Flash,

1) Friend and local repair shop proprietor used his Snap-On scan tool. Tool had a display by registers of realtime sensor outputs.

2) Have we misidentified the intake temp sensor? The sensor to which I was referring is located on the airbox near the MAF. Ah, now perhaps that's why the tool failed to show that sensor reading wandering off to some default value when disconnected. Thanks, Flash. I wasn't piloting or even co-piloting the scan tool. We didn't bother flushing through all the registers to recognize which entry was way off base.

3) Forgive me, but I'm disinclined to believe the tranny's at fault. These RPM oscillations didn't begin in isolation; they are a result of the current fueling/intake problem. The oscillations do not occur while shifting, they asrise when certain load characteristics are met (upon an upshift completion and settling into steady-state throttle input just above the most recent shift point). When settling into higher speeds, hence higher RPM's in a given gear, the throttle oscillations become less noticeable and are attenuated, nearly indistinguishable.

Can't believe I'm going to say this, but for testing purposes I miss the Audi/VW Tiptronic Auto-Manual shift feature to further exploit those loading characteristics. Such a tranny would allow one to remain in a lower gear at higher RPM's without fear of upshifting. The Jeep's automatic shift characteristics you've outlined are boilerplate for most passenger vehicle specs for normal driving conditions (forgoing lead-footedness and aggressive Sports Tuning).

Besides all that, being distracted by tranny side effects violates a basic engineering diagnostic tenet; avoid troubleshooting multiple defects. These RPM oscillations didn't occur in a vacuum, i.e., prior to fuel/air intake problems. For now, safer to assert the oscillations are a consequence of the fuel/air intake perturbation and not a tranny defect initiating throttle oscillations and low power.

My vehicle starts and idles normally; no bucking, nor missing, nor awful chamber music under the valvecover, nor hesitations--whatsoever. It simply accelerates slowly, spews more soot than normal whilst accelerating, lacks power and tops out at 70 MPH on flat Interstate. Even while in Park or Neutral (engine unloaded), goosing the gas is slow and sootie.

Faulty TURBO or leaky CAC/intercooler hoses?? If so, where or what DTC's would surface? Right now, there are none.

Feels like fuel is being starved or one can't get enough air to satisfy fuel input. Even in this form of 'limp mode' the vehicle's fuel efficiency didn't precipitously degrade when used on a long highway trip (320 miles return home after problem recognition).

I really do appreciate the varied inputs, they provide great opportunities to think through issues. But if rocker arms (GDE) were broken one might expect a 1st grade speed metal-thrash band raising hell under the hood, difficulty starting and maintaining steady vehicle speed replete with hesistations, misfirings and shuddering; of which there's none.

_________________
2004 VW Passat Wgn TDi -- BSM Delete, ALH Oil Pump
2005 VW Passat TDi -- BSM Delete, ALH Oil Pump
2006 Jeep Liberty CRD -- 100% Stock, At This Moment

Small sensor on the side of the air box is a barometric pressure sensor IIRC. Intake air temp sensor is built into the MAP sensor, which is located on top of the intake manifold, towards the back.

One issue that's sometimes known to occur is the EGR valve getting stuck partially open, so that on acceleration, turbo boost is leaked from the intake to the exhaust through the EGR system. This can cause soot on acceleration. Torn intercooler hose is another possibility, but you'd probably hear a hissing/whistling sound.

Sounds like it's an air issue if it's running rich enough to blow clouds of soot on acceleration.

I think what GDE was referring to is not complete failure, but worn roller bearings on the rockers. This reduces the distance the valves are pushed open.

Here are a couple videos demonstrating worn or seized rocker roller bearings:
https://www.youtube.com/watch?v=8ELktBoWozI
https://www.youtube.com/watch?v=Kt1Rd7RCIA4

Joe,

My gratitude to you, Flash, GDE and all other respondents for their thoughful inputs.

Are your suggesting the intake air temp sensor is integrated into the MAP or mounted into the same flange or physical assembly as the MAP?

Perhaps someone can illuminate me further: From what I've read the rockers have been designed to be the first line of failure to prevent the catastrophic damage often encountered with interference engines as a result of a bad injector, stickie valves, tappets or lifters. Never expected such wear to be digital in nature; i.e., normal functioning one moment to degraded/defective (factured/snapped/broken) the next.

