1984 to 1995 601 602 603 Diesel Performance Enhancement

Quick list of things you can consider to increase performance and mileage

Produced from 1984 to 1993 these lighter weight aluminum head engines replaced the venerable cast iron 616 and 617 engines of the 1970's and early 1980's. Theses engines were more powerful and more fuel efficient. They did have a few teething problems but have proven to be very durable as long as they are treated and maintained properly. We can help you diagnose and repair common problems with these engines. They include the four cylinder (601) engine that came in the 1984-1986 190D 2.2, the five cylinder (602) engine that came in the 190D 2.5 and 300D 2.5 from 1986 to 1993, and the 6 cylinder (603) engine installed in the 124, 126, and 140 chassis 300D / TD (1987 only), 300SDL and 350SDL.

Problem & Solution

Common among these chassis:


If properly driven and maintained the engines actually require less ROUTINE maintenance than the older all cast iron 615 616 and 617 diesels. Since they incorporate hydraulic lifters no routine valve adjustment is required. Air cleaners are mounted off the engine and thus don't suffer from vibration damage. Oil and fuel filter changes are easy. Motor mounts last longer. Belts last longer and don't require frequent adjustment, etc. 

On the other hand these engines are prone to certain predictable problems primarily due to a lack of PREVENTATIVE maintenance. I suspect for some that the prevention is just too much work. For others it may just be due to a lack of knowledge. Others may just be trying to spend some money. A number of these jobs can be quite expensive if you have a shop do it. If you do it yourself you can save hundreds of dollars. That is where we can help. 

NOTE: If you have recently required one of these diesels or are considering purchasing one, here are my top SIX neglected maintenance items. 

1.GLOW PLUG CHAMBER CLEANING AND GLOW PLUG REPLACEMENT: This is the one job that is WAY more difficult than the older engines. It requires removal of the intake manifold just to get to the glow plugs!  Maybe that is why it is so often neglected. Glow plug hole reaming is a MUST on these engines. If you have no record of this being done recently get the reamer, do the job and replace the glow plugs.  Plan to ream the holes every 80,000 miles to extend glow plug life and improve smooth engine cold starts. A number of parts and kits and manuals are available for dealing with glow plugs.

  • Glow plug troubleshooting guide
  • Glow plug carbon reamer kit
  • Replacement glow plugs
  • Replacement intake manifold gasket

2. FUEL INJECTOR NOZZLE REPLACEMENT AND BALANCE TESTING: I just cant understand how some believe that fuel injectors can go forever! You should see some the the squirt (no spray) patterns I see on injectors removed from these engines. Granted, the engine will run, but if you want to discover just how well it should run - install high performance Monark fuel injector nozzles. You won't believe the difference! Smoother running, more power, less smoke and leaps in fuel economy. These 60x engines are only as fuel efficient as the balance and spray patterns of your injectors. We have everything you will need to overhaul your fuel injectors in your own garage.- including a unique injector pressure tester for under $200 that is designed and build by Kent Bergsma

3. INJECTION PUMP O-RING SEAL REPLACEMENT: If your engine is staring to show signs of fuel leaks around the injection pump it is most likely due to failed o-ring seals at the delivery valves. This is so common if your engine is not leaking now and the seals have not been replaced I guarantee it will be. Replace these o-rings before you have major leaks that can strand you on the road with some very expensive repair costs. Our kit will show you how to do this yourself! Kent will walk you through the steps to make the job doable for the average D.I.Y. mechanic.

4. ENGINE DRIVEN LIFT PUMP REPLACEMENT: From my experience the lift pumps on these engines do not last as long as those on the 61x engines. When they start to fail you can experience drastic power loss (similar to a plugged fuel filter). If this happens when you are away from home it can be very frustrating trying to find someone to repair it. The lift pumps are not expensive. As a preventative measure to maintain peak engine performance I recommend the lift pump be replaced every 120,000 miles. 

5. VOLTAGE REGULATOR REPLACEMENT: This cheap part can leave you stranded on the road miles from home. When the brushes wear down on the regulator the alternator will stop charging. If you notice a slow down in your wipers, heater blower, etc. while driving, don't wait until everything quits. It is very likely that the alternator has stopped charging and the battery voltage is being drained away. Inspect your voltage regulator every 60,000 miles and replace when the brushes are worn below 50 percent. Our voltage regulators come with instructions for easy installation.

6. FUSE BOX UPGRADE: This job is so easy that even if you have not worked on cars before, you can start with your fuse box. The old original aluminum fuse corrode and lose contact in the holders. This can create all types of electrical problems in your car. Replace those old fuses with our new copper and brass alloy fuses and you might be amazed at how those electrical glitches will just go away!

Other repair kits specifically for the DIY mechanic

  • Brake Systems Repair
  • Door panel removal and internal repair
  • Heater Blower motor repair / replacement
  • Rear Suspension Links Replacement

Troubleshooting difficult to diagnose engine performance problems

If you have done the service recommended above and are still experiencing weak power output, rough running, or excessive smoke here are some other things you should consider checking:

  • Engine Compression up to specs - complete both cold and hot cranking compression tests
  • Retarded valve and injection delivery timing  due to excessive timing chain stretch
  • Turbo charger speed and output - may require knowledgeable shop to inspect and test
  • Other exhaust restriction - possible internal muffler restriction
  • Possible crack in cylinder head due to overheating - causes rough starts and possible white smoke w/coolant loss
  • Worn delivery pump - located at bottom of injection pump - causes power loss under load
  • Malfunctioning electronic fuel controls - seek professional help to diagnose
  • Worn out or malfunctioning fuel injection pump - can only be tested at Bosch facility
  • Collapsed hydraulic lifters - usually associated with ticking noise at engine idle
  • Bad fuel (check for gas smell in tank)
  • Algae in fuel tank (black crud) - keeps plugging fuel tank outlet screen