IP FSS fuse rating

[Scratcher]

Anyone know what the fuse rating for the FSS is? My original wire burned up and I thought it was 20amp so I installed a 20 amp inline but it keeps blowing! I know I might have other issues but wanted to check what the rating was before I go digging around looking for a short. Thanks!

 

[gnathv]

https://www.oilburners.net/attachments/early-83-gp-system-jpg.60568/

Here‘s a 1983 diagram. If you unplug the wire to fss are you able to run 12v to it and it operates? The fuel heater is on that same circuit and are known to short out Also.

 

[hacked89]

You have a short. It takes very little amperage to power a properly working fss.

 

[franklin2]

Just like the later trucks, you can see from the diagram above there is no fuse, but just a fusible link. In 1986 they used a 20 gauge blue fusible link. You can buy this fusible link wire at the store. A fusible link is just a undersized piece of wire with special insulation around it that does not catch fire.

 

[franklin2]

From wikipedia

An electrical fusible link is a type of electrical fuse that is constructed simply with a short piece of wire typically four American wire gauge (AWG) sizes smaller than the wire that is being protected. For example, an AWG 16 fusible link might be used to protect AWG 12 wiring. Electrical fusible links are common in high-current automotive applications. The wire in an electrical fusible link is encased in high-temperature fire-resistant insulation to reduce hazards when the wire melts.

So the wire feeding the FSS would be 16 gauge wire (4 sizes larger than the fusible link). If you go by the chart in this link https://www.raso.name/cars/22-maintaining/54-fusible-links?showall=1
16 gauge wire is good for 22 amps. So you would think a 30 amp fuse would hold it.

 

[Nero]

Fusible links are for a slow blow, whereas a fuse is instant. I tried running a fuse once for my IP and had nothing but troubles with it. Popped in a fusible link, has been fine since 2012.

 

[Scratcher]

You have a short. It takes very little amperage to power a properly working fss.

Yep. Just can't find it though. Pulling my hair out!

 

[Scratcher]

https://www.oilburners.net/attachments/early-83-gp-system-jpg.60568/

Here‘s a 1983 diagram. If you unplug the wire to fss are you able to run 12v to it and it operates? The fuel heater is on that same circuit and are known to short out Also.

I don't have a fuel heater. The strange thing is that after I did the repair I drove 50 miles with no issues. Then I stopped to pick up parts. Came out of the store and blew the fuse. I put in another fuse and drove 5 miles home, shut it down then restarted and the fuse blew. Then I let it sit overnight. Cam out next morning and it started up. Drove two miles and it blew. So i changed it again and it took me home.
So i have an intermittent short happening somewhere. I've been under it and over the top searching and just don't see anything out of place. Really getting on my nerves. Auto electrics are not my forte!

 

[Jesus Freak]

I don't have a fuel heater. The strange thing is that after I did the repair I drove 50 miles with no issues. Then I stopped to pick up parts. Came out of the store and blew the fuse. I put in another fuse and drove 5 miles home, shut it down then restarted and the fuse blew. Then I let it sit overnight. Cam out next morning and it started up. Drove two miles and it blew. So i changed it again and it took me home.
So i have an intermittent short happening somewhere. I've been under it and over the top searching and just don't see anything out of place. Really getting on my nerves. Auto electrics are not my forte!

Chasing wires is miserable, if it was a Chrysler product that is all you ever do.
But alas, it's what you have to do some times. Just park it and when you can " get in the zone" apply all your mental capacity to just chasing the wire. @Selahdoor does it all the time and makes the most fascinating threads about it, they read like mystery novels AND he finishes them with a whole host of odd characters that show up at the very end. Good luck! You can do it!

 

[gnathv]

Unplug the wire to the fss. Connect a wire to fss with 12v and a fuse in it. Drive it and see if problem still occurs. This will help point to either wiring or fss. If it doesn’t blow fuse look for wiring, if it does blow fuse look at fss.

 

[Scratcher]

So what's the difference between a fusible link and an inline fuse of the same gauge?

 

[Scratcher]

Unplug the wire to the fss. Connect a wire to fss with 12v and a fuse in it. Drive it and see if problem still occurs. This will help point to either wiring or fss. If it doesn’t blow fuse look for wiring, if it does blow fuse look at fss.

I know its not the FSS because if I unplug it, the fuse still blows when the ignition is turned on. Now I have to try and figure out if the short is on the feed side or the harness side.

I know there are issues in the harness because the cold start and high idle stopped working a few years ago

 

[franklin2]

So what's the difference between a fusible link and an inline fuse of the same gauge?

Fusible links are rated by the gauge wire they are made of. Fuses are rated in amps.

I looked, there is really no definitive cross-over from link size to amperage. But suffice to say, fusible links are very tough and can handle a lot of current before they burn in two. A fuse is quicker and more susceptible to blowing.

The fusible link in this circuit is 20 gauge, which is very small. Thus my estimate that a 30 amp fuse would hold it, since the wiring in the circuit is 16 gauge wire.

Most other fusible links are larger, and if a fuse was to be substituted for them, it would have to be a large maxi fuse. As an example, in 1986 the fusible link for most of the electrical system and the alternator is a 14 gauge link. Since most of these trucks had a 100 amp alternator originally, you can see to substitute a fuse for the 14 gauge link, you would most likely need at least a 125 amp maxi fuse to hold that circuit.

 

[Nero]

Start chasing the wire. The fact that it blows at different intervals means it's a wire that the casing has worn through and is grounding out on the frame.
Start at one end of the circuit (I suggest the pump) and work backwards. The circuit is very simple. Goes from the IP to a big connector on the passenger side valve cover, then from there it goes to a split, then the fusible link.

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[Scratcher]

Start chasing the wire. The fact that it blows at different intervals means it's a wire that the casing has worn through and is grounding out on the frame.
Start at one end of the circuit (I suggest the pump) and work backwards. The circuit is very simple. Goes from the IP to a big connector on the passenger side valve cover, then from there it goes to a split, then the fusible l