can help isolate the problem.
Furthermore, always address the potential for a burr forming where the injector body contacts the cylinder bore. This burr must be removed before reinstalling an injector to avoid damaging the seals. Damaged seals, especially the lower black seals, can lead to fuel leaks and significant power loss. Replacing the TTY hold down bolt is always mandatory.
The effectiveness of VCDS injector testing diminishes with worn injectors, especially those with reduced pop pressures. The ideal pilot pop pressure is around 220 bar (3250 psi), and the main stage pressure (NoP2) should be near 300 bar (4350 psi). A significant drop in these pressures, often down to 170 bar for the pilot pop, indicates wear and affects the reliability of balance tests. Injectors operate optimally within a specific pressure range, and deviations outside this range (typically ±5%) skew balance readings.
While some success has been observed with high-quality diesel fuels and additives in prolonging injector life, reaching 250,000 miles with the original injectors is challenging. If injectors exhibit consistent spray patterns across all five holes and can be shimmed to specifications, VCDS data becomes more reliable for qualification. However, attempting to revitalize old injectors is often labor-intensive and rarely cost-effective.
In conclusion, VCDS provides a valuable tool for assessing diesel injector performance. However, interpreting the results requires understanding the limitations of the test, especially with worn injectors. Factors like pop pressures, mileage, and fuel quality significantly impact the reliability of the data. While deviation numbers offer a starting point, a comprehensive diagnosis often requires further investigation and potentially professional consultation.
