Single hiccup on acceleration

[Nikkum]

Hi All,
1985.5 Electronic ignition lovely engine. Except there is an intermittent single hiccup when accelerates. Not always. slightly jolts car, feels like engine drops a beat. Before/after and at all other times its faultless. Timing spot on at 10 BTDC at 800rpm. New oils, no obvious vacuum or fluid leaks. HT leads and plugs new.
I am baffled. Any ideas how I could pin it down anyone?
v grateful for any help
Nick

[18Fiatsandcounting]

Are your distributor cap and rotor relatively new? Sounds like an infrequent engine "miss", and those can be hard to trace down. Run a can of fuel injector cleaner through the gas tank?

One trick I use to look for ignition misses is to connect a timing light on the center HT wire from the coil to the distributor cap. Watch the light as you rev the engine across its range, and it should be an almost steady stream of light. Misses are easy to spot, although the challenge then is to figure out which cylinder has the misfire.

-Bryan

[Nikkum]

Hi Bryan,
Its electronic ignition but great idea to check the HT leads with a timing light. Might well identify a culprit cylinder When it drives it "drops a beat" and when idling the revs drop momentarily then pick up again. Its often after having slowed the revs a bit then put foot on gas, ok for a few seconds then hiccups once then fine again.
Really irritating and I hope not damaging my engine etc!
Very grateful for advice and I will continue to pursue this.
many tx
Nick

[18Fiatsandcounting]

Nick, I doubt you're damaging the engine, and it does sound like you're getting an occasional misfire. At that point, could be plugs, wires, distributor cap, rotor, or even a weak coil. It sounds like you've checked all this. Try moving the plug wires around a bit, even if you have to temporarily tie them out of the way with a bread bag tie or the like. I have seen the high voltage pulse go through plug wires and short to ground, even if the plug wires are just barely touching a metal surface. Good plug wires don't do this, but old or cheap ones can. You could also run the engine in the dark and see if you see a spark where there shouldn't be one. Check your plug gap too. I believe electronic ignition uses a larger gap, but make sure it isn't too excessive. You could try reducing the gap to 0.028" and see if that helps.

Could also be a hiccup in the fuel injection system, but I'm an old school carb guy and so I can't offer much help.

-Bryan