for the ford maintenance experts.. can you answer this one....

There is an impact sensor and reset switch in the trunk (left side, IIRC, in my 97 CV) which gets tripped in the event of a rear end collision (even a mild one). A fireman told me once (jokingly, I think) that if I ever got kidnapped and thrown into the trunk, I could push the switch and it would kill the fuel pump. Is it possible something shifted in the trunk and hit the switch?

it's a 2001 police crown vic that won't start. replaced the fuel pump. didn't cure the problem. fuel pump relay is not energizing when the key is turned on. a check with the DMV shows no power at the fuel pump relay sockets on driver's side inner fender panel. so, here's the question - i have the prints for the crown vic, but can't find where it all starts at.... =A0 in other words. =A0 when you turn on the key, power should be applied to the ECU. =A0 now, is there where the signal starts at to supply power to the fuel pump relay pick up circuit, or is there something that i'm missing...??

It seems likely that the relay is controlled by the Engine computer. In some cars there is a another power source that runs thru the oil pressure switch.

That interrupts the power AFTER the fuel pump relay. If it was tripped the fuel pump relay would still have power.

it's a 2001 police crown vic that won't start. replaced the fuel pump. didn't cure the problem. fuel pump relay is not energizing when the key is turned on. a check with the DMV shows no power at the fuel pump relay sockets on driver's side inner fender panel. so, here's the question - i have the prints for the crown vic, but can't find where it all starts at.... =A0 in other words. =A0 when you turn on the key, power should be applied to the ECU. =A0 now, is there where the signal starts at to supply power to the fuel pump relay pick up circuit, or is there something that i'm missing...??

---- There is an impact sensor and reset switch in the trunk (left side, IIRC, in my 97 CV) which gets tripped in the event of a rear end collision (even a mild one). A fireman told me once (jokingly, I think) that if I ever got kidnapped and thrown into the trunk, I could push the switch and it would kill the fuel pump. Is it possible something shifted in the trunk and hit the switch?

=3D=3D=3D> thanks for the input, tim. the impact switch was one of the first items that i checked. it's not tripped and reads closed with the meter. i can't get power even to the impact switch. =A0 that is how i traced it back to the front of the car to the fuel pump relay. the relay is good. =A0 just no power to cause the relay to close. =A0 so, i'm wondering where does it get the signal from to energize the relay? =A0 also, the color of the wires are different coming off the fuel pump relay contacts that go to the impact switch. my thinking is that maybe there is something between those two points, because the colors of the wire should be the same if it was one run of wire.. ~ curtis

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It seems likely that the relay is controlled by the Engine computer. In some cars there is a another power source that runs thru the oil pressure switch.

=3D=3D=3D> is this a different relay than the pump relay? in other words= , does the ECU turn on a relay, that in turn, turns on the fuel pump relay?

~ curtis

knowledge is power - growing old is mandatory - growing wise is optional = "Many more men die with prostate cancer than of it. Growing old is invariably fatal. Prostate cancer is only sometimes so."

Have you checked fuse #1 in the battery junction box? Fuse #1 feeds 12 volts to terminal 30 of the fuel pump relay. it is a hot at all times feed.

Well, you are checking with a DMM... are you performing a proper volt drop test? Of are you just probing for volts? To be positive of our test accuracy and results, we need to load the circuits in question to verify their ability to carry enough current to perform the task.

Second... at key on, the fuel pump relay is only energized for about 1.5 seconds to 'charge' the fuel rail (bring it to operating pressure). Is it possible that the relay is "turning on" but you are missing the event?

IIRC, these cars have had their fair share of wiring concerns at the front apron... I would only feel comfortable with circuit testing that allowed loading the circuits properly...

Very true Jim, but load or no load, if there is NO voltage showing, there is a problem, However, just because a DVM DOES show power, without the load the reading COULD be meaningless.

I'm pretty sure that's the sequence. On my 92 explorer, when you turn the key to on the computer turns the fuel pump on (thru the relay) for

2 seconds and then shuts it off. That pressurizes the fuel rail. IF the relay fails, supposedly the oil pressure switch will power the fuel pump (presumably thru the relay) once cranking of the engine has built up oil pressure and closed the switch.

Yes... but we are still faced with the thought "is the power being checked when the circuit is commanded active? Or is the initial fuel pump command timing out before the measurement is made?"

If you read my statement carefully, you will see that I am trying to cover all situations because I simply have no idea of the OPs skillset, knowledge or experience. I look around at our shop and other shops that I visit... and I find that electrical is the single hardest thing for most people to grasp... When using the ohm-meter (shudder... a most overused feature that can get you into deep trouble) many experienced techs consistantly confuse "no ohms" with an open circuit.... Many techs try performing what they think a voltage drop test is without checking battery voltage first.... What doesn't help is the inappropriate test methods that Ford suggests in their very own PC/ED manual and the fact that most techs blindly follow these inappropriate test methods.

Not arguing with you Jim. Just clarifying that voltage drop due to poor connections not being caught will not be an issue that causes false FAILUREs. It can and will cause the uninitiated to think everything is checking out OK when it is not.

I also agree with you that the electrical diagnostics capability of perhaps the majority of mechanics in the feild is extremely weak, and the Ford perscribed PIN tests will have the inexperienced technician chasing his tail for hours in many cases.

The technician needs to know (understand) how the circuit is SUPPOSED to work, and why, before he can effectively troubleshoot problems with the circuit. They also need to understand basic electronics and the operation of simple test equipment.

Been doing it since 1969 on cars, and for the last 23 years on computers as well.