EFI 15 amp fuse blowing (1 Viewer)

[Anvil]

I've researched a lot and watched many Youtube videos... I'm still at a loss and need some advice. Thank you in advance!

The EFI 15 amp fuse keeps blowing on my girlfriends 1995 80. The Cruiser will travel 10 to 12 miles when cold, then the fuse blows. It then blows a fuse every .5 to 1 mile.

I have a factory service manual and used it to check the fuel pump relay with a volt meter. The relay is fine. I installed a new fuel pump today. I read the blue wire on the fuel pump assembly could be the issue, but it looked good.

What is my next troubleshooting step?

All help is much appreciate!!!

 

[OfficialGamings]

I have a 1993 80 myself and I believe the 94s are around similar. But the 95s did have a few updated things which I believe included OB2, So take my suggestions with a grain off salt because I may be incorrect. And without me actually digging in and looking at the FSM I may be guessing bad information.

Anyway. I know on my 93. There are quite a few different relays within the EFI line and overall does supply power to quite abit of things I believe. And obviously something is drawing more current then it is intended too.

Within the electrical line of my 93. I have Fuel pump relay, Fuel pump resistor and also COR ( Circuit Opening Relay), and I think the COR clicks on a few different things(Not %100 sure on that)

Have to tried to run the rig for any codes with OB2?

And With you saying it runs okay when cold. Does the fuse blow after getting upto operating temperature?

 

[Anvil]

I have a 1993 80 myself and I believe the 94s are around similar. But the 95s did have a few updated things which I believe included OB2, So take my suggestions with a grain off salt because I may be incorrect. And without me actually digging in and looking at the FSM I may be guessing bad information.

Anyway. I know on my 93. There are quite a few different relays within the EFI line and overall does supply power to quite abit of things I believe. And obviously something is drawing more current then it is intended too.

Within the electrical line of my 93. I have Fuel pump relay, Fuel pump resistor and also COR ( Circuit Opening Relay), and I think the COR clicks on a few different things(Not %100 sure on that)

Have to tried to run the rig for any codes with OB2?

And With you saying it runs okay when cold. Does the fuse blow after getting upto operating temperature?

Thanks for the input!

There's been a Check engine light on for a while, regarding an O2 sensor... I'll check again. I forgot to do that.

Yes, once the vehicle comes to operating temp, the fuse blowing is more frequent. This is why I thought the fuel pump was worn out and drawing more amps when hot.

 

[OfficialGamings]

Thanks for the input!

There's been a Check engine light on for a while, regarding an O2 sensor... I'll check again. I forgot to do that.

Yes, once the vehicle comes to operating temp, the fuse blowing is more frequent. This is why I thought the fuel pump was worn out and drawing more amps when hot.

Fuel pump should be drawing more when trying to warm up ? Thats how I thought it worked. You use more fuel warming the engine up to operating temperature. So therefor fuel pump is delivering more fuel drawing more current.

Obviously that only really applies to idle. Once your driving you would be pulling more fuel anyway. But I doubt it would be the fuel pump itself causing the issue.

Seems something else is not reading correctly and making something pull alot of current.

O2 Sensor code is interesting though because when your (Cold) and or not at operating temperature the O2 Sensors should be in open loop. and the ECU uses its own fuel mapping and once it hits operating temperature (Closed loop) the O2 sensors are used to determine fuel mapping etc.

Just a thought…

 

[Anvil]

Fuel pump should be drawing more when trying to warm up ? Thats how I thought it worked. You use more fuel warming the engine up to operating temperature. So therefor fuel pump is delivering more fuel drawing more current.

I thought a worn/about to die fuel pump would draw more amps... I could me wrong.

 

[OfficialGamings]

I thought a worn/about to die fuel pump would draw more amps... I could me wrong.

Yes you are correct. A worn out pump can draw more current to keep up with the demand. Also a blocked fuel filter(In the tank) and also the filter which is in the engine bay somewhere. Could be another reason to draw more current to keep up.

But it seems to be a more present issue when at operating temperature. From what you have explained. Which makes me think something else is wrong. But once again I could also be incorrect

 

[jonheld]

The EFI 15 amp fuse keeps blowing on my girlfriends 1995 80. The Cruiser will travel 10 to 12 miles when cold, then the fuse blows. It then blows a fuse every .5 to 1 mile.

The 15 amp EFI fuse supplies +12 to all of the ECUs sensors and VSV valves, along with the ECU itself. I would inspect the 2 well known trouble spots. The engine harness that runs next to the EGR pipe and the ECU harness that runs along the bottom support of the glovebox.

