Fuel Pump Frustrations

[BBF]

I've lost almost two days reading related threads here and diagnosing why my FP sometimes works and sometimes doesn't. Before this, the pump has always pressured up when ign was keyed on, now it's intermittent.

1999 Mounty V6 SOHC 4x4
Steps:
1. good strong battery
2. original key: no theft issues
3. FP relay swapped and has good connections
4. inertia switch untripped and connections good
5. pump runs when given 12V via batt. jumper
6. only getting 5V at FP connector when key is on and during starting

How do I know if I'm using the correct pins at the FP connector aside from the fact that I read voltage and can get the pump to spin? It's the round style with three top gold pins and four bottom silver pins. I'm connecting to the middle two bottom pins.

Also, when I turn the key to on I read 5V, engaging the starter doesn't change the voltage. Shouldn't the voltage jump when I engage the starter then drop down again when ign key is just on?
Thanks

 

[imp]

I've lost almost two days reading related threads here and diagnosing why my FP sometimes works and sometimes doesn't. Before this, the pump has always pressured up when ign was keyed on, now it's intermittent.

1999 Mounty V6 SOHC 4x4
Steps:
1. good strong battery
2. original key: no theft issues
3. FP relay swapped and has good connections
4. inertia switch untripped and connections good
5. pump runs when given 12V via batt. jumper
6. only getting 5V at FP connector when key is on and during starting

How do I know if I'm using the correct pins at the FP connector aside from the fact that I read voltage and can get the pump to spin? It's the round style with three top gold pins and four bottom silver pins. I'm connecting to the middle two bottom pins.

Also, when I turn the key to on I read 5V, engaging the starter doesn't change the voltage. Shouldn't the voltage jump when I engage the starter then drop down again when ign key is just on?
Thanks

Let's see if I understand you correctly. 1, pump works intermittently when keyed on, for two secs or so? Sometimes does not run at all?
2, you ran a wire from the battery to the pump connection at the tank, and pump always ran?
3, You measured 5 V at the pump connection, with respect to where? Other voltmeter lead connected where?

This sounds like an intermittent poor connection to ground. Some early designs used no separate ground wire to the pump, achieving ground by the pump being clamped to it's support in the tank. I believe yours has a separate ground wire coming out of the tank, part of the connector on top. It's likely a black wire or pink/black. Unfortunately I have no '99 wiring diagrams, going by '04. Do you know whether you have the "returnless" fuel line system (only one fuel line to engine)? I think that came later, if so, your pump is grounded somewhere near the tank, via the harness connecting to the top connector. That ground point is suspect.

Returnless system uses a fuel pump driver module, which constantly varies pump speed as fuel demand changes. imp

 

[2000StreetRod]

5 volts to pump

The output of the fuel pump relay is connected to the inertia fuel shutoff and the PCM so the PCM can determine if the relay is closed. The 5 volts you're reading is the input voltage at the PCM due to PCM power and not the output of the energized relay.

The PCM energizes the fuel pump relay for a couple seconds when the ignition is switched from off to run or any time the crankshaft is rotating as reported by the crankshaft position sensor. Possible sources of no battery voltage to the inertia switch:
1. Fuse 9 (20A) in battery junction box blown
2. Fuel pump relay in battery junction box bad (try swapping with horn relay if your horn works)
3. Failed crankshaft position sensor (try cleaning the connector contacts by disconnecting and reconnecting the connector a few times)
4. Broken electrical circuit wires or bad electrical connector connections

 

[Dave 1955]

I had the same prob with a old ford tarus wagon once.
Took me forever to figure it out.

The wires that run thru the car near the drivers side door were wore just about through.
I could get 12 volts at the pump but hardly no amps.
Probably not your problem but easy to check to make sure.

 

[BBF]

New day and a fresh mindset, determined to get this figured out!

Thanks for your help so far.

My Chilton 19991-99 manual only goes up to the '97 expl engine wiring and shows a Black/pink wire to the FP then black from FP to ground. My connector has 7 wires only two are thick gauge, a red w/blk stripe and an all black; the rest a real skinny. I can't recall now which I powered or checked V off of.

There's a fuel supply tube from tank to engine, and a bigger return tube from engine going past fuel tank to something above the spare tire. There's another small tube from fuel tank also going back to above the spare tire.

Today, I'll start by dropping the spare to see how many tubes are coming out of the FP unit and reground the FP ground wire if there's one.

Three yrs in a row now this rig has needed service and everytime it's in November; a balmy 23F right now.

Be back soon.

 

[Dave 1955]

The thing by the spare tire is the charcoal canister i think...evap thing.

 

[koda2000]

The thing by the spare tire is the charcoal canister i think...evap thing.

yes that's the evaporation system and canister over the spare tire. it has nothing to do with the fuel pump. if it's not giving you a CEL i suggest you leave it alone.

if you only have one actual fuel line, then you have the newer "return-less" style fuel system. I had found a good video on u-tube on Ford fuel pump diagnostics once. it explained how the voltage variation works. i think it was for a Taurus, but i'm sure the Explorer fuel pump of the same year works the same way.

 

[BBF]

OK, just videoed top of fuel tank. One tube runs from FP mount forward to engine, and 4 wires connect to FP mount, fuel line? One tube runs out of a green cap near the inboard rear corner of tank to the canister above spare tire, vapor line? Three wires from a black connector farthest back inboard corner, unknown? I didn't see any wire or cable attaching the tank or pump to the frame or body, so maybe the all black wire in the framerail connector is a ground?

