Hot-start issue with EFI - who has it, who doesn't

[Zed Head]

Many people have reported having the typical 280Z EFI hot-start problem, where after ~10-20 minutes after shut-down (hot engine), the engine starts but runs very rough for what seems like 5 minutes but is actually about 30-40 seconds. Some people with EFI though, report that they don't have the problem (see #43 here - http://www.classiczcars.com/forums/fuel-injection-s30/51601-hellfire-status-release-date-annouced.html#post452357). If we collect enough information, maybe a common solution (or non-cause) will appear. So far, headers and a straight fuel rail seem to be common to one engine that does not have the problem.

If you have the hot-start issue, or if you don't, and have the time, please report here what you're running on your 280Z/ZX EFI system engine. For the sake of the passengers in these embarrassing situations, please.

1. Me - 1976 280Z, stock EFI system, stock fuel rail, 1978 stock injectors, 1978 stock exhaust manifold and 1976 intake with heat shields intact. Consistent hot-start issues if the cooling fan (my own modification) is not turned on

[FastWoman]

Thanks for starting this, Zed!

Mine is a 1978, stock EFI with new Standard FJ3 injectors with plastic insulators, stock exhaust manifold, all 1978 heat shields intact, and fuel rail covered in rubber hose. The engine is tight and runs very well with a CTS resistance mod. I USUALLY don't get hot restart issues. But SOMETIMES it does happen. Engine starts easily, but seems to be running on 2-3 cylinders. All cylinders fire up the first time I put the engine under load and stomp on the gas. Just revving the engine will work, but I have to do it for a while.

FAIW, my hot restart problem was worse before I rebuilt my intake system. When I changed out my injectors, I retired the aluminum insulators and installed plastic. Perhaps that helped?

Edited March 20, 2014 by FastWoman

[rcb280z]

Mine is a 1977, stock EFI, I also have the Standard FJ3 injectors (ebay $150), exhaust header (not wrapped), manifold heat shield (no pcv heat shield), stock fuel rail, FPR, etc. From Oct. to the end of Feb. CA puts additives in the fuel. I notice during this time of year I have an occasional "Hot start" issue but it only lasts for about 5 seconds. No other time have I experienced it. But then again the weather is usually beautiful year round here. Rarely gets above 80 deg. So I will assume that if I lived where the climate was warmer I would probably experience the worst case scenario. If the fan really does help then it sounds like the fuel is vaporizing in the fuel lines, injectors, or both. Maybe it has something to do with the type of fuel we all use now? This didn't happen when these cars were new or fairly new anyway. I didn't have this problem when I lived in Vegas for 17 years either so forget about what I said about warmer climates. Good thread! Need to think about this some more.

[hr369]

adding additional fuel during heat soak starts via cold start injector or main injectors won't work if there is only fuel vapor in the fuel rail. Perhaps a timer function for the fuel pump after engine is shut down to circulate fuel thats temperature activated. We all have various reasons

for heat soak. Bad check valves, leaking injectors, higher percentage ethenol, vacuum leaks

etc... Wouldn't it make sense to keep the fuel from vaporizing in the first place?

I tried a manual switch to the fuel pump to prime the fuel rail before starting but it didn't help. Perhaps it was too difficult for the old worn out fuel pump to displace the vaporized gas? So maybe a couple 30 second or so cycles of the fuel pump immediately after its

shut off will cool it down enough along with also some additional fuel enrichment would work.

My band aid that works now 100% of the time is a zx injector fan on my 100% stock engine.

Edited March 20, 2014 by hr369

[FastWoman]

hr369, several of us have ruled out leak-down issues. My Z will hold fuel pressure just about forever, and it still has occasional hot start issues. I think our operating conclusion is that it's a design problem, hence Nissan's approaches of introducing hood vents in 1977 and an injector cooling fan with the ZX in 1979, and possibly even replacing the aluminum insulators with plastic. It might also have to do with ethanol gas, or winter gas formulations used in summer, which might vaporize at lower pressures.

Edited March 20, 2014 by FastWoman

[rcb280z]

2 more things to add here. My pressure bleeds off about 1.5 hrs after shut down and I have the cowl induction hood on my Z, which I want to get rid of! So the heat has a large opening to escape.

[superlen]

Sarah,

I just watched a video last night of an MIT professor discussing winter blends and they do of course flash over a lower pressure/temp. I hadn't thought of this with regards to hot start, but it's right inline with what rcb reported in post #3.

Len

[siteunseen]

Re-posted from another thread mentioned in post #1 here, thanks Zed Head, you're a REAL problem solver , I'm shooting in the dark.

"I didn't mention that I have the ceramic coated header from MSA. That could be important as I've never had the hot start problem since the header and new injectors on a open fuel supply with the aluminium rail and the FPR out the rear barb to the return line to the tank. It recirculates but not on top of the intake manifold."

As soon as I can find one I'll get one of those infrared thermometers you can point at something to get the degrees and get some readings while it's hot, then after it sits for 10 or so minutes.

[TheCrazySwede]

Hello, my name is Mike, and I have a hot restart problem :disappoin:

1977 280Z. Stock injectors. Stock Headers with MSA Twice Pipe exhaust. Car will run great, both in the cold and in very warm temperatures, but will have the hot restart issue regardless. I've noticed that the problem goes away if I rev the motor up to 2,000+ for a few seconds and then let it idle. I've tried revving it up to 1,600 and 1,800 multiple times, for much longer than a few seconds, and the problem would still be present. Could there be a reason for this?

[FastWoman]

To be clear, Swede, the stock configuration is with a cast iron exhaust manifold, not headers. If you have headers and hot-restart issues, then that would put a dent in the heat-soak theory.

Where are you in the US? And is your hot restart problem a summertime problem, or is it year-round?

[Zed Head]

Don't forget interacting variables. Not enough data to draw a conclusion yet. The more stories, the better.

CrazySwede, do you have heat shields over your headers? Siteunseen has his heat shields intact, as you can see in the pictures.

Edit - also, we're really just working on about a twenty minute window where there's too much heat. Right on the edge. It could be some small thing that is enough to stay below the threshold. Who knows, if it's radiant heat that's the problem, ceramic-coated injectors might do the job.

Edited March 20, 2014 by Zed Head

[Captain Obvious]

Hello, my name is Mike, and I have a hot restart problem :disappoin:

Haha! You've taken your first step towards recovery.