4 Liter Jeep Engine – A Favorite Among Jeep Enthusiasts Worldwide

4 Liter Jeep Engine - A Favorite Among Jeep Enthusiasts Worldwide
4 Liter Jeep Engine - A Favorite Among Jeep Enthusiasts Worldwide

The 4 Liter Jeep Engine, is one of AMC’s best-known engines.

So, the 4 Liter Jeep Engine, was introduced in 1986 for the 1987 model year.

Furthermore, engineers continued to refine the engine to reduce noise, vibration, and harshness.

The 4 Liter Jeep Engine is regarded as one of the best Chrysler 4×4 off-road engines.

It is the last in the line of the (AMC) inline sixes. The (MPI) system that debuted in 1991, is what made the 4 Liter Jeep Engine famous. The 4 Liter Jeep Engine has a significantly improved head and a highly efficient and reliable fuel injection system. In a nutshell, the engineers at Chrysler took a great engine and made it even better.


The Jeep has always had an amazingly powerful appearance and you can tell they mean business just by looking at them. In fact, a lot of Jeep owners buy Jeep Wrangler car covers to make sure their Jeep’s exterior stays looking fierce. But it’s not what’s on the outside that’s most impressive about this particular Jeep, it’s what’s under the bonnet.

The power, reliability, and low-end torque of the 4 Liter Jeep Engine; has made it a favorite among Jeep enthusiasts worldwide. In addition, many parts from the 2.5 engine were interchangeable. So, in the end it was emissions standards and worn out tooling, that brought the 4 Liter Jeep Engine down. So, if you are a Jeep driver that likes to go off-road, this engine could be perfect for you. However, you may also want to invest in some more advanced vehicle parts; that will make your off-roading experiences even more fun.

Consequently, the 4 Liter Jeep Engine, was discontinued at the end of the 2006 model year.

4 Liter Jeep Engine Specifications:

  • Displacement: 4.0L (242 cubic inches)
  • Bore: 98.4mm (3.875 inches)
  • Stroke: 86.72-87.31mm (3.414-3.4375 inches)
  • Compression Ratio: 8.8:1
  • Block Material: Iron
  • Head Material: Iron
  • 1987-90: 177 hp (132 kW; 179 PS) at 4500 rpm and 224 lb ·ft (304 N ·m) at 2500 rpm
  • 1991-95: 190 hp (142 kW; 193 PS) at 4750 rpm and 225 lb ·ft (305 N ·m) at 4000 rpm
  • 1996-01: 190 hp (142 kW; 193 PS) at 4600 rpm and 225 lb ·ft (305 N ·m) at 3000 rpm
  • 2001-06: 190 hp (142 kW; 193 PS) at 4600 rpm and 235 lb ·ft (319 N ·m) at 3200 rpm

But, with all that good stuff going on the 4 Liter Jeep Engine, was not without its faults.

4 Liter Jeep Engine
4 Liter Jeep Engine

The 4 Liter Jeep Engine, Did Have Problems With:

  • Engine Noises
  • Low Oil Pressure
  • Engine Stalling
  • Engine Misfires
  • Coolant Leaks
  • Cracked Cylinder Heads
  • Cracked and Leaking Exhaust Manifolds
  • Piston Skirt Failures
  • Thermostat Issues

4 Liter Jeep Engine, Cylinder Head Cracking

Cylinder Head Cracking
Cylinder Head Cracking

Certain years were susceptible to cracked heads, due to a casting flaws. Early 0331 head castings are prone to cracking, causing coolant to contaminate the oil. As a result, this lead to catastrophic engine failure. The head cracks in the center between #3 and #4 cylinders. With the valve cover removed, the crack may be visible.

Exhaust Manifold, Cracks And Leaks

Exhaust Manifold Cracks
Exhaust Manifold Cracks

The weak point on the 4 Liter Jeep Engine, is the exhaust manifold tends to crack. When the crack is still small it leaks a little. But, as the manifold expands with heat it closes up. So, when the engine is cold, you may hear a ticking noise. Usually, due to an exhaust leak, caused by broken exhaust manifold bolts. Replacement of these bolts and associated gaskets, is necessary to fix the condition. A ticking type noise may be noted from the engine area; due to an exhaust manifold that has cracked, where the pipes are welded.

