What's the white smoke when timing is retarded? Unburnt fuel methinks...So, despite a hot injector and a flame-front from initial combustion, the flame goes out and unburnt fuel goes out the tailpipe? (fuel heating from compression in the hardlines is negated upon release and atomization methinks)TheMan53, you are following my drivel correctly, compression vs temperature is generally a constant, but the leakdown of bad rings makes it more tricky. Consider the recent topic on push-starting vs cranking.... push starting can spin the engine fast enough to reach autoignition before leakdown and before the air-charge cools on the metal surfaces. Slow crank a cold engine with low compression... no autoignition, no worky. Conversely, high compression allows earlier injection timing, earlier combustion that can continue across TDC until the fuel is entirely spent.
...BTW your Bieber avatar is awesome.-Malone
Your imagination is, in a way, interesting... Your premise seems to be that, based on your imagination, compression that is half of spec might affect injection lag on a fully warmed up engine, making a more advanced timing spec beneficial. If a more advanced timing spec might be beneficial on a vastly out of spec engine, then a pulse adapter, in all cases, is a worthless tool and everyone (seig heil) should (moral imperative) ditch all non-subjective timing tools and embrace hillbilly timing their engines.If you want to argue the uselessness of a tool that you've never used on the basis that it can't optimize a thoroughly worn out engine, that doesn't seem either logical or useful to anyone. Although, it is, arguably, entertaining. If you have a particular beef against diesel pulse adapters, then I can probably help you imagine even more potential issues... Let's consider the dynamic advance and case pressure. If someone installs an IN bolt in the Out bolt location, the vane pump is worn out, the pressure regulator is whacked out of adjustment and the dynamic advance piston bore is gouged, the dynamic advance will not work correctly. With the dynamic advance not doing it's thing, if you use a pulse adapter to set the timing at idle, then the timing will be progressively more and more off as the rpms increase. In that case, hillbilly timing the engine so that it is timed properly for cruising rpms will return better performance and much better fuel economy. When running a worn out injection pump with no case pressure and jacked dynamic advance, a pulse adapter is the wrong tool for the job... What about injector pop pressure? Maybe that affects the start of combustion even more than compression. You might imagine that larger droplets of fuel take longer to ignite that a super-fine mist. In that case, dropping compression would reduce injection lag as the pressure difference between pop pressure and cylinder pressure will affect atomization and a lower cylinder pressure will result in a greater pressure differential. You could argue that with injector pop pressure 1/2 of spec, you imagine the tool would also be ineffective. How about if the atmosphere had a reduced oxygen content. That also might make the tool less useful. You might imagine that if you were on a different planet then a pulse adapter wouldn't be nearly as optimal for timing your 1/2 compression, 1/2 injector pop pressure VW diesel. What if you were running it on unicorn piss? Everyone knows that the BTU content of unicorn piss is much higher than no. 2 diesel but the viscosity is proportionately lower. How do you imagine that running on unicorn piss would affect the usefulness of a pulse adapter for timing your 1/2 compression, 1/2 pop pressure VW engine with worn out injection pump, while living on the planet Zuark with it's reduced oxygen atmosphere?
This is very entertaining! I think everyone loves to have a diesel pulse adapter but don't want to spring the $$$ for one just yet without fully understanding what it can and cannot do. Since you have not answered my question from before (copied below), can I assume it is not from the SnapOn diesel pulse adapter manual?Quote from: libbydiesel on February 10, 2014, 11:49:01 AMThe piezo adapter fires at the start of injection. The micro-expansion of the metal line is what charges the crystal pickup and it fires it's pulse when the line starts to relax which is at the actual start of injection which precisely coincides with needle lift. Yes, the piezo pickup DOES detect needle lift very accurately.......................Is this info from the SnapOn pulse adapter manual? It would be interesting to verify with an oscilloscope if the injection line pulse coincides with needle lift. Wouldn't be too difficult to set up on an engine with a needle lift injector. I think all TDI's have one. IIRC needle lift is on #3 cyl? Why did VW do that instead of on #1?
Quote from: 92EcoDiesel Jetta on February 11, 2014, 12:37:26 pmThis is very entertaining! I think everyone loves to have a diesel pulse adapter but don't want to spring the $$$ for one just yet without fully understanding what it can and cannot do. Since you have not answered my question from before (copied below), can I assume it is not from the SnapOn diesel pulse adapter manual?Quote from: libbydiesel on February 10, 2014, 11:49:01 AMThe piezo adapter fires at the start of injection. The micro-expansion of the metal line is what charges the crystal pickup and it fires it's pulse when the line starts to relax which is at the actual start of injection which precisely coincides with needle lift. Yes, the piezo pickup DOES detect needle lift very accurately.......................Is this info from the SnapOn pulse adapter manual? It would be interesting to verify with an oscilloscope if the injection line pulse coincides with needle lift. Wouldn't be too difficult to set up on an engine with a needle lift injector. I think all TDI's have one. IIRC needle lift is on #3 cyl? Why did VW do that instead of on #1?I read up on the function of the diesel pulse adapter before purchasing mine several years ago. I do not recall if the Snap-on manual specifically includes that info. At the risk of sounding redundant, if you doubt it, then I would welcome you to do your own research.I happen to have a TDI (actually three), a pulse adapter and an oscilloscope but am not inclined towards accommodating your test for two reasons. The first is that it is a waste of my time as I already did do my research on the function of the piezo pickup and the diesel pulse adapter and have no reason to doubt what I previously read. The second is that I have not read up on the function of the pintle lift sensor and how it produces it's signal and so hooking up the scope to it would not give me any helpful info. I did previously give my best best guess as to why they used #3. Which injector sends the signal to the ECU is irrelevant provided the program accommodates for which one is sending the signal. The metal lines all have to be the same length and maintaining that equal length with a tall #1 injector would be harder than doing so on the #3 which is closest to it's delivery valve.
But, how close is the book value to the typical sweet spot?
Quote from: monkey magic on February 12, 2014, 12:27:34 pmBut, how close is the book value to the typical sweet spot?In testing a wide variety of engines/pumps/injectors with the diesel pulse adapter, provided the dynamic advance is working properly, the 'sweet spot' is within 1/2° of 12°BTDC with my setup. That wide array of engines/pumps/injectors includes both fresh and well-worn VW IDI, VW TDI and Mercedes IDI engines with both fresh and well-worn pumps/injectors. On the VWs, I have also checked the plunger lift on several setups in order to find what the plunger lift measurement coincides to with a particular pump or set of injectors. The plunger lift setting can vary fairly significantly but the 'sweet spot' with the pulse adapter does not. I also recently used the pulse adapter to time a freshly rebuilt 1.6TD injection pump on a good condition engine with freshly rebuilt injectors set to spec opening pressure. Because I was sending the pump and injectors to a friend who does not have a pulse adapter, I tested the plunger lift with the dial indicator so he could repeat it. It came out to exactly 1.05mm which coincides conveniently with the VW spec. Several years ago I did the reverse on another friend's engine. We installed a freshly rebuilt injection pump with fresh injectors on his freshly rebuilt engine and then timed it using the dial indicator to 1.05mm. I then checked his timing using the pulse adapter and strobe and it was precisely 12°.