1992 Jeep Wrangler YJ Jeep 2.5L problems

Tiny
BEERMAN16
  • MEMBER
  • 1992 JEEP WRANGLER
  • 150,000 MILES
My jeep has some problems. First it has a bad mpg. Its gets like 7-8mpg. It also has a gas smell. Also the jeep doesn't get over 50 mph. It has a hard time taking off. Ive replaced:
tps
fuel injectors
map sensor
o2 sensor
plugs caps rotors wires

it doesn't have a cat converter
ive also clean out the throttle body a couple times.
whats wrong with my jeep?
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Wednesday, July 24th, 2013 AT 9:59 AM

7 Replies

Tiny
FREEMBA
  • EXPERT
Check the fuel pressure.

NOTE: The fuel pressure test port is used on certain engines only. If equipped, the test port will be located on the fuel rail. If not equipped, there is an adaptor which can be installed in the fuel line between the gauge and throttle body.
Fuel pressure should be around 49 psiat idle.

Let me know if you need more info. I have a more detailed procedure.
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Wednesday, July 24th, 2013 AT 10:23 AM
Tiny
BEERMAN16
  • MEMBER
Would that cause it to go slow and have a rough take off? . It feels like it has no power like it should
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Wednesday, July 24th, 2013 AT 11:15 AM
Tiny
FREEMBA
  • EXPERT
Yes.
Low fuel pressure means that the engine will not get enough fuel to produce the power that it normally does. This will also kill your gas mileage. And since the fuel doesn't have enough pressure to spray out of the injectors, it comes out in larger drops which don't burn as completely during the combustion process, which can cause a strong fuel smell (and ruin gas mileage).
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Wednesday, July 24th, 2013 AT 11:24 AM
Tiny
BEERMAN16
  • MEMBER
If the fuel pressure is low how do I fix it?
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Wednesday, July 24th, 2013 AT 1:04 PM
Tiny
FREEMBA
  • EXPERT
If the fuel pressure is low, it is likely caused by one or more of the following:

faulty fuel pump
clogged fuel filter
faulty fuel pressure regulator
leak in the fuel line
kinked fuel liine (not very likely).

The act of checking the fuel pressure is the first step in checking the fuel pump. I will tell more once we see what the fuel pressure is.

To check the fuel pressure regulator, while the engine is running and the fuel pressure gauge is reading the fuel pressure, disconnect the vacuum liine from the fuel pressure regulator; the fuel pressure should increase. If so, the fuel pressure regulator is good.

A clogged fuel filter is checked by removing it and blowing through it (with shop air or using your own breath) to see if it is clogged. However, once its off, you may as well replace it (if the cost isn't extreme).
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Wednesday, July 24th, 2013 AT 4:19 PM
Tiny
BEERMAN16
  • MEMBER
My fuel pressure is 35 psi when it's running
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Friday, July 26th, 2013 AT 12:59 PM
Tiny
FREEMBA
  • EXPERT
With engine at idle speed, system fuel pressure should be 338 kPa 5 kPa (49.0 psi 2 psi).

A lot more Info:(basically from start to finish on checking the fuel system - If your system passes all of the ese tests your problem could be ignition system related)

2.5L 4 cyl TJ owners for reference.

Symptoms - Long cranking times. It takes several cranks before the engine actually fires and/or runs.

Possible problems - Leaking fuel injector, bad/leaking fuel pump pressure regulator check valve, bad fuel pump, or bad fuel pump relay.

The problem with the 2.5L is it does not have a test port/schrader valve on the fuel rail.

In order to check diagnose the problem you will need a few specialty tools.

A) Fuel pressure gauge that goes to at least 60 Psi

b) Fuel pressure test adapter #6539 That will go in between the fuel rail and the fuel in-line. Found here Miller Tools 6539 Fuel Pressure Test Adapter

c) a fuel line disconnect tool that slides into the fuel in-line connector. Caution, your type of quick connect may or may not be shown in the Haynes book. You can find these at most parts stores. Be sure you get the right disconnect tool. (Mine was not shown in the book and I used a tool made by OEM part #27131 found at autozone)

Here are a few previously posted responses that will help you diagnose the problem:

FUEL SYSTEM PRESSURE RELEASE
Use following procedure if the fuel injector rail is not equipped with a fuel pressure test port.

(1) Remove fuel fill cap.
(2) Remove fuel pump relay from Power Distribution Center (PDC). For location of relay, refer to label on underside of PDC cover.
(3) Start and run engine until it stalls.
(4) Attempt restarting engine until it will no longer run.
(5) Turn ignition key to OFF position.

CAUTION: Steps 1, 2, 3 and 4 must be performed to
relieve high pressure fuel from within fuel rail.

In order to test fuel where there is no valve on the fuel line you need to use an adapter that fits between the fuel line and the fuel rail using the quick release fitting there.(Adapter #6539) The volume test requires using an adapter hose to fill a graduated container with fuel. The pump should be operated for a maximum of seven seconds, and it should pump at least a quarter liter of fuel in that time.

FUEL PUMP PRESSURE TEST-2.5L ENGINE
NOTE: The fuel pressure test port is used on certain engines only. If equipped, the test port will be located on the fuel rail. If not equipped, refer to the following procedure :

All fuel systems are equipped with a fuel tank module mounted, combination fuel filter/fuel pressure regulator. The fuel pressure regulator is not controlled
by engine vacuum.

With engine at idle speed, system fuel pressure should be 338 kPa 5 kPa (49.0 psi 2 psi).

