Written By, Mike McGlothlin
Cummins’ QSB and ISB 4.5L engines are lightweight, compact, and powerful given their size—hence the reason you can find them in so many different applications worldwide. The 275ci four-cylinder is popular in woodchippers, gen-sets and irrigation pumps, and it’s also a hit in wheeled machinery like forklifts, telehandlers, swathers, and skid steers. But just because an engine is popular doesn’t mean it’s bulletproof. Despite being renowned for its durability, the 4.5L Cummins has several chinks in its armor. Failing (and ailing) emissions equipment, a sensitive common-rail injection system, select electronic and hard-part issues, and even its swap-ability make it problematic for many buyers looking to make this off-road-intended power plant road-worthy. This time, we’ll dive into the 4.5L Cummins’ most widespread problems and, as always, close things out with a solution for each.
Problem #1: VP30 Injection Pump (Early Models)
Both mechanical injection and VP30-fueled 4.5L Cummins engines are rare in comparisonto the 16-valve, high-pressure common-rail version that came later, but the VP30-equippedengines were prone to a myriad of fuel delivery issues. Similar in design to the Bosch VP44found on the 5.9L ISB Cummins (24-valve), the electronically controlled VP30 rotary pumpshares many of the same problems. When some of these issues surface, the 4.5L Cumminsthat’s saddled with it can be down more than twice its rated horsepower—or no longerrunning at all.
What Fails
The most common failure points associated with the VP30 are: 1) a bad timing solenoid,which typically causes a rough running engine and/or a significant loss in power, 2) failureof the metering solenoid, typified by sudden stalling of the engine, and 3) a dead PSG, thecomputer bolted to the top of the pump itself, and a failure that’s commonly associated withboth intermittent engine operation issues and sudden stalling. As with the VP44 on thelarger 5.9L Cummins, the latter failure is most common, with the PSG’s internals oftensuccumbing to years of exposure to heat.
Solution(s)
While many of the minor components within the VP30 can be replaced, by the time this pump begins experiencing issues it’s usually more cost effective to just replace the entire unit. Remanufactured VP30 pumps typically retail for $2,600 to $3,000 and come with a 12-month (or longer) warranty. The best method of avoiding PSG failure (again, the mostcommon issue associated with the VP30) is to ensure ample fuel supply pressure (and adequate volume) is always on tap for the pump. An in-cab or remote-mounted fuel supply pressure gauge is always a good addition to any VP30-fueled 4.5L Cummins.
Problem #2: EGR Valve
Looking at the 2007 and newer QSB and ISB 4.5L Cummins, emissions equipment is at the forefront of its most frequent mechanical issues.
In particular, the exhaust gas recirculation (EGR) system is responsible for bringing about serious losses in performance and even engine downtime. The EGR system introduces a mixture of soot and carbon into the engine’s intake tract, which mixes with oil vapor to form a thick, sticky buildup of grime. This buildup grows as engine hours and miles increase, and not only do you lose airflow efficiency into the cylinder head but moveable parts within the system can cease to work properly. Enter the EGR valve.
What Happens
Over time, the buildup resulting from soot, carbon, and oil vapor makes it increasingly moredifficult for the EGR valve assembly’s DC motor to effectively operate the valve.
When thishappens, the EGR valve will begin to stick, and eventually it can seize in place. Loss ofpower, a drop in fuel efficiency, and fault codes often accompany a sticking EGR valve. Thisis because, depending on the EGR valve’s position when seizure occurs EGR flow can be toohigh (stuck in the open position) or too low (stuck in the closed position).
Solution(s)
There are several solutions for a sticking EGR valve, but chiefly among them is the best preventative measure: regular cleanings. Just like the 6.7L Cummins for sale, cleaning the EGR system at the proper interval can extend the life of the system’s components exponentially. However, once an EGR valve has already become problematic, it will either need to be removed and cleaned by hand or outright replaced with a new unit. In applications or geographical regions where diesel emission regulations don’t apply, it’s possible that the EGR valve (and the EGR system as a whole) can be removed.
Problem #3: EGR Cooler
Similar to the EGR valve, the EGR cooler can suffer the same fate—largely in part to its dirty operating environment. Before a percentage of exhaust gases are allowed to reenter the engine’s intake system, they must be cooled. In some instances on the Cummins QSB 4.5L that’s a process that requires exhaust gas temperatures to drop from as much as 1,200 degrees F to less than 400 degrees F. The job of carrying out this huge decrease in EGT is left to the EGR cooler. It’s a component that relies on engine coolant to help pull off the feat.
