MDS Delete: Fixing the Common HEMI Lifter and Cam Failure

If you own a 5.7 or 6.4 HEMI, the Multi-Displacement System (MDS) is the part most likely to cause you grief. Here is what it is, why it fails, and why so many owners choose to delete it.

What MDS does

MDS saves fuel by shutting down four of the eight cylinders under light load. It does this with special collapsible lifters on the deactivating cylinders, controlled by oil pressure through solenoids in the engine valley. When it works you barely notice it. When it fails you definitely do.

How it fails

The MDS lifters and their matching camshaft lobes are the weak point. A lifter can collapse or seize, and once it does it chews out the cam lobe underneath it. The usual signs are a persistent tick or tapping noise, a misfire, a check engine light, and metal flakes in the oil. Worn or dirty oil, a low oil level and stretched service intervals all bring it on sooner.

Why it gets expensive

By the time a lobe is wiped you are looking at a camshaft and a full set of lifters, plus the labour to get in there. While the engine is open, the smart move is to remove the failure-prone MDS hardware rather than reinstall the same parts that just failed.

What an MDS delete involves

An MDS delete swaps the MDS camshaft and lifters for non-MDS items, blocks off the oil galleries that feed the solenoids, and pairs with a tune that turns the system off so the computer is not looking for cylinders that no longer deactivate. Done properly it removes the most common HEMI failure point and gives a slightly smoother, more consistent engine.

The takeaway

• A new top-end tick on an MDS HEMI should be diagnosed straight away.
• Keep oil fresh and at the right level to delay the problem.
• If the cam is already going, delete the MDS rather than replacing like for like.

We do MDS deletes and supply the cam, lifters and delete components. Browse HEMI parts or get in touch to book the job.

General information only, not a substitute for a diagnosis on your vehicle.