Will not start.

tonyhartwig · 10-08-2008, 05:30 PM

1987 F250 460 w/carb, 4WD, dual tanks, automatic

I get no fuel to the carb. I replaced both in-tank pumps and the fuel selector valve. There is not any voltage to the pumps unless the motor is cranking. (Nothing happens when the key is in the 'run' position.) The switch on the dash is fairly new and I checked it with an ohmmeter. There is not voltage on this switch unless the motor is cranking. The truck will not start. I recently removed the Holley/Motorcraft and put an Edelbrock on it, but that really has nothing to do with it. The Haynes manual I got is completely useless.
The voltage to the pump is 10.6 VDC, I think it is only supposed to be 11, so this should still operate.

Oil pressure/sender is fine. How do I measure voltage if a fuse is blown?

I did not wire it wrong. I just pulled the connectors and put them back on. I did replace filters. The truck gets spark, just no fuel. I can backfill the line and vacuum keeps it going. Major pain doing it this way.

It is original with a carb. No high pressure pump on fuel line. I dunno why they did it, but they did. Even the vacuum/wiring sticker on the inside of the hood shows a carb.

The pump does work while the key is in start (noted that in original post) but does not work at any other time. Lines are not blocked.
There is not even a hint of a spot for a fuel pump on the block. I did a 100% rebuild 2 years ago, I would have seen it then. But it is a carb and electric pumps

theoldwizard · 10-08-2008, 06:03 PM

The engine control computer turns off the pump after about 10-15 seconds of key on, engine off.

Was this truck originally a carb or EFI. I don't recall Ford ever making a carb vehicle with in-tank pumps. I though all carb vehicles used the old fashion mechanical pump.

cjones · 10-08-2008, 06:59 PM

do you have power at fuse#18 15Amp with key ON??

have you check the oil pressure cutoff switch (R/Y wires)?? the power goes through that switch when key is in ON position.

BroncoJoe19 · 10-08-2008, 10:28 PM

I get no fuel to the carb. I replaced both in-tank pumps and the fuel selector valve.

Please note... you may also have a fuel pump beside the frame rail on the driver's side. I hop you replaced the fuel filter while you were at it.

There is not any voltage to the pumps unless the motor is cranking. (Nothing happens when the key is in the 'run' position.) The switch on the dash is fairly new and I checked it with an ohmmeter. There is not voltage on this switch unless the motor is cranking.

EDIT:... Oooops after reviewing my Haynes manual it appears that I was wrong!
Seems to me that you wired it wrong.

The truck will not start.
OF course not! IF there is no power to/from the switch when it is in the run position, it will not send power to the coil when it is in the run position.

theoldwizard · 10-09-2008, 04:11 AM

I still say Ford never made a carbureted vehicle with an in tank electric fuel pump.

Carbs require less than 10 psi fuel pressure. More than that and it will sink the float and overflow the carb. Aftermarket fuel pumps for carbs require special low pressure regulators.

Why would Ford install not 1 but 2 in tank pumps for a carb when mechanical fuel pumps have worked for years.

Something does not add up !

BroncoJoe19 · 10-09-2008, 06:28 AM

According to Haynes...
On 7.5L non-EFI models with "Hot Fuel" option, disconnect start wire at the starter relay and have an assistant hold the key in the START position/ The in-tank fuel pump should be heard running. Rconnect START wire at start relay. If no sound is noted, repair the circuit.

It goes on to say...

On 7.5L non-EFI models with "Hot Fuel" option, locate teh oil pressure switch on the engine and disconnect the electricl connector. Jumper both red/yellow wires together at the connector. Turn the ignition key to the RUN position. Now the pump noise should be constant. Listen specifically for the following:
1) In-tank low pressure pump.
2) on dual tank models, switch tanks (key on) and verify operation of alternate in tank pump.

It goes on for pages about how to check the fuel pressure regulator.

Also it mentions fuel supply line restriction and clogged fuel filter as cause for low pressure at the carb.

theoldwizard · 10-09-2008, 07:57 AM

There you go Joe, using hard facts to shoot hole in my heavily perforated memory !

BroncoJoe19 · 10-09-2008, 08:29 AM

Oh yeah... hard facts are over rated anyway

The challenge here is that there are too many cars, too many options, too many years, and too many changes - to be able to know everything, and to be able to give specific advice. Yet we try.. eh brother?

tonyhartwig · 10-09-2008, 06:15 PM

added more info to my post

Quote:

Originally Posted by theoldwizard

The engine control computer turns off the pump after about 10-15 seconds of key on, engine off.

Was this truck originally a carb or EFI. I don't recall Ford ever making a carb vehicle with in-tank pumps. I though all carb vehicles used the old fashion mechanical pump.

tonyhartwig · 10-09-2008, 06:18 PM

added more info to my post. I am smarter than your average bear, there is just something, somewhere that I am missing.
The 'no start' problem is fuel related - no gas, no rpm's.

Quote:

Originally Posted by BroncoJoe19

I get no fuel to the carb. I replaced both in-tank pumps and the fuel selector valve.

Please note... you may also have a fuel pump beside the frame rail on the driver's side. I hop you replaced the fuel filter while you were at it.

There is not any voltage to the pumps unless the motor is cranking. (Nothing happens when the key is in the 'run' position.) The switch on the dash is fairly new and I checked it with an ohmmeter. There is not voltage on this switch unless the motor is cranking.

EDIT:... Oooops after reviewing my Haynes manual it appears that I was wrong!
Seems to me that you wired it wrong.

The truck will not start.
OF course not! IF there is no power to/from the switch when it is in the run position, it will not send power to the coil when it is in the run position.