No power after 65 mph

Tiny
JJHRHIH@COX.NET
  • MEMBER
  • 1994 LEXUS LS 400
  • 4.0L
  • V8
  • 2WD
  • AUTOMATIC
  • 117 MILES
Stumbles off on on. Driving will not go past 4,000 rpm's in park.
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Wednesday, January 22nd, 2020 AT 4:04 PM

7 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

This can be a few things. What I suggest first is to check for diagnostic trouble codes. This vehicle has an OBD1 type system. All you need to retrieve codes is a jumper wire or even a paper clip.

Here is a link that explains how it is done:

https://www.2carpros.com/articles/lexus-trouble-codes-obd1-1990-1995-code-retrieval-procedure

Let me know what you find.

Joe
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Wednesday, January 22nd, 2020 AT 7:18 PM
Tiny
JJHRHIH@COX.NET
  • MEMBER
Check engine light is not on.
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Thursday, January 23rd, 2020 AT 10:57 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

Although the light isn't on, you should still check for codes with this type of system. As far as the limited RPM's and running issues, it could be many things. You could have low fuel pressure, a partially plugged catalytic converter, vacuum related problems, and so on. It can also be related to timing issues.

Here are a few links you can use to check the general things:

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

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

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

__________________________________

Here are directions specific to your vehicle for testing fuel pressure. The attached pics correlate with the directions. Also, the specs are included in the directions.

__________________________________

1994 Lexus LS 400 V8-4.0L (1UZ-FE)
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
PROCEDURE

1. Verify the battery voltage is above 12 volts.
2. Disconnect negative (-) terminal cable from the battery.

CAUTION: Work must be started after 90 seconds from the time the ignition switch is turned to the LOCK position and the negative (-) terminal cable is disconnected from the battery.

3. Remove the union bolt holding the left hand delivery pipe to the rear fuel pipe. Remove the 2 gaskets.

CAUTION: Put a shop towel under the delivery pipe. Slowly loosen the union bolt.

pic 1

4. Install the rear fuel pipe and pressure gauge to the left hand delivery pipe with 3 new gaskets and the union bolt. (SST 09268-45012)

Torque: 39 Nm (29 ft lb)

5. Wipe off any splattered gasoline.

pic 2

6. Using jumper, connect terminals B and FP of the data link connector 1. (SST 09843-18020)
7. Reconnect the cable to the negative (-) terminal of the battery.
8. Turn the ignition switch ON.

pic 3

9. Measure the fuel pressure.

Fuel pressure: 265 - 304 kPa (38 - 44 psi)

If pressure is high, replace the fuel pressure regulator. If pressure is low, check the following parts:
- Fuel hoses and connections.
- Fuel pump.
- Fuel filter.
- Fuel pressure regulator.

pic 4

10. Remove the jumper from the data link connector 1. (SST 09843-18020)
11. Start the engine.

pic 5

12. Disconnect the vacuum sensing hose from the fuel pressure regulator, and plug the hose end.
13. Measure the fuel pressure at idle.

Fuel pressure: 265 - 304 kPa (38 - 44 psi)

pic 6

14. Reconnect the vacuum sensing hose to the fuel pressure regulator.
15. Measure the fuel pressure at idle.

Fuel pressure: 196 - 235 kPa (28 - 34 psi)

If pressure is not as specified, check the vacuum sensing hose and fuel pressure regulator.
16. Stop the engine. Check that the fuel pressure remains 147 kPa (21 psi) or more for 5 minutes after the engine is turned off.
- If pressure is not as specified, check the fuel pump, pressure regulator and/or injectors.
17. After checking fuel pressure, disconnect the battery negative (-) cable carefully remove the fuel pressure gauge to prevent gasoline from splashing.
18. Connect the rear fuel pipe to the delivery pipe with 2 new gaskets and the union bolt.

Torque: 39 Nm (29 ft lb)

19. Reconnect negative (-) terminal cable to the battery.
20. Check for fuel leaks.

__________________________________

Here is a link that explains how to test for an engine vacuum leak.

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

__________________________________

Without codes, we need to walk through one system at a time. I will say that often times a catalytic converter can cause this as well as fuel pressure. So we have to eliminate things one at a time.

Let me know if this helps.

Joe
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Thursday, January 23rd, 2020 AT 7:30 PM
Tiny
JJHRHIH@COX.NET
  • MEMBER
  • 1994 LEXUS LS 400
  • 4.0L
  • V8
  • 2WD
  • AUTOMATIC
  • 113,000 MILES
It stumbles, falls flat. No engine codes/drives fine until 65 mph.
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Thursday, April 2nd, 2020 AT 3:52 PM (Merged)
Tiny
KASEKENNY1
  • EXPERT
Most likely this is a fuel issue or a potential throttle sensor or air intake sensor. This means we need to start checking them off until we find the issue.

Let's start with the fuel pressure when the issue happens. It should remain stable but if not then we need to go down that route.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Here is another guide that walks through hesitations:

https://www.2carpros.com/articles/engine-hesitates

Please run through this info and let us know what you find. Thanks
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Thursday, April 2nd, 2020 AT 3:52 PM (Merged)
Tiny
JJHRHIH@COX.NET
  • MEMBER
Liked and. Just wanted to know when car is running and unplugging air flow sensor it keeps running. Defective sensor?
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Thursday, April 16th, 2020 AT 2:36 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
If you disconnect the mass airflow sensor, the car should keep running. This means that if your mass airflow sensor fails completely, your car will continue running.

What are your thoughts, Kasekenny1?
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Thursday, April 16th, 2020 AT 7:43 PM

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