There is supposed to be a support that keeps the engine harness away from the EGR pipe and they tend to fracture over time and allow the harness to come in contact with the EGR tube which will melt through the insulation and cause havoc.

The bottom support of the glovebox is exposed metal that can abraid the ECU harness and eventually cause a short.

Another thought is the O2 sensor harnesses that hang under the truck. IIRC, someone had one rubbing on the front driveshaft due to a broken/missing support.

 

[TheGrrrrr]

Thanks for the input!

There's been a Check engine light on for a while, regarding an O2 sensor... I'll check again. I forgot to do that.

Yes, once the vehicle comes to operating temp, the fuse blowing is more frequent. This is why I thought the fuel pump was worn out and drawing more amps when hot.

This is all interesting as I've been chasing a code 25/26 without much luck, and going through my notes I noticed the previous owner had a repair done for a melted 15A EFI fuse that I think is the one you are describing. The code 25/26 lean/rich point to the O2 sensors which I replaced yesterday with OEM to no avail. Your post is the first I've seen where there is a correlation with an EFI fuse issue, so now I'm contemplating that the CEL codes might be related to the EFI repair. Also have long crank before start about 20% of the time, with a very occasional (5%) no-start. The CEL is intermittent and I think I'm noticing that when it goes out it doesn't come on for a couple of trips, which makes me think its an issue that trigger via a "2 Trip Detection Logic" as seen here:

What I'm now wondering is if the "Open in EII Circuit" or "Open in E1 Circuit" above could be describing the Circuit Open Relay and causing the codes and could have been responsible for our EFI fuse issue as well. I'm not blowing EFI fuses like you are, but my history indicates some correlation there, if not causation.

To date, as PM and in hopes of resolving the codes, I have replaced:

• EFI Fuse - 15amp
• 2x O2 Sensors
• VAF
• Fuel Pump
• Fuel Pump Relay
• Igniter and coil

Will replace as today with at least two at-temperature trips between them:

• Circuit Open Relay
• EFI Relay

I'll let you know how it goes. I'll also check my wiring but this engine was rebuilt and a new OEM wiring harness installed less than 6,000 miles ago, so I doubt I have wear issues there. I am seeing one more possibility that will be the next place I look if nothing else checks out:

Another EFI Fuse Blowing Thread (SOLVED!!)

'97 80 Series LC with 300k. No recent work other than oil top off's 🛢️ I will try and keep this short. I know there are several other threads pertaining to causes and troubleshooting of the EFI fuse blowing under various conditions. But none matched my exact scenario, so I am hoping my specific...

forum.ih8mud.com

 

[ZackR]

I've researched a lot and watched many Youtube videos... I'm still at a loss and need some advice. Thank you in advance!

The EFI 15 amp fuse keeps blowing on my girlfriends 1995 80. The Cruiser will travel 10 to 12 miles when cold, then the fuse blows. It then blows a fuse every .5 to 1 mile.

I have a factory service manual and used it to check the fuel pump relay with a volt meter. The relay is fine. I installed a new fuel pump today. I read the blue wire on the fuel pump assembly could be the issue, but it looked good.

What is my next troubleshooting step?

All help is much appreciate!!!

Unplug the 02 sensors for a few days and report back. On my 94' the 02 sensor wire had a wiring short and it would eat up ECU fuses to the point where it wouldn't even start unless the 02 sensor was unplugged.

Once the wiring short was fixed (in my case it was a new engine wiring harness) the ECU fuse hasn't blown. Luckily you have a 95 so the wiring harness it still available if it comes to that.

 

[jonheld]

Another possibility is connector BO1, which lives under the body on the left side under the C pillar. All fuel pump power goes through this connector and it is exposed to the elements.

 

[jonheld]

Will replace as today with at least two at-temperature trips between them:

• Circuit Open Relay
• EFI Relay

Very improbable that relays would cause this issue. They either open or close on the contacter side. If there was a short on the logic side of the COR, the 7.5 amp IGN fuse would pop.
If the EFI relay was an issue, this engine wouldn't run. On older 3FE equipped 80 Series (1991/1992), the EFI relay connectors in the relay box was a common issue due the heat of the exhaust manifold that ran just below the box. This is no longer an issue with the 1FZ-FE 80 Series.

