We have a 1978 280Z all original with only 54000 miles. Runs and idles just fine, starts fine and restarts just fine. You can drive it but once you get up to about 3000RPM the engine starts to cut out and you have to back off the gas. Below 3000 it's just ok enough to get it back home.

I ran tests on the AFM and found that is was bad so that was replaced, we replaced the plugs, wires, cap and rotor, fuel filter and PCV valve. I also have a gauge on the fuel line and we have prefect fuel pressure. I have gone to the Datsun Bible and started running other tests and a few that I found a little off was the one that OHMs should be 150 and they are at 170. Also, and I don't know if this is incorrect, but the tests for the air temp sensor and the water sensor. When I preform them both the only FLASH what seems is the correct OHM number, which is about 1950 OHMs. Again I don't know if it should be on continuously OR just give a FLASH of the number.

Has anyone else had this similar problem where the car just hits a brick wall at around 3000RPMs? 

Thank you in advance for anyone's help!!

A check of the fuel pressure would be a good place to start.  Some people have hooked up the gauge temporarily to monitor the fuel pressure under load while driving.  Also check the rubber boot that connects the afm to the throttle body for cracks / tears hidden in the rubber folds.

If you have just washed the motor and moisture is in the tvs (throttle position sensor) you will need to dry it out with canned air.

Thanks S30! I forgot to mention that I did add an inline fuel pressure gauge and she's right on the mark. Also I ran a test on the TPS and that seems to check out ok. I know sometimes that the little silly things could be the root of the problem. I've gone through and checked for air leaks etc. and haven't uncovered anything like that. This is really stumping me!

My '77 had the opposite problem of your's.  It ran like crap up until 2,500-3,000 RPM then it would pull.  I finally did the coolant sensor tweak by installing a potentiometer to increase the fuel the ECU was allowing.  It's pretty much a volume knob from Radio Shack. 

I would clean as many electrical connections you can.  Then remove the coolant sensor in the thermostat housing and shine it up.  They get covered with crud over the years and won't "sense" properly.

here's a chart Captain Obvious put together for us to use.

 

 

So now before when the car would idea fine and I use to be able to rev it it's starting to stumble in neutral. Ugh!!! I check the fuel pressure gauge and it's only running about 30 psi and drops to 20 when you rev it up... gezzzzz now what??

 

I have put an multi meter to the water temp sensor and I get nothing. Positive to the sensor and then ground, shouldn't I be seeing some kind of ohms? Is this sensor linked to fuel pressure? 

 

What's driving me nuts it that I had good fuel pressure revving it up... Now crap

Check the vacuum hose that attaches to the bottom of the fuel pressure regulator (FPR) for liquid fuel.  It might be leaking.  The rubber diaphragm inside can fail.  And I think that you're measuring the temperature sender, not the sensor.  There are pictures in the Service Manual.  Go to the site Download area and download the Factory Service Manual (not Chilton's or Haynes,  but Nissan) and the Electronic Fuel Injection Guide.  Read Engine Fuel and run the tests shown n the Guide.

After a long battle of trying to get my 75 running good at ALL rpms, I finally took it to a specialist. Prior to taking it in, I threw a lot of parts at it including a mass air flow box $$$$. I checked all the usual suspects, everything checked out. The place I took it to has a guy that has been working on z cars since 73. He checked everything over as I did. He said even though the coolant temp sensor reads inside the lines they can be bad. He replaced the coolant temp sensor and switched out the plug to it with a bosch. He also manually adjusted the fuel pressure. Car runs great now. There was a long thread on this 2 or 3 months ago when I actually had time to work on it. Coolant temp sensor was only $28 and the plug was another $15 or so, good place to start. One more thing, my engine compartment is extremely clean, I didn't find any corrosion but his trained eye said I had the slightest amount on the coolant sensor plug which will affect it. Hope this helps.

Keep an eye on your plug color to make sure the manual fuel pressure adjustment is where it needs to be...

20 hours ago, BillyD Z said:

So now before when the car would idea fine and I use to be able to rev it it's starting to stumble in neutral. Ugh!!! I check the fuel pressure gauge and it's only running about 30 psi and drops to 20 when you rev it up... gezzzzz now what??

 

Your fuel pump could be going bad?  I ran a fuel hose with a gauge stuck down inside it to my driver's wiper blade and drove the car.  That will let you know if your pressure is constant, even under load.

You can "screw" the threads down into a section of hose then put a clamp over it and zip-tie it to the wiper.  Go for a drive and see what it does.