Octane?
 

I have an 86 300zx na that will stall while driving or sometimes wont start at all for a few minutes. once started, I smell gas. I have changed the coil and the ptu to no avail. But, one day I used 93 octane and didnt have a problem at all. is it possible i have a fuel/air problem?

About the only thing octane does for an engine is keep it from detonating, or, spark knocking. The higher the octane the less detonation, especially in an engine with higher (than normal) compression ratios, or if the engine is boosted (also raises compression levels). In a properly tuned, nothing special, OEM engine running high octane fuel would decrease performance (remember we're trying to stop denotation).

With that said, if you put 93 octane fuel in the car and the problems you described went away, then I'd say you have a tuning problem. The easiest thing to check is timing. If it is too far advanced it would cause the engine to run like poop, and it would crave a sip of premium gasoline.

Bottom line is, the engine, properly tuned, should run perfect on 87 octane. I believe your problem(s) are more spark related than fuel or air.

BTW... Forgive my ignorance, but, what is a "PTU"?

i dont know about other Z's but if i have the windows down i always smell gas and i passed e-check. As far as the octane goes i'v alway used 93 octane or better. once i put the cheap gas in it and it ran a little funny so i wold just keep using high octane gas i dont think Z's like cheap gas, unless your z is your daily driver then i dont know what to tell you

Power transistor unit. I replaced mine because i got 21 codes from the ecu and thought that might be the problem. I replaced the ptu, jut by chance had to put in 93 octane in the tank and was fine the whole day. the next time i put gas in the tank, 87, the car stalled at 70, picked back up in about 20 secs but was hard to crank in the afternoon.

stock Z31s only require 87 octane. Anything more is a waste of money. You're also likely causing carbon buildup which will decrease performance over time.

Are you putting race gas in? Cause as far as I'm aware they don't sell much in the USA at normal gas stations that is above 93. I would actually say that 93 is pretty damn high octane for around these parts.

i can get 94 form sunoco i only did it once it cost way too much i think it was like 2.80 when reg was 2.20 or something.

Sounds like your timing is way advanced. I have an 83ZX that had this problem. Damned thing was a rocket when it was running and the plugs weren't fouled out, but it would very quickly and easily foul the plugs causing hard starts, rough idle, stalling etc. I reset the timing to stock and it runs great now, but it doesn't have the instant response it had with the super advanced timing.

Who refines their fuel? Sounds suspiciously like ConocoPhillips who are bad news. Pretty good price on gas tho let me tell you. The highest we can get most places on the West coast is the 92 Oct.

I ended up replacing my distributor with remanufactured one with, supposedly a beefier crank angle sensor. seems to have done the trick - 95 bucks well spent

I've been burning 87 octane in my 86na since I bought it in 1991. You should only use the fuel recommended by the manufacturer. I tried to run 89 octane in my 93 Caddy STS with the Northstar engine. Bad move, stumbled all over itself. A friend had told me that the computer would adjust for the octane. Not so, the 93 and 94 STS had higher compression than the 95 and after cars. They would run on regular but the 93-94 would not.

Gas smell, Check the fuel injectors, and see if there wet, there was a fuel injector recall in 84, I was working at the dealership at the time. My service writer ran the vin and it turned out the recall had never been done so nissan paid for the injectors. For the stall, are there any stored codes in the ECU? CPS, HTS?