Hi All

 

I've just signed up to the Briskoda forum (see my 'Hello' post), and am hoping someone out there might have an idea what's causing a very odd fault with my engine:

 

It starts and runs perfectly in every respect, as it always has done, but as the revs climb above 2,000 rpm it suddenly surges dramatically, as though the turbo is totally un-regulated. Strangely, it continues surging a moment or two after I lift my foot off the throttle.

 

Recent history:

 

* Having no specialist diagnostic equipment, I took it to the VW main dealer I normally buy parts from. They reckoned to have spent half a day trying to diagnose it, eventually admitting they didn't know what the problem was, but that the most likely candidate was the turbo. They quoted £1,700 to supply and fit a new one.

 

* This made sense to me (I thought perhaps the turbo wastegate wasn't opening and closing as it should), so I bought a standard, original equipment Garrett turbo from Darkside Developments (£700-ish), and fitted it myself (with new catalyst). Result: surprisingly, the new turbo made slightly more of a 'zzzzip' sound than the old one (which had done nearly 100K), but it ran fine. No change in the symptoms, though.

 

* I then reasoned that the vacuum solenoid/ EGR valve control on the bulkhead might be faulty and not controlling the turbo actuator properly (it had been making weird noises for a while), so I got one of those from DD, and fitted it (£300-ish). Result: no change.

 

* I was considering replacing the vacuum hoses, mass air flow sensor and boost sensor, when I thought I ought to watch the cashflow and seek further advice first. My daughter, who has a 2007 Golf with identical mechanicals, had recently had good advice from a local mechanic while I was away, so I tried him.

 

* He said there were fault codes, but they didn't help with diagnosis (sorry - can't remember what the codes were). He was adamant the vacuum pipes weren't leaking (he said that would lead to too little power, not too much), that the EGR valve was working fine, and also that the throttle pedal sensors/ switches were OK. Over a three day period he looked at the car several times and ultimately admitted defeat. However, we agreed he should replace the boost sensor (because it was cheap and easy), and also the wiring harness that sits under the rocker cover (even thought the symptoms didn't really fit, these are known to be problematic). Result: no change.

 

And that's where I am at the moment. Best ideas just now: a) both the old and new turbos have faulty wastegates or actuators (unlikely?), b) the vacuum pipes are old enough to be losing their stiffness, and are collapsing, expanding or kinking under vacuum pressure, or c) the electronic control module itself is faulty (my wife is convinced this is the issue, but she's a horse rider, so she'd better not be right....!)

 

I would really appreciate people's thoughts on this!

 

Many thanks for reading this rather long post!

 

KimT

 

PS: Can't be connected, but the only other recent change is that I've replaced the tandem fuel pump to address the issue of engine oil getting into the fuel. It made no difference to the running...just cost me another £300.....

 

 

Collapsing pipes have given me the opposite symptoms (loss of boost) but I can imagine one scenario where it could do what you describe, to be sure I would really need to see a schematic of the vacuum lines and actuators for the variable vane turbo.

 

With that it would be possible to narrow it down to one single pipe that would be suspect, they are all quite inaccessible I imagine.

You say it keeps surging *after* you take your foot off the throttle?

 

I'm no expert, but that tells me the engine is continuing to get fuel when it shouldn't have any... I don't know how modern electronics and wizardry decides under what circumstances to inject fuel into the combustion chambers, but you'd think lifting your foot off the throttle would stop that!

 

I'd be looking to rule out issues with the fuel delivery, and bear in mind that it's possible for a diesel engine to run on its own engine oil as well... Is there any sign of excess oil in the intake? Worst case, could oil be getting into the combustion chambers via bad piston rings or a hole in the piston? Keep an eye on the oil level.

Have you flushed all the contaminated fuel out of the car? If you are injecting engine oil with diesel I can imagine there being some run-on

Much appreciate the responses. Thanks guys!

 

JR: Might take me a while to produce an accurate diagram. The only 'official' one I've seen didn't look quite like the arrangement on my car. Most of the pipes are pretty easy to get to, but a couple disappear into dark recesses and it's not immediately obvious where they go. Might get chance to sort this next weekend, after I've serviced my daughter's Golf, when I'll have the gear out for jacking up the Octy if necessary.