How It Can Fail
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Gradually, the EGR cooler’s internal core becomes restricted due to carbon accumulation. This hinders flow and adds stress to the EGR system as a whole. Once plugged (or close to it), engine performance and efficiency will drop off considerably. In rarer cases, the EGR cooler core can rupture, allowing coolant to leak into the engine, resulting in white or gray smoke from the exhaust. Predictably, this burning of antifreeze leads to rampant coolant loss, not to mention the fact that coolant is a non-combustible fluid that has no business being in the combustion system.
Solution(s)
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To avoid excessive carbon buildup in the EGR cooler (and the rest of the EGR system as wellas the intake), limit engine idle time as much as possible. Any EGR system is most active atidle rpm, when the engine is under little (if any) load. Another means of limiting carbonbuildup comes from subjecting the engine to regular EGR cleaning intervals. When an EGRcooler is too far gone, complete replacement—ideally with a quality, OEM unit—is often theonly solution. In other cases, where an engine has been relocated to a geographical areavoid of diesel emission regulations, the EGR cooler and its supporting components can becompletely removed for a more permanent solution.
Problem #4: ECM Failure
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Control modules, sensors, and wiring harnesses all helped make the high-pressure commonrail version of the Cummins QSB/ISB 4.5L exceptionally powerful, fuel efficient, andemissions friendly. However, the added complexity that comes with a full-on, electronicallycontrolled diesel engine can come back to bite you when age, constant exposure to NVH,and corrosion set in. While common-rail 4.5L engines aren’t exactly dropping like flies dueto ECM failure, it is common enough that it made our list—and it’s the kind of failure thatwill land a 4.5L dead in the water.
Why It Fails
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The signs of ECM failure can come and go. Erratic voltage drops and/or gains and suddenengine shutdown are common indicators. In a lot of cases, the engine will restart after anabrupt shutdown but won’t stay running. Obviously, when an ECM finally dies, you’re leftwith an engine that’s dead, too. Corrosion (typically due to moisture infiltration), highoperating hours, and longtime heat exposure can take their toll on the ECM, but exposedwiring—especially the kind that spans to vital sensors—can cause all sorts of electricalgremlins as well.
Solution(s)
A sound solution begins with a proper diagnosis. This means calling upon the services of a trained QSB/ISB 4.5L mechanic who is well-versed in its issues, and who possesses the correct diagnostic tools for the job. Proper communication with the ECM is key. Remedies range from having the ECM repaired (the most affordable option) to sourcing a good used ECM, to full-on replacement. Just make sure the ECM is the culprit before forking over the cash for a new one. Many of the ECM-related headaches associated with the 4.5L engine stem from wiring or sensor issues.
Problem #5: Rod Failure (Early 4.5L’s Treated To Horsepower Increases)
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Back before the VP30-equipped version of the QSB 4.5L was released (and long before thecommon-rail version we know today was available), Cummins offered the B4.5L. It was amechanically injected big brother to the 4BT that used the common 4.02-inch bore but along, 5.39-inch stroke. These early engines were fitted with a mechanical rotary injectionpump, pop-off style injectors, an 8-valve cylinder head, and most were only rated between78 hp to 99 hp. However, the long stroke meant they were quite torquey, with 305 lb-ft(produced somewhere around 1,500 rpm) being a common torque rating.
Why They Fail
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Due to the B4.5L’s extra-long stroke, it sports connecting rods vastly different from what isstandard issue in a 4.72-inch stroke, 3.9L 4BT. In order to clear the cylinder skirts in theblock, the rod beams are notably narrower. The lack of meat in this vital area of the rodmakes them more susceptible to failure when forced to handle increased cylinder pressure(i.e. torque). So, while the typical mechanical injection fuel tricks can be employed toincrease the B4.5L’s power output, many owners find out the hard way that its rods aren’tup to the task.
Solution(s)
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The undersized connecting rod problem can be avoided altogether by leaving the B4.5L at the factory power rating. Or it can be avoided by sourcing a newer model 4.5L Cummins (and true QSB or ISB 4.5L) or 4BT Cummins to pursue additional horsepower with. After all, thanks to its more favorable stroke, combined with thicker rods, it’s not uncommon for a late model QSB or ISB 4.5L to turn out more than 200 hp and north of 600 lb-ft of torque. And as for the 4BT, its 5.9L parts interchangeability and aftermarket support makes it an easy performance choice for those looking to stick with time-tested, mechanical simplicity.
