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Old 08-02-2012, 11:47 AM   #1
chewbakarox
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Default Testing Fuel Pump for Power

I'm having trouble starting my car and have narrowed it down to the fuel pump (SEE THREAD). I want to determine if it's a mechanical issue with the pump or an electrical issue. Before I replace the pump I wanted to test at various places along the fuel pump circuit.

I found the following wiring diagram for my '03 (LINK). My assumption is that I should start at the FP assembly, then move to the FP controller, then the FP relay, then the ECU. Wouldn't that be the best process of elimination?

Also, how would I test each item with my multimeter? Am I just checking for 12V when I crank the engine, or do I need to check resistance? I'm a newbie with the multimeter. TIA.
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Old 08-02-2012, 06:28 PM   #2
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TTT...anyone?
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Old 08-02-2012, 07:56 PM   #3
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I would first check to see if voltage is getting to the blk/yel wire on the pin 10 of the controller. If that is good then you could move on towards the fuel pump. If you don't have power there then you move towards the power source. It is usually always best to check for voltage first when checking problems like this. Once you pin down the trouble area you can check resistances. You must remove power from the circuit when you check resistances.

Be aware that power for the pump after the controller is only on for a couple of seconds when the iginition is turned on and the engine doesn't start.
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Old 08-02-2012, 08:19 PM   #4
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Quote:
Originally Posted by Cougar4 View Post
I would first check to see if voltage is getting to the blk/yel wire on the pin 10 of the controller. If that is good then you could move on towards the fuel pump. If you don't have power there then you move towards the power source. It is usually always best to check for voltage first when checking problems like this. Once you pin down the trouble area you can check resistances. You must remove power from the circuit when you check resistances.

Be aware that power for the pump after the controller is only on for a couple of seconds when the iginition is turned on and the engine doesn't start.
Thanks Cougar. I have a clarification....on the FP (not the FP controller), do you know what the difference is between pin 1 and pin 4? Is one for priming and one for after the car is started? Or is one power and one ground?
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Old 08-03-2012, 01:41 AM   #5
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OK, did some digging tonight and got some weird results. Checked for power at the fuel pump harness, got nothing. Checked for power at the fuel pump controller harness, got nothing. Moved on to the fuel pump relay.......

I have 12V constant at pin #2. When turning the key 2 clicks to "on", I get about 1 volt at pin #1. So the ECM is sending something to the relay, but it is only 1 volt.....WTF? Does anyone know what this means? Please help!!
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Old 08-03-2012, 10:13 AM   #6
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replace the relay then get back to us, I had my relay go bad around 115000 miles.

Keep in mind the relay may only be actuated by a couple volts from the ecu.

Last edited by sorrowfulkiller; 08-03-2012 at 10:23 AM.
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Old 08-03-2012, 12:01 PM   #7
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Originally Posted by sorrowfulkiller View Post
replace the relay then get back to us, I had my relay go bad around 115000 miles.

Keep in mind the relay may only be actuated by a couple volts from the ecu.
Ahhhh....that's encouraging. When I saw only 1 volt I thought my ECU might be fried. I will try replacing the relay and keep my fingers crossed. Thanks for the response.
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Old 08-03-2012, 11:28 PM   #8
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Well after looking at the diagram I noticed something. If you will notice, the wire that goes to the relay coil and ECU is also tied to fuse 11 at the top of the page. Since you only saw 1 volt there it means the fuse is blown. It is not certain yet why it blew. That fuse is in the dash panel I believe. As a note, the relays in the car usually always use 12 volts to power the coil.

Last edited by Cougar4; 08-03-2012 at 11:39 PM.
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Old 08-08-2012, 02:00 PM   #9
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Originally Posted by Cougar4 View Post
Well after looking at the diagram I noticed something. If you will notice, the wire that goes to the relay coil and ECU is also tied to fuse 11 at the top of the page. Since you only saw 1 volt there it means the fuse is blown. It is not certain yet why it blew. That fuse is in the dash panel I believe. As a note, the relays in the car usually always use 12 volts to power the coil.
Cougar - I checked Fuse 11 and it was OK. I'll triple check it tonight. But if the fuse were blown, wouldn't it mean zero voltage should show up at the relay? Why would I only get 1 volt?
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Old 08-08-2012, 04:37 PM   #10
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Assuming you are making the voltage measurement using ground as your reference; you are not understanding the wiring diagram correctly. The drawing shows the fuse 11 is directly connected to a number of things including the coil of the relay, with the other end of the coil tied to ground. When the ignition is turned on power comes through the fuse and turns on the relay. There should be 12 volts on the wires tied to that fuse. Either the fuse is bad or there is a open connection between the fuse and the relay coil. Use your meter to see if you have 12 volts on both sides of the fuse, using the slits on top of the fuse to put your probe on and using ground as your reference point for the meter. If there is 12 volts on both sides of the fuse then check the back side of the fuse panel and see if there is a bad connection to the output of the fuse connection. If that is ok then there is a open wire connection between the fuse panel and the grn/red wire going to the relay.

