Technical Service Article | GM 5.3L, 6.0L & 6.2L LS-Based Engines
Overview
Removing Active Fuel Management (AFM), also called Displacement on Demand (DOD), from a GM LS-based engine is a common repair after AFM lifter failures. After installing an AFM/DOD delete kit, some technicians see low oil pressure, no oil pressure, abnormal valvetrain noise, or oil pressure warnings.
These symptoms do not necessarily mean the new camshaft, lifters, or valley cover are defective. A frequently overlooked component is the AFM oil pressure relief valve in the oil pan. The condition of this valve, the oil pump configuration, and the sealing of the original AFM oil passages should all be evaluated during the conversion.
1. How the GM AFM Oil System Works
LS engines equipped with AFM use a lubrication system designed to support cylinder deactivation. Depending on the application, it includes:
- A higher-volume oil pump configuration
- The Valve Lifter Oil Manifold (VLOM), which directs pressurized oil to the AFM lifters
- AFM-specific hydraulic lifters
- An oil pressure relief valve located in the oil pan
- Additional oil passages that feed the AFM system
The oil pan relief valve provides an additional pressure-relief path for the AFM system. It is separate from the pressure-regulating valve built into the oil pump.
Important: Not all LS engines use the same oil pump and relief valve configuration. Verify the original equipment for the specific engine before replacing or modifying components.
2. Why Oil Pressure Problems Can Occur After an AFM Delete
A mechanical AFM/DOD delete replaces the AFM camshaft and lifters with non-AFM components. A complete conversion generally includes a compatible non-AFM camshaft, standard hydraulic lifters, non-AFM lifter guides, an appropriate valley cover, and ECM calibration changes. Removing the AFM parts does not, however, change every feature of the original lubrication system. The oil pan relief valve and higher-volume oil pump may still be installed.
A. Oil Pan Pressure Relief Valve Leakage
A relief valve that is stuck open, damaged, contaminated, or opening too early can bypass oil back into the pan and reduce available oil pressure.
B. Incorrect Oil Pump Configuration
Some AFM engines use a higher-volume pump than comparable non-AFM engines. Evaluate whether the original pump suits the converted engine, and inspect the pump’s internal pressure regulator for sticking or contamination.
C. Improperly Sealed AFM Oil Passages
The original AFM oil feed passages must be sealed by the correct valley cover or approved plugs. An unsealed passage creates an internal oil leak and lowers oil pressure.
D. Oil Pickup Tube O-Ring Leakage
A damaged, pinched, misplaced, or deteriorated pickup tube O-ring can let the pump draw air, causing low or unstable oil pressure and oil aeration.
E. Oil Pump Installation or Priming Problems
Incorrect pump installation, inadequate priming, pickup problems, or a low oil supply can delay oil pressure buildup or prevent it entirely after assembly.
F. Excessive Internal Clearances
Worn main, rod, or camshaft bearings and other excessive internal clearances reduce oil pressure. An AFM delete kit will not correct pre-existing engine wear.
3. Should the Oil Pan Relief Valve Be Replaced?
It depends on the engine and the oil pump used for the conversion. There are two general approaches.
Option A: Keep the Original AFM-Style Oil Pump
If the original higher-volume pump is retained, verify that the oil pan relief valve is working correctly, and replace it if it is damaged, contaminated, or defective. For applicable LS engines, replacement valves are available from aftermarket manufacturers, for example the Melling MOPR100. A compatible oil deflector may also be required depending on the application. Do not remove or plug the relief valve while a higher-volume pump is installed.
Option B: Convert to a Standard-Volume Oil Pump
Some AFM delete procedures call for a compatible standard-volume, non-AFM oil pump. With the right pump, certain conversion procedures allow the oil pan relief valve to be removed and its port properly plugged. This modification must be compatible with the specific engine, pump, and oil pan. Never plug or disable a relief system without confirming the requirements for the selected pump, and keep the pump’s internal pressure regulation fully functional.
4. Oil Pressure and AFM Lifter Health
GM service information on AFM lifter concerns identifies low oil pressure, oil aeration, and oil contamination among the conditions that can contribute to AFM lifter malfunction. Whether the engine keeps its AFM system or is converted, confirming healthy oil pressure is an essential part of the repair. Check oil pressure with a mechanical gauge, and compare readings to the specification in GM service information for the engine.
AFM/DOD Delete Checklist
- Confirm the engine’s original oil pump and relief valve configuration.
- Decide whether to keep the AFM-style pump (Option A) or convert to a standard-volume pump (Option B).
- Inspect or replace the oil pan relief valve as required by that choice.
- Install the correct valley cover or plugs to seal the AFM oil passages.
- Replace the pickup tube O-ring and confirm the pickup is seated correctly.
- Measure bearing and other internal clearances.
- Prime the oil system before the first start and verify oil pressure with a mechanical gauge.
- Complete the ECM calibration changes required for the conversion.
Evergreen Engine Parts
Evergreen offers camshafts, valve lifters, oil pumps, and gasket sets for a range of GM and other applications. Use the Evergreen eCatalog to find parts for your engine, and see our related articles on AFM lifter failures and oil pump replacement.
This article provides general guidance. Always follow GM service information and the instructions supplied with your conversion components. Brand names are the property of their respective owners.
