Rough Running with Electrical Problem....Help, Please

Discussion in '40- & 55-Series Tech' started by Sandemonium, Jun 24, 2005.

  1. Sandemonium

    Sandemonium

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    I have a '74 FJ40 with an F engine Manufactured in 12/74.

    I am having some electrical related issues and need some help.

    This all started because of on off idle hesitation. I replaced the Cap, Rotor, Spark Plug Wires and Spark Plugs and set the timing.

    Now when the engine is first started it runs fairly smooth, but when it warms up it starts missing real bad and blows the 15Amp Turn Fuse.

    While trying to diagnose the problem I have also replaced the distributor since the shaft was loose and causing erratic timing, also the Ignition Coil was replaced because I thought this could be causing the problem due to heat.

    I have double checked the wiring for the Ignition Coil - Black Yellow wire is going to the Ballast Resistor, Black White wire from starter selonoid is going to + on Ignition Coil, Black wire from Distributor is going to - on Ignition Coil.

    While looking at the wiring diagram I can see that the wire off of the 15Amp Turn Fuse also goes to the Voltage Regulator and the Hazzard switch.

    I am at the end of my techical abilities and need some assistance to get my FJ40 running again.

    Sorry if this is too long or not completely clear, but I am frazzeled.....
     
  2. Pin_Head

    Pin_Head

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    Hesitation off idle is more often a carburation problem with the transition or off idle circuit.

    The ignition coil circuit is not fused, so it would be a good idea to physically trace the black wire with yellow strip all the way back to the switch and make sure that it is not shorting out anywhere.

    It is not easy to imagine how blowing the fuse would relate to the running problem because the ignition is not fused. It is possible that the short consumes enough current to drop the voltage at the ignition coil. Try checking the voltage at the coil when it starts missing to see if it drops.

    I am not familiar with any circuit that feeds the voltage regulator and hazard switch simultaneously. Maybe it is a '74 specific thing. The fact that a fuse is blowing indicates that something is sinking too much current, like a short. The way to trouble shoot this is to remove the fuse, momentarily check the current flowing across the fuse with an amp meter across the fuse contacts in the fuse holder and start disconnecting the different devices in this circuit one by one. If the current drops to zero, you have found the shorted device. Use the wire color code to help locate the ends of the wires. If you disconnect everything in the circuit and you still have a high current, the short is in the wire between any of the disconnected devices and the fuse block. These can be very difficult to find because you may need to unwrap the harness to find it. It is is more common that wires short at points where they touch the chassis metal. Sometimes it is easier to run new wire from the fuse block and the devices in the circuit than to find the short.
     
    Last edited: Jun 24, 2005
  3. Sandemonium

    Sandemonium

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    I Have A Solution

    My father in-law came over with a Dwell meter and we found out the dwell was way to low, around 18. Set the Dwell to 40, reset the timing and it runs like a top.

    Now the other electrical problem.....

    We ran some tests on the Voltage Regulator and it appears it may be bad. I have one on order and it should be here Thursday.

    The Black/Yellow wire from the ignition goes to a 15Amp fuse marked Turn on the fuse block where it turns into Green/Red, if I follow that wire one end goes to the Voltage Regulator and provides 12 Volts the other end according to the wiring diagram goes to the Hazard Switch.

    When the vehicle is running in gear and the fuse is still good the AMP Meter is at +30, this doesn't stay that way for very long before the fuse blows. At this point I believe the Voltage Regulator could be causing the fuse to blow. I guess I will find out when the new regulator arrives.

    If you have any more information I would sure appreciate it.

    Thank you for listening.

    Bob
     
  4. cruzerman350

    cruzerman350

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    your amps shouldnt be that igh for very long at all unless you have a copmpletely drained battery. i wen through the same problem a while a go and i realized that my volt regulator wasnt getting any power. if you have an idiot light or some kind of current tester make sure that your volt regulator is getting power. if you know that test and see what you input current is with an amp tester. your alternator doesnt kick in until about 1500 to 2000 RPMs so you have to rev the engine to get a reading.
    hope that helps. i wish i knew more. but dont we all
     
  5. Pin_Head

    Pin_Head

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    If it is indicating 30A to the right it is charging the battery and is unrelated to the short. If the needle stays pegged to the right, it may be a sign that your voltage regulator has failed and is overcharging.

    The fuse blowing is still mysterious as the alternator should be able to put out full power without blowing this fuse. If the VR circuit was shorted, the alternator wouldn't put out any power. Shorting is not the normal failure mode for any of these components.

    I think that is is better to diagnose the problem with a meter first than by replacing parts. If the short is in the wiring, you can replace everything in the circuit and still not find the short.
     
    Last edited: Jun 25, 2005
  6. Sandemonium

    Sandemonium

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    Thank you for the reply. I ended up removing the Voltage Regulator, put a new 15AMP fuse in and went for a ride. Turn signal and Hazard lights worked normally and the fuse did not blow.

    I opened up the Voltage Regulator and think I see where it is going to ground when voltage from alternator is required.

    Since I did not blow a fuse when the Voltage Regulator was removed I am still inclined to believe that is what is causing my problem.

    Pinhead, thank you for the reponse I'll let you know what I find out.

    Bob
     
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