Non start issues, bad fuel pump?

crzyhrse99

Active Member
Mar 30, 2005
259
3
28
Kansas
99 GT 165K
Bolt-ons, stock fuel components

Last fall I picked up a beater and parked the stang for the winter. Still started it once a week and let it get to operating temps. Well about a month ago tried to start and it would just turn over. I pressed on the check valve on the fuel rail and had no fuel there, I checked te inertia switch in trunk and no problems there.

It had about an 1/8 tank of fuel in it so I thought I would put a few gallons in it and throw on a new fuel filter (cheap fix if I was lucky). Put on new MC filter and it started right up, running rough for about 2 min. then died. Same deal as before crank but no start.

I rechecked for fuel at the rails and all I got was a hiss of air. Has not thrown any codes, I havent heard the buzz from the fuel pump at all, have banged on the tank and no sound. Could I maybe have airlocked the lines by pressing the check valve?

I am a complete noob when it comes to ignition/fuel components, I basically know how to change the fuel filter and I know the pump is in the fuel cell....and thats about it.
 
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Can you get your hands on a scan tool or a fuel pressure gauge to monitor the pressure when you cycle the key like burns suggests?

Fuel pressure should be between 30-45 psi while your engine is running.
 
Well I did the the key cycling and never heard the pump buzz at all.

Can you get your hands on a scan tool or a fuel pressure gauge to monitor the pressure when you cycle the key like burns suggests?

Fuel pressure should be between 30-45 psi while your engine is running.
I have a DSP tuner but thats prob not what youre talking about, but if i'm not getting any fuel at the rails I wouldnt think I'm getting any pressure.
 
I was just thinking that the pump could be working, but you may not be hearing it. A scan tool or gauge could confirm.

If you suspect the fuel pump, the ideal place to start is the IFS (Inertia Fuel Shutoff) Switch in the trunk. First, make sure the red button is depressed. Then, check for 12 Volts out of the IFS switch with the key on. If you have 12 volts, it is likely that the fuel pump or FPDM is bad. If you do not have voltage with the key on, the problem is upstream (fuse, CCRM, etc.).

Post what you find.

EDIT: I just reread your first post and saw that you already checked the IFS switch. Did you already check for 12 volts coming out of it with the key on?
 
If you can't hear the fuel pump the first place to check is voltage coming into the IFS. If it's there, bypass the switch and see if the pump runs. If not, new fuel pump.
If the fuel pump runs bypassing the switch, replace switch. If there is no voltage there than go back to the fuses and relays. I carry around a couple long wires that I can clip on to various points and bypass circuits to determine where the problem with no voltage exists.
 
Allright got an update, the IFS switch is depressed and with the key on I am getting 12v. So at this point it looks like either the pump or the FPDM. And just to clarify I saw you highlighed out of the IFS, I pulled the harness off and tested the middle and right side facing the harness so is this correct? Guys I am a noob at this stuff so bear with me, I didnt even have a multimeter untill yesterday lol.

Thanks for the link bbayne, and everyone else for the comments. Now what should I test next, the FPDM?
 
You got a second person to lend an ear or a hand? Either you our your buddy. Turn the key on, an the other person take a screwdriver, a flatblade works better. An put the end on the gastank an the handle end in ya ear an listen an see If the pump is coming on. Sounds like a bum'd fuelpump.
You could actually put your ear to the tank? Kinda hard with the plastic fueltank cover on the bottomside? Did it with my foxbody. Now would be the time with as little gas is in there. Makes it easier to drop the tank. Less weight. I learned the hard way went an added 3/4 tank gas thinkin need new fuel. Nope.
Because you said you have 12v? You can recheck at the fuelhat on top of the tank when you drop it an unhook the harness?
 
You got a second person to lend an ear or a hand? Either you our your buddy. Turn the key on, an the other person take a screwdriver, a flatblade works better. An put the end on the gastank an the handle end in ya ear an listen an see If the pump is coming on. Sounds like a bum'd fuelpump.
You could actually put your ear to the tank? Kinda hard with the plastic fueltank cover on the bottomside? Did it with my foxbody. Now would be the time with as little gas is in there. Makes it easier to drop the tank. Less weight. I learned the hard way went an added 3/4 tank gas thinkin need new fuel. Nope.
Because you said you have 12v? You can recheck at the fuelhat on top of the tank when you drop it an unhook the harness?

Yea I had my wife turning the key while the rear was jacked up and I couldnt hear anything. And no the tank is allmost half full, I thought maybe it was too low and added about 4 gallons.

I'm not going to attempt tackling dropping the tank, would love to save the money but the know how it being in my yard and limited tools ill have to pass.

I do have a neighbor that has his own shop about 1/4 mile away that i'll take it too, I can pull it that far. I just need to rule out everything/anything I can before throwing money at parts I dont need.
 
I am not looking at my IFS switch at the moment, but you would need to check voltage of the PNK/BLK wire with everything connected (can use a paper clip to probe). Double check that is the wire that leads to the FPDM. I would verify voltage out of the FPDM for the first 3 seconds after key on. On my 2000 GT, the FPDM is located in the trunk above the rear driver's side wheel well behind the trunk lining. The wiring diagram I am looking at for the 99 shows 2 wires leaving the FPDM and going to the fuel pump. They are BRN/PNK and RED/BLK. I cannot tell which one should you should check, so maybe check both. You can also check voltage at the connector under the car by the rear bumper behind the gas tank. This leads to the fuel pump. If you have voltage at that connector, signs are pointing to the fuel pump. The next step would be to see if you can power the fuel pump manually as described in that other thread.

FWIIW, I recently diagnosed a fuel pump issue on my car. I was able to power the fuel pump manually, so I ended up concluding that the FPDM was failing. I got a new FPDM, but the car still would not maintain the proper fuel pressure and would not start. I concluded that my fuel pump was starting to fail and was only working intermittently. I replaced the fuel pump, and that fixed it.
 
If your getting 12v at the plug for the fuel pump an its not coming on? why would the FPDM need to be "replaced" or checked? I can see if the pump is coming on an crazy fuel pressure. Your losing me with all the fuelpump, fpdm check here check there? Sounds like a dealership tech advice. Well the computer tells me when I hooked it up you need new tires crap? Lol :)