I was cruising along in my '83 Citation (the '81 X-11's "little sister") maybe 10 years ago, headed north along Scenic Highway. As I passed a last line of houses and started seeing undeveloped woodlands, I heard a loud BANG, like a gunshot.
Didn't stop to check for bullet holes. I just hit the gas and looked in my mirrors. Didn't see anything. Once I got home, I didn't find any damage. The event was shrugged off and forgotten.
The Citation's engine developed a rough idle, slightly worse gas mileage. I looked over everything, checking carb settings, ignition timing, engine vacuum. Didn't make sense. The carb settings were fine, timing was a little off but not causing trouble. Engine was breathing fine, maybe a little low.
But the idle stayed rough.
I went through the shop manual's troubleshooting guide--carb's okay, timing's good, vacuum's good...all the easy stuff got checked off the list. The manual suggested that the timing chain might have jumped a sprocket, and all the symptoms seemed to agree. I hated to think this might be the problem, since it was more work than I wanted to do.
Drove around like that for several months, occasionally trying those simpler checks--carb, timing, vacuum--in the hope that I'd missed something simple. Finally stopped putting it off, parked the car, and got to work.
Busted out the jack stands, got her nose in the air...loosen the belts, lose the water pump, timing cover...huh.
Timing chain looks fine. Rolled the engine a little to line up the crank and cam timing marks.
Oh, well, probably the original chain, and as long as I'm already here...put in the new one, double-check timing marks...new seal on timing cover, new gasket...water pump, pulley, belts.
As long as I'm here, though...let's do the valve cover gaskets, get rid of that little oil leak.
Kind of a pain in the ass. Some stuff in the way--SNAP!
There's a little trident-shaped set of pipes that are part of the emissions controls. The engine computer blows fresh air into the exhaust system through these to burn unburned or partly-burned fuel.
I'd just snapped one of the pipes. They tend to rust pretty quickly as it is, but on a 20-year old car they're brittle. Turning the nut holding the pipe in place just folded the pipe.
Wrecked all three getting the thing off of there. At first, I tried fabricating one from brake line (which is all the pipes were, basically) but couldn't bend the stuff with my limited tools. I put that project on the back burner, plugged the exhaust manifold with pipe plugs, fixed the valve cover gaskets, and buttoned everything up, pissed that I'd wasted a weekend on a not-bad timing chain.
Car started up as always, ran just fine, but that idle just wouldn't stabilize. Bugged the hell out of me. And again I tried all the simpler stuff yet again--carb settings, ignition timing, vacuum check. No leaks, no computer trouble codes, and still no idea what was causing the roughness.
A year went by. I still occasionally tried to ferret the problem. No magical new information in the troubleshooting guides. I wondered whether the engine computer might be acting up; it controls spark timing, fuel delivery, and all that. I thing I pulled it out and looked it over, decided I wasn't going to screw with it, and bolted it back in. No easy way of poking around on a plastic-sealed circuit board. Nothing looked burned or damaged.
I don't know what I was doing, the day the problem was solved. Maybe just checking the spark plugs, something I hadn't done in all the troubleshooting. I know I'd never looked at the things because...
...you car guys will love this. Really.
Put your drink down.
As I was feeling along the back side of the engine, I found the #3 spark plug hanging by its wire.
Remember that "gunshot" I thought I'd heard? I remembered it, then.
I'm guessing that I didn't tighten #3 down properly sometime before the "gunshot." Every time the plug lit off the air and fuel in the #3 cylinder, the concussion worked the plug out a little. That BANG was the final air-fuel charge blowing the loose plug out. From then on, my V6 was a V5.
Threaded the little shit back in...tightened it properly (this time). Engine ran perfectly.
The X-11 is just the latest in a line of cars with laughing rights on me.