Engine Overheating

This was a common issue, but a new thermostat seemed to cure it. As a result, the thermostat may fail to close completely; causing the Check Engine Light to illuminate. This problem will prevent the engine from reaching normal operating temperature.

Ticking Noise In Engine Bay

Duty Cycle Purge Solenoid (DCP) Causes A Ticking Sound From Engine Compartment.

The customer while sitting in the passenger compartment; may notice a ticking-like, sound when the engine is idling. The sound may be more noticeable, in colder ambient temperatures. Mechanical contact between the (DCP) solenoid and the body of the vehicle; may be the cause of the ticking-like sound. Consequently, the sound may appear to be similar to; the sound produced by a worn or loose valve lifter. Isolating the Duty Cycle Purge (DCP) solenoid from the vehicle body.

Multiple Engine Misfires (P0300);

The driver may experience an incident of engine misfire, during certain vehicle operating conditions. Usually between 50 – 70 MPH and under light loading conditions. This condition is more noticeable when, engine temperatures are less than 0 C (32 F). If the vehicle is equipped with On-Board Diagnostic (OBD), a code may also have been set. Most of the time this will be a, Diagnostic Trouble Code (DTC) P0300 – Multiple Cylinder Misfire.

Various single cylinder misfire (DTC)’s may also be present.

If the frequency of misfire is high; the Powertrain Control Module (PCM) may place the engine in “Limp-In” mode.

Misfire conditions may be caused by, one or more engine exhaust valves that are slow to close. So, late closure of an exhaust valve may be the result of; no valve rotation and build up of carbon. This may happen when the engine is not allowed to run at; engine (RPM)’s that are greater than 3,200 (RPM). At 3,200 (RPM) or higher the engine exhaust valves will rotate; if not impeded by high carbon deposits.

Consequently, high carbon deposits are associated with, short trip driving. As a result, the engine is not allowed to fully warm up to normal operating temperature. Cold temperatures will increase engine warm-up times; adding to carbon deposits building up on the exhaust valve stems. Most of the time decarbonizing the engine is the cure.

Single Cylinder Misfire (p0303)

A Check Engine Light may illuminate indicating a “Cylinder #3 Misfire”. This normally occurs in hot weather. Usually, after the vehicle has been driven; parked for ten to twenty minutes, and then restarted. Heat from the exhaust vaporizes fuel inside the #3 fuel injector and causes the misfire. Installing an insulator sleeve, normally lowers the temperature enough so the fuel will not vaporize.


Due to misfires, you may experience, a loss of power when accelerating between 50 and 70 (MPH). Also, this was more common in colder weather. Carbon buildup on the exhaust valve stems, seems to be the issue. As a result, the exhaust valves may close too late.

Decarbonizing the engine, seems to be the go to repair. This was most likely the cause of other problems like noisy lifters and bent push rods.

Oil Pump

Oil pumps were prone to early failure, due to just wearing out.

Cracked Piston Skirts

Cracked Piston Skirts
Cracked Piston Skirts

The pistons from ’96 onward are all the same. The piston skirt failures, however seem to be all around 96-2000 mark. Many think it is just a casting flaw in those years.

Crankshaft Position Sensor Failure

Heat, is the biggest issue for this sensor going bad. Yes, it will trigger the “check engine” light. But, most of the time when the Crankshaft sensor goes, the engine is dead. It will turn over, but will not fire at all. Occasionally, a (CPS) will cool down long enough, to fire up again. This usually starts, the repeated cycle of engine stalling.


So, this was the last in the line of the (AMC) inline sixes. And, they attracted a whole new generation of followers. Despite the problems it did have, the new followers seemed to actually, like the challenges it provided.

So, that is what has made the 4 Liter Jeep Engine, A Favorite Among Jeep Enthusiasts Worldwide.

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