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Testing fuel pump

This is a discussion on Testing fuel pump within the External Engine forums, part of the LSx Technical Help Section category; I'm out the other for a cruise to the store, and the car was running great. I come out, hit ...

  1. #1
    Next... MrKid's Avatar
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    Testing fuel pump

    I'm out the other for a cruise to the store, and the car was running great. I come out, hit the key, and the car fires up then stalls. Try to start it again, and it just cranks. Right away, I'm thinking fuel pump.

    I swapped the relay with the one for the A/C-no help
    Checked all of the fuses-all good
    Checked for pressure-0
    Listened for the pump-nothing

    So I jumped right into it, and cut an access hole in the floor. After I removed the pump, I decide to check the wires. I know it's a bit late for that, but I don't' have the new pump yet, and had some time to kill. Even if the pump was good, I was going to upgrade to a Racetronix. I grounded the negative to the body, and probed all of the wires. All of my "hot" leads read 5 volts. Does this make any sense, or do I have some other issues going on? Or am I just testing it the wrong way?

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    No one? I just need to know how to test voltage at the pump itself.

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    Big Gulps, huh? HOBS's Avatar
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    I'm shitty with electrical but I'll take a crack. Was it 5 volts with the key on? If so no that doesn't make sense. You shouldn't have that drastic of a voltage drop.

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    It was with the key on. I did some searching, and after going through 10 different forums (of threads on testing that die a painful death with no answer), I found the pump only runs for 5 seconds until the other sensors see the engine as running. Seeing as 5 volts is signal/sensor voltage, I'm thinking this is the pump in standby? I ordered a Racetronix pump, which I wanted anyway. I'll through it in and see what happens. Thanks for the reply!

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    Big Gulps, huh? HOBS's Avatar
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    Welcome, hope that pump works for you. Throwing parts at problems can get expensive real quick.

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    Oh, I know it does. Like I said, I wanted to do the upgrade anyway. If it works, great. If not, no biggie.

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    Senior Member JayTA98's Avatar
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    the fuel pump harness supplies 12v to the pump when the car is running. if you just turn the key on you will see 12v for about 3 secs(priming). One way you can check to see if the harness is good and the pump . is to bypass the pump relay. you have to use a test light at the fuel pump relay plug and find out which 2 wires are the 12v from battery and the one going to the pump. Use a small piece of wire and jump the 2 terminals. If you hear the pump running (if it is plugeed in) then the harness is fine. If you don't hear the pump but have 12v at the harness(when testing at the 2 wires at plug harness) then the fuel pump is bad.

    since you are replacing the fuel pump anyway don't forget to put a new fuel filter. Also a clogged fuel filter can cause fuel pressure issue if the pump is working.

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    Thanks, Jay. This is exactly what I needed. So, if I put a jumper across the two 12v supply wires, I should see 12v from the plug at the tank?
    As for the relay, do I jump it at the fuse block under the hood, or do I have to jump it at the harness in the drivers kick panel? I couldn't find a straight answer anywhere for a '00.

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    Senior Member JayTA98's Avatar
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    Quote Originally Posted by MrKid View Post
    Thanks, Jay. This is exactly what I needed. So, if I put a jumper across the two 12v supply wires, I should see 12v from the plug at the tank?
    As for the relay, do I jump it at the fuse block under the hood, or do I have to jump it at the harness in the drivers kick panel? I couldn't find a straight answer anywhere for a '00.
    yes you will have 12v at the tank plug. For the jumper do it under the hood were the relay for the fuel pump is. Pull the relay out and using a test light check the terminals for the 12v from battery 1st. then find the one that comes from the ignition switch. another one should be ground and the last one is going to the pump. Then jump the 12v from battery to the fuel pump itself. It will immediately make the pump work. if it doesn't then check the 12v at the tank. If you have 12v then the pump is bad.

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    Got it. Thanks!

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    So I am having this issue now.. 2000 WS6, just pointing uut that this thread "died a painful death with no answer" so MrKid if you are still around, how did it work out? Pump? If I jump the relay under the hood "the one in the fuse box next to the identical AC Clutch relay" I don't hear the pump run... Traced it back to the connector over the axle, but didn't know which colors should be the Fuel Pump leads, wanted to test there before cutting the panel. This car has been in my garage for 5 years, being cranked every month or 2, until now, it just turns over and over, Spray into intake will allow it to run, no fuel pressure in Fuel Rails, so I think it is the pump, just died of old age sitting there. I wasn't clear if there was another relay on the 2000 model, as the older ones had the one in the kick panel...(and I have googled for hours)

    Thanks if anyone else sees this thread.

    Quote Originally Posted by MrKid View Post
    It was with the key on. I did some searching, and after going through 10 different forums (of threads on testing that die a painful death with no answer), I found the pump only runs for 5 seconds until the other sensors see the engine as running. Seeing as 5 volts is signal/sensor voltage, I'm thinking this is the pump in standby? I ordered a Racetronix pump, which I wanted anyway. I'll through it in and see what happens. Thanks for the reply!

  12. #12
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    You should be able to hear the pump run. Since you car has been setting for so long, it's possible your filter is all gummed up. Stupid question, but is there gas in the tank? Even if you treated the fuel with a stabalizer... that be some old gas in there. Also, by "cranked over" you mean you started and ran the car, right?

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    Viper, you're giving my flashbacks!I sold that car 2 years ago.

    The problem ended up being the harness that comes through the rear firewall behind the back seat. These are known to get gummed up, become loose, allow water inside and corrode. I did a Racetronix, direct wire conversion for my pump. Didn't have a single problem after that. Before you spend the money, check out that harness, though. You may need to clean it with some electrical spray. Also, pull each female plug from the harness (one at a time) and slightly squeeze the opening to make a tighter fit. If you see signs of corrosion, clean the harness, and put some electrical grease around the perimeter of the plug.

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