cygnusx1

Ouch sorry to hear about the ribs. That's one of the most painful things, and I can't image our discussion has been that painful. Sorry you had to read it all. I am not sure where you get your definition of superheating. It seems like you are talking about sublimation, perhaps? Whatever, really. I think we have figured out that an EFI system can get vapor in it, but it's not as critical as with a carbureted system because it should never effect the pumping of the fuel. Depending on what problem the vapor causes, it may be called vapor lock, or not. Maybe we can just say, "my Z has the vapors", when it's not causing pumping issues. Question though. Isn't vapor lock really just pump cavitation anyhow? Tricks? A long time ago, I added 1/8" thick teflon washers between the fuel rail mount tabs and the intake manifold. I also had wrapped the fuel lines with a glass backed foil at one point. By far the best result has come from leaving the hood popped at least 10".

There is not much you can do to clear the vapor, other than drive it a bit after it starts. Sometimes it barely idles, so you can rev it, but the best thing is to place a moderate load on the engine which will open the injectors fairly "wide". Leaving the hood open is usually enough to prevent it in the first place. I wonder if any additives can raise the vapor pressure of the fuel, for experimentation.

It depends if the leak is in the pressure lines or in the tank side of the lines. Either way, it can effect the car negatively and needs to be addressed asap.

Yup that is possible. But according to the manual, it's not. Then again, the earth was flat once.

I am pretty sure that the old fuel injection systems in the S30's use full batch fire. All the injectors fire at once so you do have quite a bit of pressure bounce. The fuel damper is way at the back of the car too. Superheating may or may not be critical to the theory. But I now think it is. I just figured that a single injection happens pretty quickly (2-5ms), so the if the fuel is phase changing, it's happening pretty quickly. A liquid in a superheated state would be the first, and fastest to flash. So if you have a column of liquid with a pressure gradient, "above boiling pressure" at one end, and "below boiling pressure" at the other end. Naturally, somewhere in that column there is a segment of critical pressure. There is also a place in that segment where a smaller segment of superheated liquid lives. That small segment may be the "seed" for the instant flash, so to speak. This is really getting microscopic, but it's all perfectly feasible and I think it happens. It happens when the conditions, and fuel quality, fit the mold.

Could be a leak in the fuel system. It should hold pressure when the car is turned off, or the fuel could boil, or if the fuel pump check valve is stuck open, the fuel could drain back a little. Sometimes heat also plays tricks with the electronic ignition but that's not too common. Next time it won't start, just check for spark. First things first, confirm fuel pressures running, and off. http://www.classiczcars.com/forums/showthread.php?43039-Vapor-lock-questions-for-the-hotter-climate-guys

I well know what superheated means. Water at standard pressure that is at 213 deg F and not boiling, is superheated. The reason I bring superheated into my theory is that once the pressure is dropped, or the vibration of the pintle is started, THAT alone could bring the fuel to change phase, from a superheated state, or even just skipping the superheated state. Yes, it could all happen without ever being superheated. There is also hysteresis between the phases. So maybe there is some instantaneous point in time when the fuel is superheated, maybe it just vaporizes without ever becoming superheated. I don't know for sure. Fastwoman is right in the cooking pasta observation. Microwaving pure water, which boils the instant you drop something into it, is another example of superheated water gone wild. Superheated states, are highly unstable, which would make a liquid in this state much more likely to vaporize by a seemingly insignificant catalyst.

We could probably open the horses's mouth if we had a clear fuel rail and clear injector tubes. However what we do have: Difficulty hot starting some EFI Datsuns, rough idle when first started from hot, then we have datalogs of injectors feeding leaner mixtures as they heat up with a constant pulsewidth, and we have evidence that Nissan's engineers were still working on the issue from 1975-1983 by the design evolutions they made. Also, but not evidence, superheating, is relevant to this theory. In fact it's a critical point. Counter evidence is that some EFI Datsuns have never exhibited this, and the manual says it can't happen. We also know that fuel can boil pretty readily at engine bay temperatures, and atmospheric pressure.... And finally we have this: The later generations of injectors are called SIDE-FEED because they are almost fully immersed in the fuel rail flow path. Why do you think they are bathed in the fuel path?

