I have a stock 93 240sx and I'm having an issue with it. I'm pretty good at diagnosing issues, but I've reached an impass with this issue. It randomly bogs down with varying regularity and level of harshness. I drive the car 35 miles to work and the only time it seems to hesitate is when merging onto the interstate. When I leave work however it is much worse. When I first leave work it bucks really badly, almost whiplash bad then it starts to mellow out within a few minutes. It then drives fine until I get onto the interstate again. It seems to be most prevalent above 3k rpm. It has a new iacv, plugs, wires, cap, rotor, tps, injectors, coolant temp sensor, and fuel filter. I'm thinking that it is either the maf or fuel pump, but I don't really have the money to be just buying parts. If anyone has experience with this issue please chime in. Thanks in advance.

 

it's definitely your fuel pump my friend , but just incase unplug the MAF to see if it runs worse if it does run worse without the MAF its 100% the fuel pump

 

Ive tried that, and the car starts idling like crap. I was thinking that it was the fuel pump. I don't think that it has ever been replaced. I'm not looking forward to changing the fuel pump in a convertible :/

 

Pulled codes?

 

No check engine light, so I don't know if it will show any codes. Plus it costs money to have Nissan diagnose it.

 

you've checked the TPS voltage?

other than that, I'd say fuel pump.
You could get a fuel pressure gauge and see what it says. Might help you verify it before just biting the bullet and replacing it.

 

Yeah I'm gonna see if any of my friends have one. I'm pretty sure it's the pump. I don't know if it has ever been replaced.

 

Doubt its the fuel pump personally. Im guessing the coil or distributor. Heat increases, resistance goes up, stuff no-workie.

Best advice here is to buy a multi-meter and a service manual.

 

I found the problem. The vacuum line that goes from the block to the brake master cylinder was cracked. I didn't think to check because it wasn't acting like a normal vacuum leak. All fixed now .