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Ok, when #4 doesn't seem to be working, that is a definate clue. And it doesn't point to fuel supply at all.
A cylinder needs air, fuel, and spark to fire.
1) Air - Intake valve opens, closes. Exhaust valve opens, closes. The piston compresses the air. Problems can include a flat cam lobe (what, on a B20 - never!), leaking valves (burned, tight lash), holed pistons, broken rings, leaking head gasket. I'd do a compression check to make sure it is holding air, then pop off the valve cover and watch the valves go up and down as you crank the engine over. By the time a cam lobe is flat enough to cause noticeable running problems, it will be VERY evident to the eye. If you have compression AND the valves are both opening and closing, that should be good enough as far as the air part is concerned.
2) Fuel - in the case of D-Jet, the injector on that cylinder needs to be opening, and squirting out the proper (or at least pretty close) amount of fuel when open. As a holistic test (i.e. testing all the parts of the system at once) you can loosen all 4 injector collars, wiggle the injectors to break the stiction, then pull the entire fuel rail out of the injector mounts with all hoses and wires attached. Then turn the key on and off several times, and leave it on (might want to pull a LT lead on the coil) and go over to the throttle. Watch the injectors as you open the throttle by hand. The accelerator pump feature will fire them in pairs. Just eyeball and compare them to each other. It won't be an exact flow measurement, but the eye can pick up a problem large enough to cause a major running problem. Well, that doesn't quite test the entire system, you could crank the motor over and have the distributor contacts fire the injectors, but this test ensures that the computer can open the injector - so no faults in the computer, wiring and grounds, and injectors.
3) Spark - Gotta have a good spark that makes it all the way to the tip of the spark plug to fire that fuel and air. Problems isolated to a single cylinder with ignition can be faults in the distributor cap, spark plug wire, and the spark plug itself. Faults in the cap are usually cracks that can fill with conductive material (especially moisture) and short the spark off to a ground on the distributor body. Wire faults usually involve a failure in insulation that shorts the spark to something the wire lays next to, sometimes the core is eroded so that the spark has to jump a large gap and is weakened by the time it gets to the spark.
It seems a common thing for people working on a D-Jet car is to suspect the D-Jet system for almost any weird running issue that crops up. Well, to be fair it is guilty in many cases, but it usually seems to get the blame for bad valves, flat cams, bad ignition, etc. You really need to double check the rest of the motor well before starting to troubleshoot D-Jet. It isn't an adaptive system, so the motor has to be in proper operating condition for it to work correctly itself.
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I'm JohnMc, and I approved this message.
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