So from what I can tell, there isn't a return line to the tank, just a feed line. I still don't know which wires power the fuel pump.

If I apply 12v to the red w/black strip wire and ground the black the pump should run smooth right? These are the heaviest gauge wires on the connector.

If I'm backward will it hurt the pump?

 

[2000StreetRod]

fuel pump wires

pink/black is the supply
black is chassis ground
Your 1999 model is a returnless fuel system. The fuel pressure regulator is in the fuel tank. If you pull the fuel pump relay and jumper the pin 3 to pin 5 the fuel pump should run continuously. That's easier than working under the vehicle.

 

[BBF]

So if I apply 12V from batt. on the pink/black and ground the black, the FP will run normally just like it would when I turn the key to on right?

If so then I at least know the pump is good?

Then from there check power at the connector, the inertia sw, relay, fuze; then what?

 

[BBF]

Tough to tell. The pump pumps, but at times, the pins are so close together side by side, that when applying power to them and pump no run, I can't tell if the pump is bad or if the jumpers are touching.

All else checked out OK. Turned key to on about 30 times and about half powered up pump and half don't. I'll double check if pink/black is hot at the FP connector when key turned to on and pumpy don't run.

If it's not hot then I'll check up the line. These all checked out OK when it was hot at FP.

 

[BBF]

It's gotta be the fuel pump, grrrr. I repeated the key on/off game until the FP no pumpy, then I checked for hot at the connector; hot. So, put V/O meter on FP connector at frame rail. Repeated key on/off game about 30 times, every single time 11V spike then drop to about 6V. WAPITA, I shoulda done this first.

Anyone change out a fuel pump with a topped off full tank? The tanks has a flat bottom, maybe lower the front of it first then the rear hoping to minimize spash.

Anyone just cut an access hole under their seat and change pump through there?

 

[koda2000]

It's gotta be the fuel pump, grrrr. I repeated the key on/off game until the FP no pumpy, then I checked for hot at the connector; hot. So, put V/O meter on FP connector at frame rail. Repeated key on/off game about 30 times, every single time 11V spike then drop to about 6V. WAPITA, I shoulda done this first.

Anyone change out a fuel pump with a topped off full tank? The tanks has a flat bottom, maybe lower the front of it first then the rear hoping to minimize spash.

Anyone just cut an access hole under their seat and change pump through there?

you'll have to siphon most of the fuel out first. around 2 gals is very easy to handle, but 20 (figure about 6 lbs x 20 gals = 120 lbs). remove the fill and vent hoses and stick a siphon hose in one of the holes. you're going to have to remove them anyway unless you're planning on cutting a hole in the floor. of course, if you do try dropping it while full it will be much easier to put back because you'll have spilled most of it.

 

[BBF]

Yikes, complete FP's are spendy. I might as well put in a really good one.
Any recommendations?

 

[BBF]

of course, if you do try dropping it while full it will be much easier to put back because you'll have spilled most of it.

No doubt, that would be my luck.

On youtube, I saw an anti siphon device in the tank, might have been a different year.

 

[koda2000]

No doubt, that would be my luck.

On youtube, I saw an anti siphon device in the tank, might have been a different year.

my 2000 had nothing once i removed the hose from the tank nipple. i don't know if there's anything in the metal fill tube. if you can't run the siphon hose down the fill tube there may be an anti-siphon device in it, but like i said, you'll need to remove the hoses anyway. just a hose clamp holding it on.

i have a Word Document with directions for replacing a fuel pump. PM with your email address if you'd like a copy.

 

[BBF]

Thanks koda, sending PM.

 

[bluestream1]

YOu can replace the pump by cutting and access hatch under the rear seat. There was a very detailed post on this site a while ago with multiple picture. I did not bookmark it, but if you do a search you should find it. It was on a first gen if I recall, but the pump/tank are the same

 

[RomeovilleIL]

Yikes, complete FP's are spendy. I might as well put in a really good one.
Any recommendations?

Dont need the complete assembly, just the pump. Mail order is your friend here. Pretty much all of the brands of fuel pump work so long as you get the correct pressure specs. Two summers ago the local gas stations got a bad batch of gas that ruined lots of people's fuel systems. Put in a couple name brands and a bunch of Herko and other cheapies that cost under $30 with a new sock. So far had zero problems with them in either my own or other people's trucks. I do know that airtex had issues 5-7 years ago & they are the brand most parts stores stock.

Full tank is heavy but manageable. There is no anti-splash or anti-syphon device. Place a nitrile glove over each of the tank nipples and wrap with duck tape to seal them off after removing the fill and return hoses. After that best way to approach this is lift rear frame on jackstands, remove drivers side rear wheel, and use 2 floor jacks with piece of wood wired to the pans to spread out the weight of the tank. Put one jack on near each end of the tank. If you have access recommend using power tools with extensions and wobble to save lots of headaches reaching the strap bolt. Once you take off the front two bolts and strap the tank will drop about 2 inches and need to roll back 4 to 6 inches to clear the front supports. With two jacks you can lower it smoothly a little at a time to keep it from tipping and spilling. The tank does not have to get lowered all the way to the floor. You need about a foot between the tank and body to clear the pump assembly.

 

[koda2000]

i bought an Airtex pump for one of my 2000 Mountaineer's. still working great. i found it (and the sock filter) on Amazon with free shipping. wasn't that much as i recall, plus it included the in-tank wire adapter for the small-to-wide pump terminals i was telling you about. actual install time (once i bought a better 3/8" fuel line disconnect tool) was around 2 hours.