Hi guys, I have a strange issue for you. I recently replaced both valve covers on my 1970 455, and in doing so, needed to remove the spark plug wires to get the covers off. After installing the new covers, everything was cherry, the motor still ran like a top.

About a week later, I noticed the engine start to run a little less than ideal. I didn't think anything of it since the difference was so small, and I resolved to look at it later. After driving 27 miles into town for a valentines dinner with my sweetheart, I noticed the engine sounded like a cylinder was not firing. I checked to make sure all the plug boots were seated properly and disconnected each one and reconnected them one at a time. The issue persisted. I decided to investigate later and went inside to have dinner.

I came back an hour later and tried to start the car, but it sounded terrible, like several cylinders were not firing. It was idling like somebody had turned the distributor 180. I had the car towed home since I didn't have my tool kit at the time and looked at it the next morning.

All I did was remove the distributor cap and wires, inspect the cap, inspect the rotor (did not remove), put the cap back on and the wires, and the car started running fine. I figured the problem was resolved as the car ran excellent again for 2 days. I went ahead and replaced the distributor cap and rotor, and double and triple checked my spark plug order.

Now the problem is back, just not quite as bad. When starting the engine cold it idles horrible, shudders, and will stall if I don't give it gas. It seems like certain spark plugs are firing every once in a while, but not consistently, as I get spurts of all cylinders firing normally.
When the car warms up, I can still tell there is a miss, but it seems much better. When accelerating i can feel the affected cylinders firing occasionally and causing some hesistation. I took a look at the engine running in the dark, and I don't see any electricity coming off of the wires hitting the engine, but I do see a corona of electricity near each spark plug boot (I have heard this is typical with HEI). I have ensured each plug wire is firmly seated at both the plugs and the distributor. These wires are about 3-4 years old. What does this sound like to you guys?

 

its could be a fewof the wires internals were damaged, you can check resistance with a multi-tester set to ohms to start

 

Sounds like bad gas to me, try a can of seafoam or STP in the fuel tank. How do plugs look?
Steve

 

I'm with POGO, check each wire for proper resistance per foot and look for signs of shorting along their length. I used to like fixing guys missing problems by showing them the light show when I opened their hoods in the dark. Good luck.

 

If you haven't changed the plug wires and their age is unknown why not just replace them. It sure sounds like they may be the culprit.

 

If I do end up going with a new set of wires what would you suggest for HEI? I'm running NGK plugs at a gap of .45

 

Your gap is good. Is your carb running rich? I've also found sometimes the HEI caps don't seat well and cause problems similar to yours. I like 8mm Taylor Spiro-pro:


http://www.summitracing.com/search/p...-size/7-5l-455

 

With the HEI there are a few things to check:
internal wires (the vacuum advance movement can fatigue fracture them)
module
carbon button
coil

The module and coil can be susceptible to heat related issues.

 

I replaced the spark plug wires. Seemed to run a lot better at first. After traveling 20 miles started running like **** again. Seems to hesitate when accelerating from low rpm....

The carbon button was replaced at the same time as the rotor and distributor cap. is there something I may have overlooked while installing the rotor?

I was reading on how to replace a distributor cap and rotor, and the guide said the rotor needs to be pointing at the #1 spark plug position when you replace it, so i cranked it a few times to get it pointing that way without the cap on....could that have caused an issue??

 

Check your cap for condensation.

This sounds like somehow moisture is accumulating under your cap and condensing, providing an alternate trail to ground for the current. You remove the cap, release the moisture, and it's good until more accumulates.
The fact that you're in mossy Oregon helps point to this.

I'd change the cap and rotor and see whether that fixes it.

In the old days, you'd hook the car up to a SUN machine to diagnose this, but not anymore.

- Eric

 

Thanks for chiming in MD, I've already changed the cap and rotor. Only things left in the circuit is Coil, Module, or Plugs. Pretty sure plugs are good. Module must be good otherwise I wouldn't be getting spark, not sure about symptoms of a faulty coil....

All i know is definatley seems like cylinders are not firing, I know what my engine sounds like when its running right, and its definatley not right, engine shaking too... I smell gas in the exhaust, the plug deposits look normal...

 

May be coincidence but sounds like you distributor module may be going bad..sometimes they heat up and cause problems..misfire or quit running all together.

 

To assume plugs are good may not be correct either, I've had many brand new plugs that were faulty (especially those old Chumpions). The electrode gap within the plug ceramic
can carbon and cause the plug not to work, not saying this is it but start removing plug wires when it is missing and see if one cylinder makes no difference to test.

