Whaaa?! Coil replacement stumper

[Geektrucker]

So has anyone ever replaced a coil, and had it cause severely worse performance?

For the back-story, been having a problem with an off-idle stumble / miss general ugliness. At idle and WOT it will run fine, accelerate and decelerate all seem / sound / feel normal, but at cruise, especially in town, 2nd gear doing 25 or 30, it misses and bucks and stumbles etc. Any kind of hill or load, everything smooths out. If I let off, it smooths out, same if I speed up.

Now, that being said, I know I have a bad carb (Monojet). I've rebuilt it once and discovered that two screws (1 for the top and 1 for the float bowl to base) are stripped. Also, the throttle plate rod is trashed, needing bushings.

Oh, for those just joining in for the home game, it's an 81 C10 SWB, inline 6 260 with a points system (all replaced within the last month). The 250 in it, is actually from a 67 - 72 car as indicated by casting number.

So, the first thing you're going to say is to replace the carb... I already have a 2jet rebuilt and ready to go in as soon as the adapter shows up Thursday...

For those still reading.. I decided over the weekend, that the last bit of the ignition I hadn't replaced was the coil.. I've already done everything else, so I picked up an OE replacement from O'Reilly's and slapped it in last night. Drove it to work this morning and it felt like it was running on 3 cylinders. Lucky for me, I work literally next door to O'Reily's, so at lunch I swapped it out for an OE performance version... same exact problem. It won't idle for crap, and can't get out of it's own way, spitting and sputtering the whole time. The only way I can get it to move into even light traffic is if I wind the piss out of 1st and ride in 2nd keeping the rmp's much higher than normal.

To make a long story longer, I ended up buying an Accel threw that one in and still same horrid performance. I finally gave up and threw the ancient (I think original as it says Delco-Remy stamped on the top!) and things are back to driveable conditions (with carb issues).

So...am I missing something? I double checked all my connections regarding positive and negative etc each time so know that's not the issue.. tweaked the timing for each coil...I just can't for the life of me figure out why 3 brand new coils would make this thing run much much worse than before. I've replaced dozens of in-cap HEI coils and never had an issue, but my first point style coil upgrade has been an utter fail.

 

[Georgeb]

I am thinking somthing about the coil voltage. I know the earlier systems used a resistor wire and would feed the coil a lower voltage to prevent burning the points. They only saw full 12 volts while cranking the starter. I haven't researched this much but it's a place to look. Also the plug gap on the earlier systems was somthing like .030"or .035"

 

[crazy4offroad]

Check the inside of the cap for carbon traces, sounds like it is spidering. Did you get any dielectric grease for the button? It almost sounds like the rubber insulator was left out and it's just bridging every which way. If it ran half way decent before the first coil swap, something was done wrong or damaged.

 

[Georgeb]

Check the inside of the cap for carbon traces, sounds like it is spidering. Did you get any dielectric grease for the button? It almost sounds like the rubber insulator was left out and it's just bridging every which way. If it ran half way decent before the first coil swap, something was done wrong or damaged.

If I read his post correctly he is running a points ignition with a seperate coil rather than an HEI coil in cap ignition.
Switching to HEI would be a good upgrade.

 

[Geektrucker]

@Georgeb Correct on the resistor wire, althought I can't located the wire from fuse block that is braided, plus the OE & OE performance coils I tried both had printed on side it needed an external resistor. Could it be the old original coil has an internal resistor?
@crazy4offroad it is not an HEI system, the cap & rotor are new, and show no signs of carbon etc.

No doubt an HEI upgrade is planned, it has to wait until later this winter / early spring for other more pressing upgrades & repairs.

Sent from my SCH-R970 using Tapatalk

 

[Georgeb]

I think the 81 would have originally been HEI so you may not have the resistor wire but I am not sure. I would check what voltage you have at the coil with the ignition on. Also, are there any numbers on the old coil you can use to determine the specs. I do know that full 12 volt current will burn the points rather quickly, throw the dwell angle off and result in poor performance from arcing. Hopefully someone else with more experience chimes in on this one too.

