Cummins 5.9L 24v Engine Problems

The 4 Most Common Cummins 5.9L Engine Problems

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The 5.9 Cummins 12v was known for its bulletproof reliability. However, Cummins had to modernize the engine and add newer technology to keep up with the diesel power race of the 90’s, bringing the new 24v common rail engine.

The switch from a 12v to 24v and to common rail fueling lead to a number of problems with the fueling system on the 5.9 Cummins 24v engine. Furthermore, it suffered from some serious issues with the block cracking and some less serious issues with the exhaust manifold and accelerator sensor.

I’m going to discuss overall reliability of the 24v engine and discuss which of the below problems are actually problems based on my experiencing owning and modifying these engines.

Cummins 5.9L 24v Engine Problems

  • Fuel Lift Pump Failure
  • Leaking Fuel Injectors
  • Exhaust Manifold Leaks
  • Accelerator Pedal Position Sensor Failure
  • Bonus: Engine Block #53 Cracking

If you would rather consume this content via a video, check out our 5.9 24v Cummins Common Problems video below:

1. Lift Pump Failure

1998 to 2004 model year 24v’s experience common lift pump failure. These early years had their lift pumps attached to the engine block. Because of this, they were: (1) subject to a lot of excess heat, and (2) had to pull fuel a very long distance. This created a lot of undue stress on the pump, ultimately resulting in premature failure. 2005+ model years relocated their lift pumps to inside the gas tank which greatly improved reliability.

The bigger issue is that the lift pump tends to take the VP44 injection pump out with it. The later model CP3 injection pumps hold up better and do not fail as frequently, making the 2003+ models with the CP3 a bit more reliable, with 2005+ being the most reliable.

Failure Symptoms

  • Engine misfires
  • Lean AFR’s
  • Rough idling and poor performance
  • Hard starting or engine stalling while running
  • Boost below target
  • P1693 fault code

Lift Pump Replacement Options

Aftermarket lift pumps are very common among Cummins owners. While aftermarket systems can get rather expensive, most will relocate the pump closer to the gas tank. By doing so, the issues with the engine heat and pull distance are mitigated. With that being said, given the cost of replacing the OEM pump, you’re better off with the added reliability (and performance) created by aftermarket systems.

2. Leaking Fuel Injectors

Fuel injectors are known to fail around the 150,000 mile mark. The fueling system is the most problematic part of these engines, although they did tend to affect the VP44 versions more. The injectors are just naturally prone to leaking but dirty fuel is also a common cause for them failing as early as they do.

Faulty Fuel Injector Symptoms

  • Hard start or no start
  • Cylinder misfires
  • Fuel in the engine oil
  • Poor idling and performance, surging, etc.

Replacement Options

Unfortunately fuel injectors run $300+ per injector….which equates to nearly $2k per set without install. When fuel injectors fail, they fail one at a time but we usually recommend replacing all of them.

Your two options are: replacing the injectors with an OEM set, or running upgraded performance injectors. If you’re trying to make more power, get an upgraded set. Otherwise, OEM is fine and will be a bit cheaper than upgraded injectors.

3. Exhaust Manifold Problems

Unlike it’s competition, Cummins uses a inline engine, meaning all 6-cylinders are in one line. With 6-cylinders and 5.9-liters of capacity, the engine block is very long. And therefore, the exhaust manifold is also very long as there is one manifold connecting all cylinders.

The engine block is made of cast iron. Cast iron is very rigid and inflexible, which causes the block to actually expand as the engine heats up. While the block will only expand by a fraction of an inch, the constant expansion and contraction causes a lot of stress on the exhaust manifold. As a result, the manifold (also made of cast iron) can crack.

When the manifold cracks air leaks out, pressure is lost, and the engine loses vacuum.

Cracked Exhaust Manifold Symptoms

  • Loss of performance, poor idling
  • ARF running rich
  • Boost below target
  • Loud noises coming from the manifold, noise increases with RPM’s
  • Engine misfires

One the manifold cracks, it’s only a matter of time before the crack worsens. The only option here is to replace the full manifold and to do it quickly to prevent further engine damage.

