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Questions and Answers

Toyota Camry Fuel Pump Problems?

Q. Mr. Ciulla, I have a 1997 Toyota Camry 2.2 liter FS-FE engine with 68,000 miles and an automatic transmission. The car had a fault code P0171 - System Lean. At first I checked the EGR valve found it leaking slightly and cleaned it, the light came back on. I then blocked off the EGR valve and had the same code. I checked fuel pressure and found it high, 55 psi.

Toyota Camry Fuel Pump Problems?

I replaced the pump and regulator. The code has not repeated. My problem now is I do not have the two second fuel pump prime when the key is turned on. I am afraid it is a computer problem. I checked the camshaft sensor and it seems to be working fine.

The manual says this signal is needed for the fuel pump while running. The car runs fine. But twice in the last week while troubleshooting it has run rough with no power. It seemed to be missing on one cylinder.

The first time it happened was after I pulled the EFI fuse and put a jumper in to check the fuel pump with an oscilloscope. The second time was after the pump and regulator replacement. Both times it only lasted for a couple of minutes prior to being able to isolate a cylinder.

I know this will happen again. But I am not sure whether the rough running and the no two second prime are related. The only thing at this point that I can surmise that connects the two is the cam sensor. Any advice would be greatly appreciated.

Thank You in advance,
Matt

A. There are some differences between a California and non-California vehicle. For the sake of the answer I'm going to assume it is a non-California vehicle.

DTC P0171 System Too Lean (Fuel Trim) (Without California Emissions)

CIRCUIT DESCRIPTION:

Fuel trim refers to the feedback compensation value compared against the basic injection time. Fuel trim includes short-term fuel trim and long-term fuel trim.

Short-term fuel trim is the short-term fuel compensation used to maintain the air-fuel ratio at its ideal theoretical value. The signal from the heated oxygen sensor indicates whether the air-fuel ratio is RICH or LEAN compared to the ideal theoretical value, triggering a reduction in fuel volume if the air-fuel ratio is rich, and an increase in fuel volume if it is lean.

Long-term fuel trim is overall fuel compensation carried out long-term to compensate for continual deviation of the short-term fuel trim form the central value due to individual engine differences, wear over time and changes in the usage environment.

If both the short-term fuel trim and long-term fuel trim are LEAN or RICH beyond a certain value, it is detected as a malfunction and the MIL lights up.

P0171 detecting conditions:

  • When the DTC P0171 is recorded, the actual air-fuel ratio is on the LEAN side. When DTC P0172 is recorded, the actual air-fuel ratio is on the RICH side.
  • If the vehicle runs out of fuel, the air-fuel ratio is LEAN and DTC P0171 is recorded. The MIL then comes on.

There are a few possible causes. There could be a loose air intake hose, low fuel pressure, a clogged injector, bad HO2S, bad Manifold Absolute Pressure (MAP) sensor or a bad coolant Temperature Sensor (CTS).

The lean condition will make the engine run rough.

P0171 is usually accompanied by a misfire code.

  • P0300 - Random/Multiple Misfire Detected
  • P0301 - Cylinder 1 Misfire
  • P0302 - Cylinder 2 Misfire
  • P0303 - Cylinder 3 Misfire
  • P0304 - Cylinder 4 Misfire

As for the no two second prime, it has to be there as you can plainly see in this diagram.

Toyota Camry Fuel Pump Problems?

In the diagram above, when the engine is cranked, current flows from terminal ST of the ignition switch to the starter relay coil and also current flows to terminal STA of ECM (STA signal).

When the STA signal and NE, (Crankshaft Position Sensor), signal are input to the ECM, Tr is turned ON, current flows to coil of the circuit opening relay, the relay switches on, power is supplied to the fuel pump and the fuel pump operates.

While the NE signal is generated (engine running), the ECM keeps Tr ON (circuit opening relay ON) and the fuel pump also keeps operating. If the ECM does not detect the NE signal after three seconds, it turns Tr OFF and turns the fuel pump off.

Additional Information provided courtesy of AllDATA

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