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Major Backfire... Damage?

Discussion in 'Early CJ5 and CJ6 Tech' started by Wirework, Sep 3, 2017.

  1. Sep 5, 2017
    Wirework

    Wirework Navy_Jim

    Pittsburgh, PA
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    Oh... that is a great way to look at it... and it very quickly shifts the troubleshooting focus away from the voltage regulator and onto the ignition switch. 'Very helpful; thanks a lot!
     
  2. Sep 5, 2017
    Wirework

    Wirework Navy_Jim

    Pittsburgh, PA
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    Yep, if I disconnect the ignition switch feed, and hot wire the ballast resistor/coil +, the spark is bright and hot. (But to protect the coil, I'm careful not to hot wire it too long while not running.)
     
  3. Sep 5, 2017
    Wirework

    Wirework Navy_Jim

    Pittsburgh, PA
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    I pulled the ignition switch and got 3 to 7 ohms resistance so I sprayed contact cleaner into it and resistance dropped to zero. After that it operated normally again.

    I also checked for vacuum leaks. After diverting the cooling fan flow away from the top of the engine, I pointed the open nozzle of my propane can at all the vacuum joints and got no response from the engine. I tried again with MAF cleaner, and then again with Sea Foam intake cleaner... nada, no engine response. All the while my manifold pressure held at about 18-20" vacuum. So either the F134 ignores propane, MAF cleaner and Sea Foam, or I don't have an obvious vacuum leak.

    I pulled the capacitor and did a few electrical tests on it. It was not shorted. And I could watch it charge with a volt meter using battery voltage and then discharge when I took the power away. I'll buy a spare, check it, and try it anyway.

    I plugged the exhaust by hand with a rag while idling and it stalled in under 10 seconds. If there is an exhaust leak it is relatively small. If there is blockage it isn't obvious

    After removing and returning the condenser, I reset the point gap (0.020"), checked the timing (5 deg BTDC, advanced), and increased the fuel pressure slightly. Every time I change anything, I do a little test drive... no change... it sputters and stumbles and throws out a puff of light grey smoke if I load it in the slightest.
     
  4. Sep 5, 2017
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Hills of NH
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    I don't use solexes but I wonder if the backfire damaged an internal power valve or some such thing, in the carb?
     
  5. Sep 5, 2017
    Wirework

    Wirework Navy_Jim

    Pittsburgh, PA
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    I also tried to advance the timing a few degrees but realized there is no adjustment left. I can just get 5 deg advance but not a smidgen more.

    It turns out that the PO cut the two "stops" out of the timing bracket slots (both the mounting slot and the adjustment slot), but didn't file them smooth, so they still prevent anything more than a 5 deg advance.

    I'm beginning to suspect the PO cut out the end of the mounting bracket slots so he could advance his timing more than 5 deg, and that I lost his adjustment when I pulled off the stock distributor. My assumption that this had a 5 deg advance before (when it was running well) might be completely wrong.

    I see from sombody's internet posting elsewhere that if I remove, rotate, and reinstall the oil pump one tooth CCW from its current location (12 o'clock slot vs current 11 o'clock), that will rotate my reference distributor location CW, and into a shifted position on the mounting bracket which allows me to advance it more than 5 deg. The writer contends that the FSM intends this one tooth shift to properly accommodate the IYA (and other) distributors. After fighting to access to the timing adjustment and points plate attachment screws, I think he is spot on... this cannot have been intentional.

    I'll try the oil pump rotation next (after the new condenser is tested).

    I'll also try pulling the 0.010" thick fuel pump spacer back off in case it is causing too much of a fuel pump capacity reduction.
     
  6. Sep 5, 2017
    Wirework

    Wirework Navy_Jim

    Pittsburgh, PA
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    I have the old one. I'll put it back on. Thanks for the comment.

    ...although the big bad backfire was in the exhaust side, not the intake side.
     
  7. Sep 5, 2017
    Wirework

    Wirework Navy_Jim

    Pittsburgh, PA
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    If the carb is damaged, I would expect to see some evidence when I pump the throttle, but nope... it revs up and falls nicely without a stumble or hesitation. And the centrifugal timing advances smoothly and returns smoothly as the RPM does. ...stumper.
     
  8. Sep 5, 2017
    Wirework

    Wirework Navy_Jim

    Pittsburgh, PA
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    While adjusting the points, I noted once again some "excess" wobble of my old stock distributor shaft, which opened up the point gap when I pushed on the shaft.

    The points close to run a current through the coil which feeds a high voltage to the cap to bridge both the rotor and spark plug gaps. If the points were to drift open from shaft play, with shifts in the engine load, that would retard the spark, right? Bigger gap, more delay, right?

    I wonder if the PO advanced the timing to compensate for a worn distributor shaft...
     
