[BigV]

--continued--

For fire, you need the spark plug to go zap at precisely the right time. Also you need a big fat spark. Unlike fuel and air, this one is not "quantity" dependent so much, it's really hard to have too big of a spark. You can have too weak of a spark, and no spark is also bad, but there isn't a proportion "rule" unlike fuel and air. But it is definitely timing sensitive. So we're looking for possible faults that could cause a weak spark or a mistimed spark. Ok.

Weak spark could be caused by some deteriorating connection or component working your way backward from the electrodes on the plug to the connector at the top of the plug, to the plug boot, plug wire, other end of the plug wire, to the coil (or whatever is generating the giant pulse of electricity) to the ? and at this point it varies a lot depending on what kind of ignition system you have. This is the same question as what kind of fuel injection, mechanical or electronic. If it is electronic, you only have the ECM (electronic control module(s)) to rely on upstream of the plug wires. There's nothing you can do in there except replace and only on the "instructions" of the code reader (for us shade tree mechanics). You're not getting a code there, so I don't have anything to point to the electronic ignition system, sorry. If you have a mechanical ignition system with a distributor cap (the cap that "distributes" the electrical pulses by rapidly changing which cylinder has a complete electrical circuit) that could be a point of intermittent failure. It also comes with a rotor, same possible fault. There could be other pieces there that are weak at low speed (like points or a condenser). But I don't know if you have a mechanical ignition system. I have a 1996 car (VW Golf) and it has electronic fuel injection and a mechanical ignition system. I have had trouble with the ignition system before.

Trouble's not really fair, it simply needed some regular maintenance which meant replacing some of the components, like the cap and rotor. This was the best $25 I put into the car that whole freakin year. Your car? I can't say. Do you know if you have mechanical or electronic ignition?

Other causes of weak spark could be degraded or damaged plug wires. You could have a bad plug. They operate in severely harsh environments--think Mount Doom--and need to keep performing a very difficult electrical stunt, ionizing air to make a conductive path (fancy ass way of saying spark) a kabillion times. In shitty atmosphere. Sometimes that crud accumulates on the plug and interferes with the spark. Yeah, really. This is an easy thing to check, assuming you can actually get to the plugs and you have a ratchet and an extension and a plug socket. footfootfoot's car doesn't qualify here, since he can't get to all the plugs. He/you certainly could check the ones you can reach though, and if you see one that's bad, replace it. Check them all if you can. There are pics online somewhere I'm sure that show you in living color what the electrode end of a plug in good condition looks like AND what a plug in poor condition looks like. There will be lots of different "bad plug" pictures, since there are lots of reasons why a plug could go bad and be the source of bad symptoms. You can look them up. If you can't find them, report back, we'll find some for you.

So that's weak spark. What about absent spark? That's all the same, just weak to the level of zero. Fine. Oh, just thought that the coil could be weak, that's the part that generates the high voltage needed for a spark. It's like a transformer in your system.

What about mistimed spark? This is less likely, though not exotically rare. You could have a situation where the electricity that would have been your spark is leaking out before it gets to the plug. Like if a plug wire has a fault in the insulation and the spark is grounding out to the engine before it reaches the cylinder. One way to check for this would be to open the hood and look at the engine when it's displaying the symptom of roughness, but do it in a very dark environment. The idea is to have the fugitive spark reveal itself in the darkness. Doable.

Timing... thinking... A car that is mistimed could have a rough idle. What do you know about the car's timing? Have you checked it? Have you changed it? This isn't something likely to change on its own (possible, but pretty unlikely). If *you* have mucked with it or some other mechanic, it is possible that it's been changed from "best" to something less than best. I don't know how else your engine would miss a spark or mistime a spark.

Having thought out loud, it seems the most likely piece is a fuel delivery problem, junk in injector or fuel filter. Next and close behind would be an ignition fault. If it was my car, I'd do these things in this order until I found a likely problem.

1 -- visually check all the ignition wires. disconnect and reseat all these connections. this is free.

2 -- pull the plugs, check them. fouled? cracked? worn? beautiful?

3 -- replace fuel filter.

4 -- run a bottle or three of injector cleaner super duper turbo in a jug or whatever that crap is called through the car a full tank of gas at a time.

5 -- run the car on the TOP HALF of the fuel tank for a while. this probably should be item 1.5 or even item zero.

Tha's a good start. I'm interested to see what happens here glatt. Keep us posted please.