98 Crown Vic LX Fuel Pump

38k miles - hadn't been driven any distance in 4+ years when I bought it. Always starts and purrs like a kitten when cold, I've had it running in the garage for and hour or two (34# fuel pressure) with no problem. Tried to restart it when hot, no fuel pressure, no start till it cools off. Now that the weather is warmer it ran 40 minutes, pressure dropped to 0, motor died.

After watching his video on similar car I'd like to check voltage in trunk to pump. (pink/black & black) Am I correct thinking if the voltage drops then dies it could be the PCM or if car dies then I lose voltage it's the pump?

All I have for tools is a fuel pressure gauge, volt meter and 12V test light.

Thanks

If the pump dies, you won't necessarily lose voltage.
Don't overlook the fuel pump driver module (FPDM)

Yeah, I'm trying to nail it to the pump or not so I'll know where to tow it. My thinking is :woohoo: if the pump loses power before the engine dies it's not the pump, I'm just not sure.

I don't know, I'm older than dirt and live in a half-horse town and this stuff is way over my head. When I worked on my cars back in the 60's there were two bolts to the block and a couple lines... 20 minutes and $10. :lol:

Thanks

That's correct unless you have a short to ground downstream of the connector. Check the power wire to chassis ground, not just the ground wire

Not sure I've pulled up the right information. I pulled up the wiring diagram for a 98 Ford Crown Vic with a 4.6L engine. This is showing two fuel temperature sensors on the fuel pump assembly. The reason that I question this is they lead to a NGV module that should be on the front of the radiator support. If this is true, that is where I would start. I'm sending the diagram for you.

OP writes he has 34 for fuel pressure so I'm pretty sure his engine runs on gasoline and not CNG (Compressed Natural Gas), which is where you'd find a NGV (natural gas vehicle) module. Fuel pressure specs for natural gas vehicles is 80-120 psi also. Looking over the CNG wiring diagram i can't even find a fuel pump LOL. And the Fuel Pump Driver Module is on 2003 and up year Crown Vics.

I think this is the correct circuit (i edited the diagram to fit more easily just the fuel pump circuit): i.imgur.com/7Dx2shn.jpg

Also, the red wire from the PCM powers other components on the car which I have removed from the image for simplicity sake.

I would just check for battery voltage on the Pink/Black wire while a buddy is cranking car. If you see battery voltage, and still no crank, then pump is bad.

Watch at 26 mins in where Paul is in the trunk and begins power and ground testing the fuel pump.

Okay, did my test in the trunk and more confused that ever.

* temp in garage 80°
* starts right up with steady 12 volts
* after 35 minutes voltage drops to 9-10volts
* second later engine dies then drops to 0 volts
* wait a bit and both prime and cranking are 9-10 volts, engine chugs
like it's trying to start.
* I didn't have the fuel pressure tester hooked up today

I've had this happen before, after a no start try a bit later and it almost starts
but chugs like today. I'll bet the farm tomorrow I can go out and it will fire right up.


Really confused now with the 9-10 volts, not what I expected to see.

Thanks very much, now what?

dont wait until it starts up again to check for power. use your testlight hooked to ground when it stalls get back there and crank on it if test light lights power is good. dont forget to check the ground.

I agree with Cheryl test voltage while in fault mode but definitely check ground with load. I've had half bad ground on fuel pump circuit fail ONLY under load.

Sorry, maybe I didn't explain it clearly. After 35 minutes the voltage in the trunk on hot and ground dropped to
9-10 volts then it died. Maybe 10 minutes later I tried a restart and still at 9-10 volts it wouldn't start.

I just have to believe this is temperature related to something, no idea what it could be. When it's cold
out it runs much longer than in warm weather. ????

Or, could it be a bad pump that itself is overheating after a while and that draws the voltage down then it dies?

Long day and thanks for all the comments, I'll take another look tomorrow.

If it matters, this one has the coil-over-plug. Friend told me a common problem is something on the distributor,
I don't have one.

