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-   -   1983 280ZX NA - No power and then sudden burst (https://www.zcar.com/forum/10-70-83-tech-discussion-forum/419942-1983-280zx-na-no-power-then-sudden-burst.html)

Jeff Collinsworth 09-13-2019 11:57 AM

1983 280ZX NA - No power and then sudden burst
 
All,


I'm having a tough time with my 83 280zx NA. Ive rebuilt from the ground up. (Cylinder Head RnR, New Gaskets all Around, New Hoses All Around, new electrical plugs, tested and cleaned fuel injectors, etc)


Symptoms:
At about 2k RPM the revs drop down about 200 RPM and then bounce between 2k and 1800. Something is compensating for something causing this but i dont know what.


Also, when you hit the gas, there is almost 0 power and then a few seconds in revs match torque and car has power for days.


My fuel pressure is awesome, all injectors squirting, spark on all 6. No vacuum leaks that I can find. Not sure where else to go. Any help would be appreciated.

chaseincats 09-13-2019 02:26 PM

Quote:

Originally Posted by Jeff Collinsworth (Post 2773854)
All,


I'm having a tough time with my 83 280zx NA. Ive rebuilt from the ground up. (Cylinder Head RnR, New Gaskets all Around, New Hoses All Around, new electrical plugs, tested and cleaned fuel injectors, etc)


Symptoms:
At about 2k RPM the revs drop down about 200 RPM and then bounce between 2k and 1800. Something is compensating for something causing this but i dont know what.


Also, when you hit the gas, there is almost 0 power and then a few seconds in revs match torque and car has power for days.


My fuel pressure is awesome, all injectors squirting, spark on all 6. No vacuum leaks that I can find. Not sure where else to go. Any help would be appreciated.

I'd check the throttle position sensor. It's that little black matchbox lookin thing on the side of the throttle-body - it is adjustable by slightly twisting it left and right.

bificus 09-13-2019 02:36 PM

Either that or AFM. ECU kicks in full fuel after 2800 rpm (iirc) correct me if I am off on that. So off idle to then on part throttle AFM is controlling fuel.

chaseincats 09-13-2019 02:39 PM

Quote:

Originally Posted by bificus (Post 2773858)
Either that or AFM. ECU kicks in full fuel after 2800 rpm (iirc) correct me if I am off on that. So off idle to then on part throttle AFM is controlling fuel.

True.

I'd suggest he check the plugs for the AFM and throttle position sensor for corrosion and break out the deox-it if there is.


EDIT (addition): I'm not sure if this is how it works, but what if he unplugged the throttle position sensor. That would isolate it as a test but I'm not sure if/how the car will run without it.

bificus 09-13-2019 03:05 PM

Quote:

Originally Posted by chaseincats (Post 2773860)
True.

I'd suggest he check the plugs for the AFM and throttle position sensor for corrosion and break out the deox-it if there is.


EDIT (addition): I'm not sure if this is how it works, but what if he unplugged the throttle position sensor. That would isolate it as a test but I'm not sure if/how the car will run without it.


It would definitely be running off the AFM only until ecu kicks in full fuel.

Jeff Collinsworth 09-16-2019 10:33 PM

Quote:

Originally Posted by bificus (Post 2773858)
Either that or AFM. ECU kicks in full fuel after 2800 rpm (iirc) correct me if I am off on that. So off idle to then on part throttle AFM is controlling fuel.

Thanks all. AFM seems to check out and Ive played with the TPS as well without noticeable improvement. NI found a post from someone who had similar issues. He said that he found that 5th cylinder stopped firing after about 2000 rpms after car warmed up. I was curious so I checked. I have the same thing but on 1 and 2. He states that he replaced the ignition control unit and it solved the problem. Im going to see what that does.

6shutr 09-18-2019 10:05 PM

Faulty ignitor (or whatever they call it) could certainly cause a cutting out prob, but I've never heard of one cutting out just two cylinders only under certain conditions. So please let is know if that solves the problem. Also, i believe the N/As still used vacuum advance in the dizzy (didn't they?) It is common for the roller-ball assembly under the breaker plate to either lose balls or for the grease to just petrify after 30-some years and cause the advance to stop working. You can test this easily with a timing light on the marks and blip the engine - marks should move. (Can also test with cap off and sucking on vacuum line with your mouth - breaker plate should move easily.) If no movement, you need to disassemble the dizzy, clean up the mechanism, re-grease and put back together. This happened with a '76 I used to have and when rebuilt, the difference in increased power was really amazing.

Jeff Collinsworth 09-19-2019 04:48 PM

Quote:

Originally Posted by 6shutr (Post 2774006)
Faulty ignitor (or whatever they call it) could certainly cause a cutting out prob, but I've never heard of one cutting out just two cylinders only under certain conditions. So please let is know if that solves the problem. Also, i believe the N/As still used vacuum advance in the dizzy (didn't they?) It is common for the roller-ball assembly under the breaker plate to either lose balls or for the grease to just petrify after 30-some years and cause the advance to stop working. You can test this easily with a timing light on the marks and blip the engine - marks should move. (Can also test with cap off and sucking on vacuum line with your mouth - breaker plate should move easily.) If no movement, you need to disassemble the dizzy, clean up the mechanism, re-grease and put back together. This happened with a '76 I used to have and when rebuilt, the difference in increased power was really amazing.

Replacing the ICM fixed my issue. I am over the moon excited. So much work to this point. The very next day, I took it to emissions and passed. Plates on the way!

6shutr 09-19-2019 11:26 PM

Good deal. Thanks for updating us. Always good to know what works!

bificus 09-20-2019 10:36 AM

Glad you got your z going again, thanks for the update.


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