76 280z won't go over 3000 RPM

[spectrum999]

I have been working on my 280z for a while. I got it to the point where it was able to be driven, and once it hits 3000 rpm it acts as if it's banging the limiter. It idles and revs above 3000 rpm easily but once it comes to driving it just won't. Has very new distributor rotor and cap (2 months or less) and new spark plugs and wires. Motor was very recently rebuilt and has no more than 20,000 miles. Any help is appreciated.

[Dave WM]

did the problem exist before the rebuild?

Have you gone thru the FSM on EFI section?

In the EFI section have you verified fuel pressure?

Fuel volume?

does the AFM vane move freely?

How do the new spark plugs look? (rich/lean/normal).

I don't think there is a rev limiter, Not sure what that is like. I assume under load the engine will not go over 3k, I would presume that is a fuel issue, unless there is something wrong with the distributer and or Spark module, but I don't see how that would be effected by engine load.

 

Edited December 18, 2018 by Dave WM

[240260280]

unplug the throttle valve switch connector (on the side of the throttle valve. If your rpm's come back then the TVS is not clocked correctly or it is shorted internally or the wiring to it is shorted.

 

[Zed Head]

Are you easing your way up to 3000, at partial throttle, and the problem happens?  Could be the "lean" problem.  If you can finesse it to some open road, you might find that full throttle takes it right up to 6000 rpm, but part-throttle coughs, bucks and pops back through the intake system.  Full throttle adds 27% extra fuel.

If that fits, then 246's atlanticz fuel tweak is one way to fix it. 

Not sure what the exact cause is but it seems related to the AFM.  Could also be that somebody has leaned out your AFM by adjusting the spring.  Either way, it sounds lean.

[spectrum999]

23 hours ago, Dave WM said:

did the problem exist before the rebuild?

Have you gone thru the FSM on EFI section?

In the EFI section have you verified fuel pressure?

Fuel volume?

does the AFM vane move freely?

How do the new spark plugs look? (rich/lean/normal).

I don't think there is a rev limiter, Not sure what that is like. I assume under load the engine will not go over 3k, I would presume that is a fuel issue, unless there is something wrong with the distributer and or Spark module, but I don't see how that would be effected by engine load.

 

Before this rebuild the motor would not start at all. The spark plugs look rich. The afm vane does move freely but hasn't been tested with the car running. We haven't checked the fuel pressure. Also I'm not quite sure what you mean by fuel volume.  

[Patcon]

10 minutes ago, spectrum999 said:

Before this rebuild the motor would not start at all. The spark plugs look rich. The afm vane does move freely but hasn't been tested with the car running. We haven't checked the fuel pressure. Also I'm not quite sure what you mean by fuel volume.  

Pressure is one aspect, but it also needs to pass a certain volume at a certain pressure. Some pumps will pump a volume but not maintain pressure. Some will pump a certain pressure but can't maintain the necessary volume.

[Zed Head]

On 12/17/2018 at 4:58 PM, spectrum999 said:

and once it hits 3000 rpm it acts as if it's banging the limiter.

The other thing that causes rev limiter behavior is a shorted throttle valve switch (TVS, or TPS).  Washing the engine is the most common cause.

 

p.s. always nice to get the common courtesy of acknowledging someone's post.  One out of three isn't bad, but still, three is not that many.

[siteunseen]

My '77 had the lean problem also.  Idle to 2,500 or so it would cough and buck and pop through the front.  The way I finally found it was to take some type of clamping device, I used a big pair of hemostats, and clamp the return line to the tank.  Not completely closed off but almost.  That built more fuel psi richening up my EFI.  Car ran better right off but still not perfect.  I reported back to the guys and a gal here and they suggested the fuel tweak that atlanticz.ca did for us.  Went to Radio Shack (before they closed all their stores) and spent $5 and about 30 minutes, now the car runs like a new.  Thanks again to everyone that helped/helps me.

http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html