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Bad spark plug wires, symptoms?

11K views 118 replies 9 participants last post by  El C 
#1 ·
My -54 235 runs kind of bad and I´ve changed all the electricals (coil, plugs, points, rotor, cap, condenser) but not the wires. Stupid me!
All the symptoms (as far as I know) are there. What say you?
 
#3 · (Edited)
Spray the plug wires with water with a spray bottle while the engine is running. If the wires are bad the engine will run worse and there will be arcing between wires and to block. Do it in low light or at night to really see the arcing. Also as said valve adjustment is a good idea for the solid lifter engine. According to my Motors Manual, the last year for the 235 CI 6 Cyl with solid lifters was 1955. That was only with a manual transmission. The engines with Powerglide Automatics used hydraulic lifters. So there's a good chance you have a solid lifter 235. Especially if you have a manual trans. The valve lash adjustment is .006" intake and .013" exhaust with engine hot. You could start at .010" on all valves with engine cold and then warm it up and then readjust.
 
#10 ·
If you brought that truck to me I'd start with a compression check. That would tell me that the engine is mechanically sound. I learned from years of experience that you can't tune an engine that is worn out or has internal mechanical problems. Then I would get out my oscilloscope and look at the primary and secondary ignition wave forms. That would give me a good idea of what is going on with the ignition. Since you already replaced most of the ignition parts why not just put a set of plug wires on it? Also make sure you are buying good quality ignition parts. There are a lot of cheap ignition part on the market.
 
#11 ·
I´ve done the compression check and the readings were between 9 and 8,2 kg/cm² (that cirka 117 - 128 psi. There is a little bit of difference but I´m pretty happy those numbers. Do you disagree?

I don´t have an oscilloscopeat my disposal, so can´t do that.

Yes, I´m putting on new wires, I´m doing my own metalcore cables.
I just measured the resistance and condition on the old wires and they are rubbish.
 
#16 ·
Symptoms of bad wires are similar to symptoms of eroded spark plugs.

As vehicle speed increases, the misfires increase. If you have replaced the spark plugs and the misfires continue ....... It is the ignition wire.

That occurred with my 1995 Ford F-150, 300 CI six cylinder, fuel injection with electronic ignition. The engine was misfiring above 60 MPH . I checked the spark plugs and they were eroded with more than .090" gaps. I replaced the plugs and that fixed the misfire.

The spark plugs was the first thing I checked because I knew they had more than 60,000 miles on them. I replaced the ignition wire after I replaced the spark plugs, just for good measure. The wire was good.
 
#31 ·
Replace and set ignition points per spec. Set ignition timing per spec at idle.
Check mechanical advance by removing dist cap and turn rotor. It should move against the advance springs and weights and spring back. Remove the rotor and there should be a round felt disc down inside the shaft. If the mechanical advance moves properly as I just said, put about 3 drops of engine oil in the felt disc. If it doesn't move properly, pick out the felt disc with needle nose pliers and spray a small amount of penetrating oil down in the center of the shaft and work it back and forth to free up the mech advance. Wipe up any excess, put felt washer back, and put 3 drops of engine oil in the felt disc.
Check vacuum advance by disconnecting vac line and applying vacuum to vac advance unit. Application of vacuum can be as easy as connecting a vac hose to the vac unit and sucking on the hose to build vac then close off the hose with your tongue to see if it holds Vacuum. No kidding it works great. If it holds vacuum, it's OK. If it doesn't the diaphragm is ruptured and the vac advance unit must be replaced.
I would also get a Carb rebuild kit for this thing and remove the carb and go completely through it. The old Rochester 1 Barrel carb is very straight forward. Follow the directions in the kit and you'll do fine. God only knows what you'll find in that carb. Here's a carb kit from Eckler's. Chevy Carburetor Rebuild Kit, Rochester 1-Barrel, 1949-1954 - Eckler's Early Chevy Parts

And while you're at put an inline pleated paper fuel filter between the fuel pump and carb. Like this: 10- INDUSTRIAL HIGH PERFORMANCE UNIVERSAL INLINE GAS FUEL FILTER 5/16" 4"L NEW | eBay

They are available at any auto parts store and the see thru housing lets you see how dirty it's getting. With an old gas tank, all kinds of junk may be in there.
Don't use those junk inline filters like this: https://www.ebay.com/p/?iid=152164979988&&&chn=ps

They have a coarse screen for a filter and let lots of junk through. The cranking compression spec for your engine per my old Motors Manual is 130 PSI Minimum. Yours may come up a little after it runs a while. Also check it with choke and throttle wide open to let max air in. Of course with all plugs out and ignition coil disconnected. A few squirts of oil in each cylinder will bring up compression but may indicate worn rings. Get it running decent and see if it smokes and uses oil. Let us know how it goes
 
#32 ·
All of that has been done except fuel filter and that´s just because there is a new tank and new lines.

I´m leaning towards the wiring.
We did put a new wiring harness (American Autowire set) and if my memory serves, it ran better before the wiring job.
 
