The Stovebolt Site Forums The Shop Area Engine Shop 235 runs smooth only with spark wires ajar

Have a 1956 3600 in restoration.Engine runs smoothly only with spark plug wires not firmly
plugged on to plugs.with wires slightly off plug
(enough for spark to have to jump to plug) it purrs.when wires are plugged firmly onto plugs it starts to misfire badly.Have tried every thing I can think of. Any one have any ideas?

Are you sure that it is plumbed correctly?

jfralick,

Welcome to the Stovebolt. I think the first thing I would do would be to verify my point setting and make sure the coil is connected with positive to key and negative to distributor.

It sounds like you are dealing with a weak spark, and pulling the plug wire from the spark plug allows the voltage to build until it jumps the artificial gap, then fires through the plug.

When the engine is running and you hold the wire away from a grounded component, it should jump quite a gap and show some energy and color.

Have you tuned the truck up recently, and if so, did you replace the points AND condenser.

Smarter folks are probably hiding in the wings...again, welcome and good luck.

Don't forget firing order...153624 clockwise on distributor.

Stuart

Automarc is right on. Also pull a couple of plugs & see if they are carboned up. It doesn,t take much start & stop with todays gas & these old trucks run a little rich, to carbon up the plugs.

Are you running the ignition through a ballast resistor?

Hy guys, If the wires are old they may have a path to ground arced into them from miles of use, hope that helps.

3B that would be my gess, even if the wirers are new, it sound like the boots are grounding on the base of the plug. If the wirers are new make sure the boots are clean and free of moister, same for the insulators on the plugs. If wirers are old replace them. Also check to see if the gap on the plugs is not too wide.

I have tried wires, points ,condensor cap
rotor.distributor,plugs,carb rebuilt,timing
adj,alternate grounding locations non-resistor plugs. hot wiringto bypass ballast resistor
compression test(125 allcyls) I cant even think of anything else to try, I also must note that only the front 3 cyls need to be ajar (wire off the plug) the back 3 cyls run fine with the wire plugged on????

spark will jump almost a 1/2 inch to ground with good strength . tested a plug attached to wire engine running, when plug is grounded at electrode spark is evident but appears weak???

last nite i looked for spark in the dark, when i had a plug in the wire i actually got it to ground on the RUBBER heater hose???

also i have swapped wires from the cyls that worked(back three) with the ones that didnt
no change. the wires running the back3 didnt run the front 3 any better

WOW thats wierd! How did you dicover that it runs better with the the wires pulled lose?
The plug grounded on the rubber heater hose?
Did you use some kind of cleaner under your hood that that may have left a conductive film?
Try cutting the wire boots back alittle so thier like it is plugged in when thier pulled back.
Let us know what you find. This is a real head scracher. It has to be something simple. Bet when you find the problem it's one of those on sh!tter's

i have a 59 belair that does the same thing i dont know how i came upon the fact?

Don't go out in a lighting storm. Electricity dose strang things around you :p

jfralick,

You sure have covered all the bases. I have no idea where this clue leads, but the back three cylinders...4,5,6 are smack dab between the problematic cylinders if you run the firing order.

If it isn't something mechanical then it still looks like a coil/voltage problem.

If you have a ballast resistor, your rig must be 12 volts! You don't have a internally resisted coil TOO by any chance?

What exactly happens when you hook up all the wires and run the engine. Does it run poorly, snort and backfire or just act like it misses.

If you can replicate the problem, maybe you can sneak up on it by changing only one variable at a time. This should allow you to shed light on which system is a fault.

It almost seems like the coil has only enough dwell time to saturate for every other cylinder..5,6 and 4.

As HevyHauler said...this is a real toughie! :confused:

Stuart

Don't know if this has anything to do with the problem but have you checked the ground strap to the engine?

What is the resistance of the plug wires? What type of wires are they? Try swapping the plug to a different cylinder and see if the problem follows the plug. Then try the same thing with the plug wire. How are the plug wires routed, and are they fitted in some sort of loom or bracketry that might interfere.

Are the plug wires fat yellow wires? I always hated those things. After all the advice and tips here, the only other thing I can think of is checking the air in the tires.

You might also check each plug wire connection at the dist cab to see if it shorts out to any other plug wire connection at the dist cap.

jfralick,
Did you use anti sieze on your plugs? If any gets on the electrod of the plug it can cause a short or weak spark. As atomarc stated pulling the plug wire from the spark plug allows the voltage to build until it jumps the artificial gap, then fires through the plug. Something is causing a weak spark. Welcome aboard.

Glenn,

Could the distributor shaft be bent or the lobes be off, causing the points to open funny or late?

Hey what if the points cam has excessive wear on those lobes?

That would change the dwell from one cylinder to the next.

Bent distributor shaft?
Speed

We're grasping now boys.

Since we are all just guessing, I am gonna go the other direction & say the mixture is either too rich(my guess esp. if using a Roch B)or too lean, the wires being slightly ajar increases the voltage @the plug enabling the cylinders to fire better under less than ideal mixture. Brian

How well does it run with the front three not wired at all?

if it is a "drivers" resto ditch the stock distributer and put in a HEI then you have eliminated all the headaches of distributer hell!

