About four years ago, I put a Chevrolet Performance 350 crate engine in my ’65 El Camino. The previous engine had been abused as a dyno test mule and its tongue was hanging out. Before we dropped the engine into the car, a friend suggested it would sound better with a bigger cam. I had a COMP Thumpr cam left over from a previous story for one of the magazines so I installed it along with better valve springs. Otherwise the engine was as-delivered from Chevrolet Performance with its aluminum dual plane intake and HEI distributor.

Once we successfully broke-in the cam, test driving the car revealed a mild off-idle stumble which frankly, I expected. The engine combination really wasn’t the best. This 350 H.O. crate engine had 9:1 compression with stock iron Vortec heads combined with the middle Thumpr cam. The El Camino was equipped with a wide-ratio four-speed car but with rather tall 3.08:1 gears, so it wasn’t a very smart combination. If someone had asked me to recommend that – I wouldn’t have. I should have gone with a more conservative camshaft but I used what I had. Over the course of two years, I tried several carburetors and multiple tuning techniques in an attempt to solve the off-idle stumble. While I was able to improve this transition by putting fuel to it, the stumble never disappeared.

Then I tried a couple of different self-learning throttle body EFI packages as part of tests for magazine stories. This time, I expected that now without a carburetor responding to a rather low manifold vacuum signal that the stumble would finally disappear. But at various times, the stumble was evident but not consistent. All this time the engine otherwise ran fine. Spin it up to 6,000 rpm and it would sing with not even the hint of a misfire. In the past, when I have run into HEI ignition problems, the difficulties would usually surface at higher engine speeds. Many of my friends commented that my off-idle problems were ignition related. So I changed plug wires, distributor cap, and rotor, and swapped plugs several times.

Over the course of roughly 18 months, we bolted on a FAST EZ-EFI 1.0 followed by a test of Quick Fuel’s QFI throttle body fuel injection and most recently I bolted on a different fuel injection system. All three systems worked fine except that the off-idle stumble never went away. After testing three different systems on the engine, the discussion circled back to the ignition system. My thought was that the HEI distributor was brand new as I had barely put 2,000 miles on the engine. Because the ignition was so new, I discounted it as the problem seemed to be related to the fuel side of the engine.

I finally decided to eliminate the distributor as the problem and that way we could concentrate on what I felt was a poor cam choice. This went so far that I decided I would rather yank the engine out of the car and do the work on an engine stand rather than swap cams with the engine in the car.

So one Saturday a couple of friends and I removed the existing HEI distributor and installed a different ignition system –a brand new ignition that these same friends have designed but are not yet ready to go to market. The change to the car was astonishing. It appeared that the HEI module was the problem the whole time. Previously, I could not accelerate lightly below 1,500 rpm without the engine stumbling badly. Above 2,000, the engine would run fine with good throttle response. With a functional ignition system, the engine now is much smoother and much more fun to drive. As a final test, I pulled it down to 1,000 rpm in fourth gear and accelerated away with not a hint of hesitation or surge.

Clearly, the ignition had been the problem the entire time. I was so focused on blaming the camshaft that I never tried something as simple as swapping the module just to eliminate that as a possible problem. Obviously, this was my mistake. What’s worse, I was ready to pull the engine and perform major changes before I had exhausted all the simple repairs first. That’s the real point of my story. I was so focused on blaming the camshaft that I never tried a different HEI module that might have required 10 minutes to replace.

Anybody who works on cars probably has similar stories where the solution is incredibly simple despite the fact that we’re convinced major components are more likely responsible. I’m also embarrassed to admit that I was laying the blame on that camshaft when I should have been focused on intelligently trouble-shooting my own car. Sometimes you have to step away from the problem to really see it. I’m also surprised that my friends have not all banded together so they can say in unison – “We told you so – a dozen times!”

My friends were right. That’s probably why they are my friends. But why they put up with me is perhaps a better question.