Car lacks boost above 3,200RPM (3.0 TDI - CAPA)

Vappy

Registered User
Hey there guys.

So my car seems to be lacking any boost or push above 3,200RPM when doing a full throttle pull in third gear. It struggles to redline. I can hold it there in third with my foot to the floor down the dual carriage way and it just cannot do it. Lower down it comes on early and strong, but then it just runs out of breath entirely. You can feel it hit this wall, and the turbo quitens a little.

I saw my Lambda sensor was 1.06 fully warmed up when idle, with a 78 Air/fuel value(?). I read that it should be at least half that for a normal sensor, so I bit the bullet and changed that. It now read 0.97 idle when fully warmed up, with no improvement at all in the top end - that's going back for a refund. MAF reads 17g/sec at idle and responds immediately to my input. At idle both MAP requested and actual are the same. I can try use the Torque app to log MAP values under load.

No warning lights, no DTCs, no limp mode, and the top air intake was fully cleaned out yesterday. The lower intake was basically spotless, so no blockage there to worry about either. In another thread I made about an EGT sensor being stuck at 222*c and having not done a regen in almost 50k, plus having soot in the muffler, it's possibly had the DPF gutted and then mapped out, so I don't imagine it's blocked. The small cat before the DPF looked free flowing when I took the lambda sensor out. The turbo actuator seems to be able to move the full distance no problem also.

I'm at a bit of a loss now if i'm honest. Any thoughts?

Thanks in advance
 

Vappy

Registered User
It does make boost, but it's at that high RPM where it just drops off on boost or power. Below 3,200 RPM it picks quick and early, although there are some days where it seems a little lacking in boost even in lower gears at lower RPM. However, this drop off at the top end is consistent and repeatable.

Should I measure the rail pressure vs RPM on a graph, or is there a better measurable reference?
 

Vappy

Registered User
I did a quick log, although Torque doesn't have a very good graph capability, so next time I can use my other app, which seemed to do better.


3rd gear, @1800RPM to redline it managed it without a hickup, but I was going down a long slip road onto the dual carriage way. 1600 bar peak from my eye @5000RPM
yYOsdfL.jpg


3rd gear, @ 1200RPM, flat road and it struggled to make it past 3,500RPM. No boost beyond that, really struggling to climb to 4000RPM. Also seemed to peak at 1600 bar.
Eedxltq.jpg


I will do much better data logging next time hopefully. My apologies for the terrible graphing.
 

Vappy

Registered User
Some progress: a P0299 fault code when doing a third gear pull. As usual it ran out of puff at 3,200RPM and slowly crawled towards 4,000RPM before the glow plug light came on and flashed at me. "Turbocharger - Low Boost". Yeah, no kidding.

The turbo actuator seems to have full travel capability and moves back and forward when rev'd. However, I have not taken the clips that hold the actuator arm off and checked the smoothness and distance of this travel. The clips that hold it on seem rather fiddly and tough to get off, but at least I have an idea of what area could be at fault. I don't hear air escaping during idle or normal driving conditions. There's no visible damage to either cold and hot side of turbo blades, as well as no wobble - had an old 1.9 PD TDI that had a wobbly turbo shaft, and that made a right racket coming off throttle. None of that here.
 

Vappy

Registered User
I took the actuator arm off and checked the movement of the vanes, and it's super, super easy to move. Like, a gentle breeze could make that thing move.
 

Vappy

Registered User
An update: car is booked in for a leak test next tuesday, but I have bought some chimney smoke pellets to see if i can do the same but for cheaper. I also measured my requested boost vs actual boost, and actual boost is definitely lower than requested. I've got sensor blanking nuts for my exhaust coming so I can do some DIY cleaning of my DPF; my logic behind this is that my DPF flow rate at idle is 140 mi/h, where as it appears it should be 330/340+. If this is the case, then this would explain a low boost situation at high end.

Will update when I have more information and progress :)

Specified boost value:
NLlSHcN.jpg


Actual boost value:
8BegJAs.jpg


P.S. I checked the MAF for any build up and it is very clean. The intake itself actually in pretty good condition regarding very little to no build up.
 

Vappy

Registered User
The issue now seems to have been resolved: Garage did a leak test of the entire intake system, intercooler and all, and it was solid. No leaks there. I then used some DIY chemicals and sprayed it into my DPF via the G448 sensor hole, let it soak for 2-3 hours, rinsed it through with water (without removing DPF), gave it a blast, and then did it a second time. I then went for a manual regen down the dual carriage way for a good 30-40 minutes, and while my DPF flow rate has not measurably improved, it now boosts to redline every time, it picks up slightly quicker, there is noticeably more torque, particularly when in high gears at high speed, say 40-70mph. The car overall goes really well and caught me off guard this morning when giving it a bit of push in third. It comes on about 1500RPM and really goes for it.

Future plans: gut the DPF, and then later in the year see if Bobby near London is available for a custom tune.

Have a good day everyone.

P.S.: I don't know how to edit the thread and put "(solved)" in it :/
 
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