#33 ·
El C. I just had an A HA moment. I just ran into a similar problem on an old Chevy 2 weeks ago. The car was rewired and he was getting 12.4 volts to the + side of the coil with Ig on, points open, and eng not running like you are. There's supposed to be around 7 volts. His as your voltage was high because the resistor wire to the + side of the coil was eliminated. This caused the new points to burn in a matter of minutes and the car ran terribly in short order. The original Chevy resistor wire on a point system with 12 V system is supposed to be 1.6 Ohms. We replaced the quickly burned points and put a 1.6 Ohm ballast resistor in line with the coil and the car ran great. Don't get a 0.8 Ohm ballast resistor like your local parts guy will try to sell you. Make sure you get the 1.6 Ohm resistor like this:
1.6 OHM Ignition Coil External Ballast Resistor | eBay

It should say 1.6 Ohm right on it. Let us know how it goes.
 
#34 · (Edited)
When I measure it it says 2.2 ohms (meter itself is 0,5) so the resistor is about 1,6 ohms.
So no luck there.

When I measure the volts on either side of the resistor (when ig on) it says over 12,6 volts before and 5,9volts after the resistor?
So maybe I need just that 0,8 ohm resistor??
 
#39 ·
5.9V after the resistor is good.
JMHO, 5.9 volts after ballast is too low, should be 9-10 volts, suspect resistor is incorrect. Coil may not be building enough voltage to fire plugs correctly. As I mentioned earlier pull the plugs to see how they are burning, it will tell you a lot.
Check coil some have a ballast resistor built into them and require no external resistor. Normally a 12 volt ballast resistor is .5 to 1 ohm, suspect you are using a 6 volt ballast resistor.
An easy way to check for a bad condenser is to watch the points as you crank the motor, a bad condenser will cause the points to flash outside the points, a good condenser will be a small flash between the points only.
 
#41 ·
I would not recommend running without ballast resistor if it's required even briefly. The resistor limits the current the coil can build in its coils and prevents runaway (meltdown). Get the correct ballast resistor for your coil and see if it helps. BUT, first pull your plugs and see what they say. You maybe chasing more than one gremlin..
 
#44 · (Edited)
This may be the mother of all stupid questions but when I put my multimeter on "beep" and touch the + on battery and the body of distributos, there is a connection. Same with - on battery and the body.
That can´t be right?
Also, when other needle of the meter is on + battery then the body of distributor reads 12,8 same as the battery charge??
 
#45 · (Edited)
I again just checked my Original Chevrolet Shop Manual from 1963 for 12V breaker point ignition trouble shooting. It says resistance of primary wire from ignition switch to + side of coil must be 1.40 to 1.65 Ohms. Chevy originally used a resistance wire which is no longer available. That's why we use a Ballast Resistor now a days. Your 1.6 Ohm Ballast resistor will work perfectly. The manual also says with points open, ig on, not running, you should have Normal battery voltage at + side of coil. With points closed, ig on, not running, you should have 5 to 7V at + side of coil. To get the 5-7V try 0.8 or 1.6 Ohm Ballast Resistor. I expect you will end up using the 1.6 Ohm Ballast Resistor. The manual also says to carefully check the wire from - side of coil to the breaker points for loose connections, breaks, or grounding to distributor where the wire goes thru a rubber grommet thru the base of the distributor. Also make sure the points and condenser have good clean grounds to the base plate in the distributor. To test for ig switch problems, try temporarily running a jumper wire from the + side of battery to the Ballast Resistor and start engine. Obviously to shut engine off, you'll have to disconnect the jumper wire. If all this checks out you should have a good ig system. Let us know how this goes.
 
#52 · (Edited)
You should have 2 wires to + side of coil. 1 from ballast resistor fed by key switch for when the eng is running and 1 from the starter solenoid which bypasses the ballast resistor when starting the eng. Disconnect both wires from + side of coil and determine which one is powered with key off. They should both be dead with key off. With key on only ballast Resistor wire should have power. The wire from solenoid to + side of coil should ONLY have power while the starter is cranking over the eng. If the wire from the solenoid is powered with key off it is wired wrong at solenoid or something is flakey with the solenoid. If you're getting power to the + side of coil with key off, the points are burnt and the block that rides on the distributor cam maybe melted. If the block is melted , you gotta replace the points. If the block is OK make sure the points are not pitted or show signs of over heat. Take the points out and clean them up with strips of 220 sandpaper until they look like new. Then reinstall points, set gap, etc. Try starting and running the eng with the wire from solenoid disconnected from + side of coil. That solenoid wire is really for cold Winter starts and for now can be left disconnected for trouble shooting. Wrap some tape around the end so it doesn't short out on something during cranking. Let us know what happens.
 
#54 ·
There is only one wire to coil + and it comes from the resistor.
There is one big wire on the bottom side of the resistor, one small goes from resistor to coil.
I see yor point now! That tiny wire can´t deliver all the current the car needs (I think :confused:)
Here is a pic of it.
 
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