*Journal Thread* Solving the melted 25A EFI fuse issue

[creakycruiser]

I will be journaling fixing my dreaded melted 25A EFI fuse issue here. This has been a tough one for me, since it has caused me to lose faith in my trusty steed.

WHAT HAPPENS

25A EFI fuse in the driver's side engine room J/B melts. When it melts, it loses connection with the fuse contacts and disables the fuel system.

WHAT'S SUPPOSED TO HAPPEN

25A EFI fuse has a proper load, generating not enough heat to melt contacts/wires – creating a reliable circuit for the EFI system.

TEMPORARY FIXES (TRAIL)

• Wiggle the 25A EFI fuse (wiggle, wiggle, wiggle)
  • If wiggling doesn't work, replace the 25A EFI fuse and bend the legs apart () to ensure a tighter fit for the contacts.
  • Note: Pretty trusty method on the trail for me. You leave the ignition to ON (II), wiggle the fuse and listen for the EFI relay to make an audible click/for the fuel system to "bzzzzzzz". Sometimes, if the contacts are just beginning to fail, you'll hear a rapid series of "clickclickclickclickclick" like a machine gun, as the fuse contacts arc.
  • Note: Using liberal amounts of dielectric grease on the fuse legs isn't a bad idea, but I found it doesn't help this issue much.
• Use mini fuse power taps and run a jumper wire.
  • Note: Yes, these will eventually melt/corrode as well.

TEMPORARY FIXES (GARAGE)

• Replace the fuse box
  • Note: I've done this, and after 1.5yr, the same issue happened again.
    • [INSERT EXPLETIVES HERE]
• Splice the EFI wires before the J/B and add a separate fuse box with higher gauge wiring.
  • Note: If you bypass the EFI fuse, then that could cause issues with the transmission electronics and/or cruise control, since it appears these components run off the same fuse.
  • See EWD #1.
• EFI relay bypass kit hooked up to the battery instead of the 25A EFI fuse.
  • Note: At first, I was like, "How would this help...?" but after continuous afterthought, it makes sense. If you use this kit to bypass the 25A fuse and connect the EFI relay directly to the battery, then it seems like a decent solution. But you've still got an issue somewhere in the wiring, causing excessive load/heat, which begs the question: "What's next?"

RELEVANT WIRING DIAGRAMS (EWD)

(#1)

(#2)

(#3)

(#4)

 

[creakycruiser]

Joey shared pics of a local friend opening up their fusebox and confirming that the fuse contacts were the immediate issue.

I'd still like to not go this route since it's still a temporary fix albeit a clean one.

 

[creakycruiser]

PLAN OF ACTION

• Identify what's causing the excessive load and then replace/repair. Ideally this repair will be done without touching/modifying the fuse or fusebox.
• This post will be updated soon. I'm currently trying to figure out how to best isolate each circuit. Any advice is appreciated.

 

[creakycruiser]

Big update. I ended up chasing the issue to the internal fuse contacts. I bit the bullet and purchased a brand new engine room fusebox from a local dealership (~ $500 USD). No issues since after 4 months.

 

[creakycruiser]

Reserving this post.

 

[creakycruiser]

Reserving this post.

 

[jLB]

If you use this kit to bypass the 25A fuse and connect the EFI relay directly to the battery, then it seems like a decent solution. But you've still got an issue somewhere in the wiring, causing excessive load/heat, which begs the question: "What's next?"

Wouldn’t you want that circuit “switched”, and not “always hot” (directly connected to the battery)?

 

[medtro]

I will be journaling fixing my dreaded melted 25A EFI fuse issue here.

If this is for your 1999, then EFI fuse is 20A from the factory, not 25A.

Splice the EFI wires before the J/B and add a separate fuse box with higher gauge wiring.

• Note: If you bypass the EFI fuse, then that could cause issues with the transmission electronics and/or cruise control, since it appears these components run off the same fuse.
• See EWD #1.

If you bypass the EFI fuse, you can back feed the circuit using one of the relay receptacles. No need to splice EFI wires.

This EWD doesn't apply to your 1999.

 

[medtro]

Wouldn’t you want that circuit “switched”, and not “always hot” (directly connected to the battery)?

Always hot to the relay, but not energized until the ignition is switched. The EFI fuse circuit in the fuse box is always hot too.

 

[BullElk]

I may be wrong but I believe the most efficient and cost effective solution to this rare Toyota error has already been created and solved by @medtro.

 

[medtro]

Replace the fuse box

• Note: I've done this, and after 1.5yr, the same issue happened again.
  • [INSERT EXPLETIVES HERE]

Is this a new fuse box?

 

[creakycruiser]

Is this a new fuse box?

Nope, used in great condition with "no known EFI issues".

 

[creakycruiser]

I may be wrong but I believe the most efficient and cost effective solution to this rare Toyota error has already been created and solved by @medtro.

Yep, and that's the route I'm taking in the meantime – Would still love to determine if the issue is caused by fuse contacts or something else.

 

[dealmaker]

@creakycruiser , can you update your first post to include the year make and model of your 100?

 

[Dirt J]

Bump for any ideas/progress on diagnosing this issue. If I'm looking at the WD right, it looks like this circuit leads to the fuel pump, via two additional replays?

 

[creakycruiser]

Bump for any ideas/progress on diagnosing this issue. If I'm looking at the WD right, it looks like this circuit leads to the fuel pump, via two additional replays?

Big update. I ended up chasing the issue to the internal fuse contacts. I bit the bullet and purchased a brand new engine room fusebox from a local dealership (~ $500 USD). No issues since after 4 months.

 

[AimCOtaco]

Sound right. Sometimes a fuse fails because of a downstream load (textbook fuse pop), often times its just bad connections at the fuse it'self that cause heating and resulting load increase and opening. Good clean connections are the key, an old fusebox will have some loose fits and a high constant load like the EFI system would be amoung the first to fail.
Glad you got it fixed and 4 months of confidence back!