87 F150 Won’t Start

[Mhfco6]

Yes, with key on and engine off, those should be the ONLY WAY to get power to fuel pumps(A/B switch)

Fuel pumps should NOT run with key on/engine off that's dangerous

If the fuel pump doesn’t run with the engine off, how is it supposed to build fuel pressure to start? Every pump should run and then shut off, correct? Mine is not, even when the engine is cranking.

 

[RonD]

If the fuel pump doesn’t run with the engine off, how is it supposed to build fuel pressure to start? Every pump should run and then shut off, correct? Mine is not, even when the engine is cranking.

The fuel system should HOLD pressure when key and engine are off

When you first turn on the key and computer is booting up, computer will activate FP relay for 2 seconds, that equals about 10psi of pressure
You can cycle key off and then back on and get another 2 seconds, repeat as you see fit

But on a working system in 1987 you should have 30psi - 40psi engine running
When you shut off the engine the HP pump and FPR should HOLD at least 15-20psi in the fuel rail, for MONTHS and MONTHS
So at next key on(+10psi) you should be above 20psi which is plenty of pressure to start the engine
at 400rpm the computer will activate FP relay full time
Engine crank speed is only 200rpm

The reason for this 2 second thing is safety
If there should be an accident or roll over and a fuel line broke then the electric fuel pump would just keep pumping out fuel until battery died, or vehicle exploded in a fireball, lol
So if engine rpms drop below 400 then fuel pumps are OFF


It has been that way since the first use of electric fuel pumps, biggest fear is they will feed a fire if they just keep running, mechanical pumps stopped when engine did
So in the days of carbs, no computers, the FP relay was grounded, activated, by an oil pressure switch
Carbs have a float bowl that holds gasoline for the next startup
So when engine started oil pressure went up and oil pressure switch closed and FP relay was activated and electric fuel pump came on
So this 2 second thing is just a carry over safety feature

 

[Mhfco6]

Excellent info, Ron thanks agin

Okay, FPR activates at startup for 2 seconds.. should the pump run for those 2 seconds? If not the initial running Ive experienced since I’ve owned the truck is really playing with my head.

What about in tank pumps, same deal, because the relay gives the A/B switch power, which gives the inertia switch power.

So with the way my trucks fuel system is currently operating, I should be able to turn the key and start the truck. Since HP pump doesn’t run it’s got enough pressure already?

 

[Mhfco6]

That's a Crystal its used for timers in the "chips"
You could replace it
And I would replace both caps if there are only 2

With the crystal being damaged/removed what would this affect? A lot? Or should the truck still start?

 

[RonD]

You would have to get a diagram of the wiring in that 1987 computer to know what would be effected but in my opinion no nothing would work as it should without all parts installed and working

FPR = Fuel pressure regulator
FP Relay = fuel pump relay

FP relay activates for 2 seconds with key on

FPR is just a valve with a spring holding it closed, its on the fuel rail, when fuel pressure gets above 43psi its pushed open and fuel flows back to gas tank in return line, until pressure is below 43psi
It will have a vacuum hose attached for 2 reasons, when engine is running the intake vacuum pulls against the spring pressure, making fuel pressure drop to about 35psi
When you are accelerating more fuel is needed and vacuum also drops, as vacuum drops fuel pressure increases but fuel use is up, so this vacuum assist helps maintain a steady fuel pressure, doesn't jump up and down with fuel demand

2nd reason is that if FPR should leak, fuel would get sucked into the engine not drip on HOT engine parts

 

[Mhfco6]

You would have to get a diagram of the wiring in that 1987 computer to know what would be effected but in my opinion no nothing would work as it should without all parts installed and working

FPR = Fuel pressure regulator
FP Relay = fuel pump relay

FP relay activates for 2 seconds with key on

FPR is just a valve with a spring holding it closed, its on the fuel rail, when fuel pressure gets above 43psi its pushed open and fuel flows back to gas tank in return line, until pressure is below 43psi
It will have a vacuum hose attached for 2 reasons, when engine is running the intake vacuum pulls against the spring pressure, making fuel pressure drop to about 35psi
When you are accelerating more fuel is needed and vacuum also drops, as vacuum drops fuel pressure increases but fuel use is up, so this vacuum assist helps maintain a steady fuel pressure, doesn't jump up and down with fuel demand

2nd reason is that if FPR should leak, fuel would get sucked into the engine not drip on HOT engine parts

When I pull the tank, should the in tank pump have power with key on engine off? I’m assuming not with the A/B switch having no power.

Looking at computers the available numbers are as follows with federal emission/manual trans: E7TF-(KA,KB)(BKA,BKB)(BKC)(MA,MB)
Which one do I need?
To start, I’m going to replace the computer and all vacuum lines.

