Ignition short, fuse blowin' troubles...

Alright TW, let's see what you've got... This will be a long-winded one. As a part store friend said at some point in this saga: "Electrical issues will drive a man to drink"

I've stalked the forums for various problems in the past, but here I am getting sucked in. Finally signed up! Sorry for not introducing myself first but we've got a pressing issue.

Got a very enigmatic electrical short in my 2000 Taco 2.7 4WD (Hmm... SR5 I believe?)

It all started when I ran out of gas 2 blocks away from the station - We live in a quite rural area and that just happened somehow. Not enough trips to town I guess. Ran out, filled 'er with about 5 gallons, nothing. My thoughts immediately were fuel filter/fuel pump but I was on the side of main street and wasn't up for it there. After checking the fuse box, noticed the AM2 fuse was blown, a 30A fuse that seems to govern all things ignition, from what I can tell on fuse diagrams/etc. A mechanic buddy came and chain-towed me to his shop, and he started diagnostics action (not my fortay)

Part way through his diagnostics the fuse stopped blowing, but he had narrowed is down to either a bad coil or the ignition switch, from what he could tell on wiring diagrams.

I had it for a few days, started up plenty of times, and then one day it didn't start - fuse blew again.

So I picked up where he left off - replaced the ignition switch. No dice. I unplugged one of the coils (the 1&4, this truck runs coil packs) and it started without blowing. Turned off immediately cuz man what a noise.

So I replaced that coil with a freshy, to no avail. then swapped the other one, nothin'. I had a funny feeling about the spark plug wires going into the coils - there was a little metal debris in the connection, thought something could be up with that...

So I go get fresh spark plug wires, more fuses (I've gone through 7ish fuses at this point, should have taken advice and acquired an automotive breaker at the start) and replace the wires, and put in both of my fresh coil packs. Yahoo! She starts. Started up probably 5-6 times, a couple times the next day - Great, going to the town we used to live in 2.5 hours away for work, and I can even take the truck! Of course I get to a gas station 30-45 minutes drive out and go to start the beast after fueling up, and we've got a blown fuse. Back to the drawing board! Now the truck is parked behind the gas station, and I'm working for the week because my dear partner came and grabbed me and we set off. I'll be back up there by the weekend, and hope to be armed with the parts and knowledge to get my truck on the road for good.

I've got spark plugs on the way (wanted to replace them anyhow, I don't think it will solve the problem but the truck would like them if she gets going again)
And NGK coils coming to replace the short-notice NAPA purchases, just in case that makes a difference. Otherwise at this point it seems there must be a shorting wire somewhere outside of a part...

Thanks for reading if you've gotten this far, any thoughts are well appreciated from this fella from WA State.

 

From what I can see the AM2 fuse powers the headlight relay, the horn fuse, the EFI fuse, the OBD fuse and the dome light fuse.

When the fuse blows is important as the fuel pump does not come on with the key turned to on so we can eliminate that. You would think that if the problem was in one of the protected circuits listed that that lower amperage fuse would go before the AM2 fuse. The problem is that you wiggle this wire, check the fuse, wiggle that wire, check the fuse etc.

Sometimes just swaping out a relay is the fix, pull the horn relay and swap out the EFI relay and see if it "fixes" it.

 

I think that it is notable that you have only blown a fuse when STARTING. You did not blown anything once the truck was running. Perhaps there is a big draw from a certain component when you start the car, but not so much when it is already running. I wonder if there is a bit too much resistance in a frayed wire, but the only way to really find this out is to chase both ends down and use a multimeter to test for resistance.

What if you pulled the other fuses that the AM2 fuse operates and then put them back one by one and crank the truck in between? Perhaps it will blow at a certain point? Maybe not the best idea, but could work?

Did you ever swap the relays as @Glamisman suggested?

Intermittent problems are such a pain.

 

That am2 fuse line goes right thru the ignition switch to the coils.....

mine I had a bad ignition switch....worked couple days and then blow am2 at startup or heavy acceleration
was intermittent.....then slowly got worse

check all those wires each side of switch and going the coil.......and all respective grounds

dont have alarm or auto doorlocks ?.........or wire cut or damaged from a previous one



all vehicles this age should carry around a spare switch.......two screws and one plug could get you going down the road

 

Thanks for all of your thoughts! I'll try swapping the EFI relay as another thought as @Glamisman suggested, have not tried that. The fuse does only blow when the engine is cranked, not when the key is just put in the "on" position, which led me to write off the fuel pump/filter as potential issues. It also certainly never goes when I'm driving (so far, which is atleast a splendid thing)

@O'Silver_Taco I did already replace the ignition switch, and I inspected the wires inside which seemed to be fine, but hey there's plenty of wires and it's dark in there. Maybe worth another look-see. No alarms or auto door locks here.

If there is a short somewhere in the wiring, I feel like it's in the engine compartment - because when I muck about with the coils and plug wires things seem to change (sometimes). So maybe it's the wiring heading for the coils, if it's a short of that nature...

I've been trying to find some kind of automotive breaker that'll work for my 30A guy but haven't had any luck online... Everything I find seems to be not quite right. Anybody ever tried using a breaker from a house panek or something? I've bought my valley out of those 30A Littlefuses! If I can't find a breaker option I might just order a chunk of them for cheaper online somewhere.

 

As with things auto repair and my brain... I fix more things at 2 AM than 2 PM. Replace the ignition noise capacitor, it is a grey 2 wire red/black bit on the passenger side fender well area.

 

How would replacing that capacitor make any difference? Has that worked for you in the past? I have not found any threads with AM2 blowing being fixed by that capacitor being replaced.

Edit: I did find this post which alludes to the noise capacitor being the issue. That is for a 1995 Taco, so I am not sure if it would be different for the OP's truck.

