Loss of power for a split second on off (72 Vette 454) Help please

[1972corvette]

:confused;helpTook the Corvette out for a run,
My issue is without any warning I suddenly lose power for a split second, it's as if you are driving and you would turn the ignition off for a split second and then turn it back on.
It does this 3 to 5 times while driving for about an hour in the city, even on the highway cruising at 60 MPH it cuts out for a split second.
Where do I begin to find the root cause of this?

Coil? Points? Distributor cap? Ignition wires? Spark plugs? Gas? Gas Filters? Fuel pump? Carburetor?
How do I find out what is causing the loss of power for a split second?

I received this response from a Corvette owner:
If it dies for nearly a second, then the ignition is essentially 'dead' [all cylinders]. That rules out plugs, wires, and distributor (mechanical part). It also rules out the rotor and cap except for the central feed paths; but such an intermittent fault in those items is highly unlikely. That leaves coil, points, condenser, electrical wiring in distributor and coil power supply voltage from the vehicle. I just traced down a weird problem with mine that was not too much different. It turned out that the lead wire from the distributor to the coil had an intermittent short. The brass ferrule (strain relief) clamped onto that wire [inside of the dizzy] had worn through the insulation...and when vibration/accel/decel forces caused that brass piece to contact any metal, the ignition shorted out. Wierd!!

My bet is that it is an electrical fault: either in the voltage feed to the coil, the trigger line from the dizzy, or the coil itself (swap the coil out to test). You could hook a digital voltmeter up to the coil power feed line and to chassis ground with some long leads so that it could be inside the car. Take it for a spin and see what happens.

I did the following:
I changed the coil and still the same problem,
what I forgot to mention was this problem started after I put in some gas, is it possible I ended up with bad gas?

What is the specifics of the voltage feed to the coil, and the trigger line from the dizzy?.
vadelsohn@cogeco.ca

 

[Jimmy C]

If the ignition cuts out f/ that split second, like turning the key off and back on, would you not get a back-fire from that? This is, as kids, what we'd do when driving along to scare people, supposed fun. (Looking back it was stupid) But doing this would cause the fuel in the chamber to ignite and explode at the "wrong" time. Just a guess/and I suppose a question also.

 

[JohnZ]

That's not unusual, and frequently it's a result of an intermittent connection in the terminals inside the multiple connector on the engine side of the fuse block. Pull the connector off and check for corrosion or damaged terminals.

 

[jeffn]

Check the hot ,(big red), wire to the distributor also....Make sure it isn't loose and the such...You know the drill.....

 

[1972corvette]

I cannot see any loose or broken wires, checked the fuel filter in the carb, super clean.
Still have the immediate loss of power for a second on off on off.
Help please

 

[Jimmy C]

I cannot see any loose or broken wires, checked the fuel filter in the carb, super clean.
Still have the immediate loss of power for a second on off on off.
Help please

I think I'd go in the direction of the carb/fuel system. I'd say that's where the problem is. Do all the lights on the dash suddenly come on f/ that split second? Or does the tach and gauges bottom out when this happens/at the same time? I'd say it's the carb more likely than ignition (only) or electrical system. Only my opinion.

 

[1972corvette]

Loss of power ?????

I think I'd go in the direction of the carb/fuel system. I'd say that's where the problem is. Do all the lights on the dash suddenly come on f/ that split second? Or does the tach and gauges bottom out when this happens/at the same time? I'd say it's the carb more likely than ignition (only) or electrical system. Only my opinion.

It has to be electrical, everything else keeps working,
lights radio and so on.
What a pain these old Vette's are, sometime's I say I'm too old for this, sell it and buy the New Camaro SS with 425 HP
Vic

 

[1972corvette]

I checked all the wires, changed even the coil wire to the distributor.
Very strange Corvette was running fine then it started to cut out, at times it felt like I was riding a bronco horse.I let it idle and you can hear the intermittent engine idle.
Please click the following to hear how my Corvette is running raise the volume on your PC.
WHAT is going on with my Corvette???
MOV07007.flv video by Canada53 - Photobucket
MOV07008.flv video by Canada53 - Photobucket
MOV07009.flv video by Canada53 - Photobucket
MOV07010.flv video by Canada53 - Photobucket
MOV07013.flv video by Canada53 - Photobucket

 

[jeffn]

Hmmm...That's not cool...Look at the vacuum lines from the carb .Maybe one of them is off or rotted.

