Vapor lock questions for the hotter climate guys

[Z train]

Time to play with trains.See ya Thursday-ish.

[doradox]

Right, because yours does not vapor lock, no cars with FI do? Read the FSM. What is the allowable decay time for the factory fuel pressure after shutdown?

I was doing a little light reading and found this little tidbit in the 76 FSM.

[cygnusx1]

Yes, then why did Nissan have to add hood vents, and then add a blower, that takes cooler air from under the passengers side frame rail, and blows it directly onto the injector bodies, for a period of time, after the engine is shut off? Clearly, the EFI Z cars had issues with heat and fuel injection. What was that issue? Safe bet that they were battling vapor lock in the injector bodies. I see it all the time, even in a perfectly functioning EFI system. Newer injection systems are designed much differently than the L-Jet, so that the vaporizing fuel inside the injector issue is even more rare.

Saying that a fuel injected Z won't vapor lock is false. Shouldn't vapor lock, is more accurate. How many EFI Z owners have had hard starting after parking hot for 10-15 minutes? Especially the early models without vented hoods. My 76 did this occasionally when it was bone stock, and was in perfect working order. Fuel types/brands might also play a small part in why peoples experiences differ.

[doradox]

Yes, then why did Nissan have to add hood vents, and then add a blower, that takes cooler air from under the passengers side frame rail, and blows it directly onto the injector bodies, for a period of time, after the engine is shut off? Clearly, the EFI Z cars had issues with heat and fuel injection. What was that issue? Safe bet that they were battling vapor lock in the injector bodies. I see it all the time, even in a perfectly functioning EFI system. Newer injection systems are designed much differently than the L-Jet, so that the vaporizing fuel inside the injector issue is even more rare.

Saying that a fuel injected Z won't vapor lock is false. Shouldn't vapor lock, is more accurate. How many EFI Z owners have had hard starting after parking hot for 10-15 minutes? Especially the early models without vented hoods. My 76 did this occasionally when it was bone stock, and was in perfect working order. Fuel types/brands might also play a small part in why peoples experiences differ.

I'm not the one saying it never happens. You said read the FSM. So I did. Be careful what you ask for. You just might get it.

Steve

[cygnusx1]

Well, there is scientific proof then. I must be wrong.

[FastWoman]

FAIW, I understand that ethanol gas has a higher vapor pressure than genuine 1970's gas, so it's more prone to vapor locking. Furthermore, gasoline blends are varied seasonally with more volatiles during the winter. When these mixes are not conscientiously managed by the gasoline suppliers, you can get almost anything from the pump -- even gas blended for cooler climates with up to 30% ethanol. I suspect that's why some people have vapor lock problems and others don't. Where I live, most gas is @#$%.

[doradox]

Well, there is scientific proof then. I must be wrong.

I didn't say you were wrong. Other sources are saying that.

I said "A properly functioning FI system is highly unlikely to vapor lock.'

I spent 20 years as an auto tech in Tucson and never saw or heard of an injected Z vapor locking. My 75 never did it. Apparently you have some trouble.

Steve

[Bruce Palmer]

Bruce,here it's actually the heating radiating upwards off the asphalt that magnifies the heat.If i pop the hood and leave it sit on the safety catch,i have no issues restarting.

THe wifes 620 is my only carbed vehicle.I have a functioning return system and NO insulation and i have zero vapor lock issues.

Me thinks that were I to live where the pavement temps got high enough to cause vapor lock, I'd be searching for a new location. nyuck nyuck

'Sposed to rip up into the low 80's now thru the weekend here in God's country......

[cygnusx1]

Been working on EFI Datsun's myself for over 25 years. I see vapor lock issues, even when the system holds pressure. It very well could be the fuel formula we get here in the Northeast.

[sblake01]

I didn't say you were wrong. Other sources are saying that.

I said "A properly functioning FI system is highly unlikely to vapor lock.'

I spent 20 years as an auto tech in Tucson and never saw or heard of an injected Z vapor locking. My 75 never did it. Apparently you have some trouble.

Steve

The confusion here is in the semantics between true 'vapor lock' and 'vapor lock type symptoms'. In the combined 18 years of the 'joy of ownership' of mid to late 70s Datsun EFI vehicles the only time I ever experienced that was when the check valve went bad on my 810. Replaced it - no further problems. It gets well over 100 degrees everywhere I've lived here in those 18 years. If it happens on a carbed car it's vapor lock if it happens on an EFI car is a mechanical problem that manifests itself with vapor lock type symptoms. When everything is right, it will never happen. That can't be said of carbed cars. Even with wrapped fuel lines the fuel pressure is only, what, 3-5 psi.?

[cygnusx1]

I will repeat. Fuel that sits under pressure, behind the injector pintle, becomes superheated. Superheated is a technical term. What happens to superheated liquids when a catalyst is introduced or the pressure is suddenly reduced? It flash vaporizes. This DOES happen inside of the injectors when the pintles are fired from a superheated state. Nissan, not me, installed a cooling arrangement in an effort to keep the injector bodies from becoming holding chambers for superheated fuel. Again, not my idea, it was the idea of Nissan engineers. The flash vaporization on hot start, can also happen in the fuel rail as the pressure sine waves bottom out, as the BATCH injectors all fire at once. The fuel damper is too far away to absorb this wave fully. Sequential injectors minimizes the amplitude of the sine pressure waves in the fuel rail, which can prevent this effect from creeping into the rail. When it happens, you have a situation where you are injecting vapor into the combustion chamber. Vapor will not burn. Thus it's a sort of vapor lock. Call it what you will. Yes, it is probably fuel dependent.

Now, can anyone answer why the cooling fan for the injectors was added?

Edited July 27, 2011 by cygnusx1

[sblake01]

Alot of what I've seen makes it unclear as to whether it was for emissions purposes or for the reason you say. Can anyone answer why it was only used on the 280ZX and not the 79-83 810/910 Maxima or any of the 4 cyl EFI Datsun/Nissans of the era? You can 'repeat' as many times as you want. I know what vapor lock is. Fuel could well be a factor. Never ran any of them on ethanol. All we can do is conjecture and agree to disagree.....

Edited July 27, 2011 by sblake01