390 No Spark? Help Please!!!
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390 No Spark? Help Please!!!
My truck died on me yesterday. I was just driving and it died. I checked for spark and there was a very very weak spark from the coil. The spark plug wires had no spark at all. I changed the points and the condenser and now I have no spark from the coil. I then replaced the coil and still no spark. I have read many threads on this website so I even replaced the resistor wire to the coil. I have power to the coil but no spark. The points even spark when the rotor turns and they open. The ground wire is good in the dizzy, the wire from the dizzy to the coil is good. The gap is set at .017. Can anybody help me troubleshoot this to figure out how to get spark.
Post Fiend
Joined: Mar 2007
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From: springfield il
run a wire from the battery directly to the coil for power and see what happens ........ then start trouble shooting . done it before and it worked , and took me a while to figure it out as i'm an electrical tech tard ...................... and it's been so long ago i dont remember for sure but i wanna say it had something to do with the ignition switch { key switch } . i think the wire had corroded or was partially broken . it was an older vehicle < 62 galaxy 500 with an fe , and all the power supply came through the switch . hopefully that will give ya a couple of brain farts ........................
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OK. I tested the wire directly to the coil and I have spark. I then plugged the resistor wire back into the ignition switch and I have spark at the coil but not at the plug wires. I replaced the plug wires and now they have spark and it started but it ran really rough and backfired a lot. I double checked the timing. #1 is at TDC on the compression stroke with the timing marker on the crank pointing at 10 BTDC and the rotor was pointing to the #1 wire on the distributor cap. I towed it home finally where it sat the last two days. I came out and tested for spark today and it was very strong from the coil. When I was testing for spark from the spark plug wires, the truck actually started and ran great and ran even greater when I put the spark plug wire back on #5. I was then going to check the timing, it was about 40BTDC with the vac advance, I then unplugged the vac tube to the vac advance to check timing and the truck died. I can't get it started again and spark from the coil is very very weak.
Post Fiend
Joined: Mar 2004
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From: Union, Washington
So do what you should have done by now. Change the cap and rotor.
Oh and you should never run manifold vacuum to the vacuum advance unit. That's what God and automotive engineers created ported vacuum for.
Oh and you should never run manifold vacuum to the vacuum advance unit. That's what God and automotive engineers created ported vacuum for.
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Ok, I have changed the cap and rotor. I pulled the distributor and took it apart to check mechanical advance. When I got it all put back together and put back in, it fired up right away. It sounds great at idle but when you drive it pops and misses during acceleration. I tested the vacuum advance and it was bad so I replaced it. A friend of mine said it was a fuel problem so I rebuild the carb. I am running an edelbrock 600cfm 1406. The carb rebuild made it start up greater than it has since I bought it but the popping and missing during acceleration is still there. Also, how do I know which vacuum port is ported and which is manifold?
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Post Fiend
Joined: Mar 2004
Posts: 6,056
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From: Union, Washington
Ok, I have changed the cap and rotor. I pulled the distributor and took it apart to check mechanical advance. When I got it all put back together and put back in, it fired up right away. It sounds great at idle but when you drive it pops and misses during acceleration. I tested the vacuum advance and it was bad so I replaced it. A friend of mine said it was a fuel problem so I rebuild the carb. I am running an edelbrock 600cfm 1406. The carb rebuild made it start up greater than it has since I bought it but the popping and missing during acceleration is still there. Also, how do I know which vacuum port is ported and which is manifold?
If that doesn't do it, pour a couple of cans of SEAFOAM into the tank and start it up and let it runn in the driveway for 30 minutes anf if it does run right then, you got me buffaloed.
I don't and won't run an Edelbrock carb. I quite using them back in the 1960's when I had a pair on a 426 Hemi Belvedere. Back then they were called Carter AFBs. The carb fires were to often for my taste and I noticed a few years later that Chryler finally quite using them too.
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I forgot to mention I changed the spark plug wires also. So I guess I have changed everything in the ignition system that would cause this problem. I will get some sea foam and see what it does. Thanks,
Elder User
Joined: Jun 2009
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Well my no spark has led me to the time set change. It had a steel set on it but very loose. Had a real pain over the oil pan. But what got me was when I had the old set there and lined up the rotor was pointing to # 5. HMMMM So I put the new set on and confirmed TDC then installed the diz at #1. So it was one full cylinder off. Other than that every thing lined up including my balancer marks. There wasn't anything in the pan and the screen was clear. The bottom end was clean and in great shape. It seems that the PO had performed a top end a few years ago. Heads, Cam(seems to be of a mild RV grind perhaps as he towed a horse trailer) Kit, Time set.
I have degunked, new carb, replaced the rocker assembly, distributer, new straight up time set, new oil pump, new starter, new battery, Water pump, Radiator, hoses, belts, manifold work, duals and overall clean up. I hope I get spark. I want to get finished with this and light er up today.
At least I know this engine is solid.
I have degunked, new carb, replaced the rocker assembly, distributer, new straight up time set, new oil pump, new starter, new battery, Water pump, Radiator, hoses, belts, manifold work, duals and overall clean up. I hope I get spark. I want to get finished with this and light er up today.
At least I know this engine is solid.
Post Fiend
Joined: Mar 2004
Posts: 6,056
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From: Union, Washington
Have you run a jumper wire from the +12 volt post of the battery to the (+) terminal of the coil with the resister ignition wire removed? That would include the tach wire as tachs have been know to kill the ignition system.
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