After some head-scratching and troubleshooting, the fueling issues initially suspected in the Mercedes Om606 swap project turned out to be something completely different. Despite swapping out the entire fuel system, cylinder #1 remained stubbornly inactive. This led to a compression test which, while revealing impressive ~320psi compression on the other cylinders at a 5,000ft elevation, showed a stark 0psi on cylinder #1. The mystery deepened when compressed air blown into the cylinder #1 glow plug hole was audibly escaping through the exhaust – valve trouble was the diagnosis.
Fortunately, the issue was less severe than a full valve job. Upon removing the camshafts, a stuck lifter on the exhaust side of cylinder #1 was discovered. This simple culprit was preventing the valve from seating correctly, explaining the lack of compression. Interestingly, cylinder #1 had never fired, even before the previous camshaft incident. Adding to the puzzle, the glow plug from cylinder #1 was remarkably clean during the compression test, a detail that initially seemed inconsequential but now added to the unusual nature of the problem.
With the stuck lifter freed, compression was fully restored to cylinder #1. A test drive confirmed the engine was running smoothly on all cylinders.
Beyond the engine repair, significant progress has been made on the chassis wiring, now 99% complete. A minor grounding issue is preventing the headlights from working, and the 4×4 wiring needs finalization due to differences in the “new” manual transmission transfer case. The coolant temperature gauge also presented a minor hurdle, выяснилось that the vehicle utilizes two separate sensors – one for the gauge and another for the ECU. Selecting the correct sensor resolved the issue. The alternator signal wire is now connected, and the system is charging at a healthy 14.5v.
Leak detection and rectification have also been ongoing. The transfer case output shaft seal, initially leaking significantly, has been replaced. Delivery valve leaks on the “new” injection pump led to reverting back to the original pump, which had recently been resealed. A junkyard-sourced hydroboost unit, while a welcome upgrade over the old vacuum system, unfortunately had a substantial leak and is currently being rebuilt. The hydroboost system is already proving to be a worthwhile improvement, offering enhanced braking performance.
Overall, the Mercedes OM606 engine swap is proving to be an incredibly rewarding project. The HE221w turbocharger delivers an impressive 25psi of boost by ~2000rpm, accompanied by an exhilarating sound. While boost and power begin to taper off around 4000rpm, typical for a smaller turbo, future plans include compounding with an HX super 40 and a 7.5mm EDC pump for higher RPM power. The current “stock turbo” tune is estimated to provide around 200 horsepower, comparable to a stock 5.7 TBI, but with noticeably increased torque. Further tuning will unlock more of the OM606’s potential after initial shakedown mileage accumulation.
The NV4500 5-speed manual transmission swap has been well worth the effort. The manual gearbox paired with the turbocharged diesel creates an engaging driving experience. The transmission, believed to have 115k miles, is in excellent condition, free of any grinding or popping, despite its robust, truck-like nature. The Bendstens clutch setup is currently handling the power output effectively, with future power increases serving as a further test.
The Mercedes OM606 engine itself is remarkably smooth for a diesel. Power delivery is excellent, and it operates relatively quietly when not idling. Even without boost, it maintains 50mph on flat roads in 5th gear at around 1300rpm, impressive for a 3.0L IDI engine propelling a heavy vehicle at altitude. The engine’s distinct sound is a major highlight of the swap.
This Mercedes OM606 engine presents itself as an ideal middle ground between the LS and 4BT engine options, offering a compelling blend of torque, horsepower, streetability, and fuel economy, all enhanced by its unique and appealing engine note.
The project continues with a list of remaining tasks before completion. Gauge wiring, body panel reinstallation, leak sealing, and enjoyment of the vehicle are the immediate priorities before tackling paint and body work.
A short video showcasing a 2nd to 3rd gear pull is available here: https://photos.app.goo.gl/uoDk1jnT8q7qZwSy6.
