Rough outline on how to diagnose/fix Running Problems/Missing cylinder
 

Hi Guys,

I am in need of some guidance. I have a 1966 F-100 with a 300 inline 6.

Long story short, I paid a guy to install an electronic ignition but the truck was running terrible afterwords. He convinced me it was the carb and after he rebuilt the carb, its still running terrible (its running rough and missing). So I paid him for his time & parts, $425, but refused to let him do anything else.

I'm fairly good mechanically. I've replaced oil pans, water pumps, etc....but I've never tuned an older engine.

Can someone give me the steps I need to go through to diagnose the rough running/one cylinder missing problem? My dad said I need to first check the compression on each cylinder. Next would be start looking into the vacuum, valve adjustments, advance on the ignition etc....

I have the 1966 F100 shop manual, a vacuum gauge, pressure gauge, timing light, and lots of tools....so if an experienced individual could outline the steps that need to be taken, I would know where to start reading up/researching.

Thanks for the help!

James

if this is indeed related to a specific cylinder- the fast/easy way to figure out which one is to remove one spark plug wire, then start the truck. if the miss is gone, you've found the problem cylinder.

but first...two questions:
did it run rough before the new ignition?
what electronic ignition did the guy install?

if it didn't run rough before...you may need to start troubleshooting the guy's work.

As for the missing, I was planning on letting the engine idle and pull out spark plug wires and see if the engine idles differently. If I come to one where the engine idles the same whether the spark plug wire is connected or not, that would be the missing cylinder....right?

It ran nicely before I dropped it off. However, when I dropped it off an odd thing happened - when I turned the truck off, the engine stumbled around a second, turned off and then a few white whisps of smoke came out from under the hood. I'm not sure what caused that.

As for the ignition, he installed a Petronix II ignitor. He mentioned he burned out the first Petronix kit he attempted to install and had to get another kit.

I also thought he should have been trouble shooting his work because that was the last thing that was messed with, but he was certain rebuilding the carb would do it, so I gave him the go ahead. Nice guy, but I don't think I'll be having him work on my trucks mechanical issues again. He's a good electrical guy tho (if anyone needs an electrical guy in Seattle, I can give you his name).

Correct.


He admitted to burning up the first Ignitor...and after installing a second one, the truck isnt' running right?.....
That would be a red flag for me. You sure he's a good electrical guy? :)

That is correct. Also, if you find that each is firing correctly, that is to say that each is contributing, then you can pretty much eliminate spark as being the issue.

Ha, true. He was able to get all of my dash lights working, my gages working, installed a single speaker/amp/ipod hook up...so Im happy with that. So I guess non engine related electrical, I'd recommend him.

i'm not sure i agree- the Ignitor could be acting wonky and intermittently crapping out...

I did say "pretty much" not "completely". :D

Pertronix IIs can be a little temperamental and in a 300 I6 I would have used a Pertronix I instead. The II requires you to bypass the resistor wire so the Ignitor gets the 12V it wants. Also means using a coil that can handle the higher voltage in the "RUN" position.

So is there still a resistor wire?
Is there still a stock coil?
After installing any Pertronix many times you need to revisit your timing.

Thanks for the replies.

- So far my first step is to check the compression on each cylinder.

- Second is to remove the spark plug wire from each cylinder while it is idling. If I run into one where the idle does not change sound, I have found a missing cyliner.

- Third is to adjust the valves to make sure they are gapped correctly.

- Fourth is to check the vacuum off of the carb to make sure the vacuum is correct.....how do I check the vacuum advance?

- Fifth is to mess with the Petronix II (they can be tempermental). Mike - I dont know if I still have the resistor wire....is that the wire under the dash that gets hot? Im not sure about the coil. I'll have to look into that.

Im not super knowledgable about getting an old engine running well, but once I get all of these steps outlined....I'll start researching them one by one and try to go through all of them

Thanks for all the help guys.

Almost forgot - hopefully the Ignitor was gaped correctly.

Very near the ignition, from under the dash, you might see a pinkish wire which has a bullet connector on it. This plugs into another wire leaving the ignition directly. You could call that a pig tail wire and that is where the resistor wire starts. My 65 has a Pertronix II with a new ignition wire connected to the Flamethrower coil, through the dash grommet and connected to that pigtail after removing the resistor wire. Was a seamless operation.

Don't know if this will help but it sounds like your troubles started after the electronic ignition was installed, when I put the Pertronix on my V8 460 I had the same problem, miss firing and very difficult starting, did some research and I was sure it was wired properly, one of the posts said to add a 1/8" thick rubber washer (I made on by cutting a piece of hose) on the distributor shaft under the magnet, I also had to shave the same amount from the bottom of my rotor to make it fit, worked perfectly after that fix, I guess it had everything to do with the position of the magnet inside the distributor.