 

[Anvil]

The 15 amp EFI fuse supplies +12 to all of the ECUs sensors and VSV valves, along with the ECU itself. I would inspect the 2 well known trouble spots. The engine harness that runs next to the EGR pipe and the ECU harness that runs along the bottom support of the glovebox.

There is supposed to be a support that keeps the engine harness away from the EGR pipe and they tend to fracture over time and allow the harness to come in contact with the EGR tube which will melt through the insulation and cause havoc.

The bottom support of the glovebox is exposed metal that can abraid the ECU harness and eventually cause a short.

Another thought is the O2 sensor harnesses that hang under the truck. IIRC, someone had one rubbing on the front driveshaft due to a broken/missing support.

Thank you for your input! You and a handful of other Mudders always peak my interest.

I spent the day in another Cruiserhead's shop and here's what we found/did.

Replaced the fuel pump relay with OEM.
Replaced EFI relay with OEM
Inspected the wiring harness where it was touching the ECR tube, wires looked fine. Reattached harness to holding bracket with zip ties.
Dropped the glove box and inspected the wires going to ECU. The wires weren't touching the metal bracket and looked good.
Repaced the fuel filter.
Pulled the fuel pump resistor and tested per service manual. The service manual calls for .7 - .76 resistance. My resistor measued .2. ??? Is this my issue?
After all of this... There is no CEL ! First time in two years!!!

Thanks again!

 

[Anvil]

This is all interesting as I've been chasing a code 25/26 without much luck, and going through my notes I noticed the previous owner had a repair done for a melted 15A EFI fuse that I think is the one you are describing. The code 25/26 lean/rich point to the O2 sensors which I replaced yesterday with OEM to no avail. Your post is the first I've seen where there is a correlation with an EFI fuse issue, so now I'm contemplating that the CEL codes might be related to the EFI repair. Also have long crank before start about 20% of the time, with a very occasional (5%) no-start. The CEL is intermittent and I think I'm noticing that when it goes out it doesn't come on for a couple of trips, which makes me think its an issue that trigger via a "2 Trip Detection Logic" as seen here:

View attachment 3564818

What I'm now wondering is if the "Open in EII Circuit" or "Open in E1 Circuit" above could be describing the Circuit Open Relay and causing the codes and could have been responsible for our EFI fuse issue as well. I'm not blowing EFI fuses like you are, but my history indicates some correlation there, if not causation.

To date, as PM and in hopes of resolving the codes, I have replaced:

• EFI Fuse - 15amp
• 2x O2 Sensors
• VAF
• Fuel Pump
• Fuel Pump Relay
• Igniter and coil

Will replace as today with at least two at-temperature trips between them:

• Circuit Open Relay
• EFI Relay

I'll let you know how it goes. I'll also check my wiring but this engine was rebuilt and a new OEM wiring harness installed less than 6,000 miles ago, so I doubt I have wear issues there. I am seeing one more possibility that will be the next place I look if nothing else checks out:

Another EFI Fuse Blowing Thread (SOLVED!!)

'97 80 Series LC with 300k. No recent work other than oil top off's 🛢️ I will try and keep this short. I know there are several other threads pertaining to causes and troubleshooting of the EFI fuse blowing under various conditions. But none matched my exact scenario, so I am hoping my specific...

forum.ih8mud.com

Thank you for chiming in! Please keep us posted with your results. I'm very interested. Damn, I love MUD!

 

[Anvil]

Unplug the 02 sensors for a few days and report back. On my 94' the 02 sensor wire had a wiring short and it would eat up ECU fuses to the point where it wouldn't even start unless the 02 sensor was unplugged.

Once the wiring short was fixed (in my case it was a new engine wiring harness) the ECU fuse hasn't blown. Luckily you have a 95 so the wiring harness it still available if it comes to that.

Good to know! Thank you!!

 

[Anvil]

Another possibility is connector BO1, which lives under the body on the left side under the C pillar. All fuel pump power goes through this connector and it is exposed to the elements.

I'll check that connector. Thanks!

 

[jonheld]

Thank you for your input! You and a handful of other Mudders always peak my interest.

I spent the day in another Cruiserhead's shop and here's what we found/did.

Replaced the fuel pump relay with OEM.
Replaced EFI relay with OEM
Inspected the wiring harness where it was touching the ECR tube, wires looked fine. Reattached harness to holding bracket with zip ties.
Dropped the glove box and inspected the wires going to ECU. The wires weren't touching the metal bracket and looked good.
Repaced the fuel filter.
Pulled the fuel pump resistor and tested per service manual. The service manual calls for .7 - .76 resistance. My resistor measued .2. ??? Is this my issue?
After all of this... There is no CEL ! First time in two years!!!

