Big garage discussion last night with all us old timers. Has been talked about before; but many say rubbish,no truth in it. ( Engine SBC w. HEI Ignition Plug wires running from Spark plugs to the dist. ) Half agree there is sometimes a problem the biggest issue is with number 5 and number 7 wires on driver s side next to ea other Can cause a misfire that that can be hard to find & determine Any opinions on this?? gene in Mn
It's my understanding that its easy to get those wires crossed when plugging them onto the cap which would cause a misfire.
Nope ( not) referring to plugging them in the dist wrong A issue when they touch or are to parallel to one another
Ford had a issue in the 90s where 7 and 8 ran parallel to each other causing a intermittent misfire allegedly. Can’t say I ever verified one but it was a bulletin from Ford
Running them parallel for a ways can let one wire induce voltage into the other. Whether it's enough to cause a misfire...hmmm....I guess you can try it and see. Chevy usually separated them.
Ford's recommended wire routing for the 90s has an S shape. Not mine, just a picture from the internet.
I have heard that for a very long time. Ford did indeed have a bulletin to be sure and not run 7 & 8 parallel and close. You were supposed to cross them at the hold down. However, I ran my plug wires on my race car all taped together and run under the headers (SBC). Never had a problem and that was with a magneto.
The Ford problem was on 5.0 and possibly 5.8 liter pickup truck engines. FoMoCo even went as far as putting a decal on the core support showing how the wires are to be routed.
It's not a myth. GM had problems with misfires on new cars in the early eighties. Moving location of certain plug wires solved the problem.
@blazedogs , On my SBC I have the left side wires in order: 5-1-3-7 (left to right in photo) to prevent 5 & 7 from cross firing.
Ford had issues with FE engines and crossfire on one bank (can't remember which bank) but if you ran the wires over the valve cover the way it looked the most organized it would crossfire at high RPM. I am talking the early 60's. Later OT Mopar V8's and V10's had a problem as well and it would actually get bad enough to cause engine damage. There was a couple TSBs on the correct routing of the wires. I never worked at a chevy dealership but I have no doubt they could have had problems with crossfire as well. The advent of HEI higher voltage type ignition systems just made the problem get worse from wire to wire induction.
Induced voltage between plug wires is a problem with the two cylinders in a V-8 engine which fire sequentially. This will be the back two cylinders on the lefthand side or the first two cylinders on the righthand side, depending upon the engine's firing order. This is because the second cylinder in the firing order is close to ignition and the premature firing will cause a rough running condition. Induced voltage between the other plug wires is not a problem because the adjacent cylinders are not close enough to ignition to cause a rough running condition. Best to separate the two plug wires as far apart as possible.
This is more common than you might think. Where this manifests itself is where you have two cylinders that fire sequentially next to each other; the 7 and 8 on Fords, you'd have to look at firing orders on other motors. Not a problem if you have a rats-nest of wires, this occurs when the wires are neatly routed with the wires running parallel to each other for a bit of distance. As noted, the firing of one plug can induce a voltage in the adjoining wire, sometimes enough to fire that plug also. In most cases no harm comes of it, but if you have a cylinder that has fuel mixture present (on the intake stroke) that induced spark may be enough to partially ignite the mixture before reaching the compression stroke, upsetting the mixture and leading to a misfire or even knocking. If this happens between two non-sequential cylinders with no ignitable mixture present in the 'second' cylinder, it's just a wasted spark. I've never heard of this being an issue on 4- or 6-cylinder motors or 8-cylinder inlines, only v-configured ones with 8 or more cylinders. Fewer cylinders mean the ignition events are further apart, a V8 has an ignition event every 90 crankshaft degrees, close enough that you can have some overlap.
Seems the Iron Duke 2.5L (not a 153 Chevy II engine) in my Model A sounds like it's sputtering sometime just cruising down the road. The plug wires are "almost" new and I just replaced the cap and rotor and spark plugs and it seems less noticeable, but I think I still hear something odd at times. When I replaced the plugs #2 was really black but a compression check came out good on all cylinders. My plug wires are loomed parallel (1,2,3,4) around the back of the engine and I wonder with the firing order 1-3-4-2 if either 4 or 1 firing could be affecting #2, but unless my thinkin' is stinkin' with 180 degrees between ignition of cylinders that's not likely an issue. I need to pull the spark plugs to see if there's still a sooty #2 but haven't gotten around to it yet.
