2008 MC 6.7 - Derate Issues

[Rogan]

160k miles on it.  G56, RaceMe Tuner, deleted.   Truck has newish Bosch injectors (OE), 5" exhaust, stock airbox, deleted egr/dpf, etc.

Recently, it's developed this issue of falling on it's face when hooked up to something (dump trailer, hay wagon, etc).  It does it empty, or not.

I have Alfa OBD, and hooked up, and I see the following:

 

No codes that I find.  When it falls on it's face, it dings and I get the 'see dealer now' message..  After about 5 secs, it picks up where it left off and drives normal..  then it may/may not do it again..

 

Fuel filter changed, newish in-tank pump..

 

crap, wrong section of forum..

 

[Mopar1973Man]

@Rogan got you covered.

[Mopar1973Man]

 

I'm assuming this is all the high pressure rail pressure being what the display says. I would consider the pop off valve as a replacement maybe its sticking in the open side?

[Rogan]

Yeah, I wished it would give me a code, or be a little more explanatory, but that's too much to ask for, I'm sure.  lol

Prolly one of those 'hidden, dealer only' codes.

 

[Rogan]

@AH64ID you got any thoughts on this?  Today, I was able to get it to do it climbing a 3%, 5th gear, 60mph, empty, no trailer..   "Ding!  See Dealer now"   5 secs later rpms drop and drop..   downshift, try to keep pushing up the hills as there's nowhere to pull over..    this goes on for about 20 secs, then it picks up like nothing happened.. 

 

[AH64ID]

How long has the current tune been in the truck?

[Rogan]

About 5 yrs-ish.  this issue has been about the last 5-6 months.

[AH64ID]

It sounds like an emissions/DPF derate. I would check all the disconnected plugs for corrosion or something else that might be causing a short. 

 

I see AlfaOBD shows low fuel pressure derate, but the dash indications aren't appropriate for that. 

Edited July 12, 2021 by AH64ID

[Mopar1973Man]

The pop off counter is what I'm looking at. Something told the ECM that rail pressure was too high and popped off 29 times to bring it back down. Then it acted like the valve stuck open long than needed which now the ECM records that fact the rail pressure is too low now for 43 times. 

 

Just think things out a bit...

 

If it was a derated for emmisions you should not see the high pressure pop off. Still in all the ECM should not derate so deep that the rail pressure drops out to trip the low pressure message. Like with the 2006 I've got when the waste gate solenoid had broke wire it derated but just enough that boost was only 20 to 25 PSI roughly. After fixing the wires it picked back up to normal power but never let the rail pressure drop complete out to trip errors.

 

Possibly is the tune making the high pressure pop off message?

[AH64ID]

High pressure pop off isn't all that uncommon and why FPRV delete's are not recommended. The injectors stop injecting much faster than the CP3 reacts to huge changes in load, i.e. WOT to 0% throttle. It also happens at much lower loads, but not as easily. Bottom line, the PRV gets used. Even shutting the truck down can cause spikes above 26K from 5K. 

 

Realistically anything with too high or too low of rail pressure that is causing derate's would set a CEL. Emissions related issues create the "See Dealer Now", nothing else that I am aware of. There should also be a CEL with it, but that CEL is likely disabled with the tune. The only other thing similar is the "Perform Service Now" for the CCV change. 

 

 

With the 2006 if you didn't get a CEL then it wasn't derated as 23 psi is enough for 100% fuel. The boost was limited by the wastegate as the solenoid defaults open without power applied, such as with a broken wire. Rail pressure isn't driven by boost levels, so it's not surprising you didn't see low rail pressure.