The 77 280z is hemorrhaging fuel somewhere (getting 12ish MPG

>>16550344
worth a shot
thanks /o/

If its carb'd it could be running rich as shit and dumping fuel in like a madman, but you'd usually see a bit of smoke on startup.

>>16550344
Mess with the fuel tank more to unfuck it and then check fuel system in engine bay as previous anon said.

>>16550531
First gen EFI

are you getting any smoke on start up? I had a 280zx, same fi system, that had a bad throttle position or something else. Used lots of gas and bogged down easily.

>>16550576
no smoke. I just tried at it started up and idled smooth.
I don't understand.
What could be shitting my MPG up by that much? I'm almost empty on 190 miles and I usually get 280.

>>16550344

>getting 12ish MPG and it can no longer hold idle without assistance

Cylinder head temperature sensor is fucked bro.

>>16550629
what happens if you rev the engine around start up? rev fine?
If you have all the power you have ever had, i guess you can rule out the fi system on first pass and look at the pump and tank.

ack wait, you said at first it wouldn't hold idle without assistance.. then it could be the fi system. I would check contacts, check fuel pressure. etc etc.

>>16550647
Im not following.

>>16550660
its idles fine now, not super sure why. revs fine.

>>16550666

Cylinder head temp sensor is one of the sensors the efi uses for tuning, if it goes bad or is disconnected the ecu goes into limp mode.

Meaning the engine will run like complete ass, shit mileage, bad idle, lack of power etc.

>>16550666
not that guy, but a cylinder head temp sensor is a sensor that measures the temperature of the head, it uses this to control fuel mixture. It could cause a lean or rich fuel mixture. Its screwed into the head.

If you have a volt meter you can test if its giving the right signals to the ecu. You can diagnose the entire system with a volt meter to be honest. Cleaning all the contacts wouldn't be a bad idea either.

>>16550729

it's also a really common issue.

>>16550729
>>16550731
Gotcha thanks.
I'm sure there's a guide on the harness I can find online to test that wire.

Took a look at the fuel pump. No wet spots to indicate a leak. There are no internal parts to the tank right?

>>16550629
on the old NAPS-Z/X engines any number of sensors cause the same loop conditions:

Bad thermostat will cause it to always run cold and therefore run in "fast idle mode" which dumps fuel to warm up.

There is also a heated wax diaphram "fast idle valve" that looks like a trumpet. There is a heater strip inside that eventually closes the trumpet off as the wax disk expands. These often fail open when the heater strip dies, resulting in too much air bypassing the TB.

Bad CHTS will cause all sorts of A/F ratio problems. (a failed one causes no starts between ~30F and ~70F) one thats out of spec or reading too cold just tells the ECU to dump fuel, and since this is a batch fire EFI, you start dumping tons of fuel.

Bad Airflow sensor will cause it to dump fuel for a limp mode.

Stuck Raising Rate pump (pulls vaccum on Fuel regulator on the fuel rail) Boosts fuel Pressure when cold start or HOT restarting to prevent vapor locking. If it fails on you will be up nearly 50% from normal injection pressures.

Frozen Vacuum advance mechanism in the dizzy : would run okay at idle with little to no issue, but would bog and run more and more poorly/less efficient burn and loss of power as revs increase.

Bad Dizzy Cap/Rotor/Tension cables/sparkplugs/coils also can cause a lot of fuel consumption issues while still allowing the car to be drivable for normal usages. Hard accelerations in higher gears would result in lots of after/backfires or stuttering though.

>>16550884
Appreciate the big ass post I saved it in a txt so I could later troubleshoot these.
>Bad thermostat
Replaced it a few months ago so thats probably fine.
>no starts between ~30F and ~70F
We can rule out this then
>loss of power as revs increase.
I'm not feeling a loss of power, maybe just not yet though.

Haven't had any backfires although it's typical the car stutters if I dont warm it up.

>>16550344
sounds like it could be your fuel pump. check it for leaks and make sure your seals are good

File: IMG_20151030_173710844_HDR.jpg (252KB, 728x1296px) Image search: [Google]

252KB, 728x1296px

>>16550923
basically every batch-fire Nissan EFI is the same set up from the mid 70's through the early 90's. Any FSM for an L, Z, CA, VG, KA sohc, and RB sohc engine should have most of the steps to walk through.

The L has a lot less to go wrong, but its also harder to tell which things are going wrong because everything throws the computer into "fuck it, dump gas" mode. I wish i had a definite answer.

Last nissan fuel consumption issue i fight was due to a partially failed coil
It worked, it made spark, but it was insanely weak so it was not fully burning the fuel. I had go through basically everything on the fuel side of things, all the sensors in the block etc.

pick related : burned coil

>>16550979
Fuck man. Sounds shitty I'm tempted to dump it on my mechanic.

>>16550923
>no starts between ~30F and ~70F
We can rule out this then

Not exactly, thats just the result of a pure open contact, internal break or disconnect.

A short or the resistances being out of spec could still allow the car to start normally then fuck up things later as it gets hotter

>>16551050
A good amount of this can be tested via multimeter right?

>>16550531
>how millenials think carbs work

>>16551089
most all of it can, including heat-resistive faults.

An FSM should have all the specs listed, and the PDFs for these things float around all over the internets

>>16551097
Alright senpai thanks a bunch. Gonna go to the uni now hope I dont run out of gas.