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Old 08-27-2003, 10:51 PM
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Default bench testing a fuel pump

On the way to work yesterday the Jeep died. After getting it towed home and diagnosing the problem I've come to the conclusion it's the fuel pump. Here's my evidence:

1. I don't hear the familiar buzz when I turn the key - (the pump priming)
2. I relieved the pressure from the fuel rail. It doesn't pressurize again.
3. I'm getting the voltage pulse at the pump on ignition.
4. I've got good spark.

I'd bet my socks that it's the fuel pump but the cost of a new one is about 300 bucks so I want to be absolutely positive. I dropped the tank and pulled the pump unit. I momentarily tested it with my battery. I can hear a relay clicking, but again no familiar buzz. Is there anyway I can reliably bench test the pump before I drop $300. I know some will say I should buy a used one but based on the fact that there is substantial labor involved with pulling the tank, I think I'd rather go new and be sure. Opinions?

-JL
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  #2  
Old 08-28-2003, 08:35 AM
tom3
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Default Re: bench testing a fuel pump

Not sure of the exact type of pump in the 91 but those pumps weren't so good, most fail at about 90K miles or so. Really shouldn't be that expensive, say 40 dollars with new suction strainer. Later models with high pressure EFI are a whole different matter.Check Autozone or Advance Auto on the web for prices if you want. Doesn't hurt to drop tank and clean it up every now and then anyway.
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Old 08-28-2003, 09:46 AM
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Default Re: bench testing a fuel pump

Looked at autozone for you. If is has enclosed terminals, it's $95. If it has exposed terminals, it's $78. Both with lifetime warranty.
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Old 08-28-2003, 10:28 AM
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Default Re: bench testing a fuel pump

A buddy had one die just like that. it was suggested by a certified D-C wrench to either give the tank a good kick [img]images/graemlins/laugh.gif[/img] or whoop it with a baseball bat [img]images/graemlins/shocked.gif[/img]. Chances are the pump will begin to function again long enough to diaganose it as the problem... [img]images/graemlins/smirk.gif[/img]
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Old 08-28-2003, 10:38 AM
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Default Re: bench testing a fuel pump

The one in my wife's 93 YJ is going out as well. It quits once in a while and I have to give it a good smack on the side of the tank for it to start going again. [img]images/graemlins/spank.gif[/img] I still have to drop the tank to see what pump is in it before I go to the parts store. [img]images/graemlins/cussing.gif[/img]
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Old 08-28-2003, 12:15 PM
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Default Re: bench testing a fuel pump

1. Bench testing is simple.
2. Hook up the fuel pump to siphon into, and
3. Pump back into a can of fuel.
4. I use clear plastic tubing.
5. Then appy 12 volts to the pump.
6. I usually "Pluse" the pump with the 12 volts.
7. Also I dump a can of SeaFoam into the fuel..
8. It will help remove any gas varish build up in the pump.
9. Is this a reliable test?
10. Who knows...
11. It works for me...
12. But only tells you the pump is cycling,
13. Not how fast or what the pressure is at...
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Old 08-28-2003, 03:43 PM
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Default Re: bench testing a fuel pump

Thanks for the feedback. I ordered a new one. Will I pay too much. Yes. I guess I don't mind because I usually have pretty darn good karma when it comes to a cheap fix. I'll overpay once every 7 years or so. I'll update in a couple of days and let you know the result.

-JL
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Old 08-28-2003, 09:09 PM
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Default Re: bench testing a fuel pump

A word of warning. You should NEVER hook up any electric fuel pump to a 12 volt source without being completely submurged in fuel or something like SafetyKleen. It can explode like a hand-granade. Fuel vapors in the presence of air can create an explosive mixture. There should not be any reason to bench test a pump if properly diagnosed the first time in the tank. Hooking up a 100 lb. fuel pump in a open can of gasoline isn't the brighest thing to do. Get yourself an old set of R-12 guages, and hook them to the rail for pressure, and test volume on the return line.
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