Blown AM2 30A Fuse

[hachuelo]

Hello everybody I have a 97 Corolla with the AM2 fuse blown I crank the engine but doesn't start,today I replaced the fuse with a 12V bulb and it lights so that is a clear indication that I have a short somewhere.Does anybody have faced that problem before? Thanks

[kevmac]

symptoms?

thoughts:
check the distributor for a problem with the coil,etc.
Maybe a leak in the ignition system that is shorting to ground because of insulation break. Disconnect the wires to the diustributor (not the plug wires) and retest test light.
Maybe a bad ignition switch.

[hachuelo]

Ok I checked the ignition and pickup coil according to Haynes manual and they are fine the only thing was the condenser that was shorted but I replaced the distributor without the condenser and still the same.

[kevmac]

I'm lost.

You put the old distributor back without a condenser?
Unplug the connectors to the distributer and see if the leak still occurs at the fuse. Remove the ignition switch and test again for the leak. I assume what you meant in OP is that you found a leak while the key was removed.

[Spelick]

Hello, i had this happening to one of my customers cars once. If i remember correctly the AM2 fuse also powers the injectors, turned out he had done his valve cover gasket a month prior and pinched the wire under his valve cover. Just some food for thought. But I def remember the AM2 being the supply for the distributor and injectors.

[hachuelo]

Originally Posted by kevmac

I'm lost.

You put the old distributor back without a condenser?
Unplug the connectors to the distributer and see if the leak still occurs at the fuse. Remove the ignition switch and test again for the leak. I assume what you meant in OP is that you found a leak while the key was removed.

Well correct me if I'm wrong but the function of the little condenser inside the distributor is avoiding sparks cause any interference on the radio right? Is there any chance that it would be caused by the igniter or the ECM? Thanks

[Bitter]

Basically the function of a condenser in a coil ignition circuit is to reduce the spark at the contact points as they open in the distributor and thus minimise burning and pitting of the points. Arcing is caused by the effect of self induction in the coil as the points interrupt the flow of current. The resultant collapse of the magnetic field produces a high voltage to be generated in the primary winding which then tends to flow across the points, thus causing burning or pitting. This current flows into the condenser and charges it as the points open the rapid collapse of the magnetic field produces this high voltage in the primary windings, which can be as high as 250 volts. This further charges the condenser and the consequent collapse of the field causes a high voltage to be induced in every turn of both primary and secondary windings. As the secondary winding has about 100 times the number of turns of the primary, the voltage can reach as high as 25000 volts. Normally this voltage is not reached as it is limited by various factors such as point gap, compression, engine revs. Etc. so only sufficient voltage is produced to produce a spark at the plug. As the spark is produced at the plug gap the energy in the coil, stored in the form of magnetic flux, begins to drain from the coil through the secondary circuit thus sustaining the spark for a fraction of a second or several degrees of crankshaft revolution. During this interval the condenser discharges back through the primary winding producing an oscillation of the current flow in the primary circuit for the brief interval that is required for the primary circuit to return to a state of equilibrium. The condenser DOES NOT DISCHARGE UNTIL AFTER the spark has occurred at the spark plug.

http://www.austin7club.org/Ignition%20Condensors.htm

while we have no points, the condenser now just serves to quiet ignition noise these days.

[hachuelo]

Today I installed an ignition module and still the same:engine cranks but no spark.

[kevmac]

Your confusing me

o.k., you have a blown fuse. You removed the condenser. You replaced the ignition module. Did you replace the blown fuse? Is it blown again?

I think your distributor is probably bad.

[hachuelo]

No I haven't replaced the fuse yet because I'm afraid of blowing it again (they are almost $5 a pop) I'm still using the light bulb instead,tomorrow I'm going to get a new distributor a new fuse and give it a shot.

[kevmac]

Might be worth one more $5 pop to see if that condensor trick worked before paying for a new distributor. Also before shelling out $125, double check the wiring to see if any wire is pinched or burnt. Just a thought. BTW, don't screw up the distributor rotor direction when install the new one (and the one you put back for that matter). You have to point to the current cylinder plug in the firing order as I'm sure you already know.

[hachuelo]

Finally this morning I found the problem,The first thing I did was to replace the bulb for a new fuse and the car started right up so next I connected my old ignition module back and the car started right up again so obviously my module is fine (returning the module back to the junkyard is not accepted so they gave me credit on another parts that I needed);while I was doing the final checkup after finished working I found another fuse close to the one that was blown with signs of a green rust inside so I came to the conclusion that it was the cause for the fuse to gave up.Well the important part is the car is working fine now.Thanks for all your replies specially to kevmac.