Thanks again!

As stated earlier, it is VERY VERY VERY unlikely that a relay would cause the EFI fuse to pop, and if the EFI MAIN relay was an issue this engine would not run at all.
When you say "no CEL" is that no CEL with the key in the ON position before cranking the starter, or no CEL while the engine is running?
No CEL with the key in the ON position before cranking the starter = no start. This engine will not run as the ECU is not in a "ready" state.
No CEL with the engine running simply means that past error codes have been cleared. If you had previous error codes, this could be due to removing the 15 amp EFI fuse or the fuse popping, which is the same as removing one of the battery terminals. This clears old error codes from memory and forces the ECU to "relearn" all the sensors. After a few drive cycles, a persistent code will come back indicating an issue that needs to be resolved.

You are looking for an intermittent short to ground downstream of the EFI fuse. This is best done with a multimeter rather than continuously popping 15 amp fuses. Some percussive diagnostics and sequentially disconnecting sensors and VSVs while following the pages in the EWD will help you, rather than guessing and shotgunning about things on the internet.

 

[Anvil]

As stated earlier, it is VERY VERY VERY unlikely that a relay would cause the EFI fuse to pop, and if the EFI MAIN relay was an issue this engine would not run at all.
When you say "no CEL" is that no CEL with the key in the ON position before cranking the starter, or no CEL while the engine is running?
No CEL with the key in the ON position before cranking the starter = no start. This engine will not run as the ECU is not in a "ready" state.
No CEL with the engine running simply means that past error codes have been cleared. If you had previous error codes, this could be due to removing the 15 amp EFI fuse or the fuse popping, which is the same as removing one of the battery terminals. This clears old error codes from memory and forces the ECU to "relearn" all the sensors. After a few drive cycles, a persistent code will come back indicating an issue that needs to be resolved.

You are looking for an intermittent short to ground downstream of the EFI fuse. This is best done with a multimeter rather than continuously popping 15 amp fuses. Some percussive diagnostics and sequentially disconnecting sensors and VSVs while following the pages in the EWD will help you, rather than guessing and shotgunning about things on the internet.

Great info here. Thank you!

I took a break from this for a few days. I'll try again this week. Today I'm smoking a brisket!

 

[Two 3FEs]

Very improbable that relays would cause this issue. They either open or close on the contacter side. If there was a short on the logic side of the COR, the 7.5 amp IGN fuse would pop.
If the EFI relay was an issue, this engine wouldn't run. On older 3FE equipped 80 Series (1991/1992), the EFI relay connectors in the relay box was a common issue due the heat of the exhaust manifold that ran just below the box. This is no longer an issue with the 1FZ-FE 80 Series.

my 91 ran fine and fast getting home and now doesn't have injectors firing. Runs on starting fluid. Plenty of fuel pressure in the line to Cold Start Injector. Replaced the EFI Relay with one off Amazon; that didn't help then ordered the OEM from Matt yesterday in case the Amazon was junk. The FSM says there's a Fuseable Link to that relay. Anyone know where that might be? Or what else might have triggered the failure?

 

[jonheld]

my 91 ran fine and fast getting home and now doesn't have injectors firing. Runs on starting fluid. Plenty of fuel pressure in the line to Cold Start Injector. Replaced the EFI Relay with one off Amazon; that didn't help then ordered the OEM from Matt yesterday in case the Amazon was junk. The FSM says there's a Fuseable Link to that relay. Anyone know where that might be? Or what else might have triggered the failure?

There are 3 fusible links in an 80 Series, and they're all off the positive battery terminal and grouped as 1 part number.
2 go to the junction box and the other one goes to the grey connector.
This is all shown in the EWD power source section.
The injectors are fed from AM2. All injectors get a constant +12 from the ignition circuit and are pulsed to ground in groups of 3 by the ECU.

 

[jonheld]

The FSM says there's a Fuseable Link to that relay. Anyone know where that might be? Or what else might have triggered the failure?

Do you have the Toyota EWD? This is all laid out for you.
The EFI relay gets +12 on pin 2 from the 15 amp EFI fuse. The 15 amp EFI fuse is fed from the MAIN fusible link.
However if the MAIN fusible link was faulty, you'd have no headlights, no tail lights, no brake lights, various others, and no CEL with the key in the ON position.
The combination of the FSM and EWD is invaluable.