Edit:
Refering to your question about the 1 volt reading you saw. If the only thing that fuse supplied power to was the relay coil and the fuse was blown your meter would show zero volts. The thing is that the fuse is tied to other things, which includes the ECU. We don't know how things are designed inside the ECU but chances are that something inside the ECU is back feeding the 1 volt unto the lead. It really doesn't matter what is causing it, you just need to understand Ohm's Law explains why that sort of thing happens.

Last edited by Cougar4; 08-08-2012 at 04:54 PM.
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Old 08-08-2012, 06:44 PM   #11
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Quote:
Originally Posted by Cougar4 View Post
Assuming you are making the voltage measurement using ground as your reference; you are not understanding the wiring diagram correctly. The drawing shows the fuse 11 is directly connected to a number of things including the coil of the relay, with the other end of the coil tied to ground. When the ignition is turned on power comes through the fuse and turns on the relay. There should be 12 volts on the wires tied to that fuse. Either the fuse is bad or there is a open connection between the fuse and the relay coil. Use your meter to see if you have 12 volts on both sides of the fuse, using the slits on top of the fuse to put your probe on and using ground as your reference point for the meter. If there is 12 volts on both sides of the fuse then check the back side of the fuse panel and see if there is a bad connection to the output of the fuse connection. If that is ok then there is a open wire connection between the fuse panel and the grn/red wire going to the relay.

Edit:
Refering to your question about the 1 volt reading you saw. If the only thing that fuse supplied power to was the relay coil and the fuse was blown your meter would show zero volts. The thing is that the fuse is tied to other things, which includes the ECU. We don't know how things are designed inside the ECU but chances are that something inside the ECU is back feeding the 1 volt unto the lead. It really doesn't matter what is causing it, you just need to understand Ohm's Law explains why that sort of thing happens.
Cougar - Again, thanks for helping me troubleshoot this. I'll check voltage at Fuse 11 tonight. Do you think there is a chance that my ECM is the culprit? Or would this purely be a fuse/open connection issue?
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Old 08-08-2012, 09:02 PM   #12
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UPDATE: I replaced the relay, no luck. I checked for voltage at Fuse 11 and I am getting one volt. I checked the fuse for continuity and it is good to go. Must be a problem upstream between Fuse 11 and the battery? HELP!!

If I don't get this solved soon I am going to have to take the car to the shop, which I am terrified of.
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Old 08-08-2012, 10:36 PM   #13
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Well if you have 1 volt on both sides of the fuse then you are correct, the fuse is ok and power isn't getting to it for some reason. I assume you are turning on the ignition switch when you check the voltage. Check fuses 6, 17, and 18 and see if they have voltage on them. They are on the same bus as fuse 11 and power from the ignition switch supplies the power to all of them. If all those fuses don't have 12 volts on them then the ignition switch is the next suspect or the wiring in between those points. I assume the warning lights at least turn on when you turn on the ignition switch.

Last edited by Cougar4; 08-08-2012 at 10:47 PM.
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Old 08-09-2012, 12:48 AM   #14
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Quote:
Originally Posted by Cougar4 View Post
Well if you have 1 volt on both sides of the fuse then you are correct, the fuse is ok and power isn't getting to it for some reason. I assume you are turning on the ignition switch when you check the voltage. Check fuses 6, 17, and 18 and see if they have voltage on them. They are on the same bus as fuse 11 and power from the ignition switch supplies the power to all of them. If all those fuses don't have 12 volts on them then the ignition switch is the next suspect or the wiring in between those points. I assume the warning lights at least turn on when you turn on the ignition switch.
Yup, I was testing Fuse 11 with the ignition to "on". I checked Fuses 6, 17, and 18 with the ignition "on" and had zero volts. I hadn't even notice before, but I'm not getting any lights on my dash on ignition either.. So it must have to do with my ignition....

Any pointers where to start? Thanks again.
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Old 08-09-2012, 09:39 AM   #15
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We do have some pointers. Since it appears that the ignition switch isn't getting any power check fuse SBF-4 in the panel under the hood and see if it is blown out. If it is ok then see if voltage is getting to it. If you have no voltage there also then most likely the main fuse, SBF-1 is blown out. If fuse SBF-4 has voltage getting to it then there is a problem between the fuse and the output side of the ignition switch.