Yup, the 77 and 78 clocks were the ones that almost ALWAYS work.

Yes, the 240Z clocks lastest much longer than the gen1 280Z clocks. In fact, I carved out the guts from my 76 280Z clock, and grafted the 240Z mechanical internals. So it looks like a 280 clock but works and sounds like a 240 clock. They just need some cleaning and light lube after 30 years or so. Cleaning every year, seems overkill, or a disclaimer. Very interesting tag though.

Of course vapor burns, but fuel pumps are not good at pumping vapor, and injectors flowing vapor bubbles into the intake cannot deliver enough molecules of fuel to ignite the charge properly. Did I say vapor doesn't burn? I said it would require different conditions. What I referring to was concentration.

No. Just take it apart when it stops ticking. About every 6 months.

Here is my theory. I think the fuel is sitting in the heat soaking injectors and rail, with a vapor pressure of, say, 10psi. Note: it's not a vapor yet because it's safely compressed in the system at 30psi. Say the rail and injectors reach 190 degrees F in heat soak. You turn the key. When the injector opens BAM. In slow motion. The injectors pressure drops suddenly and dramatically, as one end of it is exposed to either atmospheric pressure or engine vacuum. The rail pressure drops too. The system then recovers pressure as the injectors close and the pressure restores. So lets take an instantaneous look. The injector is open. The pressure at the pintle exit is "manifold vacuum". The pressure in the fuel feed lines is 34psi. What you have is a gradient of pressure tapering from 34psi down to vacuum. Somewhere in that gradient path, from fuel pump to pintle, there is a point, eg. 10psi, where the superheated fuel will vaporize. That point could be in the injector body, the hoses, or the rail. You end up with vapor pockets. Now for a few seconds, or minutes, you have vapor passing intermittently through the injectors. OK They are not locked. SO maybe it's not technically vapor lock. One thing is for sure. With Winter or marginal suburban fuels, and higher elevations, with approaching 200 degree-F injector bodies, the conditions are right for flash vaporization. Why do I call it superheated? http://en.wikipedia.org/wiki/Geyser Read the section about ERUPTIONS. It's the same effect. Transparent fuel rails anyone! I bet Nissan has a few in the engineering R&D archives. Why the injector cooling fan in the ZX? Still no answers. Do I hear crickets? For carbs, you can build heat sheilds, try other fuel brands, pop the hood, insulate the lines...all the same thing EFI cars can do really. newsflash...do I see posts from VERY knowledgable people about EFI cars vapor locking? :eek: http://forums.hybridz.org/index.php/topic/101376-vapor-lock/page__pid__949958#entry949958

OK we get it, none of your vehicles exhibit this behavior. Does not make it impossible. Try to open your mind and envision vapor lock inside the injector when they initially fire, on a micro scale. If you can't understand this or don't want to call it vapor lock then say so, or call it what you will. At this point it's a theory, that others besides me also have. Maybe it's not fuel vaporizing. Maybe heat effects the injection in some other way. Can you offer any explanations? Some more reading: http://www.crxsi.com/info/fuel-related/Diagnosing-Returnless-Fuel-Injection-Systems.htm

Just make sure your system is holding pressure after you turn off the car. That is usually the first thing to eliminate when faced with this issue. How long it should hold pressure? I can't find that number anywhere so in my logical opinion, "long enough for the engine to cool down a bit" ;-) If you do hold pressure, then you are seeing exactly what I am talking about...assuming of course all other components of the EFI check out...and it's a pretty long list. I like to compare specs to the FSM right from the ECU connector where you have access to all FI components. Of course theres more stuff that needs to be checked out. It's so easy to say something else is causing the issue, and it CAN'T happen, but I know that this CAN happen due to a vaporizing fuel issue.

