Diagnostic Procedure with ICE and GDI
August 7, 2019
Diagnostic Procedure with ICE and GDI
So the internal combustion engine, to keep in mind, has never been a really clean design which is why all the technology is trying to get away from that and they started with hybrids and now they’re going to full electric vehicles. It’s never going to be 100% efficient of a power plant because every one of those piston rings, even if the engine wasn’t worn at all, every one of those piston rings have a ring end Gap, and I know we’re supposed to stagger them everything else but we never have 100% efficiency going on inside of a gasoline engine or a diesel engine as a result of those piston rings. So what the manufacturers have tried to do over the years, if they try to add subsystems to the vehicle, to try to clean up the fact that we’re not dealing with 100% efficient gasoline engine.
It’s not really a dedicated GDI presentation here but one thing I wanted to take a little side note cuz this is kind of dangerous you guys know that GDI now. Sprays the fuel directly inside the cylinder the GDI (Gasoline Direct Injection) gas filling pressures could be in the Thousand or higher PSI range.So a little piece of information that I wanted to throw out there is: you never wanted to open up the high side pressure of a GDI system without first relieving the available fuel pressure. So we can see on our graph, that are actual fuel rail pressure at the time happens to be over 1400 PSI. If I were to just take a couple of wrenches and start loosening up one of the fuel lines. That could, in fact, injure me quite severely. So the easiest ways to do this if you have a factory scan tool A lot of times you can bleed down the fuel pressure or you can simply just go ahead, remove the fuel pump relay out of the fuse box, crank the vehicle over, and allow that pressure to drop normally.
Stoichiometric Graph
You can see it on your scan tool once it gets to be about, you know, 30/50 PSI (somewhere around there). It’s safe to go ahead and work on the fuel system on those GDI vehicles. So the conventional perspective of the internal combustion engine has always been sensing and adjust. We have to go ahead and toggle that fuel mixture rich and lean, back and forth, over and over again to achieve the stoichiometric graph. So in a nutshell anytime we had too much fuel in the system we need to go ahead and immediately the oxygen sensors would tell the computer to go ahead and lean out the fuel mixture and it does this by shortening the injector pulse width time that it’s on. We need it to also be runnin’ lean at times because we were dealing with the three poisonous gases of HC, CO, and NOx. Well, in order to clean up HC & CO, we need to add elements of oxygen to those gases. If we had two elements of oxygen THC we turn it into H2O which is just water. If we had two elements of oxygen to CO we turn that into CO2 (carbon dioxide) which is harmless for us to breathe.
The Take-Away
So that’s the whole theory behind there but to clear up nocks we have to take away some of the heat of the engine. The easiest way to accomplish that is to go ahead and richen up that fuel mixture. So that the way how they are car manufacturers have developed all this to go back and forth is they start using a three-way catalytic converter. The ICE is nothing more than an air pump remember that when we’re doing our diagnostic procedures. So anything that restricts its ability to breathe will and can cause any type of drivability complaints. This could be a stumbling complain could be a rough running complaint, it could be a misfire complaint… anything along those lines. Including poor fuel economy, could even be a no-start. So keep that in mind when you’re trying to approach some of these diagnostic jobs that we’re just dealing with an air pump outside, underneath the hood.
[dn_related_product title=”Fixing What The Vehicles Immune System Can’t” description=”Using your scan tool and labscope to accurately decipher engine PIDS, mechanical issues, fuel issues and ignition issues. Instructor John Forro will show the students how to get the most out of your diagnostic process to get to the root of drivability issue without spending needless time performing many diagnostic tests.” link=”/shop/all-access-pass/lbt-355-fixing-what-the-vehicles-immune-system-cant/” image=”/wp-content/uploads/2019/08/WATCH-N-WIN_Fixing-What-The-Vehicle’s-Immune-System-Cant_480x320.jpg”]
