Why wont it fire?

[don t. - 72gmc]

Yesterday was my grand daughters b-day and I just hadda drive the 70 GMC for the 1st time this year. Checked fluids, all looked good. She fired right up. Drove around for 15 miles or so. Tranny was a little low, topped it off. All looked good, off went me and the wife. About 50 miles later, at a stop light, the truck started bucking abit. Threw it into neutral to keep her running. Never did die. Had to make 1 stop on the way, fired right up, things didn't change. Made it to the party. Went to leave was the same. My SIL said stop by and we'll fix er up.

Cleaned up the points, made it worse. It fired but was bucking worse than b/4. Cleaned points again, back to original condition. Went to the local AutoZone, which was a joke. Besides not having a clue, parts were not in stock. They did give me directions to NAPA. I bought a dizzy cap, points, rotor, condensor and a ballast resister. Replaced all but the ballast resister. Truck cranks real well but does not fire. Pulled cap, rotor does spin. Pulled coil wire to dizzy and grounded to block. Little or no spark. At this point, I didn't have a multimeter to check volts. SIL handed me his keys and said see ya tomorrow.

While lookin around I noticed....
....black wire into dizzy has a flat spot, kinda like it got caught under the cap. It doesn't look cut but???
....There is a condensor on one of the coil posts. This is inaddition to the condensor under the dizzy. What's this for? Don't remember ever seeing one there b/4. Sorry, don't remember which post.
....Is there a ballast resistor? I am unable to locate something that looks like what I bought. My other truck is a 72 GMC 2500, but its HEI and aint got these parts.

Things you'll prolly need to know....problem truck is a 70 GMC 2500 400BB w/a 4-bbl q-jet. Auto trans w/factory ac. Coil is stamped as 12v, use w/external resistor. 93,000 miles on original engine. Truck appears to be original, no mods that I can tell. I did show it off to y-all about 4-6 weeks ago. I would have attached a link, but Im at home currently connected at 19.2K, and its taken me about 30 minutes to get this far. The dog needs to go out. I'll try and find my prior post and reply back.

FWIW....4 of the 5 parts I bought from NAPA had "Made in the USA" on a sticky label on the box. All were Echlin.

Thanks inadvance for your time.
I do appreciate it.
Have fun.....don t. .....

[hilljob26]

you really ought to get a hei,these babys are on ebay for 45 bucks,and they are really nice as well,other then that,i think you have a dist. issue

[LONGHAIR]

Just from what I see in you post (assuming the that points are ok) I would look at the coil itself. If you get little/no spark from there....it doesn't really matter what is going on downstream. T

There is a condensor on one of the coil posts. This is inaddition to the condensor under the dizzy. What's this for?

Radio noise suppressor

[don t. - 72gmc]

Thanks for the info so far. HEI is prolly in my future, but hoping to "cheap out" at this point. I plan to test volts to the coil. I agree it may be bad.

Here is a prior post that contains pics of the truck.
Hope this works..... http://67-72chevytrucks.com/vboard/s...d.php?t=274880

Im about ready to leave. SIL has DSL, so I can check from there.

Thanks. I do appreciate it.....don t. .....

[68gmsee]

Lots of things that can cause the symptoms you gave... Gas problems-moisture, old gas, etc. Ground cables- Battery, engine flat ground cables. Make sure they have good solid, clean connection.

Ignition. Look like you've taken care of preliminaries. I usually work myself backwards starting with spark to the plug, then remove cable at dis end and see if spark jumps to the cable. One thing to remember-you can't always tell if the spark is good by looking at it.

A weak or defective battery can give you a weak spark so make sure your battery is at optimum and that your alternator is charging at the correct rate when running. If the battery is bad and alternator not charging properly, your truck will have those same symptoms you describe.

Let us know what you find.

[67_C-30]

I'll offer three suggestions:

H
E
I



Seriously, I would replace the wire you said that is flat. The wires could be broken inside. Also, check the point gap and dwell with a meter. The point gap should be .018" IIRC. The next thing was be the coil wire connection and possibly even the coil.

With that being, I really would swap it over to electronic ignition. If you want to reatin the stock distributor, you can buy a kit from Pertronix and others that just replaces the points.

[DREAMS OF A 67]

Since you have already bought all those parts, I would check the voltage from ignition switch.(+ side of coil) If that is good I would change the coil. A bad coil will most of the time give trouble after it gets warm.

[VetteVet]

Hi Don t
First I want to commend you for a very detailed post. I don't see many as descriptive as yours and it makes it easier to find a solution. All the posters have given good responses so I will add mine.
GM quit using the ballast resisters in 65 or 66 and went to a resistance wire in the harness from the key to the coil. You should have a yellow or orange/purple wire from the starter solenoid "R" terminal to the coil positive connection to supply 12 volts when cranking. Otherwise the engine may not start or will start hard. Be sure you have the coil wired correctly or you will get the symptoms you are having. Setting the points is critical so be sure you have them on the highest point of the lobe and set at .019.

Here is a very good site for points ignitions.
http://abbysenior.com/mechanics/ignition.htm

You did remember to put the rotor button back on? LOL.

[Luvlegs]

If you haven't found it yet - mine had a quick non-start, retired and it fired up - went down the road and started smoking under the dash - I actually had a MAJOR short where the harness runs over the inner fender behind the hinge area- no telling how long it was there until it acted up.

[El Jay]

Originally Posted by DREAMS OF A 67

Since you have already bought all those parts, I would check the voltage from ignition switch.(+ side of coil) If that is good I would change the coil. A bad coil will most of the time give trouble after it gets warm.

I'd lean toward the coil starting to go south, especially since you've replaced everything else.

Also, if my memory serves, the extra condenser on the coil is to reduce ignition induced radio interference.

BTW, I also agree with all the pro-HEI guys. That's definitely the way to go.

Good luck.

[don t. - 72gmc]

Its a Monday morning sick day for me. I got 12v at the coil, battery may be at bit low at 12.82v. Made sure everything I did day b/4 was ok. No change. Got a new coil, no change. I went to call for a rental trailer, forgot my receiver at home. Good side..wife and I got to see the daughters family.
I follow up later when its fixed. Might not be for a while.

Thanks again.....have fun.....don t. .....