In retrospect from 2010. An engine miss, but only on a certain piece of road.

While replying to a question on the VCCA site http://vcca.org/ I recalled a problem that had me stumped for about 2 weeks back in June 2010. I changed spark plugs from Champion W14's to Autolite 3077 plugs after reading that several Chev 4 owners were running them with better performance. The Red Chev had always used W14's and to be honest at that time I did not know any better.

After fitting the 3077's the change was amazing. The engine started quicker, the idle was a lot smoother, engine response was improved, there was more of a distinctive change from engine retard to advance and even the exhaust note changed.

That was just idling in the shed, what would it be like on the road?

The first test drive showed a definite increase in power, especially on hills where I could increase speed up hill in top gear. Previously the best I could hope for was to maintain the same speed on a hill.

I was doing a lap of a 5 to 6 kilometre test track that I had driven on for many years. Approaching the 3/4 mark, and going up a moderate incline, there was an engine miss, cough and splutter, and the Red Chev was not a happy camper.

Pulling up rather quickly and revving the engine a few times everything returned to normal and the Chev ran fine, until the same spot the next time around. Another lap confirmed that the Red Chev had an engine miss only in one spot on the track every time.

What was causing it to miss and almost stall in one 400 metre section of road, and then run better than ever for the rest of the time?

Changing plugs back to W14's the miss disappeared, but so did the improved performance as well. I then launched into a prolonged test of various types of spark plugs. You would not believe how many plug changes I did over the next 2 weeks. Its a wonder I did not wear out the threads in the head.

Believing that removing the miss by changing the spark plugs was only a symptom of the problem and not the cause, I saw no other option than to go through a process of elimination.

It had to be either a fuel or electrical problem, so I started a process of changing parts, testing at every stage.

I replaced the following the fuel system parts:

1. Removed the in line fuel filter
2. Checked all the vacuum lines for air leaks
3. Stripped and rebuilt the carter carby I was running at the time
4. Removed the top of the vac tank and ran it like a mini fuel tank
5. Swapped the carter carby for one from my spares

After each part was replaced, and a lap of the test track, the miss was still there at the exact same location. But I was now convinced it was not a fuel problem.

The next step was to change the following electrical parts:

1. Replaced the coil
2. Replaced the Condenser
3. Replaced the distributor cap
4. Replaced the points

After spending well over a week changing parts and over 100 miles of testing I still had this damn intermittent miss.

Consulting wiser heads than mine they believed it could not be the plugs as the car was running  better for the rest of the time. Engine timing was also discounted as when the engine missed I would immediately retard the spark, with no improvement. The only way to stop the miss was to pull up and rev the engine for a few seconds. The engine would then run OK until the next time I hit that same spot on the mountain.

By this time with no idea what the problem was, I was starting to get a bit cranky. The easiest solution would have been to throw the 3077's out the window and go back to the old cold W14's, except for one thing. Apart from that uphill section of the test loop the car had more power, was more responsive, idled smoother and pulled so much better on hills, except for that damn one spot.

Then, a few days and many miles later a breakthrough. I did a test lap with no miss. What had changed? I could not see anything until I noticed the advance retard lever was not fully advanced.

BINGO.

The ignition timing, which had been perfect or near enough is good enough with W14 plugs for well over 30 years was not 100% right for the long reach 3077's.

How did I fix it? I did lap after lap to prove the point. Then I backed off the advance to the point where the miss would stop. Another few laps, beautiful.

The position where the miss stopped became my new fully advanced setting.

All was right with the world, and has not been a problem since.

So the moral of the story is never assume the obvious, persevere and look at what you think it could never be.

I came so close to reverting back to W14's with poorer performance, but would have always had it in the back of my mind that the Red Chev ran better on 3077's except for one that 400 metre section.

I hope this may help others.