'78 280z fuel issues, and beyond- Help?

[STeeleMarine]

Good day to all, 

I am a first time Datsun owner, and looking forward to some fun with my new 56k mile survivor. When I acquired the car, it had been sitting for ??? years in the possession of a daughter who's mother had died and left her the car.  I purchased the car in belief that it was sorted by a mediating broker, but within the first 30-40 test miles I noticed a hiccup (slight miss) when I feathered the throttle from acceleration to less than acceleration.  I figured it was just because it had not been run in such a long time, and inquired to the seller who assured me it was sorted when it was re-comissioned.  I removed the plugs and they looked 40 years old so I replaced them, did a compression check while they were out and proved all cylinders werel within 5psi of each other, so I directed myself towards the fuel system before the electrical.  I cracked the fuel filter supply line and drained it and it showed some water and rusty debris, so I worked backwards towards the tank. When I dropped the tank.... OMG! Rust galore!!  This is where I thought I was onto something.  So, an acid bath later, some cleaning and sealing of the tank, fuel sender reconditioning, I reinstalled everything.  I inspected fuel lines, and blew some compressed air through the hard plumbed lines towards the disconnected fuel filter in hopes of getting all the rusty plaque out.   When I reconnected everything, I turned the key to accessory, thinking the fuel pump needed to prime the system, and turned the car over.... and over.... and over... and she finally fired up. She ran for a bit, then hiccuped, missed, backfired a bit, and died. My first thought was air in the fuel lines, and it would work it's way out, but after starting again... another spit and sputter session, and dead. Lather, rinse, repeat for another few times and it never got any better. SO- being that the fuel filter was so gooked up in the initial session, I removed all the injectors and sent them for service figuring we had something not spraying properly.  Tests showed that 2 of the 6 were underperforming, but the proverbial "smoking gun", I did not find.  Reinstallation went well, and I read in either the FSM, or an additional Fuel Injection manual that the fuel pump could have a problem priming the system if the tank runs dry.  So, with the assistance of a few jerry-cans of fuel, the tank was topped right off.  Hooking up the battery and the moment of truth, I turned the key.  Attempt 1- nothing.  Attempt 2- sputter.  Attempt 3- ITS ALIVE!  She ran and idled smoothly in the driveway for 10 minutes or so, so decided to do a road test. Here's what's going on, and it's similar to my initial problem before the rust started gumming up my fuel system:

Under hard acceleration, she pulls like a bat on fire! Under "feathered" acceleration, there's still a miss in the low rev range. It happens from idle to about 2500rpm, and then it pulls without the sputter. It is particularly obvious in 1st and 2nd gear because the revs are lower. I also notice it when I am cruising at 55mph or so just trying to maintain highway speeds.  When I am feathering the accelerator lightly off to on, it sputters.

Would love to have some expert ideas on where to look next.  Electrical maybe? TPS?  Maybe someone here can offer a rabbit hole for me to crawl down?  Thanks!

[siteunseen]

I'm no expert but you've described what many of us have gone through with seemingly '77 & '78s only.  The ecu needs a little help on the coolant temp sensor that adds more fuel.  Google "fuel tweak classiczcars.com" and read a few threads.  I had to do it to my '77 and the way I found my problem was to clamp off the return fuel line about half way, increasing the fuel pressure.  It ran better right away so reported back on here and was told to try the potentometer add on.  Car runs strong all through the rpms now.

Here's what I followed...

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

Thank you @240260280

 

Edited January 10, 2019 by siteunseen

[Zed Head]

31 minutes ago, siteunseen said:

I'm no expert but you've described what many of us have gone through with seemingly '77 & '78s only.  The ecu needs a little help on the coolant temp sensor that adds more fuel. 

The earlier 280Z's and the ZX's have the problem too I think.  The ZX people often find a 10 ohm resistor in the wiring harness.  FastWoman wrote about that, and she also used the tweak on her 78.  I did it to my 76 car.

Not sure why exactly the problem is there, maybe the fuel changed over time and/or the cars were tuned to perfection for emissions purposes.  But adding the resistance makes a great tuning and troubleshooting aid for not much effort.

Another clue that that's the problem is if you get popping back through the intake manifold and bucking at low throttle settings, trying to accelerate.  That's a bad case.  The milder version is just a hesitation though as you pass through the mid-range RPM at part throttle.

[Patcon]

Check your profile settings and make your actual address private. No reason to share that with the world

@STeeleMarine

[STeeleMarine]

Thanks for the input all.  Maybe this is the quick fix that I was praying for, and I can get back to enjoying the car instead of trying to remedy gremlins.  Now I am looking forward to the spring so I can test and trial.