Problem #6: SCR System
When nitrogen oxide (NOx) emission standards began to progressively tighten up,
Cummins implemented the use of selective catalytic reduction (SCR) on the QSB/ISB 4.5L platform. This method of reducing NOx requires the use of diesel exhaust fluid (DEF), a mix of de-ionized water and urea, to turn the pollutant into harmless nitrogen and water before
it leaves the tailpipe. Neat tidbit: Cummins QSB4.5 engines have been able to meet stringent diesel emission standards without the use of a diesel particulate filter (DPF) in recent years. In a perfect world, SCR performs its job well. Unfortunately, most of these enginesdon’t work in anything close to ideal conditions.
What Fails
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First and foremost, added complexity through the use of sensors, wiring, a fluid tank andlines, and fluid dosing components are all part of the SCR system—and they can all fail orstop functioning at any time. Failed or faulty sensors are common, and once inaccuratereadings are discovered by the engine’s computer they can lead to immediate power derateand even place a piece of equipment in limp mode. In particular, DEF level sensor issues arehighly frequent, and DEF head failures aren’t far behind. A bad DEF head will often throwcodes for DEF fluid level, quality, and temperature.
Solution(s)
You know the old saying “it’s not a matter ofif, butwhen...” Well, it applies to virtually everycomponent on the QSB or ISB 4.5L’s SCR system. The best way to keep an SCR system on theup-and-up is to perform regular maintenance, run routine system checks to ensure thesystem is operating as it should (example: making sure the DEF tank heater is working incold weather), and always keep fresh, high-quality DEF in the tank (it has an expirationdate). That, and make certain any issues associated with the SCR, DEF or oxidation catalystsystem are addressed in a timely manner to avoid downtime or further damage.
Problem #7: Broken Exhaust Manifold Bolts
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This failure is often encountered during disassembly of a Cummins QSB or ISB 4.5L, but itcan also be something a mechanic faces (or notices) in the midst of a turbo swap.Regardless of when it strikes, a broken exhaust manifold bolt can throw a serious wrenchinto the works of what would’ve otherwise been a simple repair or teardown.Unfortunately, due to the nature of a 4.5L engine’s typical workspace (especially the QSB,Cummins’ off-highway power plants), which can include exposure to high moisture, salt,and other elements, broken exhaust manifold bolts are fairly common.
Why And Where They Fail
Heat cycles and age, weather exposure, and harsh working environments can all play atypical role in a broken manifold bolt scenario. The OEM bolts themselves are prone to rustand corrosion, which significantly weakens the fasteners over time. In many cases, the boltsbreak off at the threads during their attempted removal. In other instances, the bolt headwill break off completely. And as any mechanic will tell you, rusted, broken bolts can turnany quick job into a very time-consuming endeavor.
Solution(s)
Although you can’t turn back the hands of time for a fastener (or take back the onset ofcorrosion), there are a few techniques that offer the best chance of removing the 4.5L’sexhaust manifold bolts without breaking or damaging them.1) Douse the bolts (heavily) inpenetrating oil prior to attempting to loosen them.
2) Take care when attempting to initiallybreak them free—i.e. don’t go hog-wild with the impact.
3) For stubborn bolts, use a heatsource to help relax the fastener material enough to get them turning.
4) Always start overwith fresh manifold bolts during reassembly.
Problem #8: Injection System (Common-Rail)
High-pressure common-rail injection brought precise control, reduced emissions, andincreased horsepower and torque to the Cummins QSB and ISB 4.5L platform. However, thecommon-rail system is much more sensitive than the injection system(s) that preceded it.Tighter internal tolerances mean it won’t tolerate any debris or virtually any level ofcontamination like the earlier models would (especially the Cummins 4BT). Thecomponents most effected by contamination or debris in the high-pressure circuit are thefuel injectors—and in common-rail applications these electronically controlled units aren’tcheap to replace.
