Running rough

Hi,

Since you have done the tune up, it could be related to a few other things. Have you checked to see if there are any engine vacuum leaks? Have you checked to make sure it is getting proper fuel pressure? Last, have you checked to see if there is any restriction in the exhaust system?

Do me a favor. This vehicle has an OBD1 computer system. Scan the computer and see if any codes show up. Here is a link that explains how to get codes from this system:

https://www.2carpros.com/articles/toyota-trouble-code-definitions-and-code-gathering-method-1990-1995

Also, here are a few links you may find of interest or help when testing:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

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Here are directions specific to your vehicle for testing fuel pressure. The attached pic correlates with the directions.

1991 Toyota Truck Pickup 2WD L4-144.4 2366cc 2.4L SOHC (22R-E)
Fuel Pressure Test
Vehicle Powertrain Management Fuel Delivery and Air Induction Fuel Pump Fuel Pressure Testing and Inspection Component Tests and General Diagnostics Fuel Pressure Test
FUEL PRESSURE TEST
1. Turn on the ignition but DO NOT start the engine.
2. Connect terminals +B and FP of the check connector with a service wire.

pic 1

3. Check that there is pressure in the hose to the cold start injector and that you can hear fuel return noise from the fuel pressure regulator.
Checking The Fuel Inlet Hose For Fuel Pressure

pic 2

4. Remove the service wire and turn the ignition off.
5. If there is no pressure check the following parts:
a. Fusible link
b. Fuse (EFI 15A, IGN 7.5A)
c. Circuit Opening Relay
d. Perform pressure test with fuel gauge, refer to FUEL PRESSURE REGULATOR/FUEL RAIL
e. Wiring connections to Fuel Pump
6. If no problems are found, replace the Fuel Pump.

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Here are the manufacturer's specs for fuel pressure.

1991 Toyota Truck Pickup 2WD L4-144.4 2366cc 2.4L SOHC (22R-E)
Pressures, Vacuum, and Temperature Specifications
Vehicle Powertrain Management Fuel Delivery and Air Induction Fuel Pump Fuel Pressure Specifications Pressure, Vacuum and Temperature Pressures, Vacuum, and Temperature Specifications
PRESSURES, VACUUM, AND TEMPERATURE SPECIFICATIONS
FUEL PRESSURE REGULATOR VACUUM:

At Idle .................... 17.32 in.Hg, 58.6 kPa or more

FUEL PRESSURE:

At Idle .................... 33 - 37 PSI (226 - 265 kPa)

At WOT .................... 38 - 44 PSI (265 - 304 kPa)

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Keep in mind, if the fuel filter hasn't been replaced in a long time, it could be restricting flow as well. That also can cause low pressure.

https://www.2carpros.com/articles/how-to-change-a-fuel-filter

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Here are the directions specific to your vehicle for filter replacement.

1991 Toyota Truck Pickup 2WD L4-144.4 2366cc 2.4L SOHC (22R-E)
Procedures
Vehicle Powertrain Management Fuel Delivery and Air Induction Fuel Filter Service and Repair Procedures
PROCEDURES
NOTE: If vehicle has been operated within an hour, the fuel system is probably under pressure and requires caution when removing filter union bolts.

REMOVAL:

1. Locate the fuel filter on the right side of the engine.
2. Slowly loosen the filter union bolts. Some gasoline may escape, so ensure that the potential for fire is minimized.
3. Remove the union bolts and four gaskets.
4. Loosen filter clamp and slip filter from clamp.

INSTALLATION:

1. Slip new filter into clamp. Ensure that flow arrows are in the correct direction.
2. Position filter in the middle of the clamp and tighten filter clamp.
Replacing The Fuel Filter

pic 3

3. Reinstall both union bolts with four new gaskets.
4. Torque union bolts to 18 Nm (13 ft lbs). DO NOT overtighten union bolts.
5. Clean any gasoline that may have escaped.
6. Start the engine and check for fuel leaks.

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Let me know if any of this helps or if you have other questions.

Take care,
Joe