Plug Wires are crossfiring. Need help please
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Instructor
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From: Lake Villa Illinois
Plug Wires are crossfiring. Need help please
This has been going on for quite some time now. Im at my wits end. Ive tried Jacobs HEI 8.5 mm ceramic wires as well as Taylor '409' 11 mm Race Wires -- same thing happens. Wires are new on a horizontal wire seperator and neatly run in parallel, new rotor, new cap, new plugs which ive tried gapping at .045 and .035 " -- made no difference. I have a fairly new MSD6T box and a new MSD HVC2 Coil . Motor misses especially at higher rpms. Firing order is correct on the cap . Dont know what to do. I am really stumped and upset also. Thanks.
Race Director
Joined: Sep 1999
Posts: 11,361
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From: Plano TX
"Neatly run in parallel" may well be your problem. That's how inductive crossfire is created, especially on cylinders that fire next to each other (5&7 on a Chevy). Run another wire between 5 & 7 and see if that helps.
Le Mans Master
Joined: Jul 2005
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From: Austin Texas
I doubt there is any cross-fire with those plug wires. Look at other tuning/performance areas for the miss. Check the fuel pressure, do compression and leak-down tests to rule out valve or head gasket issues. Check rocker motion for evidence of a worn cam lobe. G/L 
Burning Brakes
Joined: Nov 2000
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From: Johnston Iowa
I know with the MSD 8.5MM wires there is a spec on how much resistance the wire should have for how long it is. If the wire has to much resistance problems can occur according to them. Like Swede said make sure you keep #5 and #7 away from each other. I also like using di-electric grease on all of my plug boots. If you only get the pop under heavy load or high rpm it sounds like you might have a "lean" pop. Hook up a temp fuel pressure gauge and take it for a run while someone watches it and see if your fuel pressure falls off under heavy load. If it does your problem might actually not be the plug wires at all.
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From: Lake Villa Illinois
Originally Posted by James
I know with the MSD 8.5MM wires there is a spec on how much resistance the wire should have for how long it is. If the wire has to much resistance problems can occur according to them. Like Swede said make sure you keep #5 and #7 away from each other. I also like using di-electric grease on all of my plug boots. If you only get the pop under heavy load or high rpm it sounds like you might have a "lean" pop. Hook up a temp fuel pressure gauge and take it for a run while someone watches it and see if your fuel pressure falls off under heavy load. If it does your problem might actually not be the plug wires at all.
Le Mans Master
Joined: Jul 2005
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From: Austin Texas
Just curious...how did you "see" the cross-fire?...on a 'scope? If anything, carbon tracking or moisture in the distributor cap are the only cross-fire situation I can imagine. Minor static discharge seen in the dark is not really cross-fire, it doesn't have enough energy to jump a spark gap under compression, IMO.
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From: Lake Villa Illinois
Originally Posted by big_G
Just curious...how did you "see" the cross-fire?...on a 'scope? If anything, carbon tracking or moisture in the distributor cap are the only cross-fire situation I can imagine. Minor static discharge seen in the dark is not really cross-fire, it doesn't have enough energy to jump a spark gap under compression, IMO.
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Le Mans Master
Joined: Jul 2005
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From: Austin Texas
I'm still thinking that the arcing you see is inconsequential to the engine miss at high rpm's. I think the problem may be elsewhere, maybe the distributor (points or module). Also, look at max timing, try running without vacuum advance and see how it runs.
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From: Lake Villa Illinois
Originally Posted by big_G
I'm still thinking that the arcing you see is inconsequential to the engine miss at high rpm's. I think the problem may be elsewhere, maybe the distributor (points or module). Also, look at max timing, try running without vacuum advance and see how it runs.
Burning Brakes
Joined: Aug 2005
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From: Hudson Falls, N.Y. 76 Vette Modified L-48
Originally Posted by SwaveDave/1970 BB
REPLY: By crossfiring, im referring to a Lazer Light Show in the dark between wires as well as to the chrome dipstick and chrome valve covers that some of the wires come in contact with. Ive even had this problem with the extra thick Morosso 11 mm top end Wires . Ive used dialectric grease on the ends and have seperated #5 and 7 with a different wire inbetween--still get the Lazer LIght Show with other wires. Have tried a chrome loom as well as plastic snapping type looms. Im really at a loss.
1) Basic electronics...electrons will take the least path of resistance to ground..i.e., if the spark plugs have a bad ground surface, and the spark can get to ground at, say, the valve covers...they will discharge at that point.
2) Is the coil a performance coil making ultra high voltage, are you saturating the system with voltage so that the plugs can't handle that "WACK" of 42,000 or more volts?
I hope this give you some help...good luck
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From: Lake Villa Illinois
Originally Posted by kb2fzq
Aside from the other good suggestions above, I have 2 thoughts:
1) Basic electronics...electrons will take the least path of resistance to ground..i.e., if the spark plugs have a bad ground surface, and the spark can get to ground at, say, the valve covers...they will discharge at that point.
2) Is the coil a performance coil making ultra high voltage, are you saturating the system with voltage so that the plugs can't handle that "WACK" of 42,000 or more volts?
