AM2 fuse continually blows

[kev12mich]

I have a 1992 Camry (5SFE).

Yesterday, I was driving like usual when the engine suddenly died. I had it towed back to my house. I suspected it wasn't getting fuel, so I removed the back seat and the service cover to get access to the fuel pump. I turned the key to on and I couldn't hear or feel it pumping.

Naturally I checked the fuses and the AM2 fuse was blown. It's normally a 30A fuse and I temporarily replaced it with a 20A fuse just to try. The engine started up fine and I let it run for about 5 minutes. I shut it off and went to the hardware store to buy some 30A fuses. When I took the 20A fuse out that was in there, I noticed it was blown. I replaced it with a 30A and that blew too. Replaced it with another 30A and it blew too. It's gone through 5 fuses now...

It blows the second I turn the ignition to "on". Any ideas on what could be causing this?

[Eye8Pussies]

I would check the wiring harness around the pump inlet first, as it sounds like you have a short somewhere. It's possible that the harness has frayed and a wire is shorting out on the metal mounting plate.

otherwise, it is also possible that it is shorting inside the pump assembly- you can take it out to see.

hopefully though, it is one of these two possibilities, otherwise you will have to run down the entire harness to see where the short my be, and that would not be much fun...

[kev12mich]

Originally Posted by Eye8Pussies

I would check the wiring harness around the pump inlet first, as it sounds like you have a short somewhere. It's possible that the harness has frayed and a wire is shorting out on the metal mounting plate.

otherwise, it is also possible that it is shorting inside the pump assembly- you can take it out to see.

hopefully though, it is one of these two possibilities, otherwise you will have to run down the entire harness to see where the short my be, and that would not be much fun...

After lots and lots of research, I found it does not have to do with the fuel pump.
Here is the path of the AM2 Fuse:
Battery----AM2 Fuse----Ignition Switch----IGN Fuse----Relays for Ignition Coil and Fuel Pump.

So, if the AM2 Fuse is blowing, that must mean there's a short between the AM2 fuse and the ignition switch, or there's an internal short in the ignition switch.

So now the question is how do I test which it is?

[kev12mich]

Ok, after some more googling, I found out a common reason for the AM2 fuse blowing is a shorted condenser (capacitor) inside the distributor. All this condenser is supposed to do is to limit static for the radio, so I just clipped the wire. I replaced the fuse, and it started and ran fine. Drove for about two blocks, then the fuse blew again.

I am going crazy.

Oh yeah, here's where I found the info on the condensor:
http://www.toyotaownersclub.com/foru...showtopic=6852
http://www.automotiveforums.com/vbulletin/t522792.html
http://www.automotiveforums.com/vbulletin/t223185.html

[kev12mich]

Alright, so I replaced the condenser and still no go. The fuse still blows.

Here's an odd patter I've noticed. If I change a fuse right after I tried starting the car, it will blow instantly when the ignition is turned to ON. However, if I leave the car sit for a while and replace the fuse, the car will start and run, but only for a few minutes. This has me EXTREMELY confused.

I found lots of electrical manuals for this car:
http://www.camrystuff.com/manuals/Ge...ry94wiring.pdf (Page 72)

So, if I examine that schematic, I see the path is in fact:
Battery --- AM2 Fuse --- White/Red Wire --- Ignition Switch --- Black/Orange Wire --- IGN Fuse --- Ignition System

So all I need to do is isolate where in this path the short is. I removed the IGN Fuse, and the AM2 fuse still blows, so I know the only possible short points are:
White/Red Wire --- Ignition Switch --- Black/Orange Wire

So tomorrow I will be trying to isolate the short out of these 3 possibilities. I'm hoping it's the switch so I don't have to run new wires....

[kev12mich]

Ok, I replaced the ignition switch AND THE FUSE STILL BLOWS!!!

It's the same as before. If I leave the car sit for a few hours and try to start it with a fresh fuse, it will run for ~30 seconds, then the fuse will blow. If I replace the fuse and try to start it right away, it will blow the fuse as soon as I turn the key to "on".

The fact that it works briefly if I let it sit has me confused. I don't think it's a short in the wiring, because if it was in the wiring, it would be consistent. It would either always blow the fuse or never blow it, not let it work for 30 seconds after sitting then blow it.

Can anyone think what might causing this short?

[kev12mich]

Alright, I just replaced the ignition coil thinking it was that. The fuse still blows. I am even more confused.

