Hello All,
I did a 98 302 EFI engine swap into my 54 and up until a few days ago all has been working as it should. Now I have an "Engine cranks but no start" situation.
I have determined that the fuel pump is not getting the usual 12 volts. I have checked continuity of all wires from the Power Distribution box
through the inertia switch to the in-tank pump and all is good. The inertia switch checks good. There is only 6.70 volts at the inertia switch and at the fuel pump connection right
outside of the tank. I checked the operation of the PCM Power relay and the Fuel Pump relay and both check good.
I checked the fuel pump ground wire connection and that is a good clean connection.

So normally when I turn the key on, all gauges light up and can hear the fuel pump come on. I press the start button, the engine cranks and starts immediately.
However, now no fuel pump sound and no start.

There is one other connection that may be the problem but i don't know how to check.
The wire that runs from the fuel pump relay pin #5 to the inertia switch also connects to the PCM at pin #40.
Could the PCM be causing the voltage to be only 6.70 at the inertia switch and the pump?
If this is the case what can be done to fix the problem,
What does the PCM do with the connection at pin 40?
Can this PCM pin 40 connection be disconnected with no adverse effects?
If anyone has comments and or suggestions it will be very much appreciated.
I am at a dead end with what little knowledge I have of this crank no start problem.
Thanks,
Bob

 

I can't answer your specific questions, but I've gone rounds with my 86 F150 5.0 crank but no start condition. Here's a couple of ideas to ponder.

If you have an ignition control module on the side of the distributor, they are a know weak spot (thin film module burns out easily from engine temps).
What I don't know is, did the 98 use the same system? I used to keep a spare ICM in the glovebox along with the special socket to remove the bolts.

One other possibility is the inertia switch malfunction. I finally cut the wires and twisted them together to bypass that unit which failed to reset after an accident.

Some of Detroit's magic solutions really suck! Good luck with your issue!

 

I am not thar familiar with the wiring of OBD 2 vehicles. But some questions come to mind. First thing you will need is a good schematic from the '98 vehicle your motor came out of. Its the roadmap I think you will need it to get to your destination of getting it fixed.

First thing I would look at is to make sure the fuel pump relay is getting a full 12 volts. Is the fuse good? If so next I would wonder about the fuel pump relay itself, the contacts inside of it may be burned, thus creating a voltage drop. Can you swap out the relay with another one? I am not sure about how the interia switch is set up. If it is in series with the fuel pump relay switch contacts or is it fed back to the PCM? I don't know. I know we have some great guys here that could give you better help. And you could also post this in this forum for guys who have the same year motor to see what they have for you.

https://www.ford-trucks.com/forums/forum25/

 

Thank you for your input and thoughts. They are all good but this 302 EFI has no distributor, but two coil packs. I don't think they would affect the voltage at the fuel pump.
The inertia switch checks out good as far as trip and reset.

 

Thanks Hooler for your reply.
I am only getting 6.7 volts at the inertia switch and downstream at the pump. The fuse that protects the fuel pump relay is good and I do have a full 12 volts at the relay.
The relay works and I even switched out the relay for a couple of different ones to eliminate the thought of bad relay.
Looking at my electric schematic, I see the connection at the PCM pin 40 (which is the same wire that runs to the inertia switch) is for the fuel pump monitor.
There is another wire from the fuel pump relay that connects to the PCM pin 80 that has something to do with the fuel pump control.
Since I have good continuity on all the wires to the fuel pump I am thinking there might be an issue with the PCM connections.
I am stumped....

 

On your schematic is the interia switch fed 12 volts directly from the fuel pump relay? (The wire to PCM pin 80 could be powering the coil of the relay, telling it to pull in when they key is on and the crank sensor is sensing the motor turning over. Speaking of....you might want to look at the crank sensor and it's connections)
And then the fuel pump fed 12 volts from the interia switch?
Just trying to get a bettet idea about current flow in the circuit.

 

The inertia switch is fed 12 volts directly from the fuel pump relay. (Dark Green/Yellow) (This same wire is the one that connects to the PCM pin 40. Fuel pump monitor input) I am getting 6.7 volts at the inertia switch at this wire.
The fuel pump is then fed 12 volts directly from the inertia switch but a different wire. (Pink/Black). I am also getting 6.7 volts at the Fuel pump at this wire.
The other wire from the fuel pump relay (Light Blue/Orange) connects to the PCM pin 80. (Fuel pump relay control.)
So would the problem be more likely at pin 40 or pin 80? or both?

 

If you unplug the inertia switch from the relay, what is the output of the relay?

 

Great Idea!

