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Not firing on cylinders one and four

Discussion in 'XJ Technical Chat' started by William Thompson, Sep 18, 2019.

  1. William Thompson

    William Thompson Active Member

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    Hi all,

    I'm in the Pittsburgh area and have a 1981 xj650 maxim. It was running great till the other day when it decided to no longer work on cylinders one and four. I suspect my TCI.

    That said... Immediately prior to the sudden not working, I removed a shim on each of my carb needles. I had shimmed it due to installing a 4 into 1 exhaust when my old one rotted out. Today I put the shims back, thinking that was inexplicably the issue. It had been running decently with the shims, but I felt it was missing some on the top end and decided to take them out to see the effect. Given the net change here is zero, I don't think this is my culprit, but I mention it anyway in case someone knows something I don't.

    Thus far I've done the following:

    Pulled spark plug wires while the engine is running. One and four had no effect. It died immediately when I pulled two and three.

    Pulled one spark plug wire at a time, and fitted a spare plug. Verified spark (albeit weak looking) at each wire.

    Outright swapped my coil packs. Swapped the plugs leading to them as well as the wires on plugs. Same behavior when pulling plugs.

    Checked resistance across the coils. Got about 12k from wire one to wire four (without the boots). This was the same on both coils.

    Checked resistance across the boots. Each one was just under 5k.

    Anyone have any guesses? I'm flummoxed. Valve clearances were adjusted this year about a thousand miles ago, carbs were synced at the same time. Running stock airbox and filter with a 4-1 exhaust.
     
  2. tabaka45

    tabaka45 Well-Known Member

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    Bad plug caps or possibly corrosion at the end of the plug wires. Unscrew the plug wires and see if there is any corrosion. If so, and if you have enough room snip off about 1/4 inch and see if that helps. In any case, it sounds like the problem is with the wires or caps, assuming the plugs are ok.
     
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  3. William Thompson

    William Thompson Active Member

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    The plugs both tested at 5k ohms, and I got 12k ohms from the tip of wire one to the tip of wire four. Could they still be bad even so?
     
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  4. tabaka45

    tabaka45 Well-Known Member

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    Not sure about ohms testing. K-mode or xj550 know more about that stuff. I know that on my XJ700N the number 1 and 4 have resistor caps.
    Are the sparks you are getting on 1 and4 similar to 3 and 3? If so, I would expect some fuel issue.
     
  5. Polock

    Polock Well-Known Member

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    this doesn't test the plug that's in the engine
    if you swap a good coil onto a bad plug this is expected.
    get a new set of plugs and end that mystery
    shimming needles doesn't usually solve anything, one size main jet is all it should take, maybe not even that.
    make sure the diaphragm is seated when the top goes on
     
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  6. XJ550H

    XJ550H Well-Known Member Premium Member

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    1 and 4 fire from the same ignition coil . could be a bad pickup coil not making the tci fire it needs to be ohmed out with a meter

    unplug the connector at the tci it will have a black ,orange and gray wire ohm between the black and gray and the black and orange. also ohm black wire to ground should get no reading for the black to ground

    Pick-up coils:
    1980-81 XJ650 Maxim and Midnight Maxim: 700 ohms +/- 20% = 560 ohms to 840 ohms acceptable range. do this for any connector you unplug

    clean the tci connectors with electronic contact cleaner and apply a little silicon grease to them before replugging them
     
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  7. William Thompson

    William Thompson Active Member

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    For the top plug (4 spot) I got

    Grey-black 12 ohms
    Orange-black open circuit
    Black-negative terminal of battery : continuity

    Does the position of the crankshaft affect the above readings, or should I get the numbers specified no matter where the motor is?

    For the lower plug (6 spot) I had no continuity anywhere. But that's the output of the TCI, right?
     
  8. Polock

    Polock Well-Known Member

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    that's not good. lay down and take a close look at the wires from the tci to the pickups.
    crank position doesn't matter
     
  9. XJ550H

    XJ550H Well-Known Member Premium Member

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    4 position is tci to ignition coils you can read ignition coil primarys from plug but if off then read at the ignition coils connectors under tank.

    open for orange and black is why you have 2 cylinders not firing if you check the coil pack you should see orange wirs connecting to the pack on left for sparkplugs 1 and 4 and orange wire running from tci,
    12 ohms is bad as well .

    as suggested open up left crank cover you will see pickups follow wires back both black wires will be spliced together but you should not have any continuity to battery negitive.
    you may have a shorting wire to frame or internialy from pickup coil to base(frame).

    you will find that the wires run betweeen lower frame and motor to tci

    edited out incorrect info
     
    Last edited: Sep 23, 2019
  10. William Thompson

    William Thompson Active Member

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    I pulled the crankcase cover and took another set of resistance measurements. I apparently was hasty the first time when I got an open circuit orange to black because both measurements came in at about 12 ohms this time. These measurements were taken with the key in off. When I took them with the key on (I didn't crank, just turned it on) 20190923_012508.jpg 20190923_012938.jpg 20190923_012957.jpg , the resistance climbed into the Megaohm range. Is this expected?