14- 6 FUEL SYSTEM DIAGNOSIS AND TESTING (Continued)
WARNING: THE FUEL SYSTEM IS UNDER CONSTANT FUEL PRESSURE EVEN WITH THE ENGINE OFF BEFORE DISCONNECTING FUEL LINE AT FUEL RAIL, THIS PRESSURE MUST BE RELEASED. REFER TO THE FUEL SYSTEM PRESSURE
RELEASE PROCEDURE.

(1) Release fuel pressure. Refer to the Fuel System Pressure Release Procedure.
(2) Disconnect latch clip and fuel line at fuel rail. Refer to Quick-Connect Fittings for procedures. This can be found in this section of the group.
(3) Connect adapter tool number 6539 or 6631 into fuel rail. Be sure adapter tool is fully seated into fuel rail.
(4) Install latch clip to fuel rail. If latch clip can not be fully seated into fuel rail, check for adapter tool not fully seated to fuel rail.
(5) Connect vehicle fuel line into adapter tool. Be sure fuel line is fully seated into adapter tool.
(6) Remove protective cap at test port "T" on adapter tool.
(7) Connect the 0-414 kPa (0-60 psi) fuel pressure gauge (from gauge set 5069) to the test port "T".
(8) Start engine and note pressure gauge reading. Fuel pressure should be 338 kPa 5 kPa (49.0 psi 2 psi) at idle.
(9) If pressure is at 0 psi, connect DRB scan tool and refer to the appropriate Powertrain Diagnostics Procedures service manual.
(10) If operating pressure is above 51.0 psi, fuel pump is OK but pressure regulator is defective. Replace fuel filter/fuel pressure regulator assembly.
(11) After performing pressure test, install fuel line into fuel rail. Install latch clip into fuel rail. Refer to Quick-Connect Fittings in the Removal/Installation
section of this group for procedures.

FUEL PUMP CAPACITY TEST
Before performing this test, verify fuel pump pressure by performing the Fuel Pump Pressure Test. Use this test in conjunction with the Fuel Pressure Leak Down Test found elsewhere in this group.
(1) Release fuel system pressure. Refer to the Fuel Pressure Release Procedure in this group.
(2) Disconnect fuel supply line at fuel rail. Refer to Quick-Connect Fittings in the Service Procedures section of this group for procedures. Some engines
may require air cleaner housing removal before line disconnection.
(3) Connect appropriate Fuel Line Pressure Test Adapter Tool Hose (number 6631, 6923, 6541 or 6539) into disconnected fuel supply line. Insert other
end of Adaptor Tool hose into a graduated container.
(4) Remove fuel fill cap.
(5) To activate fuel pump and pressurize system, obtain DRB scan tool and actuate ASD Fuel System Test.
(6) A good fuel pump will deliver at least 1/4 liter of fuel in 7 seconds. Do not operate fuel pump for longer than 7 seconds with fuel line disconnected as
fuel pump module reservoir may run empty.
(a) If capacity is lower than specification, but fuel pump can be heard operating through fuel fill cap opening, check for a kinked/damaged fuel supply line somewhere between fuel rail and fuel
pump module.

TJ FUEL SYSTEM 14 - 7 DESCRIPTION AND OPERATION (Continued)
(b) If line is not kinked/damaged, and fuel pressure is OK, but capacity is low, replace fuel filter/fuel pressure regulator. The filter/regulator may be
serviced separately on certain applications. Refer to Fuel Filter/Fuel Pressure Regulator Removal/Installation for additional information.
(c) If both fuel pressure and capacity are low, replace fuel pump module assembly. Refer to Fuel Pump Module Removal/Installation.

FUEL PRESSURE LEAK DOWN TEST
Use this test in conjunction with the Fuel Pump Pressure Test and Fuel Pump Capacity Test.

Check Valve Operation: The electric fuel pump outlet contains a one-way check valve to prevent fuel flow back into the tank and to maintain fuel supply line pressure (engine warm) when pump is not operational. It is also used to keep the fuel supply line full of gasoline when pump is not operational. After the vehicle has cooled down, fuel pressure may drop
to 0 psi (cold fluid contracts), but liquid gasoline will remain in fuel supply line between the check valve and fuel injectors. Fuel pressure that has dropped to 0 psi on a cooled down vehicle (engine off) is a normal condition. When the electric fuel pump is activated, fuel pressure should immediately (1 2 seconds) rise to specification. Abnormally long periods of cranking to restart a
hot engine that has been shut down for a short period of time may be caused by:
Fuel pressure bleeding past a fuel injector(s).
Fuel pressure bleeding past the check valve in
the fuel pump module.

Testing for fuel pump check valve, filter/regulator check valve or fuel tube/line leakage:

Clamp off the rubber hose portion of Adaptor Tool between the vehicle fuel line and test port T on Adapter Tool. If pressure now holds at or above 30
psi, a leak may be found at a fuel tube/line. If no leaks are found at fuel tubes or lines, one of the check valves in either the electric fuel pump or filter/regulator may be leaking.

Note: A quick loss of pressure usually indicates a
defective check valve in the filter/regulator. A slow
loss of pressure usually indicates a defective check
valve in the electric fuel pump.

The electric fuel pump is not serviced separately. Replace the fuel pump module assembly. The filter/regulator may be replaced separately on certain applications. Refer to Fuel Filter/Fuel Pressure Regulator Removal/Installation for additional information.
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Friday, July 26th, 2013 AT 5:44 PM

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