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  #1 (permalink)  
Old 05-30-2005, 02:55 PM
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Default Spark plug gap and MSD

I was reading an old post about plugs and now i have a question. I am running a MSD Pro billet ready to run. I was seeing everyone saying that they gapped their plugs at like .040 or .050 Where my stock gap is .034. should i be enlarging my gap also or is this for a different type of setup not pertaining to my equipment
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  #2 (permalink)  
Old 05-30-2005, 03:35 PM
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oldmachdriver, my MSD literature says to use .050 - .060 for a starting point in engines running up to 10.5:1 compression; the recommended gap decreases as compression goes upward from there.

Terry
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Old 05-30-2005, 03:41 PM
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im looking at all the literature i recieved from the previous owner about this dist, says nothing about spark plug gap....I do have TRW 10:5 to 1 pistons.....when i pulled the plugs out they were at around .032 gap. could this be the reason im having problems with rich fuel, missing under load.....etc etc...


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Old 05-30-2005, 03:56 PM
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im looking at all the literature i recieved from the previous owner about this dist, says nothing about spark plug gap....I do have TRW 10:5 to 1 pistons.....when i pulled the plugs out they were at around .032 gap. could this be the reason im having problems with rich fuel, missing under load.....etc etc...


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Old 05-30-2005, 04:26 PM
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32 gap shouldn't be causing probelms running rich, etc. .040-50 is better, hotter\longer spark etc. but your plugs should be firing "OK" and not fouling at 32. I'd keep looking for additional problems.
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Old 05-30-2005, 04:37 PM
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OMD, do you hav e the MSD ignition box or only the billet distributor? if you aren't running the MSD box, you wouldn't do anything different...the larger gap is for the higher ignition energy. Just using the distributor wouldn't require any spark plug gap change.
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Old 05-30-2005, 04:55 PM
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just the distributer.....not the box....i should have said that originaly....
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Old 06-03-2005, 06:27 AM
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Quote:
Originally posted by oldmachdriver


just the distributer.....not the box....i should have said that originaly....
I'd go no bigger than .040. There is more of a chance to encounter the symptoms you described by having too large of gap than .032 being too small. You have fuel issues. -Bob
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Old 06-03-2005, 11:40 AM
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Fuel issues can be mistaken for a "weak spark" condition also! The weak spark fails to properly fire the plug, leaving the plug "wet". Which leads to a "fuel" problem as the likely diagnosis. Of course the worst of both worlds is BOTH, then it's really tough making the diagnosis!

The first question is ALWAYS:
Is it fuel or is it spark?

I had this BRAND NEW Dodge truck (dealership) prepping it for the lot to be sold (carb, this was many years ago). Fouled plugs, ran rich, etc. Tore my hair out trying to find the problem. Electronic ignition. Turns out the reluctor air gap in the distributor was SO close it could barely signal the ignition module to fire the plugs. Weak spark, kicked my butt figuring it out!

Agreed, .032 is fine for gap if not running high energy ignition system. The spark should be BLUE, jump a good distance to ground and have a nice crisp "snap" sound to it. Yellow spark? No "snap" sound? Doesn't jump a good gap (1/2" or so)? Not good!

Last edited by Excaliber; 06-03-2005 at 11:43 AM..
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Old 06-03-2005, 09:45 PM
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Ernie

So what's the correction for your "NOT Good" comment in that scenario?
I'm just trying to learn, not being sarcastic or anything, 'cuz if that was me you posted to I'd really be confused

I may have the same problem on my POS SB.
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Old 06-03-2005, 10:23 PM
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So you got the yellow "not good" spark, thats a general rule. I've seen yellow spark that snapped loudly and jumped far and worked good. Blue, loud, jumps far is BEST!

Weak spark: Air gap that triggers your MSD or whatever is to close, thus a "weak trigger". Something wrong with the trigger mechanism in general, this one is very tough to diagnose.
Bad coil wire, to much internal resistance.
Bad dist cap bleeding off current by internally shorting, look for black little "arc" trails leading from one (or more) of the plug wire terminals. OR the center terminal. Weak coil, coils DO have a specific OHM reading you can measure for THAT coil. Out of range on OHMS, replace coil. LOW VOLTAGE to the positive terminal of your coil due to bad\dirty connection AT the coil or the wire that COMES TO your coil. Faulty bad ignition box, like MSD or Mallory. VERY tough to diagnose.

Key switch faulty not allowing enough voltage to pass to ignition system. The "rotor" in the center of the distributor is shorting straight DOWN to the metal distributor piece it sits on! I've seen GM HEI rotors literally burned through in the dead center of the rotor!

Old school point systems:
Burned points! Gap to small, gap to big. Condensor is bad, bad connections, low voltage, resistor that lowers voltage from 12 to 7 or 8 volts reducing voltage TO much, or not at all! Full 12 volts burns up the points in short order!

Good strong spark from the COIL, but WEAK at the end of the spark plug wire? Bad wire or bad "delivery system" TO the wire!

...I wish there was a simple straight forward answer!

Last edited by Excaliber; 06-03-2005 at 10:37 PM..
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Old 06-03-2005, 10:54 PM
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All right lets break it down to a few more simple steps.
Find out the correct voltage YOUR coil should have at the positive terminal with the key "ON" (NOT CRANKING the engine). Measure this with a quality volt meter (digital is best). Within range, move on.

IF possible find out the specifications for the OHMS resistance of YOUR coil. Measure this with your meter, within range, move on.

Measure the OHMS of your coil wire, TRY to find out what "OHMS per foot" is spec for your wires. Measure your plug wires also. Within range, move on.

IF your distributor trigger device does have an "air gap" spec, find it and measure it and make it correct. Move on.

Examine carefully your "rotor bug" UNDERNEATH for signs of burn through or shorting. Check the cap for black "arc" trails. Check the wire connections for loose or INTERNAL BREAKS. I've seen wires that looked good on the outside (insulation in place) and were broken INTERNALLY (rare). Measure OHMS while wiggling wire.

Does voltage STAY within range as the car warms up or revs up? Is the spark good at idle AND higher rpm?

...sheesshh, I could write a book on this.
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