1990 240sx. Car bucks, loses power. Had fuel pump replaced. Still bad? GRRRRRR!

[RamonetB]

My car is losing power and feels like it's not getting enough gas, and bucks when i try to accelerate.

The quick and the short:

3 weeks ago, during a normal in town drive, the car starting bucking just like when someone doesn't know how to drive stick properly. Eventually she died and wouldn't start. She'd turn over, but never "Catch". I had it towed and was told that I had no pressure on the fuel line.

Replaced the fuel pump.

Car works great for 2 weeks.

Then, all of a sudden, it starts bucking again. But this time things are a little different:

It never actually stalls and dies.

If I turn it off, she'll start right up.

When driving, it usually takes about 30 minutes before the bucking starts. Once it does, it's minor, almost like hitting a rumble strip. Then it gradually gets worse. This whole time there is a loss in power and accelerating exasperates the problem. Eventually, I can't even maintain speed without bucking. Then, I can't even give the car gas while going downhill without it bucking.

When idle after these events, it idles very low and very erratic.

Now here's the strange bit: If I turn the car off and let it sit for 30 seconds to a minute, she operates normally for about another 5 to 10 miles and the process repeats itself.

WHAT'S GOING ON? Is the fuel pump that was replaced defective? Is it overheating and therefore not operating correctly?

Is there a ground somewhere I should check? Before all of this happened, I put a new heater core in, which meant removing the dash and disconnecting a lot of the interior wiring harness. I hooked everything back up, but is there a ground in there I didn't tighten correctly or something?

Any help, please! I'm really confused on this one.

-kirk

P.S. It seems to take longer for the events to happen when it's cold out vs when it's warm out. (IE, 30 degrees vs 45 and up).

[RamonetB]

Mass Air Flow sensor maybe?

I keep wanting to think it's a fuel pump issues. But why would turning the car off and then back on cause a temporary correction? Repriming the fuel pump bring the pressure back up?

[RamonetB]

hmmm...

Also sounds like it might be an issue with a flooding engine. Perhaps a bad injector that can't maintain pressure or a faulty pressure regulator?

Time for the pressure gauge....

[HyperVerbal]

Same exact s*** word for wor is happeneing to me in my s14. no idea and i dont want to put more wasted money into the car if i dont need to. did u ever find the root of them problem?