    Visually, I can't see a whole lot troubling. No obvious signs of impact or wear. No frayed wires or signs of maintenence gone wrong.

    The one thing I did notice was a number of metallic filings that were clinging to the pickup coils due to the magnetic attraction. I'm not sure where the metal dust came from, but I blew it all away with an air compressor. I should have taken pictures. It was all clinging to the base of the pickup coil. Could this have been a grounding path?

    Attached are pictures of my pickup coils, and my resistance measurements.
     
  11. Rooster53

    Rooster53 Well-Known Member Premium Member

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    The 4 pin connector that goes to the TCI is for the ignition coils:

    R/W power, B ground, O (orange) 1 and 4 coil, and Gy (grey) 2 and 3 coil, so you are checking the primary side of the ignition coils if you are ohming from R/W to O and R/W to Gy. If you are measuring from B to O and B to Gy you are going to get a strange reading as that is effectively measuring from battery to ground, which has all sorts of things tied to it.

    The pick-up coils are on the 6 pin connector that goes to the TCI:

    O to B for 1 and 4 pick-up, and Gy to B for 2 and 3 pick-up.
     
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  12. William Thompson

    William Thompson Active Member

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    I redid my resistance checks on the six pin connector, and this is odd. It looks like orange to black is actually checking out. About 640 Ohms. But I'm showing an open circuit on grey to black. So the pickup for the cylinders that aren't firing, is correct, and the circuit for the working cylinders isn't... Wut? 20190923_115530.jpg 20190923_115642.jpg
     
  13. Rooster53

    Rooster53 Well-Known Member Premium Member

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    Yep, that will happen and it is how the TCI works. If only the 1 and 4 pickup is good the 2, 3 cylinders will fire. If only the 2 and 3 pickup is good the 1, 4 cylinders will fire. This is why you can't be logical and think if one pick-up is bad the bike should run on 2 cylinders. It will instead backfire when trying to start as the spark that is occurring will be 180 degrees out. I can't explain how in your opening post you seemed to have the bike running on just two cylinders as it really shouldn't do that - unless the black label TCI is a bit different than the red label that I tested. I can't quite see what your meter is set to, but maybe try the next higher scale to see if you get any reading - it could be the pick-up is providing enough of an input to the TCI to sync to the correct cylinders, but that is just a guess.
     
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  14. William Thompson

    William Thompson Active Member

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    For the resistance measurement that came back as an open circuit, I had set the multimeter up all the way to 20Mohm. So it can't really be scaled up further.

    Is this my smoking gun then? The 2-3 pickup coil has gone bad?

    As far as how my bike ran on just two cylinders... Really not great. It was enough to move the bike down the road. I went about ten miles like that (not my druthers. I don't want to wash my cylinders). But riding conditions were rough and it stalled frequently. It was WAY down on power.
     
  15. Ryengoth

    Ryengoth Active Member

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    The pickup is bad or you have a broken wire on that one. It should be spec around 650ohms. I'm in the midst of troubleshooting my 550 first-fire after a rebuild and going through all of this stuff.
     
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  16. XJ550H

    XJ550H Well-Known Member Premium Member

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    set meter at 2K range
    Pick-up coils
    :
    1980-81 XJ650 Maxim and Midnight Maxim: 700 ohms +/- 20% = 560 ohms to 840 ohms acceptable range. do this for any connector you unplug
     
  17. William Thompson

    William Thompson Active Member

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    Since I was 95% sure of my issue, I engaged in a little bit of destructive testing. I stabbed my multimeter probe through the wire insulation of the gray wire approximately 0.25" from the pickup coil and measured continuity to the plug at the TCI. It had continuity easy, so I knew I didn't have any issues with the wire between TCI and pickup.

    I'm going to roll the dice with a used ebay part. There are a handful on there at reasonable prices. I'm not super keen on equally as old electronics going in where it just failed, but, for the price, I'll take the risk.
     
  18. Franz

    Franz Well-Known Member

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    Just wondering how this works. I thought 1 &4 pickup would be linked to ignition on cylinders 1 & 4. Just interested can you explain in more depth thanks. I am missing something here.
     
  19. XJ550H

    XJ550H Well-Known Member Premium Member

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    when you get the pickups you can remove them from plate and install them on existing plate. easier than removing the plate. make sure you put them in proper location
     
  20. Ryengoth

    Ryengoth Active Member

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    Yeah, I was thinking about pickup orientation as well but with the way the wiring is done and the grommet it's hard to get them backwards. Which wire is assumed #1 from the TCI to the pickup? Orange? The #1 pickup should be almost touching the plate when the U timing window is pointed to by the stationary metal timing tab on the case.
     

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