Fuel Pump Kill Switch Guidance

[arctictraveller]

It's best to use a relay rather than just a switch. If I'm not mistaken the pump can draw more than 15A at times.

[posplayr]

Originally Posted by arctictraveller

It's best to use a relay rather than just a switch. If I'm not mistaken the pump can draw more than 15A at times.

I just happened to measure it (1997 5.4L E-350) today.

The current (peaks at about 17A or 3X steady-state of 6A).

I also looked at the fuel pump relay. It is a standard 40A/30A relay.

Scope display here.

https://www.dropbox.com/s/cgio3fe6n4...utoff.png?dl=0

[arctictraveller]

Wow, that’s a pretty fancy / accurate way of measuring current. Where does it show amps? It looks like the display is showing MV.

[posplayr]

Originally Posted by arctictraveller

Wow, that’s a pretty fancy / accurate way of measuring current. Where does it show amps? It looks like the display is showing MV.

The A622 has two scales 100mV/A and 10 mV/A. I had it on the former.

https://www.testequipmentdepot.com/t...rent-probe.htm

I also confirmed the steady-state using this.

https://www.ebay.com/itm/333681392226

The only thing I miss about my old THS730A is that the input scaling on the scope probes can be set to amps. It is set up beautifully for the A622 current probe; the display reads out amps directly.

https://www.valuetronics.com/product...illoscope-used


I originally bought the THS730A and A622 clamp in 1997 when it first became available as a 1Ghz sample rate digital memory scope (about $4500 purchase). With the new low-priced Chinese scopes dropping in price ($350), I sold the 20+ YO THS730A (NiCad batteries, 9600 RS232 interface, 32bit SW case and all) in 2020 to (belatedly) justify buying the newer SDS1000X-E in 2017 (I finally decided there was no need for the THS730A portability and high voltage isolation doing Arduino projects).

Unfortunately, the SDS1000X-E does not (appear) to have any way to make the screen display in amps. Fortunately, you can have it display 1 A/V as in this display.

[Scalf77]

Nicely done. Sadly, I remember when taking a picture of a scope shot, was literally a polaroid add on. No worries about colors either. You had to read schematics on microfish. Back when a processor was composed of boards, not a single chip.

-greg

[posplayr]

Originally Posted by Scalf77

Nicely done. Sadly, I remember when taking a picture of a scope shot, was literally a polaroid add on. No worries about colors either. You had to read schematics on microfish. Back when a processor was composed of boards, not a single chip.

-greg

I think I still have some circ 1980 from a spectrum analyzer. Single Sideband modulation of pseudo-random noise.

In-house board production was stitch wire and manual layout.

My whole department shared one HP computer.

Tandy 1000 double floppy drive mainframes LOL.

The progression of electronics is mind-boggling. The bulk of that Oscope is largely one dual-processor SOC. One for the Java VM GUI and the other for the scope functions. When you open it up it is mostly air.

[porschedpm]

In addition to theft deterence, anyone use a fuel pump kill switch to bring the oil pressure up before a cold start?

[JWA]

The best device IMHO for theft deterrence is the Ravelco or something similar. There was a brief time I found and bought the same assemblies their so-called authorized independent installers use through eBay but Ravelco complained they were counterfeit and eBay removed the listings----they just can't be found there any longer.

To me ANY device that's wholly electronic or has moving parts for user convenience are just too prone to failing at the most inopportune times. Something like the Ravelco has about 99% less likely to fail as there is just one part needed to enable or disable your starting and fuel systems.

Originally Posted by porschedpm

In addition to theft deterence, anyone use a fuel pump kill switch to bring the oil pressure up before a cold start?

For that operation you'd want to research engine pre-oiling systems.

[nyyankees588]

Just wanted to wrap this up by saying that I finally slowed down to install the fuel pump cut-off switch in my van (moving and life got in the way since I first posted).

At the end of the day, it's a really quick install (<2hrs). Once you locate the fuel inertia switch, just cut one of the wires (I cut the green wire, as it was what received the voltage when the ignition is turned on) and install a switch in-line. As suggested by boywonder and others, I installed the switch wires using quick-disconnect connectors, so that the cut wire can be connected back together without the switch (in case of a failure of the switch).

I used a switch rated at 20a that I had laying around, hopefully I don't have any issues as others have pointed out regarding the higher voltage that the fuel pump inertia pump can pull at times.

I have to say, I'm really pleased. The hardest part is figuring out a good place for the switch that is accessible when sitting in the driver's seat, while also being hidden from any potential thief. I obviously won't give my location away... but you can be creative. The best thing, IMO, is that the car still turns over, it just doesn't start. Aka it sounds like it has a problem. Which hopefully is just enough to cause a thief to say screw it and leave.

[nyyankees588]

I should add - I bought some "viper alarm" window stickers and added to the van. While they may just be stickers... it's a cheap added deterrent.