I am at my absolute wits end and would greatly appreciate any suggestions. Its my 1978 280Z that I have owned for the past 14 years and I have turned darn near every single bolt on the car myself. Its been my Saturday car, autocrosser, and occasional test-n-tune drag car. Its been reliable and strong running. It has a stock engine internals, deleted emission controls, 6 to 1 header, Pallnet fuel rail, and the Pallnet 240sx 40mm TB swap (and a home-ported intake manifold to match). That’s about it for engine mods.
After my local autocross club shut down because of COVID, I prepped the Z and took it to an HDPE at Sebring in April 2021, had an off-course excursion at the end of the last session, pulled into pit lane and to check the car out, shut it off, went to start it and it wouldn’t start. Walked back to my truck, loaded things up, pulled the ramps off the trailer, walked back to pit lane, got in the Z and it fired right back up. Parked it in my garage, fired it right up again in May 2021 and put it on jackstands to change a weeping head gasket and a leaking oil pump (that little car gave me everything it had at Sebring).
In June 2021 I pulled the head with the intake manifold and header. Cleaned the mating surfaces really well, replaced the head gasket, checked to make sure no rags/tools were left in work area, then put everything back together during a very busy summer. Tried to fire it up in October 2021 and here is what has consistently happened ever since:
Turn key to “on”:
all relays click
volts read normal (13 on the 12 to 16 scale)
fuel pump chirps on
Turn key to “start”:
engine fires up no problem and sounds ok (maybe a little weak)
fuel pump running (normal)
volts read normal (15 on the 12 to 16 scale)
vacuum at 18 (usually 22, this is not normal)
fuel pressure 40 psi at rail (normal, I run a nonraising rate FPR)
5 to 8 second later:
volts start fall from 15 to 0
vacuum falls from 18 to 0
fuel pressure falls from 40 to 20 psi
engine dies slowly but if I hit the gas or feather the gas pedal it kills it
fuel pump keeps running until relay kicks it off
FSM tests all normal except I failed 2(2) Power Line Circuit; and 2(3) Injector 1 through 6 and resistor. I also have the EFI Bible and again, all tests passed, but failed the corresponding 2(2) and 2(3a through 3f).
So I went through the FSM EF and EE testing all (and I mean ALL) components with a multimeter and a 12 volt battery; and they all test fine (battery, relays, dropping resistor, transistor, injectors, AFM, TPS, coil, fusible links, wiring harness, and fuel pump). I double checked the connections under the dash and checking/cleaning grounds; then checked each component in the engine bay plus all the grounds (cleaning everything with fine grit sandpaper and brake cleaner). I even replaced a burnt out side-marker bulb I found. I checked for vacuum leaks at the distributor, manifold, PCV, and AFM. I pulled the valve cover and the distributor cap and checked the engine timing. I also used a grease pencil and checked to make sure I didn’t get the fuel lines connected incorrectly. Everything was fine, as it was before when I took it all apart.
Since I have been stalled on the engine running issue I have done some much needed maintenance to get the Z back to Sebring. I replaced my aging MSD225 fuel pump with a new one, MDS Blaster2 coil, distributor cap and rotor, plugs, oil pump/gasket, fuel filter, changed oil/filter, replaced my 10-gallon Summit fuel cell with a 15-gallon ATL fuel cell, replaced my Hawk pads with Porterfield pads, then bled clutch, and brake hydraulic system. These maintenance items have not affected how long the engine stays running or what happens when it starts to stumble.
I know this post is long, but thanks to all who read through it and have a suggestion or two for me.