 

[RonD]

The pumps should have no power(after 2 seconds) with key on, assuming no jumpers are being used

E7TF means 1987 Truck electrical part
12A650 is the Ford part number for ALL engine computers, still used in 2020, not model specific
L2C is the revision number, refers to hardware and firmware updates

FL2 <<<< this was the software loaded when vehicle was assembled, this is the number to match if possible

Ford never published any cross reference for revision or software for these engine computers

What you need to match is engine size and manual or automatic transmission, those are not negotiable, lol
If not rebuilt inspect capacitors before installing

A radio/electronics repair shop can replace the crystal and caps in your unit, or if you know someone with a solder gun he or you can do it, need a "solder sucker" to suck out the old solder, $9

 

[Mhfco6]

The pumps should have no power(after 2 seconds) with key on, assuming no jumpers are being used

E7TF means 1987 Truck electrical part
12A650 is the Ford part number for ALL engine computers, still used in 2020, not model specific
L2C is the revision number, refers to hardware and firmware updates

FL2 <<<< this was the software loaded when vehicle was assembled, this is the number to match if possible

Ford never published any cross reference for revision or software for these engine computers

What you need to match is engine size and manual or automatic transmission, those are not negotiable, lol
If not rebuilt inspect capacitors before installing

A radio/electronics repair shop can replace the crystal and caps in your unit, or if you know someone with a solder gun he or you can do it, need a "solder sucker" to suck out the old solder, $9

I’d like to repair it. I’m not sure what is damaged though, as the pumps don’t come on for 2 seconds. I’m sure ford can hook it up and test it for bad vs good, for a price. And they probably won’t know which exact points are trashed.

 

[RonD]

No, Ford can't do that, not sure any one can, the test if a computer is working is to put it in a compatible vehicle and see if all the systems work

You have obvious damage, the crystal, and I would replace the 3 capacitors as well, then plug it back in and see if it works, it should, these computers were overbuilt for what they do, and tend to last
Yours is 33 years old, what electronic device have you had that lasted over 15 years, lol, very very few I am sure, older TV maybe


There was no reason to build a "tester" that would work on all the different sub-models of engine computers, if a dealer/tech determined there was a computer issue then it was replaced to see if that solved the problem
The time it would take to test every sub-circuit in an engine computer would cost 3 or 4 times the cost of a new engine computer and you may not even find the problem on a bench test

 

[Mhfco6]

No, Ford can't do that, not sure any one can, the test if a computer is working is to put it in a compatible vehicle and see if all the systems work

You have obvious damage, the crystal, and I would replace the 3 capacitors as well, then plug it back in and see if it works, it should, these computers were overbuilt for what they do, and tend to last
Yours is 33 years old, what electronic device have you had that lasted over 15 years, lol, very very few I am sure, older TV maybe


There was no reason to build a "tester" that would work on all the different sub-models of engine computers, if a dealer/tech determined there was a computer issue then it was replaced to see if that solved the problem
The time it would take to test every sub-circuit in an engine computer would cost 3 or 4 times the cost of a new engine computer and you may not even find the problem on a bench test

Once again thanks for the help and keeping this thread alive. I dropped the front tank this morning.. the ground wire at the pump was broke. I repaired it but pump still won’t turn on. Gas needs to be drained out anyway, it is horrible. I cannot get the fuel gauge to move with the pump hooked up to the connector, moving the float by hand.

 

[Mhfco6]

I just found this in the frame rail. I disconnected the grey connector to get a better picture. Great connector was disconnected behind HP fuel pump and black connector was laying loose in front of fuel filter. Black connector two wires are black/pink stripe and purple/orange stripe. Grey connector is a looped red/blue stripe, black/pink stripe and purple/orange stripe.

 

[Mhfco6]

Selector valve is to blame for no fuel pressure. It must have started working, then crapped out again shortly after. I ruled it out because when I took it apart and cleaned it, was working fine. I have fuel from tank B but nothing after the vacuum selector.

 

[RonD]

You can get the electric 6 port dual tank selectors, about $60

You would ground switch to frame and tap B tanks fuel pump 12v wire, so when B tank is selected it switches to B tanks 2 lines, when A is selected 0volts to switch so A tank is selected by default

Switch draws less than .5amp so won't effect fuel pumps available power or fuse/fusible link on that circuit

You can find them at wrecking yards, just take a 9v battery with you to test them, it will "click" when you apply power, that doesn't mean it works definitively, just means the solenoid part works, lol, if you want to blow thru it you can test the valve part works

 

[Mhfco6]

Ive got the truck starting now, but shuts off soon after. I took the selector valve off and cleaned it again, worked the crap out of it. Not totally sure what’s going on, could be ECU. Fuel pumps shut off at 45-50 psi. I reckon they ran for all that time before because pressure was not satisfied.

Once the truck starts and shuts off, it won’t start again for a while.

 

[RonD]

What engine in this truck?

There is no Fuel Pressure Sensor, so pumps may be shutting off but not because of pressure

Do not try to start engine
Jumper the OBD1 fuel pump slot
Turn on key
Watch pressure at the rail, should go up to 42-44psi and FPR will open and fuel will start to flow back to the tank, pressure should remain at about 43psi as long as key is on, and pumps should stay on the whole time
If pressure goes above 45psi then FPR is bad, assuming pressure gauge is acurate

FPR has a vacuum hose attached, check it for gasoline, shouldn't be any of course, if gasoline is in that hose then engine is being flooded out because of leaking/bad FPR