Fuel pump not working

Tiny
RICKYROMA
  • MEMBER
  • 1998 PONTIAC FIREBIRD
  • 3.8L
  • V6
  • RWD
  • AUTOMATIC
  • 114,000 MILES
There was no fuel pressure at all in this car, I replaced fuel filter, new fuel pump.
Fuse is good and relay is good. However, no fuel pump prime at all. I tested the relay circuit and I get twelve volts. The fuse circuit it jumps erratically. I test the fuel pump connector and only get five volts. Battery is new by the way.
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Thursday, May 18th, 2017 AT 2:46 PM

14 Replies

Tiny
CARADIODOC
  • EXPERT
You need to specify exactly where you are finding these voltages, the wire colors, and whether or not that is while a helper is cranking the engine.
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Thursday, May 18th, 2017 AT 6:27 PM
Tiny
RICKYROMA
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Ignition key on engine off, under hood fuel pump Relay circuit voltage 85 and 86 side has 12.6 volts. While the 87 and 30 has has four volts.
Fuel pump three wire connector, gray positive outside wire to other ground outside wire gives five volts. I also tested resistance between these two wires and it has 50 ohms. All this with key on engine off no cranking. If I am not mistaken I should get twelve volts.
I cant even hear fuel pump priming.
Under hood fuel pump relay works I tested it as well as the fuse.
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Thursday, May 18th, 2017 AT 7:21 PM
Tiny
CARADIODOC
  • EXPERT
The fuel pump relay should only turn on for one second when you turn on the ignition switch, then not again until the engine is rotating, (cranking or running). At this point I think that is irrelevant because you already found a clue in the pump does not run for that one second, and you are missing a voltage. If you have a helper turn on the ignition switch, you should be able to feel the relay click on, then off.

Your relay numbers do not match what is on the wiring diagram. You listed numbers used with Chrysler relays, and I am very familiar with them. You found twelve volts on 85 and 86. Those are for the relay's coil. The engine computer grounds 85 to turn the relay on. These two voltages are normal for now.

At issue is the four volts on terminals 30 and 87. I suspect your meter is picking up stray voltage and you actually have
zero volts there. To prove my suspicion, measure those terminals with a test light while you have the voltmeter there too. If connecting the test light takes it down to zero volts, that zero volts is the accurate reading. My reason for thinking this is there cannot be any voltage on the line going to the fuel pump, at least if the relay is out of its socket or if the relay is turned off.

If you really do have four volts on terminal 30, there has to be a broken wire with a carbon track inside the insulation, or a corroded connection. Start by looking at the 15-amp fuel pump fuse. If it is not blown, measure the voltage on its two test points. If you have twelve volts there, it should be at the relay, terminal 30, too. If that is not correct, the wire between them has a break in it.

If you have zero volts on the fuse, I will have to study the diagram to see where to look next. Most likely there would be a break inside the fuse box. Also be aware that related to my corroded connection comment, GM was famous during this time period for experimenting with aluminum wiring. They were attached with brass rivets to the buss bars in the fuse boxes. Add salt from your feet, or when driving in salt, and moisture, and two different metals, and you have a battery. Specifically that causes "galvanic action", which is a fancy name for corrosion. Also, it is never acceptable to pierce a wire's insulation to take a voltage reading. When that is done to a copper wire, it can be expected to corrode through in a few years. Do that to an aluminum wire, and it will corrode through in a few weeks. The powder left behind can conduct enough current that a digital voltmeter can pick up some voltage further down the line. You will not get enough current through that powder to run a test light. That is why I suggested measuring terminal 30 with the voltmeter and the test light at the same time.
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Thursday, May 18th, 2017 AT 10:10 PM
Tiny
RICKYROMA
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Actually I was wrong. With the key in the on position, I only have 4-5v on the 85 relay side that comes straight from the computer. I tryed something, I cut the 85 wire and spliced it to the ign relay positive wire for when the key turns on to get a full 12v on the original 85-86 fuel pump relay circuit, sure enough the fuel pump kicked on and I have 50 psi at the rail. But Why would I only get 5v on the computer to relay 85 wire? Could the computer be bad? I have never heard tjis car run. Whats worse is that with the fuel pressure is good and I still have a crank no start situation. Any help will be appreciated thanks caradiodoc
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Tuesday, May 23rd, 2017 AT 6:57 AM
Tiny
RICKYROMA
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I have noticed that spark is there, im not sure if injector pulse is there
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Tuesday, May 23rd, 2017 AT 8:36 AM
Tiny
HMAC300
  • EXPERT
Try another key first it may be security system holding you up. Then have a mechanic scan for codes to verify it. Auto parts scanners don't work on this part of car only engine/trans.
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Tuesday, May 23rd, 2017 AT 9:45 AM
Tiny
RICKYROMA
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I have no injector pulse at all can you guide to find rhe reason why? At least a schematic from yohr database?
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Tuesday, May 23rd, 2017 AT 10:09 AM
Tiny
CARADIODOC
  • EXPERT
If you found 5 volts on relay terminal 85 with that relay out of the socket, you're seeing the 5 volts the Engine Computer puts there to check if that line is shorted to ground. With the relay in the socket, you should see 12 volts coming from terminal 86, then through the relay's coil. The computer will ground that wire when it wants the relay to turn on.

