Compression
| WARNING | DO NOT use ignition switch during compression tests on fuel injected vehicles. Use a remote starter to crank engine. Fuel injectors are triggered by ignition switch during cranking mode, which can create a fire hazard or contaminate the engine's oiling system. |
Ensure battery is fully charged and starter motor is in good operating condition. Clean spark plug recesses with compressed air and remove spark plugs. Lock throttle in Wide Open Throttle (WOT) position and Remove Auto Shutdown (ASD) relay. Install compression gauge. Using a remote starter switch, rotate engine 3 revolutions. Record compression pressure from third revolution. Continue test for remaining cylinders. See COMPRESSION SPECIFICATIONS table for correct engine compression pressures. A 50-70 percent reduction in compression between adjacent cylinders indicates a head gasket leak.
| Application | Specification | |
|---|---|---|
| Compression Ratio | ||
| 2.5L | 9.1:1 | |
| 4.0L | 8.8:1 | |
| 4.7L | 9.0:1 | |
| Compression Pressure | (1) | |
| (1) Information is not available from manufacturer. | ||
| (1) | Information is not available from manufacturer. |
COMPRESSION SPECIFICATIONS
FUEL SYSTEM
| WARNING | ALWAYS relieve fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components. |
| CAUTION | When battery is disconnected, vehicle computer and memory systems may lose memory data. Driveability problems may exist until computer systems have completed a relearn cycle. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION before disconnecting battery. |
Basic diagnosis of fuel system should begin with determining fuel system pressure.
Scheme 1
Scheme 2
Scheme 3
FUEL PRESSURE RELEASE
- Remove fuel fill cap. Fuel filler tube contains a spring-loaded door, located below fuel fill cap, which is used to seal fuel tank if fuel cap is not properly tightened. Using a non-metallic object, depress flap to relieve tank pressure.
- Remove fuel pump relay from Power Distribution Center (PDC). For relay location, refer to label on PDC cover. Start engine and run until it stalls. Attempt to restart engine until it will no longer start. Turn ignition off.
- Disconnect wire connector from any injector. Using a jumper wire with alligator clips, attach one end to either injector terminal. Attach other end of jumper to positive battery terminal.
- Connect one end of another jumper wire to other injector terminal. Momentarily touch other end of jumper wire to negative battery terminal for no more than a few seconds.
- Place a shop rag below quick-connect fitting at fuel rail. Disconnect quick-connect fitting at fuel rail. Reinstall fuel pump relay. Using scan tool, erase any DTCs caused by removing fuel pump relay.
Cherokee
- Perform FUEL PRESSURE TEST and FUEL PUMP VOLUME TEST before performing this test. If fuel pressure and fuel volume are okay, ensure fuel tank has fuel. If fuel tank is empty or near empty, amperage readings will be incorrect. Ensure fuel tank temperature is more than 50°F (10°C). WARNING: With ammeter installed in place of fuel pump relay, fuel pump will be activated even with ignition off. Before connecting ammeter, ensure all fuel lines and fuel system components are connected.
- Remove fuel pump relay from Power Distribution Center (PDC). (Scheme 1) Set ammeter to 10-amp scale. Connect negative lead of ammeter to terminal C2 (Dark Green/White wire) at fuel pump relay socket in PDC. (Scheme 1) Connect positive lead of ammeter to terminal C1 (Dark Green/Black wire) at fuel pump relay socket in PDC.
- If fuel pump current draw is 10 amps or more, replace fuel pump module. See FUEL PUMP MODULE under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION article. If fuel pump current draw is less than 10 amps, fuel pump module is okay.
Grand Cherokee
- Perform FUEL PRESSURE TEST and FUEL PUMP VOLUME TEST before performing this test. If fuel pressure and fuel volume are okay, ensure fuel tank has fuel. Ensure fuel tank has fuel. If fuel tank is empty or near empty, amperage readings will be incorrect. Ensure fuel tank temperature is more than 50°F (10°C). WARNING: With ammeter installed in place of fuel pump relay, fuel pump will be activated even with ignition off. Before connecting ammeter, ensure all fuel lines and fuel system components are connected.
- Remove fuel pump relay from Power Distribution Center (PDC). (Scheme 2) Set ammeter to 10-amp scale. Connect negative lead of ammeter to terminal No. 87 (Dark Green/Black wire) at fuel pump relay socket in PDC. (Scheme 2) Connect positive lead of ammeter to terminal No. 30 (Violet/White wire) at fuel pump relay socket in PDC.
- If fuel pump current draw is 10 amps or more, replace fuel pump module. See FUEL PUMP MODULE under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION article. If fuel pump current draw is less than 10 amps, fuel pump module is okay.
Wrangler
- Perform FUEL PRESSURE TEST and FUEL PUMP VOLUME TEST before performing this test. If fuel pressure and fuel volume are okay, ensure fuel tank has fuel. If fuel tank is empty or near empty, amperage readings will be incorrect. Ensure fuel tank temperature is more than 50°F (10°C). WARNING: With ammeter installed in place of fuel pump relay, fuel pump will be activated even with ignition off. Before connecting ammeter, ensure all fuel lines and fuel system components are connected.
- Remove fuel pump relay from Power Distribution Center (PDC). (Scheme 3) Set ammeter to 10-amp scale. Connect negative lead of ammeter to terminal C9 (Dark Green/White wire) at fuel pump relay socket in PDC. (Scheme 3) Connect positive lead of ammeter to terminal C10 (Dark Green/Black wire) at fuel pump relay socket in PDC.
- If fuel pump current draw is 10 amps or more, replace fuel pump module. See FUEL PUMP MODULE under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION article. If fuel pump current draw is less than 10 amps, fuel pump module is okay.
IGNITION CHECKS
Note. For ignition system spark and component testing, see appropriate NO TROUBLE CODE (NTC) TEST and NO START (NS) TEST in CHRYSLER CORP. - SELF DIAGNOSTICS - JEEP, TRUCKS & RWD VANS article.
SUMMARY
If no faults were found while performing basic diagnostic procedures, proceed to CHRYSLER CORP. - SELF-DIAGNOSTICS - JEEP, TRUCKS & RWD VANS. article. If no hard codes are found in self-diagnostics, proceed to TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.