68 ignition trouble
 

Hi All,
I have a 68 327 with a strange ignition issue. I have replaced all the main parts..Ie.. points, cap, rotor, plugs and wires, coil, and still have stalling at low RPM. I have tried 2 rebuilt carbs...1 Q-Jet 1 Holley with the same result. Some of the cyl's seem to be misfiring. If I remove the plug wire from the cap and let the spark arc from thecap to the plug wirethe cyl. will fire. When the wire is pushed all the wayinto the cap it will stop firing. I tightened the gap from .35 to about .30...same problem. The plugs I'm using are ac delco r45s. andstandard silicone 7.5mm wires. My thought is that the old points type ignition is just not putting out enough juice to fire the modern plugs and wires reliablyat low RPM.The fact that I can get them to fire leads me to think it's not a valve/head problem.
I was thinking of trying the pertronix ignition conversion to up the volts to the plugs.
Has anyone had this problem, and if so, what was the solution?
Any help or suggestions would be GREATLY appriciated.

RE: 68 ignition trouble
 

Hi ax, welcome to the forum. Your point style ignition should have no trouble firing the new age plugs IF the distributor is in decent shape. Did you use high quality parts? Plug wires are not actualy wire but a carbon core to reduce radio interference, make sure to use a wire designed for the lower voltage system. Pull the cap and rotor back off and check the distributor shaft for worn bushings, you should not be able to wiggle the shaft sideways, any movement in this area will change the dwell as the engine changes speed. If the shaft and advance weights check out OK then double check the dwell, also I would not use the UNI-POINT kit, I don't know if that is still available but they were not as high quality as the seperate Delco points and condenser. Again I stress use good parts and the proper dwell and timing and it should not have an ignition missfire at low RPM, let us know what you find.

RE: 68 ignition trouble
 

Thanks Buckshot,
The points I was originally given at the parts store were the uni-point type,and I also have tried the2 peice set. I was going to try a different set of wires, and will get a low voltage set,(actually didn't know they had specific low volt wires)as that is my last resort before giving the pertronix conversion a try. The distributor seems in good shape. I removed and cleaned all the parts, and everything seems to be working properly. I might just get a dist. rebuild kit as well, just to be sure. The conversion kit uses the stock dist. anyway, so it can't hurt. Thanks for the tips!!

RE: 68 ignition trouble
 

Hey ax, one other thing I thought of, check the primary voltage at the coil, that's the small wires on the threaded teminals, should have full battery voltage, you might see only 9-11 volts while cranking but with the engine running it should jump up to 12.5-14.5 roughly. Low or intemittent primary could cause weak spark.

RE: 68 ignition trouble
 

I think you have this backwards. You get full battery voltage during cranking, then it drops due to the ballast resistor or resistor wire to prolong the life of the points by limiting the current during normal running. Also full voltage during cranking helps make up for the voltage drop caused by the starter motor and/or poor condition of electrical system in general.

RE: 68 ignition trouble
 

Got 12 volts with Ign. on, points open.....6v when points are closed. 12 v when cranking or running.

RE: 68 ignition trouble
 

Sounds like the ballast resistor/resistor wire has been removed. Running 12 volts all the time will make short life of your points. [:@]

RE: 68 ignition trouble
 

GM did'nt use a ballast resistor but there may have been a resistor wire, 12 volts with it running should be OK.

RE: 68 ignition trouble
 

There are 2 wires( red with white cloth cover) coming from the coil + side that are crimped to the same spade terminal,but 1 wire is not connected to anything, just cut with elec tape on it.There is also the condenser wire, and selonoid wire on the coil + side.it looks like someone may have cut the ignition wire and put it's own connector on. (maybe wire was damaged). I wouldn't think that would make any difference would it?

RE: 68 ignition trouble
 

I had that same problem on a bike. it wouldn't fire if the wires were pushed all the way on the plugs but would run fine if I held them off a little. turned out the gap was to close. I opend up the gap and it ran fine. Not sure if that was the actual cause of the problem but it worked. Good luck with it. Let us know when you get it figured out. Cheers.

RE: 68 ignition trouble
 

Hi ax, congratulations on getting a vette and welcome to the forum. I'll try to answer some of your questions and then I have some for you. Yes you should have two wires connected to the + side of the coil. (and a condenser), when you turn the key to on (or run) voltage goes thrua resistor wire to the coil, when you turn the key to start you get full battery voltage thru the other wire on the coil as soon as you put the key back to run your back to getting voltage only thru the resistor wire.
Can you tell me what you have done since it ran last?
Is the point gap at .019 ?
Was the distributor out ?
Do you have the cap wired with the correct firing?
Got any books like a Haynes manual?
Hope this helps, PG.

RE: 68 ignition trouble
 

Hey PG,
got the gap set at .19.....also have dwell meter set ao 30.
Dist was out to clean....was replaced at TDC cyl #1 with rotor at about 45 to front pass. side of motor.
wires are correct.
It will run, just seems to miss and stalllow RPM.
can you discribe the resistor wire so I know what to look for?
and I do have a shop manual.

RE: 68 ignition trouble
 

Hi again Ax, you say the distributor was out are you sure you didn't miss by one notch on the dist gear? Wheres the timing mark at?
In the Shop Manual on page 13-18 is a "Starting circuit diagram" outline,
on page 14-20 you'll find the actual diagram and all the other info. PG

RE: 68 ignition trouble
 

Timing mark at "0" TDC when Dist was installed.
The Dist will only fully seat in a couple of positions.
I did check the wiring diagrams, but will double check them.
Thanks AX

RE: 68 ignition trouble
 

Ax, if you reinstalled the distributor like the book says on page 4-4 and everything else is correct, than you've got me. PG

RE: 68 ignition trouble
 

Yea, I'm startin to think the new plug wires have too much resistance for the old system.
I can get it to run but it still misses at low rpm. especially when I put it in gear.The thing I can't figure out is why I can get the plug to fire when I pull the plug wire off the cap and let it arc from the cap to the wire.

RE: 68 ignition trouble
 

When you pull the plug wire off, it increases the amount of voltage build-up in order to jump the air gap. Can you tell if it is one specific plug that is missing? If so, I'd check that plug and maybe switch with another one or a known good plug. I've seen bad new plugs, just not very often.

The resistor wire on my car has a hi-temp, braided insulation on it. Since you have 12 volts when running, I'm guessing yours is either disconnected or missing altogether. But that's not your problem.

RE: 68 ignition trouble
 

Good call 73, possible cracked ceramic insulator from installing the new plugs.

RE: 68 ignition trouble
 

OK........everyone together>>>>>>AX IS A DUMBASS<<<<<<....lol.
I just put a whole new set of plugs in today and presto....runs perfect....had 2 bad plugs ,either from new(which i doubt) or from the 3rd time the P>O>S Q-Jet dumped huge amounts of gas into the intake.

BTW....if anyone is looking for a used Q-Jet ,let me know.........I have one for sale....CHEAP

RE: 68 ignition trouble
 

Forgot to add.........
A BIG thank you to everyone that responded to my post....you info helped me rule out my potential problems and get to the bottom of this.
Now that thats fixed I can get back to the neverending sanding and body work. (yea)