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Dead spark plugs ?

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I fought a very hard starting MGB for 20 years before I finally figured out the coil was bad. Had good spark, I though, but but not hot enough to start the car if the air temp got down close to freezing or if I didn't choke the car just right.

Kurt.
 
sim said:
Hi
I think this coil is ok as it is only 2 years old.
thanks
rod
Click to expand...
I will share with you some data......at the risk of jumping into the "my taillights don't work", followed by "change the coil".....
The First Rule of automotive repair states (quite clearly):
Just because it's a new part...doesn't mean it's a good part.

Using a test light to confirm spark intensity is not quantitative.
Due to an incident in 1974 involving 10KV DC, I am unable to use a non-heavily-insulated hand probe to test for high voltage.
I use a screwdriver (usually wood handle Phillips) stuck into the boot of the wire, see how fat the spark jumps from head or block when cranking...OR....my old handy dandy Snap-On spark intensity tester.
When that shows a questionable result, I use a very old Snap-On (pre-OSHA) coil tester to see how much I really have with existing power feed at the coil.

If you want to just throw parts at it, and not be certain of the problem, you will end up with a lot of time, effort, and possibly money.

What is causing the plugs to fail?
If you blast them and they work, we know something is glazing the insulator.
Generally not a spark issue if they are not black.

Heat range, fuel or contamination, excessive heat.
Something along those lines.

Locking gas cap?
Stored in a locked garage?
Any chance of someone doctoring the contents of the fuel tank?

Dave
 
Rod remind us of year of Spridget. Could there be a ballast resistor in there left over from pre dizzy replacement that is lowering coil voltage. Later Spridgets IIRC used a ballast resistor. And I agree if you have spark doesn't mean you have enough spark.
 
TOC said:
If you want to just throw parts at it, and not be certain of the problem, you will end up with a lot of time, effort, and possibly money
Click to expand...

I did not mean to advocate throwing parts at it. Sometimes if you don't have all the required tools and test equipment, changing parts ONE-AT-A-TIME, will shake out an intermittent problem.
 
That is true. Having your old plugs cleaned lets us know if it actually is glazed insulators, that's all.
Another tool for troubleshooting.
Plus, gives you a spare set for storage in the boot.
Seeing how far the spark jumps is VERY helpful, not only for you, but those who are trying to troubleshoot long distance.
Tells condition of wires, coil, cap and rotor.
If you don't have a Phillips to stick into the plug boot and try, a Phillips is a good tool to have, so you might want to purchase one.
Dave
 
Something isn't right.

1st, al head= cooler chamber temps so up a range (down NGK)to get back to normal just for starters.
2nd, I'd have to ohm the center electrode and make sure the plug is bad, I find that hard to believe.
3rd, sure you aren't cracking the plugs when installing?
4th, and most likely IMO, you have a problem somewhere else


Where's Jeff?
 
TOC said:
If you don't have a Phillips to stick into the plug boot and try, a Phillips is a good tool to have, so you might want to purchase one.
Dave
Click to expand...


I like to stick a small flat head b/w the boot and the end. It'll always be held against tight the end no matter the id of the clip. This will also allow the center to be resized from pulling off and on.
 
I never jam a Phillips in. Rather, I have found the round end with insulated handle allows you to put a sideways "bite" that holds the boot end on the tip, and you can then hold it close to a head bold/stud.
A GOOD system may give you 1/2" or more. A BAD system will give something barely discernible.
Cracking plugs is more than likely, the color of the inner porcelain is of question. Sometimes it's hard to see the glazing. You'll know once you've blasted on and compare it to an unblasted one.
I've got plugs I've used a long time. I keep a set here for the daughter and son-in-law's Mustang....with over 275K, we need to swap them out on occasion. I just clean the old ones, put them back on the shelf.

Somewhere I seem to recall seeing a T series Mowog that the guy drilled 4 holes in an underbonnet brace, put in grommets, stuck his freshly cleaned plugs threaded side up into those grommets. When his car started acting up, he'd swap them, putting the old ones in order so he could identify any issues when he got home and had time.

Dave
 
I think the plugs are a red herring. Having all 4 plugs go dead at the same time causing a no start (Most A series engines will at least start and or fire with only one or two cylinders working) is pretty far out there.

Same thing with the wires. My current daily driver 69 Vauxhall Viva is using 3 wire extension cord for ignition wires, with, no brass end clips at the cap end, runs fine (and, no, I didn't install them, just been too lazy to change them). Just about any wire that isn't physically damaged, or, burned internally, will fire a plug.

