Vapor Locking, Causes, Cures

[Wade Nelson]

My car has a noticeable problem vapor locking on warmer days. Today's "low-emissions" "oxygenated" fuels with added alcohol are MUCH more prone to this problem, when I fill up at a particular fuel wholesaler that has "no-alcohol" gas the problem goes away completely.

Has anyone solved this problem FOR GOOD on your 280Z or ZX?

I've replaced the Wells, SW541 switch that controls the auxiliary fan that's supposed to cool the injectors after shutdown. Problem is my coolant never seems to get hot enough to kick it on. Yes, i've tried grounding the wire, and the fan runs just fine, times out, etc. Yes, thermostat working fine.

So I went to the Wells site, hoping to find a switch (mine has 210F printed on it) with a lower rating, maybe 190F. Unfortunately they don't have anything with the same thread pitch 1/4 x 19 as the SW541 to replace it with. Anybody know anything about Beck/Arnley or other suppliers?

How often does YOUR aux fan run? Every shutdown? Occasionally? or Seldom, like mine? Maybe some hard water crud deposits in the flange itself is preventing hot water from directly hitting my sensor...

I'm thinking of mounting a toggle switch on the dash to ground the circuit on hot days and just flip it back off in the wintertime when the aux fan is unneeded. Fool the system into running the AUX fan every time I shut down. Esp on sunny days.

The idea of a "prime" toggle switch to run the fuel pump and circulate cooler fuel for 20 seconds before cranking makes sense, that's got to be cheaper than replacing worn out starters.

I have to believe a lower kick-in temp on the aux fan would make a big difference.

[hr369]

for me the fuel pump running before startup didn't cool down the injectors. i saw no improvment with hot starts.

i cured the problem with installing a zx injector fan in my z. right now i'm just using a toggle switch to run it. it starts

up beautifully every time now. i've got to put a timer into the circuit to complete the project.

i could run alcohol free all the time but thats damn expensive here in hawaii. they sell it at the marina and its over 5 bucks a gallon.

could you just take the thermostat part out of the loop and just have the timer run the fan for its duration? and in winter just shut the circuit down with a toggle switch?

Edited May 20, 2012 by hr369

[Zed Head]

Yours is the first account I've seen of an actual comparison between ethanol-free gas and the 10% blend. Pretty interesting.

Newer cars are all running 45 psi fuel pressure or higher. I've wondered if a higher fuel pressure might solve the problem and actually spent a lot of time trying to find a fuel injector model that I could retrofit to my engine and run at a higher pressure, but with the right flow rate. I haven't found one yet but I'm sure there's one out there somewhere. One problem is that almost all of the injectors made after the 80s are high impedance, so there would also be some wiring changes involved.

It seems that the only other option is a better cooling device. Maybe something more focused than a fan blowing air all over a hot engine. I've had a few ideas on that also, like a cooling tube with air pointed directly at the injector bodies but haven't done anything there either. But it sounds like the fan with a timer or a better thermostat might just do it.

I did connect a potentiometer to the coolant sensor circuit and use it on a regular basis to dial up some fuel when it shows the hot start problem. I have a knob under the dash that I crank up to keep it running smooth for about 15 seconds which is about how long it takes to cool things down. At least it sounds good while I'm waiting.

[Wade Nelson]

I went ahead and wired up a toggle switch for the injector fan, timer should still limit it to 17 minutes. Much more than that and it's likely to cause battery drains.

What I find peculiar is that SOMETIMES it will start right up despite being hot. Seems to be luck of the draw. Any ideas on how to CONFIRM that vapor locking is the actual problem?

[black gold man]

I used this timer put it on the side of the console with just the knob showing no face plate.

That is on my 78.

http://www.lowes.com/ProductDisplay?partNumber=311473-207-TMSW30MS&langId=-1&storeId=10151&productId=3387086&catalogId=10051&cmRelshp=req&rel=nofollow&cId=PDIO1

I have a 83 in five years only once the fan came on.

[Wade Nelson]

It's gotten pretty hot here (for Colorado), in the '90's in the afternoons. I just made the extra trip and filled up with the alcohol free gas. I'll report back on how it does vs my last tankful of "oxygenated" gas in this higher heat.

I've had several ..crank 3-4x before it start episodes in the past 2 weeks on the last tankful.

[Wade Nelson]

Well, even WITH the alcohol-free gas my car still starts first crank 90% of the time, and 2nd or 3rd crank 10% of the time. That's AFTER tightening up a loose fuel hose too.

I'm just throwing my hands in the air and driving it.

[Jeff G 78]

Add me to the vapor lock blues list. My 260 with SUs was a mess last fall during a 25+ hour race. At every daytime pit stop, it would refuse to restart and we lost a ton of time trying to get the carbs cool. We eventually found that opening the hood before we shut it off to fuel was just enough to keep the carbs cool. I plan on reworking the fuel rail and attachments and adding a ZX injector fan as well as cutting a hole in the hood for venting. I already have a large heat shield, but I might make a larger one. We go though way too much fuel in a race to run alcohol-free. Last fall, we burned 150 gallons in one day.

[Wade Nelson]

More follow-up. By only filling my tank 3/4 or 5/6 I'm having a lot fewer problems, fumes, vapor locking, etc.

I suspect the fuel expansion in hot weather is CONSISTENTLY filling the vapor recovery line with liquid fuel, so then it can't do it's job properly of venting the tank.

With fuel leaks fixed, never filling it to 100%, a toggle switch for the auxiliary fan, and alcohol-free fuel, my vapor locking problems have almost completely gone away