Had to modify my thought process regarding engine/head (cam, followers, lifters, valve stems, etc.) wear since VW TDi's are dependent on the use of factory specified/approved (505.01, 506.01 & 507.00) synthetic motor oil. Use of anything else results in a slow death by sludge, warping of tappets and lifters, irregular cam lobe wear, or reduced oil flow/pressure due to the accumulation of contaminants blocking the oil pump pickup tube's screen. To the trained observer, the deleterious effects are gradual with decline performance and intermittent lose of oil pressure; to the untrained they miss the early signs and appear instaneously and catastrophically.

If the rockers on my Libby are bad I'd expect degraded fuel efficiency at a minimum and a loud screaming chatterbox, coughing, hesitating, and belching at the worst; you get the picture. I'm not ruling it out, but current operating conditions suggest otherwise.

_________________
2004 VW Passat Wgn TDi -- BSM Delete, ALH Oil Pump
2005 VW Passat TDi -- BSM Delete, ALH Oil Pump
2006 Jeep Liberty CRD -- 100% Stock, At This Moment

Joe pretty much covered it.
Just to reiterate...

Black exhaust smoke = too much fuel or not enough air
In most cases, its not enough air.
If it were a turbo problem or boost leak, you would be getting P0299 underboost code.
Given your problem with IAT, I suspect a bad MAP sensor.
Its more accurately identified as a TMAP because it also measure temperature.

As Joe mentioned, worn rocker arms, not fully opening the valves, can also stave the engine of air.
Yes, if worn they should make noise, but it can be hard to identify that noise above the normal diesel clatter.
(A stuck open EGR valve can also starve the engine of air)

In the event of piston to valve contact, the rocker arms are designed to break.
But the roller bearings can and do wear out.
Usually due to poor lubrication and soot contamination of the oil.
Good quality sythetic oil for deisel engines is reccomended. (i.e. Shell Rotella T6 5w-40)

RPM ocsillations...
Now that that you know the speeds that the torque converter is locked, any steady speed above 50mph should have zero RPM fluctuations. Any change in RPM will directly effect vehicle speed.
If you have cruise set at 55 mph (or whatever) and rpm is changing but vehicle speed is not, then I suspect a transmission problem.
Because RPM is measured by both the crank sensor and cam sensor its certainly possible either of those could be at fault. However, typical failure mode of a cam or crank sensor involves engine stalling and not wanting to restart.

None the less, it cant hurt to check transmission fluid.
Engine at idle, parking brake set, transmission in neutral.
Fluid level should be at, or above, the full hot mark. Even when cold.

And if you havent yet, check out IDparts.com for parts.

_________________
U.S. Army Retired

Worn rocker arms resulting in partially opening valves does cover the most all of the symptoms described. It just doesn't account for no precipitous drop in fuel efficiency. Perhaps I'm missing something.

Regarding a TMAP failure, should one expect something other than a P009A DTC?

_________________
2004 VW Passat Wgn TDi -- BSM Delete, ALH Oil Pump
2005 VW Passat TDi -- BSM Delete, ALH Oil Pump
2006 Jeep Liberty CRD -- 100% Stock, At This Moment

There are several possible codes related to MAP failure.
But given that the scan tool was reporting a abnormally high temperature it seems like the best place to start.

_________________
U.S. Army Retired

Source identified: Air Charge Inlet Hose (driver's side) has a 3in slit. Part is on order.

_________________
2004 VW Passat Wgn TDi -- BSM Delete, ALH Oil Pump
2005 VW Passat TDi -- BSM Delete, ALH Oil Pump
2006 Jeep Liberty CRD -- 100% Stock, At This Moment

I would get a Samco or mishimoto silicone boost hoses for better oil resistance.

I don't think the IAT is totally out there. I've seen close to 200 degrees before and at a 2.3:1 pressure ratio on the turbo that air is entering the cac at close to 300 degrees.


Sent from my iPhone using Tapatalk

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2006 CRD - GTB2056 turbo by Dieselguy86, Eco Trans Tune, Lift Pump, Week's, HDS Tstat, Racor Filter, ARP's, OME 790's+Top Plate, JBA 2.5", JBA UCA, Moab's+265/75R16, ARB Bull Bar, 4.10's, TrueTracs