If all plugs stop firing, it can ONLY be something from the cap back, including, the cap, rotor, coil, coil wire, coil low voltage feed (I would really look into what was suggested earlier about the resistor wire for the earlier 8 volt coil systems.).

One thing I have seen, is, using the earlier small rotor with the larger late cap, leaving about a 3/8 in gap between the end of the rotor, and, the terminals in the cap. It didn't give this problem, but, did make the ignition generally erratic.

The only plug I ever used in all my British cars (and, customers cars when I did this full time) in the last 30 years is NGK BPR6EY-II gapped to 50 thou (I've been a wide gap guy for over 40 years).

So, things I would check, are, correct rotor, Coil low voltage feed wire (for resistance or not), using a 12v coil on an 8v (early) system, or, vice versa, the coil itself for output, the coil wire, or, electronic module for intermittent operation.

Things I would doubt causing the problem are plugs and wires.
 
except...if you read back...they didn't.
"Was going up a hill and lost one cylinder due to no spark. The other 3 went off one after the other before the top of the hill."

He has said new plugs fixes if somewhat. I keep thinking heat or something in the fuel. But without any further information, like length of spark, hard to tell.
 
TOC said:
except...if you read back...they didn't.
"Was going up a hill and lost one cylinder due to no spark. The other 3 went off one after the other before the top of the hill."

He has said new plugs fixes if somewhat. I keep thinking heat or something in the fuel. But without any further information, like length of spark, hard to tell.
Click to expand...
Back from vacation I just order these https://www.aircraftspruce.ca/catalog...pkplugwire.php 7mm wires and 1/4 in shielding.
I replaced the spark plugs and it almost starts. The coil has about 1/8 to 1/4 inch spark with a copper wire to ground. I ran the test that Moss has on their site for coil and distributor and they both were ok. Only thing left are the wires which are only 2 year old.
 
My guess is not enough spark.
My six volt positive ground vehicles do more than that.
Carbon core wires....manufacturers used to recommend two year replacement intervals, if I recall.

I just use Belden solid cores, and I have one set been on the car for at least 30 years.
 
TOC said:
My guess is not enough spark.
My six volt positive ground vehicles do more than that.
Carbon core wires....manufacturers used to recommend two year replacement intervals, if I recall.

I just use Belden solid cores, and I have one set been on the car for at least 30 years.
Click to expand...
Things have sure changed. every 2 years WOW . I just bought solid cores and will slide them into a braided cover to make the electronic distributor happy
Thanks
Rod
 
I think that Pertronix recommend's carbon cored if I remember correctly. I also believe you are not getting enough spark.

Kurt
 
nomad said:
I think that Pertronix recommend's carbon cored if I remember correctly. I also believe you are not getting enough spark.

Kurt
Click to expand...
yes they want carbon core but going to use copper core with grounded shields. will post a picture when done. Ya not enought spark caused by carbon core wires i think.
Thanks
rod
 
The old rule was ten thousand ohms per foot. Measure them.
New wires won't fix lousy spark at the head end.
The spark you get out of the coil isn't good, and that's not even including the rest of the wires.
Out of that system, at the end of the coil wire, you should be throwing over 1/2" blue.

"Over time however, with heat and vibration the carbon fibers tend to loosen which degrades conduction and eventually requires replacement. For this reason some OEMs (original equipment manufacturers) recommend replacement every 3 years or 60,000 KM. Carbon core wire is quite economical for manufacturers to use while suppressing sufficient RFI. This wire typically has a resistance of 3,000 to 20,000 ohms /ft. depending on the manufacturer."
 
TOC said:
The old rule was ten thousand ohms per foot. Measure them.
New wires won't fix lousy spark at the head end.
The spark you get out of the coil isn't good, and that's not even including the rest of the wires.
Out of that system, at the end of the coil wire, you should be throwing over 1/2" blue.

"Over time however, with heat and vibration the carbon fibers tend to loosen which degrades conduction and eventually requires replacement. For this reason some OEMs (original equipment manufacturers) recommend replacement every 3 years or 60,000 KM. Carbon core wire is quite economical for manufacturers to use while suppressing sufficient RFI. This wire typically has a resistance of 3,000 to 20,000 ohms /ft. depending on the manufacturer."
Click to expand...
every thing was replaced 2 years ago New Pertronix Flame Thrower Electronic Distributor cap and rotor new wires new plugs and Pertronix Ignition Coils not sure which one[FONT=Arial, Verdana, sans-serif]. all bought from Moss. if any of these items besides the wires are bad, I most likely will switch back to Lucus the prince of darkness. As the new stuff is far worse.
[/FONT]
 
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