P0304 ugh.

[Jcasagra]

I'm not as automotively literate as some of the other posters on here but thought I'd give it a shot. Bought a 96 sl1 automatic about a month and a half ago with 140,000 miles on it. Test drive it. Ran great. After the first 100 miles or so after purchase, I got a flashing SES for about 5-10 flashes and then it stopped flashing and went away completely. Read the code and it was a P0304 pending. Checked the spark plugs, wires, and pack, Replaced all the aforementioned. Bc we have another Saturn with spare parts. Possibly seemed a little better after replacements. Another 50 miles or so the ses flashes 5-10 times again. Has done it a couple more times over the next 50-100 miles, finally left a solid SES light with a P0304 code. Maybe another 50 miles on it before I was able to get it to a garage. On the way to the garage, the solid light went away and mechanic was unable to diagnose the misfire. Weird. Ran a premium fuel injector cleaner through on the next fill up. Solid SES came back intermittently that flashed only with a load on, seeming to be more present in 4th gear around 1600-2200 rpms. Don't have time nor facilities or confidence to remove fuel rail and change injectors. But is it most likely a faulty/clogged injector?

[RobertGary1]

How's the compression? How did the plugs look? Were they oil fouled?

-Robert

[fdryer]

It's not likely to be an injector problem. While great for the imagination, EFI systems depends on an intricate cooperation of car manufacturers making reliable vehicles, oil companies making fuel and oil and vehicle owners maintaining their vehicles. Suspecting one fuel injector out of millions around the world running every fuel grade may be a little short sighted. If one injector is faulty, why not the rest? They're all using the same power and flow fuel. The final filter before crap clogs any injector is the fuel filter in every vehicle. A fuel sock filters fuel in the tank before the pump. The final filters are used in every gas station pump to ensure vehicles don't get crap from underground tanks. The fuel farms holding millions of gallons of fuel probably use filters too. Millions of injectors are used around the world with very few failing. It would be rare to find a faulty one. One way to have a faulty injector might be a damaged wiring harness to that injector but not likely. Other issues are more likely.

Some of the other issues to single cylinder misfiring; spark plug, ignition coil, ignition control module, damage to piston rings/intake or exhaust valve. Examining the spark plug on the misfiring cylinder and comparing it to the other three or searching for plug charts showing what makes plugs appear discolored can help. Plug reading. A compression gauge used to determine the state of mechanical health of each cylinder helps determine if mechanical wear is causing intermittent misfiring.

You're not 'automotively illiterate' the moment you ask questions.