Yes, it is a real phenomenon, and it is not just something that happens with sparkplug wires, and the wires do not have to be old or worn for it to happen. It's called Inductive Coupling, and as Squirrel mentioned above one wire that has a current running through it can induce a current in another wire laying in close proximity. This is a common problem in audio designs that can result in a lot of noise and distortion. Amp techs deal with "lead dress", or the layout of wires in a chassis; and sometimes it is the cleanest looking amps that have the biggest problems, if the wires are bundled or routed close together, parallel. Typically you want them to cross at right angles to minimize the problem. The higher the gain of an amp, the more critical this is; as well as where in the circuit it occurs. But yeah, you can get cross fire between 2 spark plug wires. With that said, I do have the wires of the SBC in my A pickup running parallel close together, and so far have not had a problem. But I knew the potential was there when I installed them that way, I just wanted to do it for the cleaner look, and if it becomes a problem I'll have to deal with it.
I've personally never had crossfire problems with plug wires close to each other, as long as the plug wires are good quality. Heck I even use wire ties to bundle them back behind the heads to keep them away from exhaust, and out of sight; and still don't get crossfiring. Yes, good or bad plug wires can induce noise on other electrical wires nearby in your 12v. system, but that's different than plug wires crossfiring to each other. If there wasn't some voltage from the spark plug wires your inductive timing light wouldn't function like they do.
Here's my 10 cents (inflation ya know...), I think it was an old problem. Today's wires with fiberglass inner shields around the core, hi-temp silicone insulation and a hi-temp rubber cover? Probably a lot less issue than days of old. Older carbon core wires, especially black (carbon is used to blacken stuff) might have liked to have low amp high volts leak a little. Grounding the set as seen in older Vettes sometimes helped stave that off a little giving those impulses somewhere to go. The distributor shields helped with radio interference cuz 'glass bodies and little space for body grounding, as in NONE. Sort of like old batteries used to slightly drain because their cases were actual rubber, add some condensation to the mix, voltage can "creep" into the cement, slow voltage drain. Not today, completely water proof plastic cases. I have batteries on the floor right now, for months on end, and other than some natural I-ain't -been-used-in-a-while voltage drop they're still ok. Now, would I want to grab a wire on a running car even if it was a new top flight uber wazoo wire? Fuck no. I have slid an arm over 1 or 6 now and then and got nothing, but be grounded just a bit and you'll see how much it leaks if you do grab a handful. But the big question, enough to give the idle qaulity a shiver? I'd bet a coffee that no. Running some NOS solid core wires? Found an old supple set of the venerable 440s? OG style cloth covered? Those silly clear red ones? Split dem bitches up a little. Like a gun, better have it and not need it... 1 last thing, flatty Ford? Metal tubes? All the wires inside together? Packard 12 is the same thing. Nope, no issues. You can rest your hand on the tube too. No BZZZZT!! through your shoulder. Is that tube giving that flux a ground to go home to? Because it is "flux" or an electrical field around, at the wire. Whatcha think? Now if you have a sloppy shaft (no I'm not gettin personal) and there's a situation under the cap then sequential cylinders might argue over who gets the buzz 1st. That;'s a different issue.
The tubes I'm familiar with are individual, each wire gets it's own tube. The tubes are metal, and provide a path to ground when they are attached to the block, or anything that is attached to the block, making them a shield, which would prevent cross fire between the wires.
Interesting. I don't recall having any issues with crossfire in the G226 I used to have. I believe the tube, being grounded, is a path of least resistance for any inductance, keeping it from energizing the higher resistance wires/plugs.
1 tube, 4 wires. 5 on the other side with the coil wire. Here's a Packard 12, 2 coils, 8 on 1 side and 6 on the other. And I'd guess some impulse grounding is happening. Both have solid core wires.
I thought you were talking about these: So those tubes have all the wires running together, all within the same magnetic field. The tube may provide some shielding, but for the wires together, not individually.
I had those tubes (above) on my '50 Olds. Ran good for awhile then would not start one morning. Went to a lot of work to pull the ends off the wires and reinstall without the tubes. Still wouldn't start. THEN I pulled the front cover and found the timing chain had jumped a couple teeth.
And in that same early 80s era a real good Goodwrench mechanic was taught in his Goodwrench class that when tuning an HEI equipped 350 with suppression wires to lay one crossing over the other I wanted to hit him for such strange information but Uncle Francis claimed his truck ran better with the wires one layed over another .
Yes that is how the Goodwrench mechanic said to me and that is to crass them at right angles and as close to the cap as you can that is with suppression wires used with HEI and I don't know about with other types of cored plug wires also to use the dielectric grease to keep spark isolated and also protected
I like some of you I thought it was a myth too There was a lot of mechanical knowledge in my garage that evening .I thought it was best that I didn't argue the point. SBC with HEI was the biggest subject 5 & 7 wire ; were the culprit Gene
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