4. Accelerator Pedal Position Sensor (APPS) Failure

The accelerator pedal position, referred to as APPS, is responsible for telling the ECM how depressed the pedal is. This controls throttle and tells the ECM to open or close the throttle body, affecting engine RPM’s. When the sensor fails, the ECM doesn’t receive a signal from the pedal, therefore not knowing what to do with engine speeds.

This problem is mostly limited to 1998-2004 5.9 Cummins diesel engine. When the sensor fails it usually sends no signal to the ECM. However, it can occasionally flash back on and send a signal to the computer which can cause the engine to surge or lunge forwards. Driving with a failed APPS will be nearly impossible and certainly dangerous.

Failure Symptoms

Replacing the accelerator pedal position sensor is a pretty simple DIY. The APPS sensor is around $100-250 depending on whether you get an OEM or aftermarket replacement.

Bonus: #53 Engine Block Cracking

This problem is only common for a small number of 5.9 Cummins so I’m adding it as a bonus as you should beware of the issue if you are looking at buying an older 24v. From 1998.5 to 2002, Cummins had two manufacturers producing their engine blocks: TUPY in Brazil, and Teskid in Mexico.

The blocks manufactured by TUPY in Brazil have a #53 etching on the side of them and are prone to cracking. While this isn’t a guaranteed failure, it is common. The thickness of the water jacket walls was too think which caused them to crack for a number of reasons. Coolant pressure, corrosion, frequent towing, and increase power are all common causes of the block cracking. Additionally, failing to let the engine properly warm up prior to running the engine hard can also cause this.

You can read more about Cummins #53 engine block problems here.

5.9 Cummins 24v Reliability

Outside of the fuel system, the 5.9 24v is a very reliable engine. The engine internals such as the pistons, rod, and crankshaft will last a lifetime and can hold up beyond 500,000 miles. Outside of the fuel system components, you should expect to replace common items like water pumps, hoses, belts, etc. over the course of ownership. Outside of these items, maintenance is generally very manageable and inexpensive due to the lack of emissions related systems.

The turbo, which is a common failure point on a lot of diesels, is very strong. However, it is not a very power-capable turbocharger which leads a lot of folks to upgrade this item when searching for significant power gains.

Approx. 50% of these engines will last beyond 350,000 miles without any catastrophic failure, making them very reliable. Just know that you will likely need to replace some expensive fueling parts long before you hit that kind of mileage.

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  1. This is my first Cummings, 2001 2500 4×4 manual 6 spd. I found out really quick about the Lift pump and my first FASS replacement pump worked fine for over the 4 year warranty. A wire broke and the mechanics replaced it with a life time unit, with water and fuel filters.. I have 258,567 miles on the truck. I have a VP44 issue, it got galled when the Fass went out, still runs and trying to save up to buy a new rebuild from Thoroughbred Diesel. The Mechanic wants 6 hour shop time and that would be about $1900 + I am studying how to do this insolation. I am very good at most work on trucks.. Thank you for all these facts and good reading, I have learned a lot of beautiful Facts.

  2. I have a 2003 Ford F650 5.9 Cummins and I’m having a hell of a time with loss of power. I’ve already replaced the accelerator position sensor and the lift pump. I had power back for a day and then it was back to topping hills at 25mph or slower (normal hill topping was 50mph before the issue began) and on the flat I’m lucky to keep my speed. it feels like the pedal is not telling the engine that I’m pressing it for more power. Anyone else going through this and found what the cause was?

    1. Having the exact same issue, and was just contemplating changing the exact same two parts. Have you got yours running yet?

      1. my 5.9 125000 miles puffs smoke out the exaust once in a awile going down the road runs great what is thw problen

    2. I had a international that gave me a hell of a time and we found a piece of rubber in the gas tank it was sucking into the fuel line..

  3. @ AR: the only time my 1999 5.9 Dodge Cummins had symptoms like that, it was a loose clamp on the turbo hose. Limped 100 miles and diagnosed and fixed in 5 minutes. That was at 250K; now at 365K and still purrs along jest fine. I won’t comment on the Ford thing – never knew there was such a thing.

