What sets codes for Turbo underboost and overboost?

[goldcoast]

MK7 2008 T350 140 RWD 2.4 TDCI LWB high Roof

What sets dtc codes for turbo overboost and underboost?
Could it be the fuel pump pressure control valve again, (last replaced 100,00km ago) or perhaps the common rail pressure relief valve?
Or is there another likely culprit?

HISTORY:
I had a code for faulty egr and power kept dropping until a re-start to reset the computer. So I had a faulty egr valve which I replaced. The error code for the egr fault is gone but now I have turbo under boost and overboost codes set.
While I was installing the replacement egr valve I installed an egr restrictor plate with a 6mm centre hole (to let some gas through to fool the computer). I do not think this is the fault. I think the fault is the fuel pump pressure control valve again, (last replaced 100,000km ago by Ford) or perhaps the common rail pressure relief valve?
Any constructive ideas?
Thanks
Will

[ake]

Electronic turbo actuator may be failing, or the joints on the rod may be partially seized

[Jim Archer]

Is the 'new' EGR valve working correctly?

Jim

[v8dave]

What sets dtc codes for turbo overboost and underboost?

What codes do you get ?

There are so many things that can go wrong, guessing where the fault is is pointless.

Try clean the air sensor by the filter and one just before the inlet manifold. It can't hurt.
When was the air filter last changed?

[knobby1]

What ake said....also.... the "overboost/underboost" codes are often the result of a poorly EGR, the codes will usually need to be "erased" or they'll probably stay in the system as "historic codes" until you do so.
The PCM is expecting to see certain air pressures and flows depending on rpm, load, turbo actuator position and throttle position etc, if these readings get disturbed by an EGR sticking open or closed messing with the expected air flows, the PCM has a hissyfit and will throw a fault code or seven..

EGR codes and the EML light will often clear themselves after a few start/stop cycles if the EGR has been fixed or replaced with a new or known good valve, but the code will stay in the system memory as a historic code.

As mentioned, the turbo actuator can also be the culprit but if faulty will normally have it's own fault code accompanied by the over/under codes too.

As v8dave said, give the MAF & MAP sensors in the inlet tract a good clean, the MAP sensor in particular gets covered in a thick oily spooge which can mess with their readings.

I carry a code reader in the van so I can plug it in every now and then to check and erase any pending or historic codes which pop up from time to time.....even a nicely running engine will get a glitch every now and then, valves and actuators stick, electronic gremlins happen and they'll throw up the odd code....perfect they ain't, but if looked after and maintained well they're pretty reliable.

Lord Knobrot

[goldcoast]

I will check the linkages and clean the sensors. The air filter is new. I cleaned the maf sensor in the intake when I changed the egregious valve. There was about a 1mm film of tar. The replacement egr was a clean used egr from a low km 40000km engine that had slipped a timing chain. I have cleared both the set and historic codes for turbo underboost and over boost several times. Each time I drive a mile or 2 and the codes reset again. The van runs well and gives about 800km 500 miles per tank. The only problem apart from the codes is a definite lack of top speed over 70mph it used to go past 70 easily. Now it struggles to go past 70mph.

[knobby1]

I will check the linkages and clean the sensors. The air filter is new. I cleaned the maf sensor in the intake when I changed the egregious valve. There was about a 1mm film of tar. The replacement egr was a clean used egr from a low km 40000km engine that had slipped a timing chain. I have cleared both the set and historic codes for turbo underboost and over boost several times. Each time I drive a mile or 2 and the codes reset again. The van runs well and gives about 800km 500 miles per tank. The only problem apart from the codes is a definite lack of top speed over 70mph it used to go past 70 easily. Now it struggles to go past 70mph.

Your "used" EGR may still be faulty or sticking...best to fit a new one it the health of a used one is not really known. You should get more than 800km per tank too...my van is the same machine as yours, I live in Sydney and I always see 950+....even with a moderate load in the back. With no load she'll always get 1000km....so better than 8L/100km (~35mpg).

Lord Knobrot