I'm confused as to what you did because you need 12 volts on 86 only, and 0 volts on 85 to make the relay turn on. It sounds like you applied 12 volts to both 85 and 86. That can't work because you need the 12 volt difference between the two terminals.
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Tuesday, May 23rd, 2017 AT 4:16 PM
Tiny
RICKYROMA
  • MEMBER
What do I do about the non injector pulse? The fuel pump runs now but I am getting no injector pulse whatsoever. I checked with a testlight. I am seeing something weird, on the fuse box where the both the inj1 and 2 fuses are, one of them has 2 pink wires, the other fuse has no wires underneath it at all. Is it supposed to be that way or did someone rip em out and for what reason would someone do that. Again I am getting no injector pulse at all on both banks. Thanks caradioac over
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Tuesday, May 23rd, 2017 AT 4:33 PM
Tiny
CARADIODOC
  • EXPERT
Go to any fuel injector and measure the voltage on the pink wire. You should find 12 volts with the ignition switch in the "run" position.
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Tuesday, May 23rd, 2017 AT 4:50 PM
Tiny
RICKYROMA
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Is there a way you can show me on a diagram or description on where exactly the injectors ground at? And where the positive pink wires come from, the battery?
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Wednesday, May 24th, 2017 AT 4:24 PM
Tiny
CARADIODOC
  • EXPERT
The pink wires feeding the injectors come right from the ignition switch, which is different that on most cars. Go right to any injector and check for that 12 volts when the ignition switch is on.

To turn the injectors on, the ground side gets grounded by the Engine Computer. It pulses them when it sees signal pulses from the crankshaft position sensor and / or camshaft position sensor. I don't know how your car compares, but on other models if either of those signals are missing, you won't have spark either.
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Thursday, May 25th, 2017 AT 8:05 PM
Tiny
RICKYROMA
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Crank sensor is mostlikely fine since I do have spark. However with a noid light across the injector terminals, I get no pulse at all. The power side of the injector has 12 volts, but the ground is not right. Is it safe to say the ecu is faulty? Thank you so much brother for all your help I greatly appreciate it
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Thursday, May 25th, 2017 AT 8:33 PM
Tiny
CARADIODOC
  • EXPERT
On some models, the crank sensor signal triggers one thing and the cam sensor signal triggers the other. On some, one signal will become a back-up signal when one is missing, but some engines will continue to run with a missing sensor signal, but once stopped, they won't restart. There's a lot of variations, and I don't want to tell you the wrong thing when I don't know the specifics of your model.

To add to the misery, fault codes don't always set right away for one of those sensors with a missing signal. It may be necessary to connect a scanner to view live data and see if the computer is seeing those signals.

The scanner will also let you command the computer to pulse the injectors. You will be able to hear them clicking when your head is under the hood. If you hear that, it proves the circuits are good and the driver circuits in the computer are good. At that point checking for a missing sensor signal becomes the thing to do.
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Thursday, May 25th, 2017 AT 8:59 PM

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