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Hey,
1987 F150 4.9. a while ago the truck left me stranded when one of the connectors going to the inertia switch had become so hot, it melted through. Spent a while diagnosing that one
So I cut out that connector and crimp butt spliced where needed. Issue is, the wires are still very warm. I've posted on facebook. Responses vary from a bad fuel link pulling too much current (CO worker has an amp clamp I'll borrow) but I don't know what it's supposed to be pulling. Another response is that maybe the inertia switch is incorrect itself . It has the ability to hold three wires but only two are used.
Can anyone help me find information on these inertia switches and how to test them? The current one has continuity where it should and none when it should not .
I dont have a good answer but the switch is not showing hot from the IR gun and if it is passing power it would be good.
The wires heating up is the weak link and will burn up again if not fixed.
The only reason I can think of the wires heating out is too high a load draw for wire size or high resistance from corrosion.
High load could be the pump going bad and drawing too much amps.
I would think you could check what the pump draws and then check it to see if within spec.
The other but a WAG is a short in the wire but not blowing the fuse.
Dave ----
I dont have a good answer but the switch is not showing hot from the IR gun and if it is passing power it would be good.
The wires heating up is the weak link and will burn up again if not fixed.
The only reason I can think of the wires heating out is too high a load draw for wire size or high resistance from corrosion.
High load could be the pump going bad and drawing too much amps.
I would think you could check what the pump draws and then check it to see if within spec.
The other but a WAG is a short in the wire but not blowing the fuse.
Dave ----
Sweet. Thanks for the help. I've never read amperage using a multimeter but I'm going to try that out tonight.
I'll spray some electrical contact cleaner on the inertia switch connections and see if those two things help me out
It may just be time to bite the bullet and replace the whole in-tank fuel pump assembly. My gauge bounces when at half and that's all the reading I get from it
I did not think of this before, dont know why? But you could bypass the switch with jumper wires of a larger size that the wires to the switch.
Again I dont think it is the switch as the IR is not showing the switch being hot jut the wires to it from what I can see.
They also say not to let tanks get too low as the fuel keep the pump cool.
Dont know how long that pump has been installed but with the sender acting up it might be time for a pump / sender swap out.
I have a John Deere garden tractor with a fuel injected engine.
When I first got it about an hour and a half the motor would start to surge. Thing is the test port was after the fuel pressure regulator so no way to know if pump or regulator was the cause.
Well taking to the dealer I was able to test after the pump and before the regulator and found the pump would start to loose pressure.
Bad pump as it heated up it would stop working. When I went to swap it out the fuel in the tanks was boiling hot and should never gotten that hot.
I bet if I was to amp out the pump I would have seen the amps went up when it got hot to the point it stopped pumping till it cooled off and would start pumping again.
I wonder if you could also see if the fuel PSI is low as the pump is not pumping as it should?
If you amp the pump let us know what you find.
Dave ----
I did not think of this before, dont know why? But you could bypass the switch with jumper wires of a larger size that the wires to the switch.
Again I dont think it is the switch as the IR is not showing the switch being hot jut the wires to it from what I can see.
They also say not to let tanks get too low as the fuel keep the pump cool.
Dont know how long that pump has been installed but with the sender acting up it might be time for a pump / sender swap out.
I have a John Deere garden tractor with a fuel injected engine.
When I first got it about an hour and a half the motor would start to surge. Thing is the test port was after the fuel pressure regulator so no way to know if pump or regulator was the cause.
Well taking to the dealer I was able to test after the pump and before the regulator and found the pump would start to loose pressure.
Bad pump as it heated up it would stop working. When I went to swap it out the fuel in the tanks was boiling hot and should never gotten that hot.
I bet if I was to amp out the pump I would have seen the amps went up when it got hot to the point it stopped pumping till it cooled off and would start pumping again.
I wonder if you could also see if the fuel PSI is low as the pump is not pumping as it should?
If you amp the pump let us know what you find.
Dave ----
You are a huge help, thank you so much.
I didn't get a chance to amp clamp yesterday. Also given that this is a 1987 4.9 I cannot find a dedicated fuse in the fusebox, thereby giving me a reference for allowable amperage. I'll have to dig into what amperage should be
The pump motor itself was replaced about a year when my ECM started acting up, followed soon after by my PIP acting up. I must've bought the pump motor from O'Reilly because I don't see the history on Rock Auto.
I think I will just buy the whole assembly. A working gas gauge would be nice
Will keep thread updated if I can borrow the amp clamp today
Sorry to say I am not up on the EFI trucks, mine is a 81 F100 so has a carb.
Is there any fuses under the hood? I am pretty sure there is a fuel pump relay under there, maybe on the passenger side inner fender area?
You know there is a 87 - 92? truck area and maybe someone would know in there what is going on with your truck?
