What a mess.
Ok, lots of things going on here. Just to make sure everything is straight, you're experiencing the following:
- Regens are too frequent.
- Low power during a driving regen
- Hesitation and bogging
When there is a problem with regens being too frequent or not completing (on trucks with just a dpf), there's a checksheet available to help. Things it mentions:
- Air filter ok?
- Any leaks in the turbo piping or intercooler?
- How's the mass airflow sensor? Compare it with a new one.
- Is the turbo barfing oil into the intake air stream?
- Is the engine overfilled with oil? *
- Is the intake throttle valve in good shape?*
- Does the VNT controller work properly?
- Is the exhaust brake set correctly?
- Inspect the hoses at the differential pressure sensor for cracks or clogging.
- Inspect the pre and post DPF temp sensors for proper resistance, and check the harness for breaks.*
- Is the exhaust brake adjusted correctly?
The mass airflow sensor is rarely the problem, but it's job is absolutely crucial for everything to work correctly. They're also sort of hard to diagnose, so sticking a new one on for testing purposes is pretty common.
In the US, we're modifying all of the Intake Throttle Valves on 08-10 trucks by drilling three 8mm holes 6.5mm from the bottom edge of the plate. One in the center, the other two 20 degrees apart on either side of the center one. Kind of like the bottom three points of a peace sign. If this thing sticks shut, it will cause havoc. The reason for the holes is to cause a controlled leak to help the little servo thing open the valve if it gets stuck. It should be wide open during a manual regen. I don't actually know what it does during a driving regen, but I imagine the same thing. Its purpose is to create an area of low pressure in the intake to help coax the lower pressure EGR gasses into the intake.
The DPF temp sensors are generally reliable, but on the conventional trucks down here the harness often breaks or degrades right behind the connector. We 'load test' the circuit by disconnecting the ecu connector, attaching a headlight on either leg of the connector down at the dpf, and forcing 12v through both legs. If the headlight lights, the harness is good. If anything else happens, it ain't.
Generally, if the thing does a manual regen ok, it'll do a driving regen well too, with a few exceptions. The exhaust brake should not be left on all the time. If you need it, pull the lever down. When you're done, push it back up. It interrupts everything when you are driving. On the other hand, it stays on all the time during a manual regen.
The exhaust brake setting changes as the injectors age. If they put injectors in it and didn't also readjust the exhaust brake again, it's probably set too high. It's essentially like shoving a banana in your tailpipe. It purposely loads up the engine to heat up the exhaust gas.
You said they were fiddling with the settings. I'd have the tendency to take a dx report and save it, then set everything back to default and see if some setting caused this problem.
Will it perform a manual regen properly?
I'm gonna pretend this thing is sitting in front of me right now, and go through some troubleshooting steps.
Start engine, warm up to 180 degrees.
Set idle to 980 rpm.
Monitor injection quantity with the exhaust brake on and off. Difference should be between 12-14 mm3. Adjust if off.
Turn engine off, turn ignition back on. Go to engine customization. Take a note of 'PM amount' and before and after dpf temps. Set 'PM amount' to 2.5. Reset dpf temp history.
Start engine. DPR graph on dash should jump from 2 bars to three, meaning that I can do a manual regen.
Set up data monitor to look at engine rpm, coolant temp, injection quantity, dpf pre and post temps, differential pressure across dpf. Hell, lets look and see if it's commanding the exhaust brake on, VNT target and actual, ITV target and actual, EGR target and actual, scv target and actual, Common rail pressure target and actual. VNT, EGR, ITV, SCV, and rail pressure actual values should all closely match their targets. These can be graphed in pairs using Microsoft Excel to visually see any discrepancies.
The pre dpf temp sensor should steadily climb up to around 1030F, maybe up to 1100. The post sensor will lag behind, but eventually make it up to 950-1000F (if it's relatively clean). If it's slammed full of soot, be careful. Around 1450F that thing will melt.
Push the regen button. See what happens. Save the data.
Go to system protection data. Note DPF outlet temp.
Turn off truck. Turn on ignition.
Go back into engine customization. Reset dpf temps again, set 'PM amount' back to 2.5. Set up another graph, same things (since we're trying to solve two things at once). Start the engine. Prop the computer up on the seat (or hand it to a passenger) and start driving. It will almost immediately start an auto regen. Hopefully you're graphing whatever parameters are actually causing the problem. IN particular, I'd be looking at mass airflow volume; scv, VNT, ITV, Common rail targets and actual values; brake light switch, Stop light switch, exhaust brake switch, and injection quantity.
Some of that stuff, like the brake light switch, doesn't make sense unless you know that the ecu will limit injection quantity if the brake is applied. Sometimes the switch gets flakey, and the ecu is sent a signal that the brakes are applied when they're not. Goodbye horsepower. A pretty common problem, actually.
We don't even have this model in the US, so all of this is based on the 338, which has the same horsepower engine. I imagine it's all very similar.
I've never seen an EGR valve hang open and cause a performance problem. Usually they either clog and don't move at all, or there's some other undefined electrical problem. I doubt very seriously that it's the culprit, but if they're gonna replace it under warranty, let 'em.
Oh, adjust your valves, too. They should have been adjusted four times by now. Have they?
