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Cross Firing |
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jesse 
AMC Nut 
Joined: Feb/22/2010 Location: Edinburg, Texas Status: Offline Points: 299 |
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 Topic: Cross FiringPosted: Aug/15/2018 at 10:40am |
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Did a google search with no luck. Are AMC V8's known for having cross fire issues on a particular area? I read that Ford engines had this problem between wire # 7 and #8 with a solution of putting wire #6 in-between to prevent cross fire. Having an issue with cough/backfire through carburetor on my 390.
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PHAT69AMX
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Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5918 |
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Posted: Aug/15/2018 at 10:50am |
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Guess maybe #5 & #7 maybe, back end, driver's side, since they fire in sequence,
and those two wires are very easy to get mixed up and connected wrong / crossed. 1-8-4-3-6-5-7-2
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White70JavelinSST
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Joined: Aug/08/2012 Location: Minnesota Status: Offline Points: 4867 |
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Posted: Aug/15/2018 at 1:50pm |
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I'd say crossfire on the AMC V8 is more susceptible when using cheap wires or old cracked wires. I haven't ever experienced it with over 135K miles of driving. But I ditched the factory wires early on, and installed Blue Max wires way back when. Now the car has MSD wires, routed neatly side by side and no issues.
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70 Javelin SST, second owner, purchased 1972
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Midnight Rambler
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Joined: Jan/17/2011 Location: SoCT Status: Offline Points: 1670 |
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Posted: Aug/15/2018 at 3:19pm |
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If you don't have a great set of wires now, replacing them with a new set of well insulated wires isn't exactly throwing parts at a problem either.
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 '66 American 440 Convertible 290/M-40/AMC 20 3.15/PS/PB '04 Jeep Wrangler X Rocky Mountain Edition 4.0 5sp |
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White70JavelinSST
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Joined: Aug/08/2012 Location: Minnesota Status: Offline Points: 4867 |
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Posted: Aug/15/2018 at 4:11pm |
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The best way I've found to determine if wires are cross firing is to open the hood in the dark and watch the wires for arcing between them. That way you don't have to through parts at it in hopes of fixing it..... That's how I solved the miss firing issue on an old Chev wagon I had. If that doesn't do it the next thing is check the inside of the distributor cap for carbon tracking between posts.
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70 Javelin SST, second owner, purchased 1972
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jesse
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Joined: Feb/22/2010 Location: Edinburg, Texas Status: Offline Points: 299 |
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Posted: Aug/15/2018 at 4:12pm |
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PerTronix Ignitor, PerTronix Flame Thrower Coil and Accel 8mm wires all were installed a few months back. The 390 is backed by the M12 Borg Warner. On second gear and at around 3500 RPM the engine starts to hesitate and as I hit the throttle some more...POP!
Edited by jesse - Aug/15/2018 at 4:15pm |
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White70JavelinSST
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Posted: Aug/15/2018 at 4:18pm |
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Timing specs please? advance mechanism functions correctly, right? accelerator pump works, correct? |
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70 Javelin SST, second owner, purchased 1972
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jesse
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Joined: Feb/22/2010 Location: Edinburg, Texas Status: Offline Points: 299 |
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Posted: Aug/15/2018 at 4:45pm |
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Initial timing is set at 12* advanced and total timing at 32. Accelerator functioning properly from what I can see. The carb is a 750 Edelbrock and the arm link is set to the very bottom hole on the accelerator pump. Going to plug the vacuum advance and run the car and see what it does.
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george w
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Joined: Jan/27/2013 Location: New Jersey Status: Offline Points: 2899 |
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Posted: Aug/15/2018 at 8:38pm |
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There is a particular factory order for putting the spark plug wires in the separators mounted on the valve covers.
Passenger side bank: wires for cylinders 2,4,6,8 go in order from front to back. wires for drivers side bank for cylinders 1,3,5,7 go in this order from front to back: front most position, Cylinder 1, second position, Cylinder 5, third position, Cylinder 7, Rear most position, Cylinder 3. If you want to see the order for the intermediate separators them PM me your email and I can send you pictures of everything. |
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Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.
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Trader
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Joined: May/15/2018 Location: Ontario Status: Offline Points: 6876 |
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Posted: Aug/15/2018 at 9:34pm |
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If firing order is correct, then cross-fire is a function of poor insulation or parallel running of ignition wires in most cases.
Non conductive spacers or running wires at 90° to each other will eliminate the problem. Start at the distributor and look for parallel running wires, reroute or space. As mentioned above, good wires are also a must.
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