Inertia Switch ('85 EFI dual tanks)

[Nemesis F150]

Inertia Switch appears to have a problem.

The reason I'm checking it is because the fuel lines need to be depressurized. The plan is to install new gas tanks but the fuel lines have to be disconnected so don't want to squirt fuel from a pressurized line.

(1) The white button on the top is totally "loose" and the directions I've read say that one needs to pry it up with a small screwdriver. Don't understand why it should be loose unless there is a problem with it.

(2) Haven't hit anything nor made any sudden stops.

(3) I've read that the catalytic converter can cause it to shut off but I don't even know if the exhaust has one, and at 44K miles it shouldn't be a problem unless there is an issue with the exhaust gases.

(4) There is no clicking sound from the high pressure pump that I've been able to hear, and there is a problem with keeping the engine running. There has been some rust in the fuel when the high pressure pump filter was changed but that has been mostly gone.

(5) As for fuel filters, the '85 pickups had a mixture of filter installations; some with one, some with two, and some with all three: (a) High pressure (HP) pump, (b) filter after (toward the engine), and, © one before the HP pump (toward the tanks). I haven't located either of the other filters, only the HP filter. It appears there is only the HP filter on this rig but I'll be checking one more time as maybe I was looking in the wrong place for the downstream (toward the front) filter. (reference: FUEL LINES and RELATED PARTS, top diagram)

Anyone have an idea why the top button should be so loose? Does it have to be energized? Or can it be broken? Or is it normal? Checked the button with the power on (Key on but engine not running) and it was loose.

[Gary Lewis]

Lets take it one issue at a time, starting with the inertia switch. Below is the diagram from the 1985 EVTM of your circuit, and you can see Connector C119, which the EVTM says is "near the inertia switch". I'd unplug it and check to see if the inertia switch itself has continuity.

Having said that, you do have a DVM, right?

[Nemesis F150]

Lets take it one issue at a time, starting with the inertia switch. Below is the diagram from the 1985 EVTM of your circuit, and you can see Connector C119, which the EVTM says is "near the inertia switch". I'd unplug it and check to see if the inertia switch itself has continuity.

Having said that, you do have a DVM, right?

Removed the Inertia Switch and measured the resistance between the two prongs that the wire cable connects to and it read 0.02/0.03 Ω with a Fluke 77. [edit: after testing again and holding the probes a few seconds longer, the reading settles down to 0.00 Ω]

Measured with the white button pushed down and pulled up; the readings were the same.

When the button is pushed down to where it touches the case, it springs back up 2 mm; all the way up with virtually no resistance (in force, not ohms) it is 6 mm off of the case.

For info, it is a Dual Tank model but I would suspect the single tank at this point might be the same. I printed a circuit diagram which I think was for the dual tank, but didn't print the part that said "dual tank", nor the URL where I got it from. Spent some time trying to find the web page where it came from but couldn't find it again.

The single tank appears to have the same circuit up to the Inertia Switch as the dual tank, and even has the same conductor code 37 Y and C119. However, after the Inertia Switch the circuit changes and isn't the same. (saved the file, see attachment). This is just in case it is needed going forward.

 

[Gary Lewis]

Removed the Inertia Switch and measured the resistance between the two prongs that the wire cable connects to and it read 0.02/0.03 Ω with a Fluke 77. [edit: after testing again and holding the probes a few seconds longer, the reading settles down to 0.00 Ω]

Measured with the white button pushed down and pulled up; the readings were the same.

When the button is pushed down to where it touches the case, it springs back up 2 mm; all the way up with virtually no resistance (in force, not ohms) it is 6 mm off of the case.

For info, it is a Dual Tank model but I would suspect the single tank at this point might be the same. I printed a circuit diagram which I think was for the dual tank, but didn't print the part that said "dual tank", nor the URL where I got it from. Spent some time trying to find the web page where it came from but couldn't find it again.

The single tank appears to have the same circuit up to the Inertia Switch as the dual tank, and even has the same conductor code 37 Y and C119. However, after the Inertia Switch the circuit changes and isn't the same. (saved the file, see attachment). This is just in case it is needed going forward.

If your DVM says there's no resistance then the inertia switch is closed and you need to look elsewhere for the problem.