I hope this give you some help...good luck
1) Basic electronics...electrons will take the least path of resistance to ground..i.e., if the spark plugs have a bad ground surface, and the spark can get to ground at, say, the valve covers...they will discharge at that point.
2) Is the coil a performance coil making ultra high voltage, are you saturating the system with voltage so that the plugs can't handle that "WACK" of 42,000 or more volts?
I hope this give you some help...good luck
Le Mans Master
Joined: Feb 1999
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From: Tampa Bay FL
Originally Posted by SwaveDave/1970 BB
REPLY: 1. I did coat the plug threads with anti-sieze but i doubt that hinders the ground. I shall take off the Motor to Frame grounding strap and clean it up real good just as a precaution. 2. Yes, the Coil is a MSD Performance 'HVC2' Coil in combo with an MSD6T box ; id imagine the voltage is up there. Im going to try switching back to my old MSD Blaster SS coil which is about half the physical size to see if there is any change. Ill post my findings (along with the distrib. module changeout) soon. Thanks.
Burning Brakes
Joined: Aug 2005
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From: Hudson Falls, N.Y. 76 Vette Modified L-48
Originally Posted by kb2fzq
Aside from the other good suggestions above, I have 2 thoughts:
1) Basic electronics...electrons will take the least path of resistance to ground..i.e., if the spark plugs have a bad ground surface, and the spark can get to ground at, say, the valve covers...they will discharge at that point.
2) Is the coil a performance coil making ultra high voltage, are you saturating the system with voltage so that the plugs can't handle that "WACK" of 42,000 or more volts?
I hope this give you some help...good luck
1) Basic electronics...electrons will take the least path of resistance to ground..i.e., if the spark plugs have a bad ground surface, and the spark can get to ground at, say, the valve covers...they will discharge at that point.
2) Is the coil a performance coil making ultra high voltage, are you saturating the system with voltage so that the plugs can't handle that "WACK" of 42,000 or more volts?
I hope this give you some help...good luck
WITH the anti-seize the low points are covered with a chemical that MAY be reducing...surface area...causing a resistor, if you will..and that super ultra high voltage has to go someplace....TADA!...you have the Iron Butterfly light show...
(those were great years....)Anyway....I'd bet that is your problem...hope it helps...
Last edited by kb2fzq; Jan 27, 2006 at 06:53 AM.
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From: Lake Villa Illinois
Originally Posted by kb2fzq
When it comes to grounding...surface area, surface area, surface area!!! Think of it this way...without the anti-seize, the high AND low points of the plug threads are making contact...surface area!!!
WITH the anti-seize the low points are covered with a chemical that MAY be reducing...surface area...causing a resistor, if you will..and that super ultra high voltage has to go someplace....TADA!...you have the Iron Butterfly light show... (those were great years....)
Anyway....I'd bet that is your problem...hope it helps...
WITH the anti-seize the low points are covered with a chemical that MAY be reducing...surface area...causing a resistor, if you will..and that super ultra high voltage has to go someplace....TADA!...you have the Iron Butterfly light show...
(those were great years....)Anyway....I'd bet that is your problem...hope it helps...
Abby Normal
Joined: Dec 2001
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From: Press "2" for English
from what you've described so far, i think your gap is actually too small. for the amount of power you have available, you probably aren't really discharging your coil through a single wire/spark plug and that's why it's jumping.
when i first put my jacob's ignition on, i opened the plugs up to .075. i later brought it down to .065 to better cope with hot las vegas summers.
it's worth a try. open those bad boys up and see what happens.
when i first put my jacob's ignition on, i opened the plugs up to .075. i later brought it down to .065 to better cope with hot las vegas summers.
it's worth a try. open those bad boys up and see what happens.
Burning Brakes
Joined: Aug 2005
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From: Hudson Falls, N.Y. 76 Vette Modified L-48
Originally Posted by SwaveDave/1970 BB
....shining up the motor to frame ground strap.....
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From: Lake Villa Illinois
Originally Posted by clutchdust
from what you've described so far, i think your gap is actually too small. for the amount of power you have available, you probably aren't really discharging your coil through a single wire/spark plug and that's why it's jumping.
when i first put my jacob's ignition on, i opened the plugs up to .075. i later brought it down to .065 to better cope with hot las vegas summers.
it's worth a try. open those bad boys up and see what happens.
when i first put my jacob's ignition on, i opened the plugs up to .075. i later brought it down to .065 to better cope with hot las vegas summers.
it's worth a try. open those bad boys up and see what happens.
Thread Starter
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From: Lake Villa Illinois
Originally Posted by SwaveDave/1970 BB
REPLY: I tried opening up the plug gap to .045" before -- didnt make any difference ; im keeping them at .035" in order to make it less taxing on the ignition system. Today, i pulled all the plugs and got every bit of anti-seize off them in addition to the threaded plug holes , carefully brushed the wire boot connectors inside / the threads on the plugs, and wire brushed the grounding strap between motor and frame. Im waiting for night-fall , then ill check the wires for arching . Will advise. Thanks for all suggestions. Dave . P.S. If this doesnt work, then im going to try a new Distributor module just for kicks ; everything else is new on the ignition system.
Dave