Weak Spark...won't start!

Discussion in '40- & 55-Series Tech' started by HappyGilmore, Mar 30, 2006.

  1. HappyGilmore

    HappyGilmore

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    I have a 77 FJ40 that died on me two days ago. Getting plenty of gas from the carb, but tracked it down to weak spark not getting the mixture to fire. I replaced the ignitor with a Mallory ProMaster coil and the points with a Pertronix unit. These have both worked well for the past year...till it died. My guess was that I have a bad cap and rotor, so I replaced those with aftermarket pieces. Still won't start and it looks like the fit of the pieces is not that great. Got bored last night and took the Pertronix out and put points/condensor back in to see if that was the problem...still didn't start. Plan is to have Toyota parts in tomorrow and replace cap,rotor,points and condensor.

    Am I on the right track?
     
  2. dfmorse

    dfmorse

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    Happy;

    Just some early morning ideas;

    Check the battery to be sure that its around 12+ volts. Does the engine crank fairly fast?

    With the engine not running (doh!), and the ignition switch ON, measure the voltage at the coil + terminal. You are trying to determine if u are getting +12 volts to the coil. There are cases where the ignition switch (or wiring) craps out on old FJ40's. U may have to hot wire system to check on this.

    How old are the ignition high voltage wires and spark plugs?

    ...
     
  3. clemson55

    clemson55

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    Could just be wires and plugs man. You'd be surprised what new plugs will do for you, I sure was this past weekend. The plugs I had seemed to spark ok when I pulled them out but once we put a new plug in and saw how they were sparking it became clear quite quickly new plugs were in order.
     
  4. HappyGilmore

    HappyGilmore

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    Here is the rundown

    New plugs, wires, cap and rotor
    New Mallory coil

    12v at the coil, spins easily. Even ran a jumper from the battery directly to the coil to bypass any voltage loss, if any, from wiring harness. Even had jumper cables hooked up while cranking to make sure I didn't have any voltage loss. Mechanic and myself hooked up a tester to check spark...have hot spark from coil to dist cap - weak spark from dist cap to plugs. My guess is bad cap and or rotor. These were not Toyota OEM parts and I didn't like the fit when put on. Rotor was a real pain to get on the shaft.
     
  5. Pin_Head

    Pin_Head

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    Swapping / replacing parts is the hard and expensive way to figure out the problem.

    Test things first, starting with the simple and fundamental and then work up. Start by checking out whether your coil is good. Disconnect the wires from it; place the high voltage wire about 1/4 away from a ground, run a wire from the battery + post to the coil + post and then momentarily ground the - side of the coil. If it is good, it will make a big fat spark that you can see and hear and will easily jump the 1/4 inch gap.

    If the coil is good, then reconnect your ignition wire from the switch (black with yellow stripe) to the + side, turn the key on and repeat the experiment. (you can also reconnect the ignitor to the + side if you have one, but don't connect the - wire yet) If you get a big fat spark, then the power feed from the switch is good.

    If the coil and power feed are good, then that leaves the distributor and ignitor as the culprits. Points and condensor are easy and cheap to diagnose: just replace and adjust them. For an electronic pick up and ignitor, it would be best to either take it to a shop that can test them or swap in known good parts to see which is bad.
     
  6. HappyGilmore

    HappyGilmore

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    Thanks Pin Head

    Tried testing the coil like you suggested and the spark was really weak. Good thing that I was getting a new Mallory tomorrow under warranty (rubber isolator feet fell off). Makes me wonder on the ability of the mechanic that worked on it Tuesday. Good thing for this forum. I can't thank you guys enough.

    I'll post after I get the new coil in.
     
  7. HappyGilmore

    HappyGilmore

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    Just got done putting in new cap, rotor, cond. and points. Also put in new coil that I had replaced under warranty. Still not sure that the spark is real hot. Wondering now if I have a bad ground or something simple. I hate electrical work!!! Still won't fire when cranking over. Unless any other ideas, going to try putting the old ignitor back in tomorrow. Any other ideas would be appreciated. Thanks.
     
  8. Texx

    Texx

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    I put about 5 days in on one like this one time...had to manually ground the distributor. Mount was corroded, try that.



     
  9. Liam

    Liam

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    could bad timing be a culperet?
     
  10. HappyGilmore

    HappyGilmore

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    Two mechanics later the saga continues....pulled everything apart 6 times in the past 18 hours.

    Texx, I ran a ground from the distributor to the battery thinking along the same line as you. Started cranking the motor over and melted the ground wire. Go figure that one out?

    Redid the timing just to make sure. Thanks on that one.

    Still wouldn't fire.

    Put everything back together and just for fun turned the engine over...it frickin started. Now I'm more scared to take it anywhere because I have no idea what the heck changed to get it to fire.

    Gotta love gremlins in the wiring!
     