 

[chengny]

Correct on the resistor wire, althought I can't located the wire from fuse block that is braided, plus the OE & OE performance coils I tried both had printed on side it needed an external resistor. Could it be the old original coil has an internal resistor?

I think the 81 would have originally been HEI so you may not have the resistor wire but I am not sure.

George is correct - breaker points ignition began to be phased out in 1974. By 1975 it was gone - all ignition systems were HEI. A truck built in 1981 will have no resistor wire.

But that doesn't explain your issue. You have a ballast ignition system - which does requires an external resistance. But, while it is true that the absence of a resistor wire will eventually cause performance problems, this takes time.

It is due to higher than design voltage across the breakers points (contacts). The overvoltage condition results in excessive arcing each time the points open. The faces of the contacts quickly (but as in weeks - not minutes) become pitted and burnt. This effects the current flow through the primary windings of the coil. As a result, the voltage induced in the secondary windings drops, a weak spark is delivered to the plugs, blah, blah .....

However, as noted, that scenario takes time to play out - you know, for the faces of the points to actually deteriorate. You have been experiencing poor performance with components that are "straight out of the box". Add in the fact that putting your old coil back in resulted better performance than when using the new ones - and it would appear that the coil is not the issue.

On the other hand if the situation were reversed - immediate poor performance due to a "standard" coil being wired through a resistance...that would make sense. A standard coil is one which does not utilize an external resistance (i.e it requires full battery voltage).

But that isn't the case. It's like they say; "If my aunt had balls, she'd be my uncle."


Bottom line:

Using a standard coil on a ballasted ignition system will result in low spark voltages probably leading to running problems which are immediately noticeable.

Using a ballast-type coil on a standard ignition system (without a ballast resistor) will
result in excessive current flowing through the ignition system. This will eventually cause premature wear of the points potentially leading to reduced coil life.


Since you have determined that sufficient (but not correct, see below) voltage is available on the positive side of the coils's primary windings and that there are no obvious problems within the distributor itself, it might be a good idea to check the condition of the ground path on the negative side.

I am unfamiliar with the physical path to ground on the negative side of the coil. All I know is that when the contacts are closed, voltage flows out of the coil negative, through the points mounting bracket and into the distributor body. After that, IDK - I assume the path is through the timing lockdown clamp and into the engine block.

As a start, maybe check for good continuity from the points mounting bracket to the engine block.

If you work this out and intend to continue running a breaker points ignition system for any length of time, the correct value of the resistance to be inserted into the pink hot wire is 1.80 ohms. That is specific to a 6 cylinder engine - the power supply to the coil of an 8 cylinder engine requires a 1.35 ohm resistance.

 

[Georgeb]

@chengny I knew you would show up and as always with an excellent post!

I originally wroke much more but it didn't make sense and I hadn't read the last two posts properly.
Carry on......

 

[Georgeb]

I would still like to identify the original coil and wonder what the voltage at the coil really is.

 

[Geektrucker]

@chengny Fantasic info there, thank you! I'm beginning to re-think if some of my current running problems are as much on the electrical side as they are carb side. According to the casting number, this engine is from a 67 - 72, the body is an 81, so that would make sense why there isn't a resistor wire.

I'll pull the points this weekend and take a look at them, in addition to checking the voltage at the coil. I've already gone through all the grounds twice on this for an earlier headlight issue, including the strap from engine to firewall, body grounds, and the block ground, so those should be good.

I returned the Accel coil today and decided I'll just drop in an HEI dizzy and be done with it. I found one on stealbay new for $60 with coil, that should get me through the winter at least. Combine that with the 2jet I have waiting to install and it should perk it up nicely I think.

@Georgeb The only markings I could find at all on it, were on the top "Delco-Remy" curved around the outer edge.