I currently own a 1978 280z.

I recently replaced the fuel pump, fuel filter, and cleaned out all the lines and gas tank due to it running extremely lean reaching 4k RPM's.

Now as i try to push the car harder into the 5k RPM range it starts to lose power and the RPM's drop then kick up then drop again.

This has also been happening in any RPM range when ever i floor it.

My thought is the new fuel pump is sending too much fuel(or not enough) and there isn't enough air getting into the engine because it has a stock air-box which i cleaned out in hopes of fixing something but I had no luck.

Ill post a video of the problem as soon as possible.

Thanks.

Edited February 19, 201114 yr by Wesley

It could be any number of things. You might try cleaning the potentiometer assembly beneath the cover of the air flow meter (AFM or "air-box"). If it's dirty, you might get false readings. You might also try cleaning up electrical connections. Most of them are probably getting pretty crusty.

FAIW, several of us have been dealing with lean-running conditions in our EFI 280s and have found that the ECU has drifted. Cozye and I have both corrected this problem by inserting extra resistance in the coolant temp sensor circuit to force the ECU to run the engine richer. However, before we could do this, we had to get EVERYTHING ELSE right with our engines (to know that we weren't simply compensating for a fixable problem -- e.g. a vacuum leak).

Thanks ill try looking over the wiring. I took the Mass Air Flow sensor off and some of the wires just fell apart haha. I posted a video up if you wanna take a look tell me what you can from the video thatd be great.

Check your TPS to make sure it's closed at WOT, per the manual.

Although your description appears to point to an ECU, or Fuel problem, it's also possible to get something like this with a bad coil, or coil/plug wires. If the coil is internally weak, or the wire insulation is breaking down, then the engine might idle and rev OK, but at high rpm you'll notice the lack of response, especially while driving (under load).

Run the car in a dark garage and look for arcs. Connect a ground wire between the blade of an insulated screwdriver and the chassis. Run the blade along the plug/coil wires and cap. If you see arcs you have a problem requiring component replacement.

pwd I think your right on that one grazed my hand against the distributor cap and got one hell of a shock. I think everything basic needs to be replaced and ill work from there. Thanks for all the help.