And to do that you need to follow along in that diagram. You "printed" Pg 104 of the 1985 EVTM, which you can find here: Documentation/Electrical/EVTM/1985 EVTM and then go down to the section on Electric Fuel Pump Control. As you can see, the inertia switch is after the fuel pump relay, so you can check at the inertia switch to see if the relay is coming in. You should have battery voltage on both sides of the switch with the ignition switch in Start or Run.

[Nemesis F150]

If your DVM says there's no resistance then the inertia switch is closed and you need to look elsewhere for the problem.

And to do that you need to follow along in that diagram. You "printed" Pg 104 of the 1985 EVTM, which you can find here: Documentation/Electrical/EVTM/1985 EVTM and then go down to the section on Electric Fuel Pump Control. As you can see, the inertia switch is after the fuel pump relay, so you can check at the inertia switch to see if the relay is coming in. You should have battery voltage on both sides of the switch with the ignition switch in Start or Run.

Thank you, Gary. The url for the diagram location is very helpful.

1. Inertia Switch (IS) circuit voltage test: This was very difficult to do; spent a lot of time today trying to do it but access to the wire harness connection end points where it attaches to the IS is very difficult. The leads for the Fluke didn't seem to really reach the connector metal terminal ends because the voltage readings were between zero and about 0.2 or 0.3 which could be attributed to static electricity.

Tried various things to contact the metal terminals but since they are recessed up inside the plastic case it was difficult. Elsewhere I've read to be careful about causing damage with the test leads. Due to the difficult access I tried everything from staples to making a couple small metal strips to simulate the two flat pins on the IS but even that was difficult. They don't make tin cans like they used to ... they're made of really thin aluminum now, and the tin snips had a difficult time cutting a narrow ~ 2mm strip with the thin meal. Then, it was difficult to put the strips into the end of the terminal. Could't get anything in the way of voltage.

2. Fuel Pump Relay (FP Relay), I guess, is the next step as I don't know where C119 is. The wire harness has an electrical tape covering. As part of prior troubleshooting the FP Relay was replaced even though I didn't know if it was bad. The wiring diagram shows four terminals and a switch. Would like to find a pin diagram with instruction about how to test it. Writing and numbers on the side: "Ford" E3TB 9345 A2A Probably jumping the gun at this point.

Any suggestions from here?

[Gary Lewis]

Thank you, Gary. The url for the diagram location is very helpful.

1. Inertia Switch (IS) circuit voltage test: This was very difficult to do; spent a lot of time today trying to do it but access to the wire harness connection end points where it attaches to the IS is very difficult. The leads for the Fluke didn't seem to really reach the connector metal terminal ends because the voltage readings were between zero and about 0.2 or 0.3 which could be attributed to static electricity.

Tried various things to contact the metal terminals but since they are recessed up inside the plastic case it was difficult. Elsewhere I've read to be careful about causing damage with the test leads. Due to the difficult access I tried everything from staples to making a couple small metal strips to simulate the two flat pins on the IS but even that was difficult. They don't make tin cans like they used to ... they're made of really thin aluminum now, and the tin snips had a difficult time cutting a narrow ~ 2mm strip with the thin meal. Then, it was difficult to put the strips into the end of the terminal. Could't get anything in the way of voltage.

2. Fuel Pump Relay (FP Relay), I guess, is the next step as I don't know where C119 is. The wire harness has an electrical tape covering. As part of prior troubleshooting the FP Relay was replaced even though I didn't know if it was bad. The wiring diagram shows four terminals and a switch. Would like to find a pin diagram with instruction about how to test it. Writing and numbers on the side: "Ford" E3TB 9345 A2A Probably jumping the gun at this point.

Any suggestions from here?

A number of Ford's connectors use 1/4" blade terminals, so if the inertia switch connector does you could just use some spare spade terminals.

But you really don't have to take the inertia switch out of the circuit. You just want to know if there is battery voltage on the output side, and you don't want to measure across the switch but from the switch to ground. So if the blade terminal approach won't work go get a straight pin and push it through the insulation near the inertia switch. Put your positive lead on that and your negative lead on ground and measure the voltage.

As for a connector's location, you go to the EVTM section that shows the connector and scroll down to the last or next-to-last page where there'll be a list of connectors and locations.

But I don't know anywhere that has a pin-out on the relay. But there are only 4 wires, so you can use the wire colors to determine what is what.