Whenever you have power problems like this the first thing to do is check all the fuses for a problem.
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Old 08-09-2012, 02:43 PM   #16
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Quote:
Originally Posted by Cougar4 View Post
We do have some pointers. Since it appears that the ignition switch isn't getting any power check fuse SBF-4 in the panel under the hood and see if it is blown out. If it is ok then see if voltage is getting to it. If you have no voltage there also then most likely the main fuse, SBF-1 is blown out. If fuse SBF-4 has voltage getting to it then there is a problem between the fuse and the output side of the ignition switch.

Whenever you have power problems like this the first thing to do is check all the fuses for a problem.
Cougar - I checked SBF-4 and the fuse is fine. I am getting 12 volts there as well. As you were saying, it must be an issue between the fuse and ignition switch. I have an after market alarm installed so perhaps that is causing it. Any pointers on where to start testing? TIA.
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Old 08-09-2012, 05:14 PM   #17
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Since the fuse is ok check the voltage on the white wire it supplies power to on the fuse panel and make sure that there is connection to that point. If that is ok then you need to check the white wire going to the input side of the ignition switch. If you have voltage at that point then the green output wire of the ignition switch needs to be checked for voltage with the switched turned on. If you have no voltage there then the switch is bad.

Your mention of the alarm system brings up a point to consider. Normally an alarm system might cut off power to the ignition system and not all power, but in this case it appears all the power from the ignition switch is being interupted somehow. If the alarm system was wired in with a relay to cutoff the white wire power lead to the ignition switch then that relay would have to be removed and the power wire connections spliced together.

Last edited by Cougar4; 08-09-2012 at 05:35 PM.
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Old 08-09-2012, 07:43 PM   #18
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Quote:
Originally Posted by Cougar4 View Post
Since the fuse is ok check the voltage on the white wire it supplies power to on the fuse panel and make sure that there is connection to that point. If that is ok then you need to check the white wire going to the input side of the ignition switch. If you have voltage at that point then the green output wire of the ignition switch needs to be checked for voltage with the switched turned on. If you have no voltage there then the switch is bad.

Your mention of the alarm system brings up a point to consider. Normally an alarm system might cut off power to the ignition system and not all power, but in this case it appears all the power from the ignition switch is being interupted somehow. If the alarm system was wired in with a relay to cutoff the white wire power lead to the ignition switch then that relay would have to be removed and the power wire connections spliced together.
Cougar, where is the white wire at the fuse panel you are referring to? Are you talking about the fuse panel under the hood or under the dash? I can't locate anything. Thanks for all the guidance.
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Old 08-09-2012, 09:20 PM   #19
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The white wire will connect to the output side of fuse SBF-4 in the panel under the hood. It goes to the ignition switch input.

While checking the wire at the ignition switch see if you can find any signs that the wiring has been modified. Chances are that if something has been done it will be near that area.

Last edited by Cougar4; 08-09-2012 at 09:26 PM.
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Old 08-10-2012, 01:16 PM   #20
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Quote:
Originally Posted by Cougar4 View Post
The white wire will connect to the output side of fuse SBF-4 in the panel under the hood. It goes to the ignition switch input.

While checking the wire at the ignition switch see if you can find any signs that the wiring has been modified. Chances are that if something has been done it will be near that area.
Thanks. I will do this tonight. I was inspecting the ignition output wiring and there have definitely been some modifications done with the alarm. Assuming the white wire to the ignition input is good to go, what would be the easiest way to check for power/continuity with the ignition output wires? Also, which ignition output wires would need to be checked (only the green)?
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Old 08-10-2012, 11:31 PM   #21
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USe your voltmeter to make all the tests. You will either have full voltage before or after the switch or something less. You should see the same amount of voltage you saw at the fuse if things are okay at the point you are testing. On the output side of the switch the green wire is the only one you need to check.

If you see something has been done to the white wire for the alarm system then you will need to remove the mod and splice the white wire back together.

Last edited by Cougar4; 08-11-2012 at 11:56 AM.
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Old 08-11-2012, 01:38 AM   #22
chewbakarox
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Cougar, you are the man. To close this out, it turns out the alarm was the culprit. I was getting voltage on the ignition all the way to the alarm brain but not out of it. The ignition kill on my Clifford alarm somehow fried. I unspliced the alarm and got her started tonight. Kind of a bummer that my alarm doesn't work anymore but at least the car runs.

THANK YOU FOR ALL THE HELP IN GETTING THIS SOLVED!
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Old 08-11-2012, 11:59 AM   #23
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You're welcome for the help. Glad to hear you got the car running again. You also gained some good experience on how to chase down electrical problems.
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