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 Post subject: 280zx Hesitation Issue
PostPosted: Tue Jan 29, 2019 10:06 am 
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Joined: Thu Oct 08, 2009 1:14 pm
Posts: 213
Location: Southington, CT
Hi all - I was recently fortunate enough to get my hands on a 1980 280zx with 66k original miles. Beautiful shape, but it had sat for many years and needed some love to get it up and running again; specifically: fuel drained, new fuel filter, cap, rotor, wires, plugs. It starts and idles just fine, but when I hit the throttle as I would normally from a stop, it initially bogs down, sputters and pops pretty significantly before regaining its footing and revving normally in the higher rpm range. I realize that this could be from a host of things, but has anyone ever dealt with this type of issue before? ..perhaps in reviving a Z from years of slumber like this?

Any input would be greatly appreciated!


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PostPosted: Tue Jan 29, 2019 11:51 am 
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Joined: Wed Apr 09, 2008 5:53 pm
Posts: 13106
Location: CT
My money is on either a vacuum leak, fuel or ignition issues.
Does engine temperature matter? Is it a turbo?

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PostPosted: Tue Jan 29, 2019 12:52 pm 
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Joined: Thu Oct 08, 2009 1:14 pm
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Location: Southington, CT
Non-turbo. And no, it seems to behave this way no matter how long it's been running (cold or idling for a long time).


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PostPosted: Tue Jan 29, 2019 6:57 pm 
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Joined: Wed Apr 09, 2008 5:53 pm
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Location: CT
This will sound weird, and it might not have anything to do with your problems, but please pull the air cleaner open and check the filter. It's on the 'cold' side of the radiator.
I helped a new zx owner start his neglected 280 once and found such a huge mouse nest in the air intake, the engine could hardly breathe, and a small mouse actually got sucked into the valveworks.
That might not have anything to do with you, but it should be on your preflight checklist, anyway.
I'm almost ignorant about the fuel injection systems, so I have nothing of value to offer there. But your electronic ignition advance should be checked for full function. Vinny's an expert on this stuff. 860-355-182nine.

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PostPosted: Wed Jan 30, 2019 10:11 am 
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Joined: Thu Oct 08, 2009 1:14 pm
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Location: Southington, CT
Thanks for the advice, Frank :thumbs_up: I did indeed check the air filter, and it looks brand new with no evidence of critters. I'm no mechanic, but I do have the factory service manual and I'll go down the checklist of possible culprits to the best of my ability. If I get nowhere I'll be sending it off to a reputable garage in town.


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PostPosted: Wed Jan 30, 2019 12:12 pm 
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Joined: Wed Apr 09, 2008 5:53 pm
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Location: CT
It's called a 'transition stumble' if you need to describe it over the phone. The engine works well at idle and at high speed, but trips over itself trying to change its mind.

Both fuel delivery and ignition 'change their job' during that transition. Either of them is designed to run at low (idle), medium (traffic) and high speeds and they have specific mechanisms to meet each of those demands. Something is preventing one of those systems from transitioning smoothly.

To check for a vacuum leak, start the COLD engine and let it idle while you spray a can of starting fluid all around the engine. If you have a vacuum leak it will suck the hi-test fluid into the engine and the revs will momentarily increase when you spray that area. That at least gives you a place to start digging.

Please don't do that with a hot engine. :roll:

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PostPosted: Mon Apr 01, 2019 5:52 am 
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Joined: Wed Jul 23, 2008 2:38 pm
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Location: rhode island
Most common issues as long as all else is normal, talking your basic tune up, no ignition problems and fuel pump is fine and the screen in the fuel pump isn't clogged. Check all, and I mean all sensors that feed the computer. Pull the plugs, file down the terminals and know yourself you have no corrosion issues, and this goes for the big plug at the computer. The car is OLD, and there can be corrosion issues in cars not 5 years old, so don't think your Z is impenetrable to corrosion. Now here's the big fix, and you can do this first, and it just might be your issue. Take the top off the Air Flow Meter off, check the carbon circuit board were the 2 needles sweep across, make sure it is clean, (Q-tip and rubbing alcohol to clean it,) and make sure there are no grooves worn through it. OK, now there is a little screw holding the plastic wheel that is SPRING LOADED. So definitely hold the wheel with one finger, loosen the screw, now gently let the wheel loose some tension, 3 or 5 notches. Make sure screw is tight, now rev her up and see how it is. If it just got better and could be a little better, loosen it some more, maybe another 2 notches. I do this adjustment with the car running and at operating temperature.


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PostPosted: Fri Apr 05, 2019 11:20 am 
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Joined: Thu Oct 08, 2009 1:14 pm
Posts: 213
Location: Southington, CT
It was the Boost Control Deceleration Device that was the root cause of the issue. It has been worked-around, and along with some fuel-system cleaner and some fiddling with the AFM, the car runs like a champ! :D

p.s. It's good to have a shop that you can trust to work on your Z's :thumbs_up:


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PostPosted: Fri Apr 05, 2019 10:36 pm 
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Joined: Wed Apr 09, 2008 5:53 pm
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Location: CT
Thanks! I just learned something. :thumbs_up:

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