Q: Last week I took my pickup in for a tune-up because it was running rough and needed to be checked out. I told the service fellow they might want to check the timing. He replied with a smirk that they "don't do that stuff anymore" and they'd "put the scanner on it to see what was wrong." It turned out it had two bad ignition coils, and it runs just fine again. How is it possible there isn't any timing anymore?
-Jake P.
A: I'm going to go out on a limb and assume you've got quite a few miles under your belt and have been blessed with trouble-free engine performance for many recent years.
Accurate ignition timing (spark plugs firing at the optimum piston/connecting rod/crankshaft position) is even more important than it was in years past, but it is no longer adjustable unless one is either a software hacker or has access to an available/appropriate manufacturer's calibration upgrade (reflash). Just as there's an optimum rotational position to press down hard on a bicycle's pedals, the expansion of combustion gasses must press on the pistons at just the right time to effectively rotate the
crankshaft.
Older vehicles utilizing a distributor ignition system with breaker points and/or mechanical advance mechanisms frequently suffered from incorrect ignition timing due to a variety of possible faults. More recent distributor systems employing computer controlled timing often required an initial/installation base timing adjustment, which rarely if ever required readjusting due to the lack of mechanical parts. Current distributorless ignition
systems have no mechanical adjustment, although some may specify the use of a timing light connected to a service loop, when necessary, to verify correct camshaft
timing.
Tune-ups are also a thing of the past, as there is no longer anything to tune! Spark plugs and filters still need to be changed at some point, and perhaps a throttle or intake valve need cleaning when appropriate, but not much else. These procedures are typically part of a maintenance schedule, perhaps with filters renewed at 60,000 miles and plugs at 100,000 miles-for example.
Your folks at the service facility used a scan tool to communicate with the truck's PCM (powertrain control module) to retrieve possible diagnostic trouble codes and pertinent engine data. You mentioned two bad coils. This confirms your
present truck is of recent vintage, with OBD-II (on board diagnostics version 2) and a coil-on, or coil-near plug ignition system (utilizing perhaps six, eight or 10 in total). Rough running may have produced an illuminated check engine/service engine soon light and related diagnostic trouble code(s) for cylinder misfiring, and/or unacceptably high misfire counts (called out by cylinder within a scan tool's mode-6 section).
When a scan tool confirms a certain cylinder is misfiring, it can be for several possible reasons. An experienced tech will next employ productive methods to narrow down the cause (in this case testing and/or swapping ignition coils) to confirm the fault. Your coils were likely leakers-i.e., they functioned but leaked spark either internally or to nearby metal at certain times, instead of delivering it to the spark plugs, a somewhat common problem.
ABOUT THE WRITER
Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at [email protected]; he cannot make personal replies.