If I am interpreting this all correctly, I wouldn't think pin 80 would have anything to do with it. Its just switching 12 volts to the relay coil to pull in the contacts to turn on the fuel pump. Pin 40? With Effies test above we'll know. But if you do get 12 volts through the relay with the interia switch disconnected, then there are 2 more places to look or maybe think about. I am wondering if you have a bad, burned, connector at the bottom of your relay. With no load (the fuel pump disconnected) you could measure 12 volts at that point and all the other points along that circuit because very little to no current is flowing. Your digital voltmeter has a very high impedance so its just "sniffing" for voltage when you test. But connect up the fuel pump, then the current has to work against a connector that has maybe corrosion, burned contact points, frayed or loose wire. The current flow will cause the connection to heat up, thus driving the resitance higher, heating up the connection more making the voltage go lower. So how do we know for sure? A couple of ways to approach it I guess would be to disconnect your fuel pump, turn the key on, and do a point to point voltage test to the same ground your fuel pump is using. If you have 12 volts all the way through to the fuel pump connector, then its time to do a voltage drop test. Here we a looking for a voltage loss across say the fuse, the fuel pump relay, and the interia switch. You might need two people for this as the PCM will only allow supply 12v to the fuel pump to run just a few seconds. Plug back in your fuel pump, turn your ignition switch back on. You simply touch your test leads across the fuse and it should measure close to 0 volts, next move on to the relay. You may need to make some temporary jumper wires so you can get access to the relay pins to meaure. Now measure the voltage loss across the relay contacts as close to the relay as possible. If you see again almost 0 voltage across the relay you are good. Next place I would check for voltage drop is across the relay socket where contact pin 80 connects to and where the dark green/yellow wire connects to your interia switch. Again, you should see 0 volts between those 2 points. But if you do have a bad, burnt connection, you will see about 5+ volts across that circuit. If though it ends up again 0 volts, now check across your inertia switch the same way.
Voltage drops in the fuel pump circuit can be quite common.
Used to be whenever you changed fuel pumps, the new unit would come with a new pigtail because the old one had burned connectors on them. And you don't want to use a burned connector on a connection point that is brand new. It too will eventually get burned up.
Sorry so much is there. Its just how I would approach it.
Hope it helps!

 

The only way I could see the voltage at the inertia switch was to disconnect the switch and measure with the key on at the end of the wire connector.
I did the same at the connector downstream at the fuel pump. Both showed 6.7 volts.

I will follow Hooler1's method of checking the system.

A thought......inertia switch
My truck was in the "paint shop jail" for over a year (Yes you heard that right) with 87 octane gas in the tank. If the ethanol had separated and settled out of the gas to the bottom of the tank, could the fuel pump have seized up due to pumping a bunch of ethanol
instead of gas? If so, would the seized pump (for whatever reason) cause a voltage drop from the fuel pump relay to the pump?

This is new information: I just disconnected the fuel pump lead that is about 6 inches before going into the tank. I stuck a couple of pins into the connector that goes to the pump in the tank. I then connected jumper wires from the plus and minus pins directly to the battery.
No pump activity! No pump sound, no pressure at the fuel pressure gauge, Nothing. With the pump still disconnected I measured the voltage at the connector that leads to the inertia switch and up to the fuel pump relay. With the key on I still get 6.7volts.So....Do I have two problems? 1. Dead pump. 2. Voltage drop.
What is next?

 

What voltage do you have on the other side of the relay? The drk/grn and yellow wire that goes back to pin 40 is fuel pump monitor. That should be pin 5(87) of relay. Pin 3(30) should have 12 volts battery power on it, lt blu/org. Pin 1(85 or 86) red wire should have 12v ignition power and pin 2 light blu/org should come from pin 80 of pcm and is essentially the ground for the relay. Basically all you are doing is controlling relay by ground through the pcm. I would remove the fuel pump relay and check voltage and jump across from pin 30 to 87 which would be the hot all the time to the fuel pump side of the relay and see if pump comes on.

 

I removed the pump relay and checked the voltage at pin #3(30) and have 12.65 volts. I then jumped across pins #3(30) and #5(87).Pump does not come on. I then disconnected the pump and with the jumper wires across pins 3(30) and 5(87) I checked the voltage at the inertia switch and the pump connections. Both connections have 12.65 volts. With the relay still removed and the key on, I checked the voltage across pins #1(85) and pin #2(86) and have 12.65 volts. Since pin #2(85) goes to the PCM pin 80, this tells me I still have a good ground in the PCM. Now that I know the ground and voltages are good but the pump does not work......I have a bad pump! This pump lasted three years so another couple hundred here, another there......why not just order another pump.

Thank you all for your thoughts and comments. It was all very helpful. Casetruck!, thank you for a great explanation. It made checking the system quick and easy.