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Flood-Damaged Nissan TruckPosted 10/7/1999By Paul Kujawa
Vehicle: 1987 Nissan Truck A technician called me about a 1987 Nissan truck that had been towed to his shop after being in a flood. He said the ECU under the passenger seat had obviously gotten wet. The engine wouldn't start and had no spark, fuel pressure or injector pulse. He had cleaned the ECU connections and replaced the ECU. When he turned on the key, the fuel pump came on for five seconds, just like it should. He cranked the engine - it still wouldn't start - and then found fuel pouring out of the injectors and filling the throttle body and the engine with fuel. His question for me was, "Now what?" Here's my advice: Try unplugging the eight-wire throttle body electrical connector and turn the key on again to run the fuel pump and see if fuel continues to flow from the injectors. Make sure the cover is still in place over the top of the injectors or the injectors can actually "lift up" slightly and allow fuel to go around them and into the intake manifold. If the cover is in place, the connector is disconnected, and the injectors still dump fuel, then the injectors are mechanically stuck open and will need to be replaced. Here is the problem you may run into: The injectors were damaged when the original ECU got wet. The new ECU was installed. The damaged injectors could have taken out the new ECU. Now you replace the stuck-open injectors and the new (now also defective) ECU damages the new injectors you just installed. This can be very costly and unproductive. When the ECU is replaced after being damaged by flood waters or if the battery is jumped backward or another similar event occurs, be sure to have the injectors unplugged electrically. Then turn the key on to run the fuel pump and see if the injectors dump fuel with them still unplugged. Ohm the injectors to make sure they are of proper resistance (approximately 1.5 ohms). Low-resistance injectors can damage the ECU. Try putting noid lights in place of the injectors and crank the engine, making sure the noid lights flash. Manually operate the injectors with the injector harness disconnected, by jumping power and ground. Make sure both injectors work. Be careful not to operate the injectors for more than a split second. Replace the injectors as necessary with the new ECU.
Fuel Pump ReplacementPosted 10/7/1999By Paul Mensink
Vehicles: 1986-1988 Taurus/Sable 2.5L Problem: Incorrect fuel pump replacement. Test and Fix: Verify fuel pump dead-head pressure by pinching the return line or hooking the pressure gauge in at the fuel filter without an outlet for fuel flow. When the ignition switch is cycled, the dead-head pressure of the pump will be shown. The dead-head specification on the 2.5L fuel pump is 25-35 psi, and is in excess of 100 psi on the 3.0L. If the dead-head pressure is too high, the correct pump for the vehicle will need to be obtained to resolve the rich running condition. Background: The 2.5L CFI engine Taurus has a nominal fuel pressure of 14-17 psi on 1986-1988 models. If fuel supply pressure (dead-head specification) is significantly higher than normal, the fuel pressure regulator will not be able to regulate pressure low enough for the PCM to still control the mixture through pulse-width. When the PCM makes an attempt to control the mixture with the minimum pulse width allowed per sensor value inputs, the car will still run rich because the high pressure will force that much more fuel through the injector. Most likely the factory-installed fuel pump has been replaced at some point with an incorrect part application. The 1989-1990 model 2.5L CFI also runs a high pressure system with the same dead-head pump pressure rating as the 3.0L. Paul Mensink is ASE master and L1 certified. He is an IDENTIFIX Ford specialist with 18 years of experience. In 1990, he worked for Bear on the development of the "FlowChart" diagnostic software.
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