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Discussion Starter #1
The situation: after head work and other work which included testing all fuel injectors, my 83 ZX Turbo is running great---up to some engine speed between 3,000 and 4,000 RPM.

Idles fine, runs fine, but for months, when I accelerate it starts missing badly above somewhere around 3K or 3500 RPM. For the past couple of months, if I drive it longer and get it good and hot, it seemed to pull better, up to 4K RPM before the missing started. It simply will not rev over 4K RPM. Won't go there.

Plugs are new and good, wires are good, timing has been checked, cap and rotor are clean and have no carbon trails. I have eliminated spark/ignition as the problem. The fuel filter is less then 1000 miles old, but I have a new one if needed. The car was on jackstands for about for years, but it has been back in service for a couple of years now. I have never had a problem with fuel tank debris of any kind.

Last night I think I got the clues I need. I made a 60 mile run to Denver and back. On the way down, the ZX ran as usual, great up until just over 3K RPM.

But when I started it after a 2-hour meeting, it would barely rev high enough to get me out of the parking lot. It was missing and stuttering over 2K RPM. For a while I wondered if it was going to get me home. After a couple of minutes warm-up, this improved. But all the way home on the freeway I had the cruise engaged, and every couple of minutes, I could feel the engine missing and the car would lose about 5 MPH. Within 10 seconds it would catch and speed up again.

I think my fuel pump is going. I think the first symptoms were inability to provide fuel at high RPM, and that created the miss. I think that last night I felt it starting to fail at lower RPM. My analysis is that the symptoms point to lack of fuel delivery that's getting worse.

Tell me if my logic seems wrong.

Suggestions on how to test the fuel pump? The problem never happens at idle, only under load, so I'd need a test that can be done while driving.
 

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Your logic is flawed without a doubt. First of all you're speculating and that's not the way to diagnose a problem unless you like wasting money. Proper diagnostic procedures are a must. Speculators mean well, but unless they have a crystal ball that's accurate, it's a waste of time and money. Put a fuel pressure gauge on your zx with a long hose so you can place the gauge under the w/s wiper. That way you can monitor the pressure and find out if that's a problem once and for all. Make sure the gauge goes up to at least 65 psi. These systems should never run that high but they have the potential of doing so. You can also pull your fuel filter and empty it into a clean receptacle BUT do it reverse flow. You'll be looking for excessive contamination like chunks of rust. Once it's empty you should be able to blow through it without any resistance. If it passes those tests then put it back on. You can also unplug your TVS and go drive the car. See if that makes a difference. If it does you have a defective TVS, if not then you haven't wasted anything. Check all your injector plug ins and make sure they're all clean and tight. It only takes a little corrosion on them to make the injectors misfire. Next, unplug your ECU for 15 minutes, then plug it in and go drive the car. That will erase the limited learnable memory in the micro processor in the ECU. All those procedures and how much has it cost you? Zero dollars unless you had to buy a pressure gauge. If none of these procedures show a problem, then proceed to the ignition system. Your symptoms could still be there. The power transistor by the coil, and the dizzy can produce those systems, as well as the ECU and the AFM. The only way to test those accurately would be to put them on a different car and see how it functions. The tests shown in the FSM are ok tests but they are only ball park tests and not 100% accurate all the time. Good luck on your problem. Z man of Washington
www.datsunstore.com will be opening back up soon. We're doing testing on the store next week. Only 500 more man hours to go.
 

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Discussion Starter #3
You have some good recommendations, thanks. The ignition system is OK, so I'll focus on fuel. I'm 90% sure there's no debris in the tank, but that's not 100% so I'll be checking it.

The fuel pressure gauge idea had occurred to me, and the long hose idea will make it work. Thanks!

Question: what does "TVS" mean? That's one acronym I'm not familiar with.
 

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Discussion Starter #4
Well, the weather got good enough to run a decent test on my '83 280ZX Turbo. I got a pressure gauge from O'Reilly's and give the car about t 30-mile drive in varied traffic. First I changed the fuel filter to assure there was no problem with it.

And I'm not sure what I learned, as the symptoms are inconsistent.

Reference info: The service manual (Page EF & EC-127) says that:
(1) at idle, fuel pressure should be about 30 PSI.
(2) When the accelerator is fully depressed, it says that fuel pressure should immediately increase to about 37 PSI.
(And it does say approximately" in both cases.)

When cold, the engine consistently missed above 3K RPM, but watching the fuel gauge it never dropped below 30 PSI, and every now and then would go to the high 30's under heavy demand...but not always.

When it warmed up, it started running BETTER than it has in recent times, letting me reach revs above 4K, and once even to 5K, although there was still some missing going on. But during all of these acceleration attempts when the engine was warm, the gauge stayed rock-steady at 30 PSI, never going higher.

I didn't see the fuel pump perform exactly as the spec says when sudden demand occurred, but it never dropped below the specified idle pressure, and during the part of the run when it ran the best, it didn't ever increase pressure to the high 30's.

So I'm not sure I have identified the problem. It concerns me that the pressure didn't increase all the time, but does 7 PSI really make that much difference?

And I still don't know what the reference to TVS in the @zmanofwashington post above this means.
 

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Hi Pilgrim, the TVS is throttle valve switch on your throttle body. My 280 hates to sit undriven. It was so bad last year I had flat spotted tires and gummed up injectors. I regularly (read as 9/10 tanks) had Lucas fuel system in it so you can understand my surprise for a low power issue. Do you have a fuel injector cleaner you like to use? If so try it and then run berryman b12 on the next tank. My v6 maxima benefitted from this too and its not expensive.
 

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Discussion Starter #6
Thanks for the help! I can easily add more Techron - tried some recently and it's easy to do it again. I'll check the manual for TVS tests.
 
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