 

[Nemesis F150]

A number of Ford's connectors use 1/4" blade terminals, so if the inertia switch connector does you could just use some spare spade terminals.

Bingo! Great idea! The blades are much smaller than 1/4", just measured one and it's a tad over 1/16", look closer to 2mm, and, they are thinner. That's no problem because I've got a lots of connectors so I can file one or two down to size.

But you really don't have to take the inertia switch out of the circuit. You just want to know if there is battery voltage on the output side, and you don't want to measure across the switch but from the switch to ground.

Actually, I was wondering about measuring the voltage to ground, tried it and that's where the ~0.2 > 0.3 V came up, but the difficulty was with trying to maintain the probe connection in a contorted condition on the seat to under the dash, while at the same time holding the the probes and the connector with only two hands. Will give it another try tomorrow.

As for a connector's location, you go to the EVTM section that shows the connector and scroll down to the last or next-to-last page where there'll be a list of connectors and locations.

I'll check it out.

But I don't know anywhere that has a pin-out on the relay. But there are only 4 wires, so you can use the wire colors to determine what is what.

Another good idea!

.... And, the saga continues...

(I'd hate to be a mechanic trying to earn a living! The word starvation comes to mind.)

[Gary Lewis]

A number of Ford's connectors use 1/4" blade terminals, so if the inertia switch connector does you could just use some spare spade terminals.

Bingo! Great idea! The blades are much smaller than 1/4", just measured one and it's a tad over 1/16", look closer to 2mm, and, they are thinner. That's no problem because I've got a lots of connectors so I can file one or two down to size.

But you really don't have to take the inertia switch out of the circuit. You just want to know if there is battery voltage on the output side, and you don't want to measure across the switch but from the switch to ground.

Actually, I was wondering about measuring the voltage to ground, tried it and that's where the ~0.2 > 0.3 V came up, but the difficulty was with trying to maintain the probe connection in a contorted condition on the seat to under the dash, while at the same time holding the the probes and the connector with only two hands. Will give it another try tomorrow.

As for a connector's location, you go to the EVTM section that shows the connector and scroll down to the last or next-to-last page where there'll be a list of connectors and locations.

I'll check it out.

But I don't know anywhere that has a pin-out on the relay. But there are only 4 wires, so you can use the wire colors to determine what is what.

Another good idea!

.... And, the saga continues...

(I'd hate to be a mechanic trying to earn a living! The word starvation comes to mind.)

Good luck! Many of us have been through this sort of troubleshooting so have worked out ways to do it. And several of us have been intimate with the fuel pump relay circuit, although yours is slightly different from the one on my 460. Anyway, hang in there you'll figure it out.

[Nemesis F150]

Good luck! Many of us have been through this sort of troubleshooting so have worked out ways to do it. And several of us have been intimate with the fuel pump relay circuit, although yours is slightly different from the one on my 460. Anyway, hang in there you'll figure it out.

Update:

The connector file-width in progress to compare it with those in the Inertia Switch; have to file some more.

While filing down a connector to insert in the cable plug that connects to the Inertia Switch there was a discovery ...

Spade connector with file job as compared to the original versions. Noticed that the spade is obviously made with thinner metal and that is folded over to make the spade thicker. The die that makes this has to be more complicated in order to blank and press at the same time, either that, or it is a multi-step process which is still more complicated.

After testing with the spade connector in the wire harness connecter, there was still no voltage between it and ground. *sigh*. Off to the next step.

[Gary Lewis]

Update:

The connector file-width in progress to compare it with those in the Inertia Switch; have to file some more.

While filing down a connector to insert in the cable plug that connects to the Inertia Switch there was a discovery ...

Spade connector with file job as compared to the original versions. Noticed that the spade is obviously made with thinner metal and that is folded over to make the spade thicker. The die that makes this has to be more complicated in order to blank and press at the same time, either that, or it is a multi-step process which is still more complicated.

After testing with the spade connector in the wire harness connecter, there was still no voltage between it and ground. *sigh*. Off to the next step.

The inertia switch was just an easy place to start, kind of in the middle. So if you don't have power to it then you need to move upstream. Check out the wires to the relay. The yellow wire should have power and when the relay closes the Pk/Bk is powered. But not if the relay doesn't close.