  4. Replaced injectors twice. replaced turbo, new exhaust manifold gaskets, new clutch cooling fan unit, new rocker arms, new MAF sensor, New MAP sensor. 2005 dodge ram 2500 5.9L Cummins, runs great when cold after engine reaches operating temp ( 195 deg.) Engine starts missing, losses power and smokes both black but mostly Blue smoke. If I force the gas it smooths out until I let up and goes right back to missing and smoking. on a fixed income cant afford new, can barely afford to fix or repair just to keep ending up with same issue. I need help!

  5. Don’t believe everything you read about the cummins being a reliable engine. First, If none of the fueling is reliable then it does not do any good for the piston and rings to last 350 K miles. All of the changes to the 24 valve made it a dog of an engine. Also, the aftermarket support sucks as they try to throw a variety of different things at it and none of them are long lasting or work well. Yes, you will hear people getting 400 K miles but they forget to mention the amount of money it took to get it to go this far. My 2000 has less than 200K miles and it has had 4 lift pumps and 4 injector pumps not to include replacement of MAP sensor, boost sensor and a variety of other things like larger fuel lines, pump moved to the rear, best filtration, all gauges for troubleshooting etc. All that is a cost of keeping one of these running and on the road. (over 10K dollars) Not to mention when they breakdown no one can repair them quickly or for a reasonable price. Skip the diesels now that the new DEF is added as that is another issue for the new ones. DEF messes up the sensors and causes problems in the emissions which are required, and the dealer will not work on them when the emissions are by-passed. Not to mention it is against the law.

  6. This is from your exhaust manifold leaks section ; When the manifold cracks air leaks out, pressure is lost, and the engine loses vacuum.

    Since when does a 5.9 have vacuum? There is no butterfly throttle valve, That’s why you don’t decelerate when letting off throttle unless you have an exhaust brake.

    How would an exhaust manifold crack leaking exhaust under pressure cause loss of vacuum on any engine?

  7. Ive had 2 03’s. First One a 5 speed, current one 6 speed. Changed fuel filter every time I change oil (7k). Only thing other than general maint. is a few stock clutches. 03’s are the best, good fuel mileage, enough power to do the job and have no complaints. When this current trk hits 300k Ill go find another 03 .

  8. Yes, the 5.9 has a vacuum pump. It runs the heater system and your cruise control.
    I had the exhaust manifold crack, actually made a hole. With a hole in the system it cannot spin the turbo, so you have no boost. Since diesels don’t have vacuum, and depend on the turbo, for boost it will run terrible. I could do 20 mph uphill towing a 10,000 Lb trailer.
    I agree that a exhaust leak will have nothing to do with vacuum.

  9. I am looking at buying an RV with a Cummins 5.9L 300 hp engine with 90,000 miles. Getting ready to to on a 40 day 7000 mile trip and don’t want to deal with breakdown. Would you suggest preemptively replacing the fuel lift pump and fuel injector pumps before the trip? Is it hard to find mechanics that will work on an engine this old when it is mounted inside and RV?

    1. 2002’s should be pretty well built. Not sure exactly about the RV applications but the fueling system is really the only thing that tends to be a problem. Lift pump which can take out the vp44 and then injectors.

  10. I have recently replaced the acelerator pedal position sensor and full bell crank assembly on my 2001 cummins. It ran fine,,like new for several weeks,,then a couple of days ago it started having the very same issues as before,,,engine stall, loss of power at the pedal,, surging until I got it up round 65-70 mph,,then no problems ! I do a lot of short trip driving rarely over 60mph,,so my question is,, what the hell is going on with my pickup??? Currently has around 253,000miles on it ,,original injectors, Air Dog lift pump was installedl several years ago along with new injector pump,,I change fuel filters at every oil change(,5000)miles,, have open air filter by K&N that gets changed anytime it looks just a little dirty,, I live in west Texas where its HOT& DUSTY most of the time,but when it gets cold its DAMN sure COLD!!! Any infrmation would be greatly appreciated!!

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