  11. FJ40Jim

    FJ40Jim The Cruiser Whisperer SILVER Star

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    Gremlins! They looks so harmless, but...

    The melted wire was because the stock ground path was/is a problem. You made a little ground wire from engine to battery. When the starter was cranking, 200A of current was trying to flow from the engine block back to the negative terminal of the battery. Some of it went through the corroded stock ground cable, but 50A of it tried to squeeze through your little 14GA wire. No can do, so wire became incandescent, briefly.

    Clean up the ground cable connection from batt to frame, and from frame to bellhousing.
     

  12. REZARF

    REZARF

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    Brent-

    I was thinking the same thing. I would really get after your ground to your frame and even use a new ground strap if you need it.

    That is wierd that it just up and died, I hope it gets running for you soon!

    Rezarf <><
     
  13. Kealy

    Kealy

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    Bellhousing? So that's where that ground cable goes.
     
  14. Pin_Head

    Pin_Head

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    Check the voltage at the + side of the coil when the - side of the coil is grounded , not gounded and when you are cranking the engine.

    Not grounded should read 12V
    - grounded should read 9-10V. If it is lower, then the ignition circuit has a bad connection somewhere between the battery and ground.
    Starting: If it drops below about 6 V, this explains why it won't start. Try running a hot wire directly from the battery + and the coil + to see if it starts. If so, you may need a coil that has a ballast resistor and a bypass wire from the starter to the coil. I believe that they still used this circuit in 77.
     
    Last edited: Apr 1, 2006
  15. dfmorse

    dfmorse

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    Happy;

    One of the really big problems with older FJ40's is the grounding system. This grounding system was not really great in brand new FJ40's, however, because they were new, there was continuity between the block (Ground [-12volts] for the distributor) and the right front fender and the firewall.

    What has to be done for all old FJ40's is inter-ground (loop ground) components in the engine bay. Here is what u do:

    Use a heavy wire (4 ga or better) between the neg 12v battery post and the right front shock tower (At the frame) - this is the stock ground to the frame from the factory on almost all FJ40's. From this point use a 6 ga [or larger] to the right front fender [this is ignition ground on later 70's FJ40's]. Run this ground to the firewall [firewall is considered primary ground for all electronic systems] and then to the engine block.

    If u want to be anal, run this ground to the left fender and then to the rear panels and lighting systems.

    If, and when, u disassemble the right front fender from your FJ40, u will see rust and/or corrosion on the joints and nut and bolts. Older FJ40's (pre '74) had the coil mounted on the block (the holes are still there) and the ground for the coil and continuity thru the distributor was self evident.

    Hope this helps a little. PM me if more help is needed! All of the advice of others is also great, but get the grounding done first.

    ...
     
  16. Texx

    Texx

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    Additionally, you really want the distributor grounded to the block/frame, not battery.
     
  17. HappyGilmore

    HappyGilmore

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    All of your help has been great. Plan is to redo all of the ground wires in the engine compartment with high quality cables. I did notice when the one time that it started spontaneously, I monkeyed with the octane adjuster on the distributor and the engine killed immediately. I think this one of the first indications to a bad ground. Since running a jumper ground, no problems. Can't thank everyone enough. Hopefully this will be the last post on this issue.
     
  18. IOKRU2

    IOKRU2

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    Weak spark. Ways to test coils?

    I have weak spark and can't get my FJ-40 going. I have combed through all my grounds body to frame to coil to distributor. I bought a new coil, but since I am at wits end (been working on this after work all this week and now this entire weekend) I am finally considering that I may have a bad new coil or it's carb related.

    Coils - I tested both my old coil and new ohm'ing out the primary and secondary windings. That appears to be in order even though I don't have the specs for the coils. Ultimatly I did the spark test by hooking the coil + direct to the battery +, gaping the high voltage lead to a ground, then intermittently touching the - to a -.... no spark on the HV lead for either of my coils which really surprised me. Does anyone know of any more difinitive coil tests?

    Here is another odd thing about my cruiser... it is a 1973 with the original F engine. I can't find anywhere in the schematic a wire running from the coil+ to a electric choke(?) on the carb. I had experimented disconnecting this in the past and the cruiser won't start, but now I am wondering what it is, since I also have a manual choke. Any ideas?

    I am really at a loss here. Any help would be great.
     
  19. bikersmurf

    bikersmurf

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    Does it have a ground wire in the distributor? I can't remember if it should it has been 14 years since my F motor died.

    In many distributors a wire connects the distributor housing to the plate the points are mounted on.
     
  20. IOKRU2

    IOKRU2

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    No wire. There was a condenser in it that had a auxillary ground cable which bridged the outside body to the inside point advance plate. I went to the parts store to get a new condenser and it did not have this same ground cable, so the ground may have been broken. I am going to try grouding the two tomorrow and will let you know.
     

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