Momentary hesitation on boost

[Aveton Gifford]

Thats it, only mine looks like this:

[te2800]

I have a used tcv here 20 pounds posted works a treat

[foggyjames]

Sorry, missed your post! Bought a new one (albeit with the VW connector) today...£34 posted.

cheers

James

[66split]

Bizarrely, my car has just started with the same symptoms

[66split]

Did you ever get to the bottom of this problem? Was it the turbo control valve? mine is still doing the same thing...

[foggyjames]

I've been meaning to update this. Not yet, but it's not the TCV, or the VNT mechanism on the turbo (well...the actuator moves under vacuum, anyway!). Vacuum level was good last time I looked. It 'feels' like a VNT / boost control problem. Is yours spoiling late in lower gears (i.e. above 1500rpm), too? My flat-spot and late spoiling appeared at the same time.

At the moment, I'm drawing a blank, unless anyone else has any inspiration...?

I'm getting to the point of doing a VIDA datalog, as well as monitoring pump vacuum while it happens, to see if it's dipping.

I haven't ruled out something else, like a fuelling problem.

Mine is also not starting well. Glow plugs and all five injectors are new. Suspect high pressure pump or compression.

cheers

James

[66split]

Thanks for getting back James. Mine seems exactly like yours symptoms wise....in third and fourth when giving it some beans there's a definite flat spot in the boost. Also, the car normally starts to boost about 1600rpm but I've noticed that has started to fluctuate and can be as high as 2600. The car's recently had new injectors and I've just changed the fuel filter thinking maybe that was the culprit. I'm thinking MAF sensor maybe but someone suggested sticking vanes on the turbo also. Sorry to be daft James but what do you mean by 'spoiling'?

[foggyjames]

Sorry...that was a phone auto-correct...should have been spooling.

I am not ruling out the new (Bosch factory re-con) injectors as being the source. This started around the time I fitted them, and I'm not convinced they're 'right' in general. Of course that could very easily be a red herring. The acid test will be to monitor boost pressure (which I can do in VIDA). If it's not actually changing the boost pressure during that dip, that points to mis-fuelling.

My spool-up behaviour is greatly increased lag, most notable in lower gears. It's more normal in higher gears, where it all happens more slowly anyway. It's like the VNT is struggling to react quickly. One possibility is that while off-demand vacuum levels are correct (measured at idle, with a Mityvac), the pump is struggling / servo is leaking / pixies are stealing the vacuum when demand is higher. I guess attaching a gauge to the pump and going for a drive would tell all.

MAF sensor is also very much an option.

I checked my VNT vanes at the weekend - at least externally, all is present and correct (could be broken vane (or vanes), I suppose).

cheers

James

[foggyjames]

Little update. I haven't really solved this, but I'm heading in the right direction...I think!

The car started going into limp-home (ECM-6805 DTC) if taken above 2300rpm or so a few weeks ago. It started off happening once in a while, but quickly developed (within a couple of days) to happening every time I go past 2300rpm for any length of time (i.e. a full-throttle pull through a 2nd gear (or above), or cruising above 80mph). It drives as it did before below 2300rpm...although it might be slightly down on boost compared with before, as the 'dip' after spool-up seems a little less pronounced. Boost control has not been right for several months (and around 30k miles), but this is a new development.

Normally I'd be looking for boost leaks, or VNT faults (both with numerous possible causes), but the usual suspects are all fine. Specifically, my engine mounts hold vacuum, the pump makes vacuum, the TCV is new, and I have just fitted a new intercooler. It's still making boost leak noises, and so far I've checked in detail everything except the pipe leaving the turbo (which passed a cursory inspection, but needs removing and checking in detail - but - there's no sign of oil egress!). There also seems to be a very slight oily leak from my 'inlet manifold cover'. I had this cover off last year, and re-sealed it with Volvo's anaerobic sealant...but presumably not well enough! That could be the source of the boost leak. If I still can't find evidence of a problem, I'll get a smoke test done.

My intake pipe (i.e. directly before the turbo) does seem quite soft, so I will most likely order a new one.

I fitted a replacement (used) vacuum pump today, and that seems to have improved the delayed spool-up and flat spot issues...maybe...I'll report back on that. It doesn't seem to have made it any less breathless from a cold start.

It has also been making a strange noise around 2000rpm (±200rpm?)...like a sort of chirping rattle. I made a recording of the sound a week or two ago. It picked up the chirping aspect well, but there's a lower frequency element to it which you can't really hear on the recording. You can also hear the "boost leak" sound! Does this sound in any way familiar...? It sounds a bit like a spring oscillating. Oscillating VNT actuator, or EGR valve, maybe?
https://www.youtube.com/watch?v=9JPssQK1ogs

Order of events:
1) Delayed spool / flat spot around 2000rpm (August 2013?)
2) Rattling / chirping noise around 2000rpm (Jan/Feb 2014?)
3) Limp home mode above 2300rpm (April 2014)

Questions:
1) Has anyone tried to pump a vacuum into their brake servo? I can't get beyond 15inhg, but it doesn't creep down from there.
2) Does a TCV / VNT solenoid leak vacuum (i.e. if you measure vacuum at the hose at the pump, does it drop)? I can pump 25inhg into this hose, but it drops, and the TCV is the source of the leak. There is an open (filtered) port on it...! It's also nearly new.

Any other thoughts? That rattle / chirping sound has to be a clue!

cheers

James

[reesky]

Mine developed exactly the same symptoms after doing the tcv. I cured it last week bg fittings recon turbo (100£ ebay, its a long story, plus 150£ fitting). The screeching was the turbo shaft hitting the housing.