The only other components in this circuit that I haven't yet replaced are the distributor and the igniter. Now, these are fairly expensive parts to replace. Can anyone think of how I can test each one to see if it's bad?

[Eye8Pussies]

sorry for not replying earlier, but I was going to say that according to the schematics, there could be a short anywhere along the line and not just between the fuse and the ignition switch

as for checking the dizzy and the igniter, I would follow the shop manual for checking their specs first, and the other thing that you could try doing is old, watching the ignition in the dark and spraying water on everything to see if there are sparks. this usually just tells you if you have bad wiring, and it theoretically shouldn't short anything, but it may be worth a try to see

[kev12mich]

I'm not quite sure that wiring is the issue. I feel if it was wiring, it would either always short or never short.

If I leave the car sit for a day and start it with a fresh fuse, it starts and runs for 30 seconds, then the fuse blows.

I found a schematic of the AM2 circuit in the camrystuff.com ignition system manual:


I tested the distributor pickup coils, and they're within range, so it's not the distributor. This only leaves the ECM and the Igniter (both expensive parts... ugh).

[71Corolla]

If after it sits for a day, have you tried just turning the car to the ON position but not starting it? Will the fuse blow? Is there anyway you can get yourself a hold of a resetable circuit breaker (they make them in various amperages) and put that inline with an amp meter?

Then you can watch how much current is going through the system and if it spikes, or if it gradually increases. It will give you valuable clues.

edit - I re-read your posts I see the fuse blows as soon as you turn the car to ON after it's run. Still would be very helpful to get an amp meter inline and watch the current flow.

[fenixus]

i'm not an eengineer but when eyeballing above diagram it seems there is nothing between battery and AM2 fuse except for main fusible link have you checked it ?

also if all main parts in above diagram are good then i would rather go check all harness grounds to be sure they look clean and make good contact. not sure if i understand electricity right, but if any other part after ignition switch makes a short or is bad then rather those parts would fail than AM2 fuse ?

i would check voltage and amperage at let's say before ignition switch and then after ignition switch (turn the ignition key to ON position at cold car after multimeter is installed) and compare readings. hopefully you have a good supply of AM2 fuses handy

i may be completely wrong on my understanding of this. actually i think i am in fact
someone more knowledgeable told me that current flows from negative to positive, so the AM2 fuse would be actually after all the parts and not before them as i see it.
anyways OP needs to do some voltmeter and ampmeter testing, how and where i do not know. FSM may have more info/clues on troubleshooting this circuit.
you need to find something like a troubleshooting tree or block diagram for this circuit with yes/no answers directing you to the next step.

have you confirmed that igniters have good ground to chassis ?

slightly off topic question ... when was the last time you replaced spark plugs and wires ? they are both part of this circuit, maybe one of those makes a short when car warms up ?
you can check resistance of plug wires, should be no more than 25kohm and each should show similar value.

EDIT:
maybe unrelated, but i found some diagnostic tips PDF and there is one regarding '92 camry and AM1 and/or AM2 fuse blowing. the tip says "check for blown/melted noise suppressor shorting in distributor".
http://www.docstoc.com/docs/37078272/DIAGNOSTIC-TIPS
page 19

[kev12mich]

Originally Posted by fenixus

EDIT:
maybe unrelated, but i found some diagnostic tips PDF and there is one regarding '92 camry and AM1 and/or AM2 fuse blowing. the tip says "check for blown/melted noise suppressor shorting in distributor".
http://www.docstoc.com/docs/37078272/DIAGNOSTIC-TIPS
page 19

Yep, I already replaced that thing. Didn't fix it.

[fenixus]

right, i missed that post. anyways good luck man!
tracking down electrical issues is no fun especially if the devil sits in harness or the ECU.

[kev12mich]

Alright, so I think I might end up junking the car.

Someone smashed the front drivers side window last night, stole my stereo and smashed my dash and gauges.

The car's transmission has been slipping really really bad lately too, so I just don't think it's worth it to replace anything in it anymore. It was nice driving you '92 camry. My first car

[fenixus]

i'm so sorry to hear that man ...

what insurance you have on it ? if liability only then it's up to you if you want to fix side windows, stereo and dash gauges (using junk yard parts except new DOT side windows).

if you had something like comprehensive (other than collision) insurance package you should be covered against theft and vandalism, so call cops, let them write the report. insurance will cover the losses (call them up to).