- I'm Nick Pregnitz and on the DYNO here
I have C4500 series truck.
This is an LMM, and we're going to be troubleshooting
a low fuel-rail pressure code.
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We get a lot of calls into the shop here troubleshooting
P0087 codes on LBZ/LMM trucks,
and the problem with these codes is
that they show up on 120 - 160,000 mile trucks
that are run hard, under hot conditions, loaded,
and it's really hard to duplicate those
in a diagnostic scenario.
So, when we get the trucks we can't get it to duplicate
the problem, so we can't troubleshoot it.
Well, we have a DYNO, we have an awesome ventilation system.
So, those days are gone.
Now we actually duplicate those symptoms
on site with the truck here.
And what that means is running the truck under
a very heavy load for a long period of time,
get the engine coolant and temperature hot,
get the fuel system hot, run the air conditioning,
really simulate the same conditions
that driver's seeing on the road.
From there we're gonna see how hard
the fuel system's working.
So we're running the truck at 300-320 horsepower,
and we're gonna see how hard that CP3 is working to keep up.
Now what happens is the fuel gets hot
and everything else gets hot.
The injectors start returning more fuel,
the fuel system starts to not be able to keep up.
And what were gonna see in the cab,
is that the duty cycle on the fuel pressure regulator,
is gonna keep creeping up as I stay on the throttle.
And eventually, it's gonna creep up to the point
where it can't keep up anymore.
And then the actual fuel rail pressure is
gonna deviate from the desired, and then P0087.
Okay, so lets take you in the cab, show you how it works.
(whirling noise)
Okay, so were in the cab, and we have the truck running.
And what I have is Owen has pulled up a data stream for us
so we can see all the important things
that are going on here.
Okay, and I'm just gonna run through them
so you know what they are.
APP is throttle position, okay, so zero.
As I rev the truck you can see it change.
RPM, engine coolant temperature, at 167 right now.
We're gonna see it creep up past 210.
Fuel temperature, as that goes up,
our problem should get worse.
Here's our actual rail pressure,
and our desired rail pressure.
And P0087 code means we have deviation
on the actual rail pressure from the desired rail pressure.
And we will be able to use these numbers to confirm that.
This 1400 number here is gonna be our
fuel pressure regulator duty cycle.
That's gonna go between 1500 and 400,
which is the factory minimum.
Now, as that thing comes under 850,
that's my indication that the regulator is working very hard
to keep up with the fuel system.
As it trends towards 400 and bottoms out at 400,
that's when we're gonna lose fuel pressure,
and we're gonna see that deviation.
You can see this next one here is our fuel volume.
That's our total volume delivered by the fuel system.
In gear, tow haul on.
And what I'm doing is a diagnostic test
where I run the truck at a constant speed under heavy load.
And that speed is 50 miles an hour.
I'm just gonna let it get up, and gear and get moving.
And I want you to watch engine cooling temperature creep up,
fuel temperature creep up, and watch this number,
which is how hard the fuel pressure regulator is working,
start to trend downward.
Now you see, we started over 840,
and now we're down in the 780s.
You can hear that engine fan kick on at 210.
Oh yeah, she's roaring now.
And when I see that thing going towards 750,
I know this fuel system's working really hard.
What I can say is that this truck
with 180,000 thousand miles on it
is just straight up running out of fuel system.
We're returning a lot of fuel.
Okay, you see things dropping?
And this is stuff you'd never seen on the road
or just taking the truck out and test driving it.
But now look, we're coming under 26000 PSI.
The truck's unable to keep up with fuel pressure command.
If I stay in much longer,
we're gonna start to see that P0078 code show up.
I don't want to beat the truck any harder then I need too.
But we've confirmed that it's unable to keep up
with the fuel command.
I'm just gonna let it cool down
because everything is very hot.
Okay, so we've gone through our test.
We've proven that the fuel system
is unable to keep up with command,
and we've proven that it takes a long time to get there,
but we've shown that.
Okay, so now it makes sense to talk to the customer
about taking the injectors out
and going through the fuel system.
What I'm going to do is just keep the oil pressure up,
keep the engine RPM over 1250,
so we keep things circulating
and letting the truck cool down.
You know, I really hate to beat things this hard,
but sometimes it's really important to validate a theory.
And, you know, we've done that.
So, hope you enjoyed this episode.
I know I have. We'll see you next time.
I'm Nick, thanks for watching.
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