79 C10/350 died...then came back to life.

[kopeck]

make sure you don't have weak springs or sticky weights in dist

Now that you say that...I fooled around with the weights because they were a mess.  I wiped them off and stuck them back in but they didn't seem any better.  The bushing were kind of sloppy but I stuck it all back figuring I would work on them later.  I wonder if they're sticking now.

I'm sort of thinking I should have just bought a new distributor.  I've already got almost as much into my old one as a new Summit aftermarket job...

K

[gunrac]

been there       best out .....is replacememt     my  oil gear had sloop to......that will cause hesitation in carb also

[kopeck]

Yeah, I'm thinking I might just get a new one at this point, it's not worth the head aches.  Seems like it has to be ignition but then again anything is possible with an old truck.

The truck was all over the place today, sometimes real crap and others as good as can be expected from a well loved 350.

Most any time you came to a hill and eased into the throttle a bit to maintain speed I could feel it miss a little, if I gave it a bit more throttle to try and gain some speed it would get worse to the point where it almost feel like there would be a split second stall followed by it coughing.

Then I took off down a main road and it ran with out a miss @ 55 - 60 MPH.  Let it cool off and it was back to missing on my way home.

K

[kopeck]

I'm dredging up a topic from last year but it's the same problem so this seem easiest.

The truck still had it's weird miss/cough issues when I put it away late last fall.  Since this all started with ignition and the distributor is the only thing I've touched (other then adding new plug wires) I'm going to assume the problem is still in the distributor.

In stead of piece-mealing my way through my old unit I was thinking I would just get one of these:

https://www.summitracing.com/parts/sum-850001r/overview/year/1979/make/chevrolet/model/c10

JEGs has a similar unit, I'm sure they're pretty much the same as the $50 dollar eBay units.  At least the Summit unit comes with a 1 year warranty and it isn't likely that Summit's going anywhere.  That and the reviews are good.

Seem like a logical next step?  I usually like fixing the underlying components but a new pickup and bushings are going to cost me nearly as much as the whole unit...

K

[bd]

Before you replace the distributor, use your ohmmeter to measure the resistance of every spark plug wire; original type carbon core wires should measure roughly 1,500 ohms per foot of wire length - any wire measuring over 5,000 ohms should be replaced.  Aftermarket spiral core wires can measure as low as 30 ohms per foot.  Inspect for black soot or any greenish discoloration inside the spark plug wire boots at both ends - traces of soot or discoloration calls for replacement.  Start the engine in a dark environment and have an assistant load the motor while you watch for arcing from the spark plug wires, especially between the spark plug boots and surrounding heat shields or exhaust manifold.  Remove the spark plugs using a rubber insert spark plug socket and inspect for a cracked ceramic insulator and general spark plug condition.  Afterwards, if you think the distributor is still the cause, the linked Summit distributor should be a suitable replacement.

[kopeck]

That's all pretty easy stuff to check, I'll give it a look before I throw more money at the problem.

It would surprise me if I needs new plugs...while it hasn't been a ton of miles it's been 15 years.

K

[kopeck]

Or maybe this is the reason why I was having issues...

That's brand new cap and rotor.  What would cause that?  The only thing I can think of is the rubber seal/dust cover that the button sits in was really stiff unlike the OE one that wasn't at all.  Maybe it caused to much friction?

K

[bd]

That's a common result of protracted arcing between the carbon button and rotor contact due to button wear.  I've seen 1 1/4" diameter windows burned through the cap center and still produce a "perfect" scope pattern and run fine.  Couldn't believe it.  Replace the coil (AC Delco or MSD) along with the cap and rotor so you don't experience a ghost misfire.

[kopeck]

Yeah, I was just reading that after doing some googleing.

The coil is brand new (CarQuest in house brand), the Cap, Rotor and button/busing/brush were all new (Accel brand I think, or maybe Summit).

I wondering if the tab wasn't bent up enough on the rotor?  It looks like there was contact being made, or was at some point.

They also talk about plug gap causing this.  As far as I know the plugs were gapped to spec (.045).  The old cap wasn't like this at all, it was age worn but not burned in any way so it survived these plugs.  I did change the wires, not sure if that could be a factor.

K

[kopeck]

A couple of more picks and observations...

First off, the cap & rotor was made in Canada...darn imports.

Second, there was some arcing around the terminals on the cap, kind of looks like the batt terminal.  Not sure if that add any clues to he mystery?

Third a picture of a messy rotor for fun.

[bd]

Those are either Accel or Echlin cap and rotor.  Post pics of the coil side of the cap and the brush contact pad of the coil.  Are you saying the cap burned away after you installed new cap, rotor and coil?  How many miles does that represent?  Did you reinstall the ground strap between the coil frame and terminal bulkhead on the side of the cap?

HEI produces upwards of 35kV across an open circuit.  That much voltage will break down dielectric components and create its own current path eventually.  Once a new current path is established, discharge becomes progressively easier, because of the resultant carbon path.

[kopeck]

That's exactly what I'm saying.  That cap, rotor, button and coil combo has around 500 miles on it.

When the truck died originally I had the cap/rotor/button & a set of wires on the shelf.  The cap and rotor very well could have be original (all Delco parts).  I had been meaning to freshen everything up (the wires in the truck were crap) for a while but it just kept on running so the parts sat on the shelf.  The first thing I tired when the truck died was a coil so I just swapped out the other new parts at that point.  The old coil did test right on the edge of one of the specs though.  The ignition module was the root of the problem though.

For the record the button was installed correctly (cap - button - rubber seal - coil) and the ground strap was installed on the coil.

I'm kind of worried that if I throw a new cap/rotor/button at it I might have the same problem all over again.

In my mind something's creating resistance.  Maybe there was an air gap between the tab and the button but it doesn't look like it.  I'm going to test plug wires tonight when I get home from work.  The old cap wasn't burned so something changed.  I don't see anything else in the cap or on the rotor that would indicate they were faulty.

Here's the top of the cap:

K

Edited to add photos of the coil.  Is it normal for the windings part of the coil to be loose on the metal frame?

[bd]

Based on the images, the issue was with the carbon button.  All of the damage is limited to the small area surrounding the button and rotor contact.  There may have been a problem with composition or manufacture of the button that caused premature wear or failure of the base material.  Once a gap developed between the rotor contact and the button, arcing rapidly eroded the remaining button away.  Gradually, arcing migrated to the larger area of the coil pad around the edges of the button flange, taking the lowest energy path to the rotor.  Again, use either an original AC Delco cap and rotor or aftermarket MSD.  Consider smearing a small amount of dielectric grease on the tip of the new button, on the rotor tip and on each of the eight terminals inside the cap.  The coating will turn to a conductive ash and decrease erosion of the terminals.

[kopeck]

Sounds good.

The local auto parts place has a MSD cap and rotor kit in stock.  I'll get it and see how she goes.  I wish the caps were not red. ;-)

Thanks!

K

[bd]

If you prefer black, purchase the AC Delco.   

What you never want to do is mix cap & rotor brands.  Although this rule pertains more to conventional ignition systems than high energy ignition, always match the cap and rotor using the same brand.  Otherwise, the air gap between the rotor tip and wire terminal maybe excessive, resulting in a ghost (intermittent and random) misfire.