Power to fuel pump?

[fechko]

I have a 99 GTP. It ran fine and the wife shut it off at the story and it would not start. It would turn over and try to sputter for a second and now it just turns over without firing. I had it towed to my house and that I would give it a try. Fired right up. I shut it off and tried it again. Fired up again. I thought i would wait til morning and take a look at it. Now it just turns over again without firing. I tried bending the tab on the resister as previously stated but nothing. I checked the fuel pump and it is not turning on. Is there a way I can see if it is getting power? Or any other options?
Thanks for the help.

[brcidd]

If you can't hear the pump (with your ear to the filler tube)- then have the wife try to start it while you whappp the bottom of the gas tank with your clenched fist- the pump will probably run until you shut the car off-- this is a true sign of a need for a new pump-- but it gets you to where you want to move it to work on it--- Heck I saw a guy drive his truck for 4 months by the Whappppp method......but the diagnosis is easy now-- you'll know it is the pump and nothing else......

[fechko]

I ve got the access cover in the trunk off that exposes the fuel pump. I smacked the edge of the topo of the pump but nothing. I smacked the bottom of the tank with my hand and still nothing. Can power be checked with a test light at the fuel pump? Which wire?

[brcidd]

It would be the gray wire-- it should be energized for 2 seconds after ignition is "on" and always during "start"- and always while there are ignition pulses (engine running)

[fechko]

OK. I ve no power to the 4 wire plug with larger size wire. I have power to the 3 wire plug to the gray and black wire with smaller wire. What do you think?

[fechko]

Also the small fuse checked out ok.

[brcidd]

the gray wire is what powers your fuel pump-- the black is its ground wire- if you have 12 volts across them- with it plugged in- your fuel pump should be humming- if not- time for a new pump.........

[fechko]

What I did was disconnect the plugs, stuck the test light in the plugs. Therefore bypassing the fuel pump. Which means the pump is not getting power. Is there another way to check if the pump is getting power?
Thank You.

[brcidd]

You can double check your circuit by putting 12v to the fuel pump primer terminal in the underhood accessory wiring junction box. This bypasses the ECM controls and runs the fuel pump full time- then you can check back at the gas tank if the 12v is present constantly- I have included the fuel pump cicuit description below for you to ponder as well... good luck

Circuit Description
When the Ignition switch is first turned ON, the PCM energizes the fuel pump relay which applies power to the fuel pump through the high speed circuit (controlled by the fuel pump speed control relay). The fuel pump relay will remain ON as long as the engine is running or cranking and the PCM is receiving reference pulses. If no reference pulses are present, the PCM de-energizes the fuel pump relay within 2 seconds after the ignition is turned ON or the engine is stopped. The fuel pump delivers fuel to the fuel rail and injectors, then to the fuel pressure regulator. The fuel pressure regulator controls fuel pressure by allowing excess fuel to be returned to the fuel tank. With the engine stopped, the fuel pump can be turn ON by using the scan tool output controls function.

The PCM alters fuel pump speed by energizing the fuel pump speed control relay Under normal conditions, the fuel pump control speed control relay is energized (normal fuel pump speed). The applied voltage to the fuel pump is controlled by a resistor assembly. When higher fuel volume is required due to increased engine load (MAP sensor value over 90 kPa). the PCM de-energizes the fuel pump speed control relay circuit. The increased voltage to the in-tank fuel pump allows a higher volume of fuel to be delivered to the fuel rail. The PCM also compensates for low system voltage by energizing the fuel pump speed control relay.

Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed through the wire insulation or a wire broken inside of the insulation.

Check for a poor connection or a damaged harness. Inspect the PCM harness and connectors for the following items:

Improper mating
Broken locks
Improperly formed or damaged terminals
Poor terminal to wire connections
Damaged harnesses

[BNaylor]

Why are you checking both electrical connectors at the fuel pump pod? Only one provides power to the fuel pump which also contains the wires for the fuel tank level sensor. The other connector is to the tank pressure sensor used for evaporative emissions control.

Have you tried swapping the fuel pump relay with the fuel pump hi-speed relay?

It might help to use a service manual with wiring diagrams and proper test equipment like a DMM.

[fechko]

Which plug would the power be in? The 3 wire plug with small wires or the 4 wire plug with larger wires?

[BNaylor]

Are you referring to the electrical connectors on the fuel pump pod? Since you have a '99 GTP your fuel pump pod top should look like this below. The right connector for fuel pump is the one at the top in the pic. Not the bottom one which only connects to the tank pressure sensor which is irrelevant. As pointed out the gray wire should be hot - up to 12 volts from the fuel pump and speed control relays.

[fechko]

With that terrific explaination, I have determined I DO have power to the fuel pump. But the pump is still not turning on. Is there another possible cause or is it for sure the pump? Any other checks that could be done?

[fechko]

Well, I was spraying off the top of the fuel pump to get ready to replace it, I thought I would spray the connectors clean, plug them in, gave the top of the pump a tap or 2 with a rubber mallet. Sure enough, pump turned on and started right up. I drove around a while and parked it back in the garage. I figure I will leave it in the garage and keep trying to start it for a while. That way I should know if it is the pump (which I figure it is) or just dirty connectors. Thanks all for the help!

[brcidd]

Basically you just did the Whappp test- which proves it is the fuel pump motor....what are you waiting on? change it out--- you sure are not going to make any money on this job- putting this much time into it- Ha Ha.....by the time you do your tenth job- you will have it down- to where once the whappp makes it run- you now drive the car into your bay (garage) and change the pump pronto....

Heck I have had them come off the flatbed- then go out and jumper the fuel pump prime lead- then whapppp the tank-- then drive them up the hill into the garage-- all before the tow driver leaves- he laughs - because he towed the car because the "car doesn't run" . Sometimes I go to where the vehicle is- and whapppp it- then drive it home---

If the whapppp test doesn't work- Sometimes I take my homemade "fuel caddy" with me- which is a high pressure fuel pump in a bucket- sealed with 3 gallons of gas inside- and a 12v cigarette lighter plug- then I attached the 10 ft pressure hose to the fuel pressure test port- and plug in my "caddy" the vehicle will start and run on my "auxillary" pump- allows me to move it- or drive it home- and proves to me it is the pump that is at fault. The only thing weird is that the fuel gauge goes up instead of down as I drive- because the excess fuel is routed back into the vehicle's tank. you always have to be extremely careful when dealing with fuel flow though.....

Once the vehicle is in position- I will use the whappp test to pump out the fuel- through the test port into either another car- or into gas cans- especially if I have to drop the tank.....it all depends on the vehicle-- any chevy S-truck pick-up, I will "hang the bed" - just 6 or 8 bolts and you can sit upright and change the pump...