Thanks

This generation Ford systems suffered greatly from vapor locked fuel systems when it gets warm out and there is a winter blend fuel still in the tank.
1st question, how much fuel is in the tank (bet it's a 1/4 tank or less)
2nd question how old is the fuel in the tank? when did you last get fuel? was it winter time?
3rd question do you live in one of the northern states?

BTW

#1) well, I keep it 1/4 to half. I don't dare drive it till I figure this out.

#2) fuel is somewhat new, I siphon it out of my truck then into the car.

#3) Indeedie, balmy Northern Minnesota

4) glad you didn't fall down the bank


Thanks

Oriley wrote: #1) well, I keep it 1/4 to half. I don't dare drive it till I figure this out.

#2) fuel is somewhat new, I siphon it out of my truck then into the car.

#3) Indeedie, balmy Northern Minnesota

4) glad you didn't fall down the bank


Thanks

And to be clear you are saying this problem didn't begin until the weather got warm? If so, go fill your tank and let us know the result.
This is a risk however because if you still have your problem, you may be dropping that tank to change that pump.

A fuel pressure measurement during the no start would be a key first step. I didn't see that you had verified that or not in this thread.

Sorry, I'll try and explain and make sense.

Cold Weather (Dec - Mar)

Car ran up to 2 hours, would not restart till something cooled for half hour or so

Warm Weather

Car would run ~40 minutes and die
34# while running, 12 volts at relay
Pressure would drop to 0 - engine dies - relay volts to 0
12 volts prime and crank at relay - 0 pressure - no start

Yesterday

Car ran 35 minutes - 12 volts on pink/black and black in trunk
Voltage dropped to 9-10 volts - engine died
9-10 volts at prime and crank - no start
Couldn't check pressure, I was in the trunk

Just like in your video, 0 pressure but almost starts - sometimes - usually just cranks.

Just a guess, could it be the pump itself overheating and drawing the voltage down when it dies?
NEVER fails to start when cold, warmer it gets the less it wants to run.

Thanks again.

From bad to really bad?

Yesterday

Car ran 75 minutes - 30# pressure - 14 volts in trunk

Pressure slowly dropped to 0
Previously it only took a second or two to 0, now ~10+ seconds
Engine dies
voltage in trunk goes from 14 volts to 7 volts till I turn key off
turn key on, prime then 7 volts constant - crank 12 volts - no start - 7 volts

Also, when the key is turned to "on" the interior heater blower comes
on for 5 seconds or so then off like it should be. ???

The bad feeling it being the PCM is back.


Thanks again..

Oriley wrote: voltage in trunk goes from 14 volts to 7 volts till I turn key off
turn key on, prime then 7 volts constant - crank 12 volts - no start - 7 volts
.

So during cranking you have 12v to the pump and then with just the key on you have 7 volts on this same wire?
This sounds like a bad ground and it is back feeding through the fuel pump motor. Please give us a measurement of the fuel pump ground wire during cranking or running and then with just the key on.
This could explain the weird blower operation too.

Please give us a measurement of the fuel pump ground wire during cranking or running and then with just the key on.

I'm testing on the pink/black and black in the trunk, is that what you mean?

If so, yesterday I had 14 volts running, 6 volts key on. This morning still 6 volts key on,
unfortunately for the first time it wouldn't start cold. I'll have to run long wires to check
on cranking, I'll be back.

I found this old Sears meter I bought decades ago and notice it has an "amps" selection,
would this help me any? Has nice big numbers I can read.




Thanks again

Without looking at a diagram, I'm not sure. There would be 4 wires total (most likely), 1 = fuel pump power 2 = fuel pump ground 3 = fuel tank level sensor signal 4 = fuel tank level sensor ground.
With the key on, your pump power feed wire should be 0 volts not 6-7.
With the key on please give us the voltage readings of all 4 wires including their colors, with the connector plugged in and backprobing.

Just throwing this out there considering you are limited on tools and don't seem to have a helper to crank for you, perhaps run the car until it acts up/engine dies, and smack the crap out of the fuel tank with a mallet or nearby blunt object and see if she fires back up afterwards Doesn't always work but might give you some direction