The 4 Liter Jeep Engine is one of AMC’s best-known engines.
The 4 Liter Jeep Engine was introduced in 1986 for the 1987 model year.
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 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.
As a result, 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
So, With all that good stuff going on the 4 Liter Jeep Engine was not without its faults.
It 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
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;
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. 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.
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.
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 noisey lifters and bent push rods.
Oil pumps were prone to early failure due to just wearing out.
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.