64fleetside,

Doesn't a rich mixture promote easier spark firing? That is what the choke does.

jfralick,

What are the specs? Plug type, plug gap, plug wire type (are they copper cored wires or new silicon carbon fiber), plug wire resistance, etc.

I would go right back to standard plugs, standard copper plug wires, standard gap on plugs and points, etc.

If you are having a problem, stop trying to reinvent it. The problem isn't going away because you use a different TYPE of plug or plug wires. You are just giving yourself a whole new set of variables to figure out.

Usually the most baffling problems are something relatively simple. If it is a carburetor issue, it will effect all the cylinders reletively the same. If it is a spark issue, it is one component or the whole ignition system will fail. Simplify your thinking.

Have you narrowed it down to the one cylinder being the problem all the time, or does the problem follow the spark plug when you switch it from one hole to the next? That would be a bad plug.

Does the problem follow to a different cylinder when you place the plug wire on a different cylinder? That would be a bad wire. Are they copper core? Are they routed correctly? Is there any other electrical components near a plug wire which could create resistance or ground?

What's the next component in line? The cap (is the housing to the tower cracked? is the contact on the inside not formed correctly?), then the rotor, then the points and their gap.

IS it a new condensor? Try the old one again.

Seldom are the coils the culprit when only one cylinder fails, but check the resistance of the primary and secondaries of the coil.

Let us know what the specifics of your findings.

Builder, a 14.7 to 1 air to fuel is the ideal mixture, too rich or too lean are both harder to fire. A choke is used to get fuel into a cold engine with no fuel in the cylinders, kinda priming the pump so to speak. The poor fuel distribution of the log-style intake of the straight six means all cylinders do not get the same mixture, therefore a carb problem will not necessarily affect all cylinders equally. They can be also a source of vacuum leaks when warped which would affect only certain cylinders. Brian

Brian,


If you draw a little picture of the intake manifold, you will see that the center runner feeds not only cylinder #4...a supposedly functioning cylinder, but it also supplies #3, a defunct cylinder.

Could this fact complicate the 'funky fuel' theory.

This is a great exercise in troubleshooting and I sure hope we see the solution to the problem.

Stuart

Stuart, as I said before we are all just guessing, hard to fix something mechanical thru a monitor. I am only suggesting maybe jfralick should widen his troubleshooting areas if he has covered all the bases on the igniton system. I have been wrenching professionally for over 20 yrs & I have seen some weird stuff cause some weird things. Since it is definately not a carb problem, I will bow to those with all the answers & keep my $.02 to myself on the subject. Good luck, Brian

Brian,

My comments were more guesses. I wasn't trying to criticize your post or demean it in any way. DO keep suggesting and DON'T keep your $.02 to yourself...share it with all of us. I am not a mechanic, so I rely on those folks that do this all day long for real world input.

I respect your knowledge and did not mean to ruffle your feathers....sorry.

Stuart

Stuart
Sorry to over-react, but my 14 m/o little girl has the runs today & her poor mood is rubbing off on me. I keep having to bathe her because she is so messy. Man, those diapers have been nasty. Back on topic, two cylinders fed on a siamesed runner can run differently w/a vacuum leak on that runner due to differences in valve & ring sealing. Brian

64Fleetside,

We all are entitled to those days and I also want to encourage discussion, even with different vantage points.

I agree with your comments on uneven distribution and fuel/air mixture, and I did read your post saying you were going in an "other direction". And you are right when you mention that we are diagnosing from a monitor. That being said....

I am, however, having a difficult time realizing that link to the problem.

How is it that the fuel will ignite and run smoothly with the plug wire removed a short distance from the plug, if the fuel rich/lean mixture is potentially the problem?

Builder, the spark jumping a short gap increases the voltage @the plug causing it to fire when ordinarily it wouldn't fire as well. I am not sure how, I am no electrical engineer but I had a shop instructor(also ex-motor pool) tell me that "back in the day"(points & 6 volt systems) that it was often done on cold mornings to help cars start. I have done it many times & it does work. Brian

Hy guys, I think this is a great thread, please don't anybody stop contributing. Now the voltage trick, the way I was taught the voltage will build at one side of the gap until it has sufficient energy to jump the gap, if you add another gap into the mix you build your energy twice, and that second or in this case artificial first gap is causing enough energy to build up to allow sufficient voltage to jump the spark plug gap. My thinking is leaning towards fuel mixture/ vacuum leak problem, hope that adds something to the discussion.

Ok jfralick where did ya go. You started this don't bail on us now. Whats happening with this?

I'm still stuck on the distributor. Couldn't the gap on the plug act like the gap on the points, causing the coil/condensor to dump. I have a couple of old mallory dual point distributors in the basement, one six lobes, one has three. The one with six opens both points at once, the other opens every other one. The second one requires two condensors to work.

Is it possible the points aren't opening or they are shorting out on every other cylinder?

I'm don;t pretend to know very much about the ignition circuit, so I could be way off. I'm sorry if I am.

this is how resistor wires help hotter spark. the coil out put has to buld higher before the spark jumps to ground. i suspect some problem with the distributor and dwell. worn or loose parts. what color is the left fender?

The right fender is closer to the ignition wouldn't it make more of a differance?