We’ve been through the low-pressure side and the components on the high-pressure side.
We’ve talked about the injectors themselves and all the related components around them.
Now, the magical question is: What if actual and desired match all the way through?
What if you don’t have any fault codes? Because that is possible. What if I don’t have a fault code, but the customer says, “It just doesn’t have the power I like to have”?
What if you have a fault code, but it’s for the diesel particulate filter clogging up prematurely?
And again, I always like to begin with those two parameters: actual and desired. I’m going to map them all the way through. If they map all the way through, then I know there’s another system creating a problem.
So, with this image right here, we’re going back to the fundamentals.
We already know the fuel side is good. We know the high-pressure pump’s good. We know the rail’s good, the rail pressure sensor, and our injectors. We have very good confidence in this area.
So what’s left? Well, we briefly talked about it:
What if the mass airflow sensor is dirty?
What if there’s a tear in this boot?
What if the boot from the turbocharger to the intercooler is stuck open, and I want 30 psi of boost but can only hit 10 or 15 psi?
What if the intercooler is plugged up with dirt?
What if there’s something going on with the throttle?
Hopefully, you’ll have a fault code for some of these items, but that doesn’t always happen.
So, after you’ve validated that the fuel side is 100% good, you have to start chasing the other items. For example:
What could be going on with the EGR?
Is it affecting the system?
Is it clogged up and not allowing the proper amount of EGR to flow at idle?
Or is it stuck open, allowing EGR to be introduced at the wrong time?
Looking at this again—common rail, European diagnostics—just two PIDs.
I showed that to you with an OBD2 generic scan tool. And guess what? Even a couple of very inexpensive, hundred-dollar scan tools had those two parameters. You don’t have to spend a lot of money to access two critical PIDs.
Now, diagnosing beyond that takes a lot more effort. You need to validate the fuel system, make sure pressures are correct all the way through, and don’t forget to check fuel quality. That’s high on the list for most manufacturers.
But if everything checks out on the fuel side, you’ll be chasing other auxiliary components that could be causing the issue.