Dave ----
Sorry to say I am not up on the EFI trucks, mine is a 81 F100 so has a carb.
Is there any fuses under the hood? I am pretty sure there is a fuel pump relay under there, maybe on the passenger side inner fender area?
You know there is a 87 - 92? truck area and maybe someone would know in there what is going on with your truck?
Dave ----
I wish mine had a carb. Wouldn't have to worry so much about sensors and switches failing.
There is a FP relay under the hood and I believe it's okay. You're thinking a bad relay could cause the heat? According to this diagram the inertia switch get battery voltage from the EEC and grounds near the driver's side headlight. Shares the same ground with wiper motor .
Using my power probe I applied 12V to the wiper motor ground wire which tripped my probe, indicating a good ground.
However when I put the probe to the inertia switch wires, each wire had 12-12.5V. How does that work??
And I haven't found specific years for this website. Still learning how to navigate it
I did not think of this before, dont know why? But you could bypass the switch with jumper wires of a larger size that the wires to the switch.
Again I dont think it is the switch as the IR is not showing the switch being hot jut the wires to it from what I can see.
They also say not to let tanks get too low as the fuel keep the pump cool.
Dont know how long that pump has been installed but with the sender acting up it might be time for a pump / sender swap out.
I have a John Deere garden tractor with a fuel injected engine.
When I first got it about an hour and a half the motor would start to surge. Thing is the test port was after the fuel pressure regulator so no way to know if pump or regulator was the cause.
Well taking to the dealer I was able to test after the pump and before the regulator and found the pump would start to loose pressure.
Bad pump as it heated up it would stop working. When I went to swap it out the fuel in the tanks was boiling hot and should never gotten that hot.
I bet if I was to amp out the pump I would have seen the amps went up when it got hot to the point it stopped pumping till it cooled off and would start pumping again.
I wonder if you could also see if the fuel PSI is low as the pump is not pumping as it should?
If you amp the pump let us know what you find.
Dave ----
I updated my fin6dingz in someone elses comment, could you take a look and let me know what you think?
I have no clue how the new power probes work as I dont have or used one so tripping or not means nothing to me sorry to say.
But from what I see from the first link of the wiring. If the wire that gets hot is BR - brown before the switch or PK / BK- pink / black after the switch the only thing I see is the pump and being you have a Fxxx truck and not a Bronco you dont have a resister.
That is telling me the pump is pulling too much power / amps but check it with a meter.
Dave ----
I have no clue how the new power probes work as I dont have or used one so tripping or not means nothing to me sorry to say.
But from what I see from the first link of the wiring. If the wire that gets hot is BR - brown before the switch or PK / BK- pink / black after the switch the only thing I see is the pump and being you have a Fxxx truck and not a Bronco you dont have a resister.
That is telling me the pump is pulling too much power / amps but check it with a meter.
Dave ----
Each wire is hot. The wire on my truck is not BROWN, but GREY/BLACK.
I ordered a new fuel pump assembly from O'Reilly's with a lifetime warranty. I'll install that over the weekend and see how it all goes. I still haven't read amperage. Co worker amp clamp didn't have DC amps, if AC and DC amps are even different.
I would inspect the inertia switch itself. As far as I have seen, all inertia switches have a ball bearing and two blades that get connected when the ball bearing falls between the two blades. It is the contact of the ball with the blades that is broken to interrupt power when the ball is jostlied out of position or falls out due to gravity. The reset just pushes the ball back into place where gravity will hold it until it is bumped/rolled out of position.
If the edges of the blades are corroded, you might find the resistance higher than normal which will cause an increase in heat.
It is not unusual for wiring to get warm. Just above hand temperature. Not hot. increased resistance will cause heat, and a festering ball that was not seated tightly could have caused your original damage.
Sometimes just dancing on the red button to jostle the ball bearing around will clean up the contact areas and reduce the resistance and thus minimize the heat generation.
Go dance on the button a few times and then check back.
tom
But I did not see the heat in the switch only the wires.
I also said try and use jumper wires to bypass the switch so it is out of the picture.
Dave ----
I would inspect the inertia switch itself. As far as I have seen, all inertia switches have a ball bearing and two blades that get connected when the ball bearing falls between the two blades. It is the contact of the ball with the blades that is broken to interrupt power when the ball is jostlied out of position or falls out due to gravity. The reset just pushes the ball back into place where gravity will hold it until it is bumped/rolled out of position.
If the edges of the blades are corroded, you might find the resistance higher than normal which will cause an increase in heat.
It is not unusual for wiring to get warm. Just above hand temperature. Not hot. increased resistance will cause heat, and a festering ball that was not seated tightly could have caused your original damage.
Sometimes just dancing on the red button to jostle the ball bearing around will clean up the contact areas and reduce the resistance and thus minimize the heat generation.
Go dance on the button a few times and then check back.
tom
