Fuel pump bad?

Tiny
JAYDAWG109
  • MEMBER
  • 1992 FORD MUSTANG
I have a 92 mustang and I think the fuel pump is bad, when I turn over the key you can hear the fuel pump kick on and it sprays good out of the valve on the fuel rail, but when I crank the car and hold the valve in on the fuel rail it barely drips out? It starts then shuts right back off?
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Sunday, September 23rd, 2012 AT 7:51 PM

23 Replies

Tiny
ASEMASTER6371
  • EXPERT
Sounds like the pump. You need at least 40 lbs for it to run.

Roy
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Sunday, September 23rd, 2012 AT 7:55 PM
Tiny
JAYDAWG109
  • MEMBER
Thanks, how can I check this?
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Sunday, September 23rd, 2012 AT 7:57 PM
Tiny
ASEMASTER6371
  • EXPERT
You can rent a tester at a parts store to verify

Roy
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Sunday, September 23rd, 2012 AT 7:59 PM
Tiny
CARADIODOC
  • EXPERT
You hear and see evidence that the pump is working so you think it's bad? Have you checked for spark during cranking?
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Sunday, September 23rd, 2012 AT 8:01 PM
Tiny
JAYDAWG109
  • MEMBER
Well, I just went out and cranked it, and it started and reved good for like 30 secs then it quit?
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Sunday, September 23rd, 2012 AT 8:04 PM
Tiny
CARADIODOC
  • EXPERT
Did ya check for spark after it quit?
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Sunday, September 23rd, 2012 AT 8:27 PM
Tiny
JAYDAWG109
  • MEMBER
Nuh uh, Should I?
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Sunday, September 23rd, 2012 AT 8:34 PM
Tiny
JAYDAWG109
  • MEMBER
The car ran perfect before this happened, I stopped at a gas station turned the car off, went in and payed for the gas came out an pumped it and when I tryed to start it, is started then went right off, would a fuel pump go out like this all of a sudden?
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Sunday, September 23rd, 2012 AT 8:51 PM
Tiny
CARADIODOC
  • EXPERT
Absolutely. If your left head light doesn't turn on do you replace it or do you check to see if ALL the lights are not turning on? You got stuck on the first thing you suspected, the fuel pump, but you never bothered to look further at other things in common with it. If a crankshaft position sensor quits intermittently, the Engine Computer will think the engine stopped rotating so it will turn off the fuel pump. Without the crank sensor's signal the computer doesn't know when to fire the ignition coil so you have no spark. The fuel pump and the lack of spark are the symptoms. They aren't the cause of the problem.

In this case there's actually four circuits; the fuel pump, the ignition system, the injectors, and what triggers them. You're spending your time in the fuel supply system, (which could be the one with the problem), but first you need to see if other systems are shutting down. That would tell you to look at what they have in common.

If you still have spark when the engine quits, then you know anything in common is not the problem and to diagnose the fuel supply system. One potential clue is if only the pump quits while driving the engine will typically surge and sputter for a few seconds before stalling completely. With an intermittently failing sensor the engine will usually stall abruptly. It may fire again for a few seconds as you're coasting to a stop, then stall again multiple times but loss of spark causes instant changes. Loss of only fuel pressure causes gradual loss of power over a few seconds. That can be hard for car owners to distinguish but it is one of the things experienced mechanics look for.
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Sunday, September 23rd, 2012 AT 8:53 PM
Tiny
CARADIODOC
  • EXPERT
Would really have been helpful to include those details right up front. The crankshaft position sensor is probably the first thing ASEMaster6371 would have suggested if he had known those secret details. What you're describing is exactly how crankshaft position sensors and camshaft position sensors fail. They become heat-sensitive and fail when a hot engine is turned off. Natural cooling air flow stops and the engine heat migrates up to the sensors. When we read through these forums we see the exact same complaints dozens of times per day except it could be the Post Office or the grocery store instead of the gas station.

Except for the very high failures on GM vehicles that suddenly let you sit on the side of the highway in a puddle of tears, fuel pumps don't typically fail once they've started running. They can produce low pressure but usually they fail to start up when you start the engine. If your engine runs for five or ten seconds or longer you know the pump is running.
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Sunday, September 23rd, 2012 AT 9:02 PM
Tiny
JAYDAWG109
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Ive called Oreillys and they said this 92 doesnt even have a crank shaft sensor listed?
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Sunday, September 23rd, 2012 AT 9:05 PM
Tiny
CADIEMAN
  • MEMBER
Will it run if u spray either in the valve body?
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Sunday, September 23rd, 2012 AT 9:10 PM
Tiny
JAYDAWG109
  • MEMBER
It is sparking after it quits
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Sunday, September 23rd, 2012 AT 9:16 PM
Tiny
JAYDAWG109
  • MEMBER
And it wont hardly hit with the intake off, I sprayed it in there and it tryed once but nothing after that, and when the fuel pump kicks on its real loud, like a humming, kinda like its a empty tank, but I kno its got a full tank
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Sunday, September 23rd, 2012 AT 9:29 PM
Tiny
JAYDAWG109
  • MEMBER
It will run as long as you spray gas in the intake
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Sunday, September 23rd, 2012 AT 9:45 PM
Tiny
CADIEMAN
  • MEMBER
U SPRAY THE INTAKE WHYLL SOME1 CRANKS THE CAR. DOES IT TRY AND START OR NOT? Check the fuel pump pressure like we asked.
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Sunday, September 23rd, 2012 AT 10:18 PM
Tiny
JAYDAWG109
  • MEMBER
It will run or TRY to run when my dad sprays that in the intake
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Sunday, September 23rd, 2012 AT 10:20 PM
Tiny
CADIEMAN
  • MEMBER
Then its a fuel problem. So check the fuel pump fuse and relay for voltage with a meter or test light. Try swapping the relay with another one in the panel to test.
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Sunday, September 23rd, 2012 AT 11:08 PM
Tiny
JAYDAWG109
  • MEMBER
Where is this fuse located? And this relay?
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Sunday, September 23rd, 2012 AT 11:14 PM
Tiny
CADIEMAN
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Use the owner manual for this. Go rent a gauge and give us the fuel pressure reading.
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Sunday, September 23rd, 2012 AT 11:43 PM

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