That is pretty much some of the basis of the CVCC from Honda, I think. The problem see with vapor in the injectors is simply from the fact that if the injector fires for 2.5ms to atomize liquid fuel, you get X amount of fuel in the chamber. If it opens up for 2.5ms and the fuel vaporizes through the nozzle path you are getting MUCH less than X amount of fuel to the chamber. This all clears up once fresh cool fuel makes it down to the pintles. Usually it takes about 30 seconds or so, once the engine fires, in my experience with the stock EFI. Now my car is a different story. It's not stock, it generates a ton of heat, no hood vents, and the billet rail does a great job of transferring heat into the fuel. With the car shut down hot, even with 30-40 psi still on the gauge, the fuel in the injectors exceeds the boiling point at atmospheric P. Even if I let it idle on a hot day the mixture will begin to lean out as the pulsewidth of the injector remains steady. The fuel rail is recirculated and I have two pulse dampers in the loop. My injectors are Bosch 440cc so they are at a pretty low duty cycle at idle which might explain why they can't cool themselves off with fuel. Perhaps? The energy of one gallon of gasoline is roughly 112,000 BTU A fully evaporated (vaporized) gallon of fuel occupies about 160 gallons. Therefore, one gallon of gasoline vapor contains only 700 BTU. You would need to inject 160 times the volume of vapor as you did liquid to get the cylinder fired off properly. So, if there is nothing but vapor in the injector OR the fuel is vaporizing coming through the nozzle, and the liquid phase fuel is not flowing through fully, you will be very lean.

Absolutely. However if the fuel injector injects a teaspoon of droplets, perse, vs a teaspoon of vapor, you have a totally different atom count. X-TAU is all about fuel depositing and vaporizing AFTER the injector. I has to come out of the injector as a mist of fuel droplets. You link does not work, but I think I am familiar with that document. I have used silicone tubing sliced lengthwise, and slipped over the injector bodies, and the fuel lines as insulation. However it didn't work too well. I don't think silicone was the right choice. It needs to be less thermally conductive and maybe even reflective. There are products designed to do just this. Search summit and jegs for heat control products for an easy idea.

Technically, it's not superheated the whole time, because the rail pressure keeps it in a liquid phase even though it's above it's STP boiling point. However it passes through a superheated state just before flashing, as the pressure in the injector column drops upon firing. In fact, the snap action "shock" of the pintle opening might be enough of a catalyst to start the boil.

Haha don't worry, I my engineering degree is mostly evidenced by the grease under my fingernails. I am no threat for sure. I am only a threat to myself. Good data that you found. Funny, I just got off the phone with a good friend of mine who is also an engineer, and worked on fuel systems for snowmobiles, now he is with NASA, and he gave me almost the same info you just did. He said that typical cold region Winter fuels can definitely vaporize in Summer conditions found in a fuel injection system. And he confirmed that fuel vapor is a completely different phase than atomized fuel. Fuel vapor is much closer to air than it is to fuel. He also said that it is possible to have a "geyser" effect. When the injector opens, the superheated fuel can instantly vaporize and apply back pressure to keep liquid fuel from entering the stream.

I am going to research the chemistry/physics of fuel atomization vs vaporization and the effects on combustion, but I know the short of it. Fuel injectors are not good vapor injectors.

Mech. Engineer but it's irrelevant. Fuel has to atomize to burn. Not vaporize (it's about droplet size). Vapor would require a different condition to ignite than present in the IC engine. I am thinking that the key to the differing experience has to do with A)Regional fuel quality and B)Condition and rate of pressure drop of the sealed system of Northeast vs Cars in warmer climates. I am not sure if cars in the warmer climates experience this, but in cold weather, the hoses in the Z's EFI tend to leak. There is actually a recall or service bulletin for the issue. It may be that the cars exposed to colder climates, do not hold pressure long enough or high enough to ward off vapor-lock, unless the owner has taken remedial actions. That's why I asked about what the spec in the manual is for holding system pressure, in case you wondered. I can't seem to find it anywhere. I know it's not indefinite though. The "cold weather fuel line leaking", is not isolated to Datsuns either. Later model Subarus also had a similar recall, last year.

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?

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.

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

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.