2004 Jeep Grand Cherokee 4.0 wont go over 25 mph. There are no fault codes.

I would think the mechanic had checked for codes or history of codes. If the cause is a defective converter there is not a lot you can do except replace. You cannot repair a catylitic converter.

check fuel pressure . check for failed cat converter blocking exhaust. run the fault codes to find any sensor that is faulty.

The code means cylinder one is not producing power.
The problem could be spark, fuel, or something mechanical.

These are the fault codes for your Jeep below;

Jeep
11 IGN reference signal.
13 Fault in the map sensor pneumatic circuit.
14 Fault in the map sensor electrical circuit.
15 Fault in the vehicle speed sensor circuit.
17 Engine running too cool.
21 Problem in the oxygen feedback circuit.
22 Fault in the coolant temperature sensor circuit.
23 Air temperature sensor.
24 Fault in the throttle position sensor circuit.
25 Fault in the IAC motor drive circuit.
27 Fault in injector driver interface circuit.
31 Purge solenoid circuit.
33 Fault in air conditioning cutout relay circuit.
34 S/C solenoid circuits.
35 Fault in fan relay circuit.
41 Fault in the charging system or no field current.
42 Fault in the ASD relay driver circuit.
43 Fault in ignition coil control circuit.
44 Battery Temp Voltage.
46 Battery voltage is too high.
47 Battery voltage is too low.
51 Lean condition is indicated.
52 Rich condition is indicated.
53 Internal problem in module.
54 Fault in the distributor high data rate pickup circuit.
55 Completion of fault code display.
62 Unsuccessful attempt to update EMR mileage.
63 Unsuccessful attempt to write to an EEPROM location by the controller.
76 Fuel pump resistor by-pass relay circuit

Check the tranmission/gearbox fluid levels.

Hi.

Common fault is fuel pump getting damaged after engine overheating.

The pump is located in fuel tank, to know if pump is working, check fuel pressure using an hand gauge. It is available for $25 or so.

Check if there is coolant. If engine restarts check coolant level, if that goes down, then the head gasket has been damaged.

If fuel pressure is OK, check injection and distribution.

Get the check engine light checked you need to figure out the codes. Could be low on tranny fluid. If rpms go up and only moves for a short distance at 15 mph. Could be tranny fluid.

Can you check that injector for pulse . May be bad wiring to pcm

you really need to get to a dealership and check for trouble codes and go from there

There is a broken wire in the rubber casing between the door and the vehicle. Take the rubber casing off and you will more than likely find a broken wire or one about to break. Been there and done that.