  9. Sep 5, 2017
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    A worn distributor with excessive shaft play will allow the dwell (gap) to wander, and vary at random. This indeed will advance or retard the timing slightly, depending.

    A dwell meter will show if this is happening.
     
  10. Sep 5, 2017
    Wirework

    Wirework Navy_Jim

    Pittsburgh, PA
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    Dang... time to buy ANOTHER tool!
     
  11. Sep 6, 2017
    Uncle Vin

    Uncle Vin Member 2022 Sponsor

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    Why don't you take a shot at restoring the distributor?
     
  12. Sep 6, 2017
    Walt Couch

    Walt Couch sidehill Cordele, Ga. 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Unless you just have a worn shaft then yes. Replace the shaft. If the bushings are wore out then you need to align the new bushings as you install them like line boring.
     
  13. Sep 6, 2017
    Uncle Vin

    Uncle Vin Member 2022 Sponsor

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    That I didn't know. Very interesting and informative Walt. I learn something about these vehicles every single time I log in to this great site.
     
  14. Sep 6, 2017
    Wirework

    Wirework Navy_Jim

    Pittsburgh, PA
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    :) I was shopping the distributor bearing yesterday. I will certainly give it a shot. Thanks.
     
  15. Sep 6, 2017
    Wirework

    Wirework Navy_Jim

    Pittsburgh, PA
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    Oh boy... we have a drill press... I might have access to a lathe.
     
  16. Sep 6, 2017
    Wirework

    Wirework Navy_Jim

    Pittsburgh, PA
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    I lucked out and found a 70's era dwell/tachometer today for $5 on Craigslist, in the original packaging, including the instruction sheet. Better yet, it was 4 miles away and the guy was home.

    The instructions had recommendations for over half a dozen tests, including fuel/air mixture and disclosing "weak cylinders".

    After setting idle and with the engine running, I pulled #2 plug wire with insulated channel locks and still got knocked on my behind. It didn't change a thing! Ugh oh.. then I shut the engine off, put #2 on and pulled #3 and restarted the engine. It didn't change a thing. Only pulling #4 or #1 caused the engine to stumble.

    So I checked the resistance of all 4 wires. They increased from 2700 to 3600 ohms as I measured from shortest to longest... but none of them open. So I re-examined the cap... no tracks no cracks, no pitting... perfect. Then I retraced the plug wires... #2 and #3 were backwards.

    I've been running on 2 cylinders ever since I pulled the electronic distributor (it has its own cap). This explains why it went gutless when I applied a load... it was a 2cyl engine. I put them in the correct locations.

    I couldn't find a condenser at PepBoys or AutoZone so I fished my old one out of the tool compartment and tested it. I performed identical to the current newer one but I installed it anyway. By the way...condensers are $7 and $8 now (!!).

    Next I filed the bracket to allow a bit more timing adjustment, then set the timing at 5deg BTDC advanced. Next, I set the dwell. With the 0.020" spec point gap, dwell was 54 deg. Spec dwell is 42 deg... the gap was too close. It took five itterations to open the gap enough to get 42 deg. The final gap was 0.035".. almost 2x spec.

    I checked the loose shaft effect on the dwell... less than 4 deg... borderline to "fail".

    The good news is the road test. It runs better than it EVER did before.

    Better yet, I learned a lot about my F134 response to a lot of different problems and adjustments.
     
    Last edited: Sep 6, 2017
    Danefraz and 75 DJ like this.
  17. Sep 6, 2017
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Sure you used the right scale for a four cylinder engine?
     
  18. Sep 6, 2017
    Wirework

    Wirework Navy_Jim

    Pittsburgh, PA
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    It only had a 6 cyl and 8 cyl scale. Multiple places say use 2 × 8 cyl scale. The meter 8 cyl scale initially read 27 deg with a 0.020" gap. I decreased it to 21 deg on the 8 cyl scale.
     
  19. Sep 7, 2017
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    :)
     
  20. Sep 23, 2018
    Wirework

    Wirework Navy_Jim

    Pittsburgh, PA
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    Two years in... my Petronics distributor has failed twice.

    The first time required an Uber ride home for tools. Petronics replaced the module, no cost.

    The second time required a 12 mi tow on a flat bed (thank you AAA). I'm done with modernizing my CJ5. 'Time to switch back to a mechanical distributor foor good!

    My original distributor is now in pieces so I can replace the bushings. I plan to thread one and pull it out, then press the second one out.

    With a caliper, the original shaft measures just about 0.4985 and the new bushing measures about 0.5015 That is more than I want, so I'm hoping the ID will shrink when the bushing is pressed in.

    Both ACE hardware and Tractor Supply have 1/2" ID x 5/8" pourous bronze bushings for under $2.50 each. It looks close but I won't know until the old one is out.

    I haven't checked, but if I fall on my face fixing my old distributor, maybe the "new" Petronics distributor can be gutted and made mechanical!
    :)
     
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