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Discussion Starter #1
Since you bought the service manuals...


Can you tell me the purpose of that big resistor that is next to the ECU box (under the hood)?

On the battery side of the car is a big resistor (with heat sink) that I found was for the daytime running lights.

On the driver side of the car (next to the ECU box) is another heat-sinked resistor but I do not know the function.
 

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That's the fuel pump resistor. It's supposed to measure at 0.30-0.35 ohms of resistance at 20 deg Celsius.
 

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Discussion Starter #3
Thats weird - I unplugged it (just for a moment) and the car kept running !?!
 

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Discussion Starter #4
I wonder why they need it. None of the cars I have owned before needed a fuel pump resistor...

That isn't very much resistance... Maybe it is designed to vary the voltage given to the fuel pump under different temperatures? So when it is really cold outside the fuel pump gets more voltage?

I dunno. Weird.
 

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Here's the answer:

"The fuel pump speed is controlled at 2 steps (high speed, low speed) according to the condition of the engine (starting, light load, heavy load).
When the engine starts, the ECM turns the fuel pump relay OFF to operate the fuel pump at high speed. After the engine has started, during idling or when the load is light, the ECM turns the fuel pump relay ON to operate the fuel pump at low speed. When the intake air increases (heavy load), the ECm turns the fuel pump relay OFF to operate the fuel pump at high speed."

Basically, there are two circuits running in parallel to the fuel pump. One branch has the resistor and the other branch has a switch (fuel pump relay). At idle or light load, the switch is open and the circuit is completed through the resistor. When you start the car or encounter a heavy load, the switch is closed, and the circuit bypasses the resistor. If your car was idling, you should have disrupted the circuit and the fuel pump should have shut off. Perhaps the ECU compensated by switching to the high-amp circuit and registered an OBD II DTC code.


[This message has been edited by DtEW (edited November 27, 2000).]
 

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Discussion Starter #7
Thanks for the info - it makes sense to me now.

I wonder if the ECU has to modify the fuel injector pulses based on the expected fuel pressure differences?

Or maybe the fuel pressure regulator always delivers the same fuel pressure, and the pump just slows down a bit when it isn't expecting much flow to the injectors...

Sortof complicated, but it sounds like they had a good idea. It probably reduces noice (FI fuel pumps can be noisy) as well as extending the life of the fuel pump.
 

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Right. There fuel pressure remains at a constant 44-50psi, because the regulator relieves the constant state of slight overpump. The two-speed fuel pump makes sure the overpump is only slight at all times.


[This message has been edited by DtEW (edited November 28, 2000).]
 
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