What Fails
Damaged passageways, nozzle orifices, and internal components within the fuel injectorscan lead to a myriad of performance issues. Chiefly among them, an operator canexperience power loss, increased emissions, smoking or hazing at idle, above normalpercent fuel content (i.e. “making oil”), higher fuel return rates (internal leakage), and evenlong-crank/no-start scenarios. Hanging engine rpm, a drop in fuel efficiency, and rough idlecan all point toward an ailing fuel injector as well. Seal and seat erosion, stuck nozzleneedles, a cracked nozzle, and even a cracked injector body can all take a QSB or ISB 4.5Linjector out of service.
Solution(s)
Full disclosure, by carrying out multiple injections per combustion event, common-railinjectors naturally wear out sooner than the pop-off style mechanical units of yesteryear.However, by taking the proper precautions and performing regular maintenance you canmaximize the longevity of the QSB/ISB 4.5L’s fuel injectors. It all starts with using onlyquality diesel fuel from a trusted and reliable source. Practicing timely (and proper) fuelfilter and water separator change intervals is a close second. Important Note: don’t stretchout maintenance intervals...filters are significantly cheaper than injectors. Also keep tabson the engine oil (specifically PFC) by performing an oil analysis at each oil change.
Problem #9: Not An Easy Cummins “Swap”
Unlike the Cummins 4BT, the 6BT, or even the 6.7L ISB it shares much of its general makeupwith, the 4.5L isn’t a very conversion-friendly engine. Especially in QSB form, it wasdesigned for off-highway applications rather than road-going vehicles like Jeeps, SUV’s,cars, and pickup trucks (the vehicles gearheads usually want to swap them into). A high-mount turbocharger, rear geartrain, and lack of a typical front accessory drive all createtheir own unique sets of obstacles to overcome, and each can require a bit of reengineering.Additionally, wiring one up can be extremely difficult without the original electronics in themix.
Why They’re Not “Plug-And-Play”
For starters (and as we alluded to above), most 4.5L engines left the factory with reargeartrains, which requires they either be converted to front geartrain or given majorclearance at the firewall of a vehicle. And because the QSB 4.5L wasn’t intended for on-highway applications, a power steering pump and vacuum pump, among other things, willhave to be sourced (typically from an existing on-road Cummins application). On top ofthat, obtaining an engine that’s void of its original ECM and wiring harness(es) only servesto draw out what is a lengthy swap process even further.
Solution(s)
Luckily, the prospect of swapping a Cummins 4.5L into the vehicle of your choice isn’t alldoom and gloom. With the right mechanical, wiring, and fabrication skills combined withresourceful and sharp parts hunting, it’s a conversion that can absolutely be pulled off.After all, making the impossible possible is what many ambitious Cummins conversionspecialists live for. Aftermarket companies such as Cummins Performance serve this nicheswap community, providing ECU adapter kits, ECU programming, engine-to-transmissionadaptor plates, and even a P-pump conversion kit for horsepower junkies.https://www.cumminsperformance.com/
Problem #10: Overheating
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The Cummins 4.5L can be susceptible to overheating in certain on-highway applications.And believe it or not, it’s often the result of the owner overloading the engine, either bytowing too heavy or hauling excessive cargo. In other cases, where the engine’s horsepowerhas been turned up significantly, the original (or custom) cooling system may beinadequate. This is common in a variety of performance engine swap applications, as manyleave the OEM water pump, oil pump, and radiator in place—only to find out later that theywere being pushed beyond their engineering limits.
Possible Causes
A whole host of factors can lead to overheating, but the most common causes stem from ablocked radiator or cooling stack, air in the cooling system due to low fluid or recent repair,a failed water pump, an engine fan hub that stopped working or, in a worst-case scenario,from a blown head gasket. Repeated instances of overheating can also serve to warp the cylinder head. This in turn, can allow an area of the head to separate from the block andlead to a blown head gasket. In most instances, overheating at the factory power leveloccurs due to an airflow obstruction, a system low on coolant, a stuck thermostat, or from afailing water pump.
Solution(s)
In swap projects and stationary equipment alike, warm coolant temps are best avoided byrunning a quality, high-flow radiator, a cooling stack with sufficient flow-through, and byregularly ensuring that all heat exchangers are free from debris or obstructions. In custom4.5L conversions, it’s vital that the radiator, its hoses, and that the engine cooling fan aren’tundersized. High cfm electric fans are a common go-to here, and they’re a sound insurancemeasure for trail rigs that spend a great deal of time at low rpm. Of course, a functioningwater temperature gauge is always recommended as well.
