My old beater truck cranks fine but won't start. Fuel rail is dry.

I checked ECC relay, fuel pump relay, both test fine. I've got B+ leaving the inertia switch (on the pink w/ black stripe wire)with initial key turn (the momentary pump-up).

I disconnected the connector feeding the in-line fuel pump and get no B+ from either round pin when key is turned.

Next I'll check for B+ at in-tank pump connector, then check wiring harness all the way back.

I looked at the autozone wiring diagram and the circuit ends at the inertia switch on that diagram. On the truck, the pink w/ black stripe wire (with it's orange/blue power wire) leaving the inertia switch goes back into the engine compartment to a connector near the relays, changes to two smaller wires, then enters the wiring harness.

Is there some failsafe I'm missing? Anybody have a better wiring diagram showing the path from inertia switch to fuel pump(s)?

Thanks in advance.

 

Put a jumper wire across the inertia switch connector...........bet it starts.

 

Wish you'da named a bet- that was one of the first things I tried! I removed and ohmed out the inertia switch, and I have B+ leaving the switch, just no power at in-line pump.

Thanks anyways.

 

My 87 B2 had a similar problem.
Does the high pressure pump under the frame come on?
I had to replace the fuel pump relay AND pull 12v from another source to it to make the high press pump run.........without it, I believe the low press pump in tank wont run.

 

I haven't been able to learn which pump is the high or low pressure pump but in a similar forum posting they said the in-tank pump was low pressure and the in-line one was high pressure. But either way, neither come on when key is turned.

My next step is to run 12V directly to a pump but without knowing the circuit, or what to energize, I don't want to fry anything.

 

Tank is low press.... under driver on frame is high press pump.

 

Thanks- that makes sense.

 

Are you certain you have 12v at the plug to the fuel pump relay?
My wiring harness was chewed by rodents or just fell apart, when I pulled 12v from another 12v ign. keyed source to the hot for the relay, I never had another problem with fuel pressure.

Check the EEC relay plug for same.

 

I followed an online ford relay diagnostics guide (Part 1 -Ford Fuel Pump Relay Test.) to test both EEC and fuel pump relays- all multimeter tests showed voltage where and when required. All fusible links coming off the solenoid are visually good.

I've had rodents wintering in the engine bay but see no signs of gnawed wiring anywhere, and the truck ran all spring and wouldn't start in the driveway minutes after shutting it off.

I'm still looking for a better wiring diagram than the autozone one, if anyone else knows of one. I think I need to know where in the circuit the inertia switch is, and where the inertia switch B+ goes.


Thanks for your thoughts, Old93junk.

 

From inertia switch to Connector 160 is pink/black. C160 to C161 is black/pink.

C161 to both pumps is also black/pink. C160 is black C161 is white, Both connectors are under the hood/drivers side fender apron.

 

Following pink/black from the inertia switch through the firewall and back to the solenoid area, the pink/black goes into a two wire connector that also houses the power wire from the fuel pump relay TO the inertia switch. (That wire goes to the computer, it looks like) The pink/black becomes a smaller gauge solid orange before entering the harness and running to the driver side through the intake manifold. I just can't find it on the drivers side.

 

No joy yet.

 

I was just poking around under the hood of my 87 & I cant find the pump wiring either. Most of the wiring on the drivers side is buried under a flexible cover that i did'nt want to fool with.

Try grounding the fuel pump pin on the self test connector & turn the key to run. This holds the pump relay closed. Now wiggle the wires on the drivers side & see if you can get the pumps to come on.

Self test connector is where you plug in your scanner & it's the tan/light green wire on one end of the connector.

 

I was just poking around under the hood of my 87 & I cant find the pump wiring either. Most of the wiring on the drivers side is buried under a flexible cover that i did'nt want to fool with.

Try grounding the fuel pump pin on the self test connector & turn the key to run. This holds the pump relay closed. Now wiggle the wires on the drivers side & see if you can get the pumps to come on.

Self test connector is where you plug in your scanner & it's the tan/light green wire on one end of the connector.

 

Another possibility at this point, as it was a sudden failure after running fine, is a EEC failure.............The problem with computer/EFI rigs............no computer, no run.