When I first picked up wrenches and started trying to get a handle on how cars worked, it was fairly simple to figure out
why an engine wouldn't start. We'd first check for spark and the proper firing order, then we'd yank the air cleaner, prop
the choke open (if it was working right it'd be closed on a cold engine) and we'd operate the throttle to watch the accelerator
pump jets. From there, we'd jerk the spark plugs out and see if they were wet and sooty or used up.
Hard starting diagnoses typically led down a slightly different path, and because we're talking about newer vehicles, we'll
fast-forward a bit and mostly try to leave the carburetors and oil-filled coils in the past.
Spark First
Photo: Getty Images/Comstock
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For years, contemporary wisdom in textbooks and some older shop manuals said to let the spark jump ¼ inch, and if you had
that much spark, it was enough. Working with my dad as a youngster, I discovered the biggest problem with that ¼-inch rule
was that a spark can jump that far in sea-level air pressure and still not have enough of a pop in the chamber to light off
the mix under compression.
The spark needs to be downright scary these days, with enough blue-white (not orange) energy to punch through nearly an inch
of air and pop loud enough to be heard three service bays away. I've seen some really good technicians stumble over that ¼-inch
spark test and then call for the "calf rope" because they had been side-tracked by weak coils that wouldn't produce sufficient
spark.
So how did they get off track? Well, the spark would traverse that ¼ inch and they didn't stretch it to see when it reached
its limit, so they erroneously figured they had eliminated spark and in error they moved away from the ignition system with
their troubleshooting.
I remember one hard starting 1988 Taurus that would actually fire up after spinning for 30 seconds or so, and it had me stymied
until I connected the ignition O-scope and found that the coil was incapable of producing the voltage needed and it would
jump only about 1/2 inch.
That was acceptable on older oil-filled coil systems, but on the Taurus I was troubleshooting, it wasn't enough. A new coil
took care of that one.
No matter what starting or performance based concern you might be chasing, it's always a good idea to check the strength of
the spark. It should pop loud and blue like this one. Spark timing can be checked with a timing light, even on vehicles where
the timing can't be set.
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So when testing for spark, make sure you stretch that blue lightning far enough to determine that it's not weak. That's rule
No. 1 on a single-coil vehicle with a hard start concern.
As far as coil packs go on Distributorless Ignition Systems, single towers or whole coils on multi-coil packs can stop delivering
spark and Coil-On-Plug (COP) coils can drop offline for one reason or another. But weak spark generally isn't the cause for
a hard-start on coil pack or COP equipped platforms.
Then there was the Bronco that would start only with the SPOUT connector disconnected. I found that problem with the Service
Bay Diagnostic System. The PCM ground traces would go crazy while the engine was spinning, and that turned out to be a voltage
drop problem at the battery cable-to-engine block connection.
There were the burned-through rotors and faulty ignition modules, but they're more likely to cause sputtering and stumbling
than hard starting.
