Momentary hesitation on boost

[foggyjames]

That has been in the back of my mind, especially as in the past week or two it has been making a sort of 'fizzing' sound when spooling...something I've only heard previously about 30 seconds before the first turbo failed (at 217k). The 'new' turbo had 120k on it, and I've put a further 85k on it since then, so I'm due another failure. The last one did about a mile between the onset of funny noises and total destruction, so I think I've done alright!

I'll get working on either a good used replacement, or a new one, ready to fit ASAP. An unscheduled turbo replacement is not high on my life wish list, so I'd rather fit a replacement ASAP, even if it's not a confirmed diagnosis.

cheers

James

[reesky]

I now have two turbos that are ripe for reconditioning. 50£ each plus postage. Drop me a line if interested �� I'll be putting them in the for sale section once I get access to a proper computer

[foggyjames]

Sorry about the delay - I've been away for a week. I'm potentially interested. Had they actually failed, or are they just untested? If they had failed, what was the failure mode, and is there any evidence of damage to wheels and housings?

My limp-home situation has gone away (after fitting the vacuum pump) - I figure the ECM needed time to recalibrate now it has the right amount of vacuum to play with! It's still flat-spotting and making strange noises, so all is not well. I can wind it out to redline at WOT now, but it's making some unhappy noises (wheezing and whining...either a boost leak, or an impending turbo failure, plus the rattling previously mentioned), so it needs some further TLC ASAP. I'll keep plugging away at it!

cheers

James

[foggyjames]

Update. I fitted a new (old) turbo at the weekend, which removed the wheezing, but not the 'chirping' noise in the video. However, the new unit does chirp/flutter on overrun (i.e. when you first lift off - as if the CBV on a petrol car was blocked or disconnected). I suspect that's only changed because the new unit is making the correct boost pressure!

The 6805 code is back, too. I suspect the turbo inlet hose is collapsing...as it's about the only thing left to check or change, and does feel a bit soft.

The two things I can think it might be - an EGR problem, and the inlet hose choking the turbo making a strange sound. Any thoughts, gang?

cheers

James

[mikealder]

Originally Posted by foggyjames

The 6805 code is back, too. I suspect the turbo inlet hose is collapsing...as it's about the only thing left to check or change, and does feel a bit soft.

You mean the hose at the back of the engine just before it goes in to the turbo? If yes double check the locator tabs on the metal pipe that goes from the front of the engine across the gearbox to the rubber 90 degree hose, if these have broken off it lets the rubber pipe flex too much leading to early failure/ weak collapsing pipe. Also when purchasing the new pipe ask for one without the sensor fitted as it's much cheaper then simply swap your old sensor in to the new pipe - Mike

[foggyjames]

Yes, exactly.

The tabs on the aluminium pipe have indeed failed on mine, and it's interesting that you mention that this can put more strain on the rubber sections - that hadn't occurred to me. I have the added complication of having swapped in an M66, so space is a little tight! I am tempted to look at a silicone alternative.

Thoughts much appreciated!

cheers

James

[foggyjames]

I pulled the air filter as a test earlier (should prevent the intake pipe from collapsing in on itself by reducing the vacuum significantly). I was in a bit of a rush, so didn't do a full-power test for a 6805 code, but it certainly didn't make the fluttering go away. I think I'll try my spare EGR valve, and see if that has any effect. Rapidly running out of things that could influence it...!

My other line of enquiry is to hook VIDA up to it, and look at the realtime read-outs while it's doing it. Just need to find some time when I have an assistant available to read the numbers!

cheers

James

[foggyjames]

A couple of potential breakthroughs...

Firstly, the funny noise. I took the FWD guru himself, Tim Williams, out for a spin in the car on Sunday, and he thought it sounded like a gas leak from the exhaust manifold area. Initially, I was somewhat unconvinced, although I would, of course, check it out.

Then I found this earlier, more by luck that good judgement. Doesn't it sound familiar?!
https://www.youtube.com/watch?v=V9_58jy4i2U
...and he says in the comments that it was the exhaust manifold. Two hints in two days? That's worth a look. I happen to have a spare manifold, which is nice.

Secondly, I have a lead, of sorts, on the hesitation. This is a screen grab from VIDA, capturing RPM, manifold pressure and VNT regulator demand during a 4th gear pull from 1500rpm to around 3000rpm (M66). This result was repeatable, but this was the best grab I got:


Plenty of 'what the...?' in there!



