[MedicWrencher]

I have a 2014 6.7L F450 ambulance that’s having recurring derate issues. The truck has been through the ringer of dealerships and mechanics to no avail.

Issues nearly always happen when the engine is cold (heated station so about 60*F). As soon as you leave the station and accelerate it gets about 50’ down the road and goes into derate mode. Sometimes it will throw codes and sometimes it wont. If it doesn’t go into derate in that beginning timeframe it will run for the rest of the call without issue. When it does derate the issue is resolved by shutting off and restarting the engine. It will not derate after the restart.

Codes found after derate are as follows:
P132B, P0234, P229E, P207F, P20EE, P1247

Most prominent to show are P132B, P0234 and P1247

I was able to get several derate episodes while on a scan tool. A few recurrent things I’m seeing right before derate is the exhaust pressure will jump from a PSI in the teens to 89 PSI, MAP jumps from teens to mid 50’s PSI and MAF from about 5 lb/m to 44 lb/m.

Would love to get this $250k ambulance back to being more useful than a boat anchor! Thanks in advance for your knowledge and help.

 

[matthewd11]

It definitely sounds like the VGT on the turbo is hanging up from carbon causing erratic boost pressure. It’s also worth checking to make sure the MAP sensor isn’t plugged with carbon.

you also have an issue with the NoX sensor and/ or an issue with the DEF system.

I would also make sure the ECM is flashed with the latest calibration using the IDS.

90% of what I work on are ambulances.

 

[MedicWrencher]

@matthewd11 Is there a reliable way to clean the turbo or is it best to just replace it? Is there anything besides MAP sensor that I should be checking prior to chasing the turbo? Would a faulty or dirty MAP sensor cause the EBP and MAF to also show high readings?

This has been an issue with this unit since 2018 and they essentially just parked it with very little use since because of the reliability issues. I started with this service about a year ago and have since taken on starting a maintenance dept. after there being essentially nothing done in house.

 

[matthewd11]

as far as the map goes, not likely. If it reads 14.7 or so KOEO (assuming sea level elevation) it’s probably not clogged. Just replace the turbo you cannot clean it like you can a 6.0L.

the P207F, P229E and P20EE could still possibly make it go into derate also depending on what’s actually wrong.

 

[MedicWrencher]

If the VGT is hung up would it always have issues with overboost/low boost? There are plenty of times where it doesn’t go into derate and all sensors show good values and the truck operates as it should. Also when it does derate, simply shutting off and restarting the engine resets everything and the truck functions normally.

 

[matthewd11]

It’s not a matter of being permanently stuck. It sticks intermittently (when you see those very high back pressure and boost numbers).

 

[MedicWrencher]

Wanted to give an update. Replaced the turbo and truck is functioning much better! Opened up the old turbo and found the VGT to be heavily corroded and seized. Had to use an air chisel to get it to move. Haven’t had any issues with it since. Thanks for the help and advice!

 

[matthewd11]

Yup that will do it. Not sure why dealers couldn’t figure that out…