 

I'd start looking for a vacuum leak. If you have a large enough one it can make you think you have a miss.
How do the brakes feel?
On my 70 442 my brakes were slightly firm, but nothing to where I had to stand on them, but it idled like crap and was down on power. I was standing next to the car with it running and I noticed a "sucking" noise that I had not noticed before. It turned out my booster was leaking....BADLY. I removed the vacuum line from it and capped it with my thumb....whadda know....it cleared right up. I swapped out the booster and all was right with the world.

YMMV.

 

Will check on those things, thanks guys!

 

Sounds like "other woman" trouble to me!

I'm leaning toward a bad tank of gas too. Have you refueled since all this started?

Even though 99% of carb problems are actually ignition, I'd look into fuel filters and possibly choke pulloff. If it's not working or weak, choke could be closing off without your knowledge.

 

I did fill up shortly before this started, but the car was running fine for a few days before the engine started running like crap. It seemed to happen all at once. I will probably end up swapping out the plugs, I have been using the same set of plugs for about 2-3 years and I drive almost 100+ miles every week.

I did inspect the choke while the car was running just to see if it was sticking (I did have an issue with it sticking a little bit ago), but it seems to be operating normally. I closed and opened the choke manually just to see if it had an effect on idle (obviously closing the choke causes it to almost die) but everything seemed normal with the choke operation otherwise.

I checked all vaccum lines last night just to see if there was any breaks or disconnects, all looks good. I kept my ear tuned to see if the booster was making a big hissing noise but I'm familiar with the way the engine sounds and I dont hear any loud hissing except from the carb drawing air in.

 

I got a tank of bad gas one time. My fuel system was fuel of water. I believe it was from a station at the bottom of the hill. In a wet climate (satuated) and back in the day when most stations had leaky tanks I think they ended up with a lot of moisture in them. Bad gas is a definite possibility but it doesn't explain why it runs good for awhile then turns.

 

Get a can of gas line antifreeze and throw it in there it won't hurt anything and get gas somewhere else next time. Look to see if the carb is dribbling fuel while the engine is running and if it smells really rich out the exhaust.

 

That is not accurate at all.

As stated, an electronic module can start failing and have all sorts of issues before it completely stops working. Operation can become intermittent and/or have degraded spark output when it gets hot and then it works fine after it cools down. The coil can have similar reduced voltage output when it's hot but work fine when it's cold.

 

I will look into the coil and module as possible culprits. Sadly I don't have a tester or a lot of time on my hands to dissasemble and take parts in for testing (full timer, and I work on the weekends). I usually only have enough time to go buy a part and install it :/ despite the fact that I don't like to just throw money at problems.

Plugs will be next since they are the least expensive component, and I happen to have almost a full set of spare plugs on hand to see if there is at least some improvment. I will also try the gas line antifreeze or STP and fill up since I'm getting low anyway.

 

Pulling each plug wire off to see if that makes a difference won't cost you a cent.

Use insulated pliers/gloves so you don't get zapped.

 

Yeah I kept reading about people who said to try that when you have an engine miss to disgnose a faulty cylinder but....I'm scared to get shocked lol. HEI has a lot more voltage than points :< I'll try it with some rubber handled pliers.

 

You guys are going to eat this up: it was bad gas

I really should have listened...at least I got a bunch of brand new ignition components out of it! heheh...heh...eh....


Anyhow, the tailpipe would puff white smoke every time the misfire occurred (i didn't realize this until right before I filled up) this was an indication of water in the gasoline.

After filling up, i had a very hard time starting my car, I believe it was because the fresh gas had not pushed the bad stuff out of my fuel lines yet.

Now she is purring like a kitten!

 

Been there, what did you do to correct it?

 

I drove really fast to the gas station and burned off all the old gas, to the point where I had about a gallon or two left in the tank, then put 40 dollars of plus in and it ran fine (after taking a while to start). The change was immediate.

 

Cool, to be on the safe side, get a can of fuel line antifreeze and add it to your full tank. It will help burn off any water that's still on the bottom.

 

We had problems with gas stations here in Idaho. Someone filled the unleaded tanks with Diesel. Thank god it didn't happen to you. I have had bad gas before. At least you know your ignition system is up to date!
Alex in Idaho USA

 

Prior to installing a non egr intake, I had an egr valve go and the car had similar findings , I hit the egr with a hammer and the car smoothed rite out. Jus sayin. Haven't ran with an egr since I put the new intake on.