The Stovebolt Site Forums The Shop Area Engine Shop Running Rough after Changing Battery Cables

Hello everyone,

My 51 3100 with 216 engine is still running on 6 volts. I have had a problem with slow cranking especially when hot. I checked my battery cables and they were much to small. Installed a set of 00 gauge cables and she now sounds like a 12 volt system. The problem now is it running very rough. I'm no expert but it sounds like it's not running on all six cylinders. I cleaned the the plugs and that helped a bit--not much though. My next step is to replace the plug wires (I don't know how old they are) and a new set of plugs. Does this sound like a logical first step? Do you think there is any connection between the new cables and the rough running? It ran great (once it started) before I changed the cables. Now it starts great, but runs poorly. Any thoughts are much appreciated.

Thanks!

Could have knocked the smaller "hot" lead loose where it connects on the same terminal as the larger battery hot lead (usually at the starter solenoid or stomp-starter contact, whichever you have). Also check the connection(s) at the coil.

It never hurts to replace plugs & wires but you could do alittle more troubleshooting 1st.

With the engine idleing, use an insulated pair of channel locks or pliers and pull one spark plug wire off at a time. Each time watch/listen for a change in engine speed. The engine should start missing on each removal. If it doesn't you've found the problem cylinder. It could be a bad plug, wire or something else like a valve not closing etc. Odd's are it's the plug or wire...

Generally if one plug is misfireing (or plug wire) the others are then suspect and replacing all would be recommended.

Trace all your steps when you changed out the large battery cables and be very observant. Sometimes it's all too easy to knock something loose on a repair and then theres always the probablility of something going bad just by coincidence when you repaired something else. As they say stuff happens.
Good luck
Dave

Thanks--some good advice. I will certainly retrace everything. The only thing I can think of that I did differently was I placed the small "hot" lead on top of the positive cable on the stomp-starter. Previously it had been under the positive cable.

I have used an inductive timing light to see if cylinders aren't firing or are firing intermittently. Should see a steady flash on each wire.

Putting it on top rather than under--the top was exposed and could have been dirty/corroded while the under was clean and gave a better connection. Suggest removing and cleaning it all good (with a fine wire brush) and re-installing.

Also check the ground connections of the new battery cable, It bolted to engine and/or frame. Pull and wire brush them good, re-install. Small wire brush is good, you can find them at Lowes and Ho Depo in the welding section in stainless and I think painting section in brass and steel.

If it still runs rough replace all wires and plugs, with plugs correctly gapped. This includes coil wire. While you are messing with it, consider new coil, points, condensor, and distributor cap if you don't remember the last time you did those. (Also inspect the 12VDC wires (to coil and from coil to distributor) and connections.) All that stuff is relatively cheap compared to the cost and inconvenience of getting towed in from somewhere.

Check the firing order. If you had any of the spark plug wires disconnected during the job it's possible you reinstalled a couple of them in the wrong location. 1-5-3-6-2-4, clockwise from the top of the distributor. Been there, done that, many times!
Jerry

What Jerry said. Getting A plug wire out of firing order will make it run rough every time! Been there, done that.

And I don't know which emotion is stronger. The joy to find out that there is nothing seriously wrong with the engine, or the utter disappointment in myself for being so stupid. I consider it a tie when I do it (one out of four times while replacing wires).

Just went through this last week end. Had to get the book out and follow directions. Did not help much, I think the head gasket let go between 4 and 5. Pulled the compression tester out, 140 at 1. 138 at 2. 140 at 3. 30 at 4. 30 at 5. and 140 at 6. Truck has been a daily driver for the last 2 to 3 years. All at once this started running rough and now waiting for time to pull it down. But yeah, we put the wires on wrong a couple of times.

Thanks everyone for all the advice. I went through everything again this morning. Made sure connections are tight and corrosion free. Put a new set of wires on, and a new set of plugs. Checked points, rotor and cap. Fired her up and she purrs like a kitten and runs down the road better than ever. Truly fun to drive now. Very possible I knocked something loose when changing the cables but it was time for a new set of wires and plugs anyhow. Best $30 I've spent.