 

[Jimmy C]

'72'Vette,
Take the air cleaner top off and look into the carb when it's idleing. See if there is any indication, at the inside bottom of the carb, as to whether the fuel supply is being cut off f/ a split second when the engine wants to die. Do you have a fuel filter that you can see the fuel through? If so, see if the fuel supply is being stopped f/ that quick second. I still say it's fuel (from what I can gather). It doesn't sound like an electrical miss. And it doesn't seem to be a vacuum leak either. It doesn't have to be fuel pressure (although that would be something to check), but could be something stopped up (a small piece of junk (dirt) ) in the carb, needle and seat, float, port...Or could it be "too much fuel" going to the cylinders f/ a second and trying to kill the engine. Do you see alittle black smoke just after the "near shut-off" of the engine? Only my opinion ofcourse, and I may be wrong, but it sounds like fuel to me.

 

[1972corvette]

I do not want to start swapping the carb / DIZZY / perhaps the whole CAR??????????

 

[Jimmy C]

I do not want to start swapping the carb / DIZZY / perhaps the whole CAR??????????

Not implying swapping carbs, and I can see and understand your frustration. I do know that big blocks tend to exagerate small misses. Only giving you some trouble-shooting suggestions from thirty plus years of experience. Best of luck.

 

[1972corvette]

Jimmy,
Thanks,
No black smoke, appears to be worse now,
I let the car idle and it starts acting up then stalls.
Starts up immediately.
This all of a sudden started happening when I put in some fresh gas half a tank, then a few weeks latter put in somemore gas from another gas station. Everyone keeps telling me it's not bad gas.
Car always ran great for years prior to this headache
Regards Vic

 

[1972corvette]

It now appears to be getting worse as if it's running on less cylinders, even a couple of backfires.
Vic

 

[Jimmy C]

Vic,
Have you replaced the spark plugs or taken them out to read them since this Mis-fire" has occured? If not, and I know especially on that big block, it's a pain in the -ss w/ the little bit of space to get at the plugs, buy a new set of plugs and as you take the old ones out, put them in order to see if it tells you whether it's just one cylinder doing the missing or the cylinders on the receiving end of one of the intake runners, etc. You very well may get an indication by the color of one, afew or all of the plugs as to what the problem is. I would for sure read the plugs as they may very well tell the tale.

 

[1972corvette]

Driver's side not to bad to remove the plugs, passenger side? Oh my G_D how to get in there? I presume I have to jack up the car and do it from underneath.
Wife is not Happy, I was supposed to take her out for a movie this evening.
I guess I will be sleeping in the car tonight

 

[1972corvette]

A Corvette owner solved my problem, you will never guess?? The Ballest resistor on my distributor was causing me all this grief, I replaced it from my spare distributor, started her up, Corvette is running like new.

 

[73shark]

FYI, that's a condensor (capacitor). Ballast resistor or the resistance wire that Sharks used (at least '73 and later) is to used to drop the 12V to 8V-9V after starting to increase the point life. It's bypassed during starting to allow full voltage to ignition system. The condensor is used to help lengthen point life by absorbing the current each time the points open.

Did you replace the points while you were in the neighborhood?

 

[Rodney Gold]

if you really want to get all the power outa the 454 , I would suggest a change to a electronic Dizzy like a MSD , the obne with adjustable timing curves and the addition of a MSD 6aL multispark ignition.

 

[Jimmy C]

Yes a condensor, the old "change every time you change the points" and came in the points kit, and I do remember that they go bad from time to time. I haven't had a V8 w/ points in quite some time either.
I'm super glad that you solved your problem. I know that you're happy and I am too.
Yes, the newer electronic systems are better, but you can still eliminate the vacuum advance and buy the centrifical advance kit w/ heavier weights and lighter springs f/ about $4.00 and get more advance at lower RPMs, and they work really well. We all used them on the older Chevy engines along w/ headers, an intake and carb, and they ran great, those were the days. But the kits were $1.99 then at the auto parts store(before the big parts chains came about).
Sorry to say that I didn't even know/realize that you had a points set-up. My bad.

SHARK, Condensor/reschmencer-the guy fixed his problem which is what is important.