Intermittent firing issues that go away when you restart the car

[AgingGeek]

Hi all, so my 280Z with stock L28 with EFI has a strange fault where sometimes when driving the car it just starts to misfire and will not accelerate, but will idle fine. It just sounds like it's firing on half its cylinders (to a layman) when you push the throttle... however, if you turn off the car, leave it for 10 seconds, and turn it back on again, it's fine and will drive no issue.

When I drove to the Fourways meet on Saturday, it didn't happen once, until I arrived and it happened when I was parking up (embarrassing), but on the drive home, it happened maybe 4 times in an hour and a half.

I'm going to be replacing all of this soon anyway with more modern injection, but it means I cant reliably drive the car as I am too worried I will need to find somewhere safe to pull over to restart the car.

Any ideas on what could be causing this? I'm hoping its something simple I can fix myself

I assume its ECU or sensor related, like something goes out of range and resetting the ECU by turning off the car seems to reset it, but I have no idea

 

[jonbills]

rust in the fuel tank?

 

[Huw]

Sounds more like an ignition issue, but without having hands on it’s always difficult to diagnose remotely. The ECU has no reset functionality it’s all analogue.

 

[AgingGeek]

rust in the fuel tank?

Sorry if its a dumb question, but how would that affect it?

Sounds more like an ignition issue, but without having hands on it’s always difficult to diagnose remotely. The ECU has no reset functionality it’s all analogue.

Ah, I had no idea on the ECU, I just assumed it was like a computer and held values in memory that went out of range or something and clears when powered down

 

[jonbills]

Sorry if its a dumb question, but how would that affect it?

after some indeterminate amount of running, the pump sucks up rust, which gets stopped at the filter. Eventually this blocks the filter, and fuel stops flowing. Turn the engine (and the pump) off and the rust drops away from where it's causing a blockage.

 

[AgingGeek]

after some indeterminate amount of running, the pump sucks up rust, which gets stopped at the filter. Eventually this blocks the filter, and fuel stops flowing. Turn the engine (and the pump) off and the rust drops away from where it's causing a blockage.

Huh, I guess that makes sense! Im not really sure how I can check that I do have an digital endoscope camera I guess I could poke down into the fuel tank...

 

[Jason McIvor]

after some indeterminate amount of running, the pump sucks up rust, which gets stopped at the filter. Eventually this blocks the filter, and fuel stops flowing. Turn the engine (and the pump) off and the rust drops away from where it's causing a blockage.

AgingGeek
I have a '78 280z and had VERY similar issues to what you describe
Turn on ok, idle fine, press accelerator and the power was "lumpy" or "breathless" and would occasionally conk out
Was greatly improved if the fuel tank was full to the brim

Fuel tank was a complete mess, fuel filter was thick with sh1t - the fuel that came out of the filter was a think brown colour

Fuel tank cleaned, line cleaned out, new filter and it's been absolutely superb since

 

[Huw]

Sorry if its a dumb question, but how would that affect it?

Ah, I had no idea on the ECU, I just assumed it was like a computer and held values in memory that went out of range or something and clears when powered down

This is good old early seventies tech so it’s all discreet transistor logic. No software in that bad boy. It’s all voltage levels and logic gates. Ahh thems were the days

 

[Rob Gaskin]

Re the rust issue, if a filter is partly blocked it can usually supply fuel for tickover or low load but falters under acceleration or prolonged faster running.

 

[AgingGeek]

Amazing, thank you all, that gives me somewhere to start looking!

 

[AgingGeek]

AgingGeek
I have a '78 280z and had VERY similar issues to what you describe
Turn on ok, idle fine, press accelerator and the power was "lumpy" or "breathless" and would occasionally conk out
Was greatly improved if the fuel tank was full to the brim

Fuel tank was a complete mess, fuel filter was thick with sh1t - the fuel that came out of the filter was a think brown colour

Fuel tank cleaned, line cleaned out, new filter and it's been absolutely superb since

Thats interesting you say that, now I think about it, it was only happening when I was lower on fuel (I think)... maybe this indeed is the issue, time to pull the filter and see what it looks like inside.

Cheers!