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Driving home my vette started popping and bucking. Limped it a half mile or so, and shut her off. Started her up again, and she wouldnt idle and was running very rough. Put a timing light on it and the timing was good. Moved the conductor around the wires on the dizzy and got no reading from wires 5 and 7. I’m assuming that means they have no voltage. What can cause this? I took the cap off and didnt see any cracks or moisture. Whats next?
5 and 7 plugs could be fouled, wires burnt or not making connection on either end, rotor or cap worn and not making good contact. Pull the wires off and see if you can get a spark off them with a screwdriver to the manifold - that will tell you which way (plugs or distributor) the problem is.
5 and 7 plugs could be fouled, wires burnt or not making connection on either end, rotor or cap worn and not making good contact. Pull the wires off and see if you can get a spark off them with a screwdriver to the manifold - that will tell you which way (plugs or distributor) the problem is.
I’ll pull the plugs tonight. The wires are good i’d made them not long ago and resistance tested them.
Pull the spark plug boot off of the spark plug. Stick a screw driver in the boot and hold it 1/4" from a ground while cranking. You should see a spark jump the gap. Check youtube if you're still uncertain.
There is a test light tool that is placed between plug wire & sparkplug that lights up when that cyl fires. Check at the parts store or EBay. Best $5 you'll ever spend.
The first clue of your issue was: "I made them (wires) not long ago".
I used to make my own. But if you don't get those terminals crimped just right . . . . . . .
Also, make sure those two cables are as far apart as possible in the looms from cap to plug. Due to the firing order, those two can cause Inductive Crossfire.
ZERO luck here as well on making wires..but i may lack skills..or using ohm meter to accurately diagnose.
the GM OEM ones on RA are very good.. they are original equipment..rare in ac delco land..
also love NGK not china crap ac delco plugs
Remove the cap and inspect the inside of the terminals. Inspect the rotor too.....
Since 5 and 7 are sequential in the firing order, my money is on the cap. To have two plugs and/or wires go bad all at once is lotto odds. A cap can carbon track underneath though and affect two terminals...fairly common thing.
I have been making my own wires for many years.....it is the only way I will do a set on a vintage car/hot rod......I use the Taylor #73051 wire set and the Taylor tool #43390....works like a charm everytime. I use a little WD40 on the boot to help it slide into the boot after the terminal is crimped. This is about the only thing I use WD40 for LOL. I also use dielctric grease on both ends of the wire.
Driving home my vette started popping and bucking. Limped it a half mile or so, and shut her off. Started her up again, and she wouldnt idle and was running very rough. Put a timing light on it and the timing was good. Moved the conductor around the wires on the dizzy and got no reading from wires 5 and 7. I’m assuming that means they have no voltage. What can cause this? I took the cap off and didnt see any cracks or moisture. Whats next?
Check 5 and 7 plugs for fouling. Could be the signs of a blown head gasket. Did you overheat the engine at any time?
My petronics just recently flew apart and I lost 3 cylinders. Those little magnets
under the round plastic wheel came off. New petronics and the problem was fixed.
Thank you all for your input. The plugs were fouled, but that may have occured while i let it run to test things out, new ones are in and nothing changed. Still no fire for 5 and 7. Took the cap off and again it looked good, but im thinking it may be the problem. I went cheapo and bought a Bluestreak one when I left my old cap and coil out in the rain. The last bluestreak part I bought was an ignition module and it died in 2 weeks. We’ll see what this new cap does.
to answer a few questions, no it hasnt overheated while i’ve owned it, but who knows. Also The wires are good, moved them to different cyl and they worked just fine. The rotor is still good as well. Can distributors go bad? I’m not well versed in how they work but i understand the basic functions.
Back in the early 70's I was towing my flatbottom home from the Colorado River during a monsoon storm, when my engine starting running rough so I pulled over and it was idling really bad then quit.
Spent the night on the side of the road.
I got up in the morning and everything looked good, wiped out some moisture in the cap, but it still ran rough.
Changed out the cap with the spare I kept for the boat and it ran perfect.
Put on a new decent cap and see if it fixes the issue.
Well guys still no fix. Tried a new A/C delco cap and i’m still having the same issue. I noticed while it ran for a bit that the timing light was flickering, Just one flicker every 5 seconds or so. Also, there are a few witness marks on the old cap, like discoloring right next to the 5 and 7 terminals. All other terminals show clean hits only 5 and 7 have the marks, and less wear on the actual metal it is supposed to contact.
11-22-2021, 10:46 PM
5 + 7 Cylinders No Spark
