I know there have been 48 million posts on this subject but i just need simple answers/opinions. i have a 1977 280z 5 speed all original. after driving and left for 15 ish minutes the car will either start and run at roughly 400 rpm or more recently it will start sputter and die. now iv heard this may be vapor lock or a problem with the cold start injector. either way what can i do to solve this problem? iv heard of wrapping the fuel rail to make sure it doesnt get to hot, and heard about disconnecting the cold start injector. i need help! this is a very embarrassing problem and id love to solve it as soon as possible. thanks!

280z's do not have VL problems, that is a carbed car's problem.

There does not appear to be an easy solution to the "hot start" problem, probably because there is not a firm idea of just what causes the problem. The factory's addition of an injector cooling fan, plus the symptoms of the problem, point toward hot injectors as the source.

You might retrofit a ZX cooling fan on to your 77. Get the temperature switch with it if you pick one up.

My 77 does the same thing. It's strange that it happens when it sits for about 5 or 10 min. but cold it runs great.

I think the cold start injector only sprays fuel when the engine is below 50 deg F, so that's not likely to be a factor in a warm engine. The cold start problem seems to be a fuel starvation problem anyway, most likely from hot injectors. Sadly, I've come to the conclusion there isn't really a good solution. My engine runs like a top, and I've got all new injectors and a new check valve. My system holds pressure just fine. I'm also in the weird habit of priming my engines before starting, even when it's usually unnecessary. So I hit that primer switch (that I installed) just prior to starting my Z -- every time. I've also insulated my fuel rail, although perhaps not well (with rubber hose, wrapped in silicone rubber tape). Even so, I'll occasionally get the rough start after 15 or 20 min of sitting. I think it's just the nature of the beast. Wait another 15 min, and it will probably start just fine. Also try a different gasoline. I think the cooling fan would fix the issue, but I'm not willing to have a ZX look under my hood.

thanks for all the help. glad to know im not alone on this! looks like it is just how Z's act. oh well!

whenever i use costco gas it was always harder to start when hot. before i added my injector fan, i tried a better grade of gas and it did help. try running chevron and see if it starts a little better.

to totally eliminate the problem the xz injector fan is the ticket. im only lacking the timer to make it fully functional. so i have to manually turn the fan off and on. but the bottom line is that the zx injector fan fixed the problem of rough hot starts for me.

i run chevron super. and ill look into a zx fan

I suspect higher octane gas might also help, as it tends not to be as volatile as lower octane gas (pretty sure).

Just a quick question, Since I have the same symptom, meaning that the engine runs fine until it has sat for lets say 5 to 15 min, then restarted it stumbles and hesitates until it runs for lets say 5 min. Does engine performance improve because gas running through the hot injectors actually cool them? Just trying to understand the symptom.

Edited February 9, 201213 yr by grantf

Yes, fresh gas through the injectors and fresh air through the intake manifold will cool the injectors. On my engine, the problem disappears when I first take off down the street. It takes much longer if I just let the engine idle. Revving the engine is also of little help, perhaps because the engine isn't under load and drinking quite as much fuel.