To re-cap...
1) The turbo is doing pretty much exactly what I would expect. Boost is rock-solid at the requested level, but...
2) ...the TCV is cutting boost dramatically around 2000-2500rpm (see "?!?!"). I monitored every parameter I could think of, and nothing appeared to be triggering it.
3) Three separate flat-spots shown on the graph ("?!?!?!"). One seems to be TCV triggered ("?!"), which I think is the dip I've been reporting.

In other words, at least some of the symptoms I've been getting have been requested by the ECU. Question is...why? Is the car possibly detecting some sort of misfire (via the crank sensor?) and pulling boost? Is it something more left-field, like falsely triggering traction or stability control? Anything else anyone can think of?

When I get chance, I'm going to do more datalogging, including monitoring the intake pipe situation with and without air filter, and getting someone to read the data live (rather than me keep pulling over!).

cheers

James

[petey]

Firstly, as a newbie, I am honour-bound to thank the many, many posts on this forum, it's an excellent source, helpful etc.

Secondly, with specific reference the Vida posts, I finally get my fault codes etc. and that didn't happen without this site either. At least my years of testing cars wasn't in vain and despite what the main dealer says, I AM able to feel a vibration at idle (Engine Pad Solenoid Control failed)


OK, platitudes over, I have a question:- what does the vacuum pump service? I get the need for evacuating the brake servo, and at a push, I can see the need to change mode on engine mounts (I used to design twin mode engine mounts many years ago...). I am confused as to its function regarding the turbo control; is the wastegate / bleed / other nefarious feature controlled by vacuum rather than the copious amount of pressure created by the turbo?


Regarding the graphs presented, I can't say I've understood the subtlety of them fully, but isn't emissions one of the main guiding controls regarding engine output? Is the output from the Hego / Lamda / Exhaust gassy measurey sensor available? Would that add anything?

And as an aside, the stepper motor on the end of the head with the control rod designed to break off:- does that perform any specific function or is it just to stop the engine drinking its own oil in the event of high revs?



Pete
(Collection of my children's fingerprints pretending to be a 06 D5 V70. In Blue.)

[foggyjames]

Hi Pete,

Sorry - totally missed your reply there. Your Euro 4 car uses an electric motor to control the VNT vanes on the turbo (in place of a wastegate). On my slightly older Euro 3 car, the VNT vanes are controlled by a mechanical vacuum actuator (looks like a pressure-actuated wastegate actuator, but isn't...). My Euro 3 car doesn't have any kind of sensors in the exhaust, unlike yours. Finally, I suspect the stepper motor you're referring to is for the swirl flaps. Again, I don't have those.

Latest news on my car...
# "New" used eBay turbo failed. Replaced with a proper Turbo Technics re-con. No effect (other than I seem to have lost some spool-up...could be VNT actuator adjustment...?)
# Replaced the turbo inlet hose. No effect.
# Replaced the vacuum pump (again), as the old one wasn't managing more than about 15inHg vacuum. Back up to 20-25, but no effect on the 6805 code, or spool-up.
# Replaced the exhaust manifold gasket, but no breakthrough on the fluttering noise.

So...I suspect that the fluttering noise, delayed spool, flat-spot and 6805 code are all linked. I now believe the latter to be caused by unstable boost pressure - initially too high (hence the flat-spot), then too low.

As far as I'm aware, a 6805 code can be caused by two things: poor VNT control, or a boost leak.

As far as I'm aware, the VNT control is A1. The pump is making 20-25inHg, the solenoid is new (although it made no difference), the engine pads, pad solenoid and all pipework hold vacuum, and the VNT actuator is new. Possible (possible!) slight leak in the servo, but the system seems to maintain at least 20inHg now. Correct me if I'm wrong, but that's all there is!

Boost leak...well that is possible, and could explain the fluttering noise (i.e. on the intake / pressure side, not the exhaust side). Having said that, there's no evidence of oily charge-air egress. I guess a smoke test will answer that.

Other, more left-field possibilities...
# M66 swap has upset the ECM (happens with some T5s, but I think it's unlikely, as it was fine for months)
# Compression has dropped so low (at 310k miles) that spool-up from cold is very slow, and it isn't flowing the right amount of air. Seems unlikely...but I can test it easily enough.
# Some sort of EGR leakage issue?
# Partial sensor (AMM? MAP?) failure?

Proposed actions now:
# Try blanking the EGR...see if it'll boost before limping-home, and if so, does the flutter vanish?
# Compression test
# Stick it on a dyno and stick my head in the engine bay under load to locate the flutter.

I'm starting to run out of inspiration. I think I've address all the obvious / usual causes. Anyone have any ideas they think I've missed?!

cheers

James