I have been restoring a 83 280zx turbo and it was running fine for a while but it started shifting bad and wouldnt go over 65mph. i replaced the transmission filter and it started running just fine, but no its back to not going over 65mph. Any suggestions on how to fix it?

 

Welcome to ZDriver!

How many miles does it have?
Has it been sitting for a long time while being restored?
When was the last major tune up?

Old gas (1yr+) can cause issues.
Worn out spark plugs, wires, cap, rotor, can all rob power.
Common problem on the 280ZXT is corroded sensor and ecu connectors. Pull and inspect... especially the AFM, CHTS, TPS, and all 3 ecu plugs.

Start with the basics. Pull and read the spark plug tips... that will tell you what's going on internally.

 

i have replaced all spark plugs, wires, and i drained all old gas.i guess ill have to look at all that other stuff too. But i recently checked the spark plugs and there is a little bit of carbon deposit on them. What would cause that?

 

I would start with the AFM and also check that fuel pressure is not dropping. Maybe the fuel pump is not keeping up. Is your gas pedal stuck or something holding it back?

When say it won't go over 65MPH what happens when you get to 65? Does it miss out, stall or just seem fine only not going faster? Also what RPM's are you turning at 65MPH?

The way it acts will help point you in the right direction, fuel, ignition, transmission etc.

 

BTW at 65MPH I'm turning 2500RPM's in 5th gear.

 

it runs really good till i get to 60 and then it will hardly get to 65, it will occasionally backfire. I have to hold the pedal all the way down. The rpms dont go all the way up but im pretty sure they are above 5000. Its an automatic, in case that helps to figure out.

 

transmission might be slipping or you might need a new torque converter..

 

If you are turning 5000RPM's it's for sure related to the transmission as icice9 already suggested. Does it seem to run through all the gears? Try driving it with 1st gear than 2nd than drive selected etc. see if there's a change in the way it acts. You might find it stays in 1st or 2nd even when you have drive selected.

If you find it stays in one gear make sure your linkage is okay and not loose or bent (is it really going into drive?). I'm not familiar with Z automatics but I wonder if there's a pressure regulator or whatever they were call it in them like old chey's had? These used to cause the transmission to not change gears.


Maybe now is a good time to switch to a 5SPD.

 

it seems to shift through all of the gears. Its running rich, which could mean that there is a loss of air flow and i know that the afm was pointed out that i should check it. But what about the turbo? Could that cause the problem also?

 

Are you showing any boost? Can you hear the turbo spool up?

Once your up to cruising speed the turbo shouldn't have much of an effect. Unless you have a clogged intake somewhere.

At 65 MPH you should only be turning 2500RPM or so. You said it's much higher. That's why we thought transmission.

 

The turbo is spooling the whole time when I am 65 and the boost gauge stays right before the point of over boosting. I checked the linkage on transmission and it seems to be fine. I'm just trying to rule out all of the cheap fixes. Do you know if the 83 yr Zs' transmissions have any sort of vacuum?

 

if your car is reving at 5000 and your only going 65mph i seriously doubt its engine related.. in your original post you stated it wasnt shifting right and you changed the transmission filter and it helped a little bit, but wouldnt allow you to go past 65mph... from what your telling us im pretty sure its your transmission!

 

Yeah. I would say your parts are bad in the drive gear. May be time for a rebuild or a 5 speed swap. Good luck with whatever you decide to do.