I have a 89 240sx with the KA24E motor, and am having a problem. I have diagnosed it to the number 2 cylinder not firing.

Here is what I have done so far.

-Replaced plugs. 1,3,4 looked ok, 2 was wet with fuel-New wires, cap, rotor.-Checked computer codes - 55, no malfunction-Replace fuel filter-Switched # 1 and 2 injectors-Checked compression - 140 or more on all cylinders-Checked injectors for leaks, don't see any.

It still idles bad. I can pull wire off number 2 plug, and motor doesn't change, where if I pull 1,3, or 4 wire, motor runs really bad. Pulled new plug on 2 cylinder and it's wet. Car starts fine and idles at 800 rpm. Just kinda sounds like a v8!

Can a vacuum problem cause a loss of one cylinder? What am I missing? Is there anything else I can check?

What you haven't checked is the IC Ignition system.To Troubleshoot it you DEFINITELY need a manual and a Digital Volt-meter.The IC rests under the reluctor, which sits under the rotor, which, of course, sits under the Cap.Good Luck on your Troubleshooting!

There is spark going to the plug.

I think I figured it out. I can't believe this was it, but my brother who is pretty fluent with engines said that it could definately be the problem.

There is a vacuum module of some sort mounted about the fuel rail by cylinder #4. There is a vacuum line at the bottom of this unit which was bad. I replaced the line and the car runs smooth now.

I was told that a vacuum leak, if it is close or is in line with the intake of a cylinder, can cause that cylinder to go lean and not fire (if the vacuum line is bad). Basically, it screws up the fuel\air mixture.

This was a good experience. Learned quite a bit about the motor.

Just to add to what you said to help people understand. That vaccum line your talking about is the line that runs to the fuel regulater. With a leak in the line the regulater bypasses the fuel because of the lack of pressure. Causing the lean condition.

Can you be a little more specific. Looking in the Chilton's manual, it looks to be the BPT valve. What does that stand for? There are 3 lines to this unit. 2 on top and one on bottom. It was the bottom line that was bad, but I changed all 3. And I'm still a little shaky on understanding why it just affected that cylinder.

I guess with my limited knowledge of engines, I assumed a vacuum leak would cause the whole engine to run bad.

I wish I would have bookmarked the site but just yesterday I was reading about air/fuel mixtures. Anyways it was talking about why people change to adjustable fuel regulaters when running a turbo. OK, the thing is the fuel pump is always pumping the same amount of pressure all the time. The regulater controls the flow. They menstioned that the intake manifold pressure in a sense tells the fuel regulater how much gas to feed the injectors and the rest of the gas that the pump feeds is sent back to the tank. So lets say when the engine is at idle there is less pressure in the manifold and most of the gas that is pumped out of the tank is sent back to the tank. At full throttle there is more pressure and less fuel is sent back to the tank. Now like I said before if you had a leak in the line from the manifold to the regulator, pressure would be lost and needed fuel would be sent back to the tank instead to the injectors.

I'm sorry if i mislead you maybe we weren't talking about the same vaccum hose. I don't know BPT stands for. Or why only the number 2 cylinder was running lean.