 

Following the current path. They call it a "Noise filter".

The symbol for the noise filter is a capcitor.

 

So I suppose a straightforward test of that component would be to somehow disconnected it and see if the fuse keeps blowing? However, it seems like the filter is a protection device for the ECU. How would one test it with a cheap multimeter? Would you disconnect, check for DC voltage (0V) and then apply 12V across the leads with a fuse and see if it will get to a 12V difference? Any idea what the part number is?

 

If there is any idea on the part # that would be awesome! I looked around a little and seems like a funny bit that's hard to pin down online. I'm pretty much down to try anything at this point, and we're past the point of "oh, maybe a defective coil" and on to the point of "oh yes that little guy in the corner, seems like a bad actor"
I'll do more searching and see if I can track one down. Heading back north today so will be back on the fixing train, hopefully she gets runnin' again this week.

 

I have texted my toyota parts guy... we will see if he can find the part# and price. If you find it before I get back with the info, get it.

 

Looks like it's 90980-04083
Sourcing now! Looks like I can get it for not too much, depending on who from. Might even be able to swing by a dealer on the way home and nab one with no shipping...
Sweet well we'll see how that goes! Now I just have to find the darn thing in the compartment!

 

The location may be in the diagram in this thread.

The location seems consistent with the idea that moving the cables for the ignition coils sometimes resolves your issue.

 

Just waitin' on the part, hopefully by the end of the week everything will be in working order! Will keep y'all in the loop, if you feel invested at this point. Thank you for all of the thoughts and help - we shall see how this goes!

 

Well team, I swapped out that N1 noise capacitor and she's startin'. Hopefully this will continue - Last time I thought I fixed it we started up around 8 times at home and then after being on the road 35ish miles and stopping for gas it didn't start up again...

So! Started up 6 times no problem, scooted the truck forward a bit, still starting. Local trips only for about a week and then she'll be off probation if we're still starting no problem.

Thanks so much for all the advice everyone and esp. @Glamisman, I never would have gotten around to that part on my own!

Praying to the Taco gods that this issue is dealt with once and for all.

 

Alright well bad news here! After starting no problem a number of times, and moving parking spots a little, went just down the road and picked up some firewood then as we were backing in to unload it the truck turned off... And the fuse blew!!

My partner was driving and is pretty sure she did not stall (a fine manual driver) but there was a lot of weight in the bed so y'know it's always possible...

Anyhow so now we're unsure if it shut itself off and then blew the fuse, orrr if it stalled and then same same.

I'm pretty stumped. Any chance that the spark plugs could be causing this issue? I have not replaced them since I've had the truck, (~3, 3.5 years) and I thought the previous owner had put new ones in... but maybe if they're having trouble they could be causing a whoopsie in the system?

 

Well, crap... I think we are dealing with a couple of things here, we are going to have to divide this problem in half and the ignition switch is the perfect point. Unfortunatly you are going to have to check the AM2 fuse everytime before you start the truck as we do not know if it blows just sitting there or after you turn the key. If the fuse is good before you try to start her then it blows then it is the wiring after the switch, duh.

Could it be one of the coils, yes, but you would think that the coil(s) test out good or shorted. Take the coils out and shake them, there should not be anything loose inside. I have only seen one coil where the iron core broke loose and would short the primary to the secondary.

Is the truck 100% stock or is there any aftermarket devices installed that could account for this?

I am not 100% convinced of the following thought... if the fuse blows while cranking dont turn the key to the off position, leave it on and replace the fuse with the key in the on position, if it blows then the good news is the condition is repeatable and you can start by locating the 2 connectors IF1 and IK2, disconnect one, replace the fuse and see if it blows. If it still blows disconnect the other connector and repeat.

 

Whoops! I thought I responded the other day, but that's okay because things have went in a new direction... Seemingly sorted out!

This black/red wire coming from the switch seems to have been the problem. Perhaps??

So I had to get over to the town we used to live in for a stint of work, and got the truck started that following morning so I figured what the heck, I'll just try getting it down there again so I can tinker with it after work. Started in the morning, then realized I needed gas and I need the key for that operation (key opens gas tank). Ah well, I'll just drive it to town and jiggle some stuff again and hope it starts at the station. Obviously this doesn't work and I'm stranded in town and need to be at my destination in the evening, so we get the truck towed to a mechanic friend nearby and I'm like "you can work on this if you want or have time, otherwise I'll sort it out when I get back"

A little sleuthing from this fella (you know, an actually car guy not a faker like me) and he has it narrowed down to the black and red wire off the switch (Which @O'Silver_Taco definitely suggested, but I've been avoiding chasing wires and just trying to swap parts like a silly guy...)

Anyhow he peeled back the wiring harness and found that number at the top of this post. Seems like we're sorted out, and I'll attempt to return the parts I can. Good lessons learned on this one for this amateur mechanic, that's for sure. Thanks for all of your help everyone, much appreciated through the dark days of trying to get to the bottom of this!

 

Good lesson in this, the am2 fuse/line is one of simplest.

It powers/runs the EFI system and not much more.

It only has/goes thru that one fuse....and doesnt power sub panel fuses.
Only goes to the injectors and coil(s).

So if your popping that fuse, really only the switch and/or wiring on each side of that switch can be involved...

And of course bad grounds would be 1st suspect.....
if its the wiring going into the coils....that usually generates a different ignitor CEL

That ignition switch has a finite life....so replacing that is not a loss....
should be done every 150K......to avoid needless walking.
there's 30amps and 40 amps going thru that....DC which arc's

 

Sweet, excellent picture too and thanks for the follow up fix. 99% of the people dont post back when they have found the problem.