 

Chrisund123: Yes, you would expect lifting your foot to stop delivery of fuel, unless the pedal is not returning to rest position quickly (which it is), or if the pedal sensors are sending the wrong signals about pedal position (which they're not, at least according to the mechanic I most recently went to). I agree over-delivery of fuel would fit the symptoms, but by all accounts the injectors are pretty reliable units and the section of wiring loom most likely to have degraded (under the rocker cover) has been replaced. The ECM itself could be at fault, of course, as could the injectors, but I'm reluctant to go down either (expensive) route without more evidence that fits the symptoms.

 

There's no sign of oil anywhere where it shouldn't be and the engine uses only a small amount of oil between services (hopefully now even less since I replaced the tandem fuel pump, which I think was contaminating the diesel returning to the tank). It runs virtually smoke-free and has loads of power, so I'm sure nothing's happened to cause loss of compression.

 

SuperbTWM: I didn't flush the system because the amount of contamination by engine oil can only have been small, given that only a little oil was being used between services. The only reason I knew it was happening was because the diesel filter and vessel were coated in a black deposit. There was no smoke at all from the exhaust (it used to smoke fairly readily when I bought it, at 62K, but it stopped soon after I got it and has been fine to date, having just turned 100K - perhaps it prefers my maintenance regime to the Skoda dealers the previous owner took it to...?).

May or may not be related, but I just stumbled across this regarding the tandem pump:

 

"

As i recall, there was a thread describing one failure mode of the TANDEM pump being that it leaked down into the  CYLINDER HEAD (YIKES) AND THUS SOMEHOW INTO THE COMBUSTION CHAMBER! Is this possible? anyway resulting in a hydrostatic lockdown causing all sorts of problems! if anybody has time to research this case I would really like to hear more about it. As in "can the T. Pump be diagnosed before this could happen?" Nick in BC. I think the tech working on this cas was in Texas, that's all I remember.

I believe this is only a problem on the newer 16v 2.0 TDi engines. A friend who is a mechanic in a dealer has just replaced an engine under warranty where it caused a runaway engine."

 

https://forums.tdiclub.com/showthread.php?t=183696

11 hours ago, chrisund123 said:

May or may not be related, but I just stumbled across this regarding the tandem pump:

 

"

As i recall, there was a thread describing one failure mode of the TANDEM pump being that it leaked down into the  CYLINDER HEAD (YIKES) AND THUS SOMEHOW INTO THE COMBUSTION CHAMBER! Is this possible? anyway resulting in a hydrostatic lockdown causing all sorts of problems! if anybody has time to research this case I would really like to hear more about it. As in "can the T. Pump be diagnosed before this could happen?" Nick in BC. I think the tech working on this cas was in Texas, that's all I remember.

I believe this is only a problem on the newer 16v 2.0 TDi engines. A friend who is a mechanic in a dealer has just replaced an engine under warranty where it caused a runaway engine."

 

https://forums.tdiclub.com/showthread.php?t=183696

 

If the tandem pump was leaking diesel into the engine oil in a seriously big way it could possibly cause runaway of the engine. You would tend to notice a rapidly rising engine oil level before that happened though.

 

By the way, the BKD is 16v and was one of the last of the PD engines. The newer common rail TDis don't have a tandem pump.

Edited 22 July, 20196 yr by nick74

Many thanks for looking into this some more, chrisund123, and for your take on the tandem pump issue, nick74.

 

I've never had a problem with the engine running on after I've turned it off, the oil level is just fine, and the oil smells sweet (well, that would be pushing it, but you know what I mean..), so I think I can discount a 'diesel getting where it shouldn't' type issue.

 

I've been trying to think of any other symptoms that might point the way, and came up with two:

 

1. Occasionally, the engine will briefly hiccup a few times if it's been cruising at 70+ for a short while. It never turns into anything more major, though (at least not so far).

 

2. Sometimes, when accelerating, the engine feels as though it's holding back a little, before going on to surge as I described in the original post.

 

It's odd that it surges dramatically between 2,000 - 2,500 rpm when accelerating, but once up to speed it will hold a steady 2,000 to 3,000 rpm with no trouble (apart from the occasional hiccup!). It tends not to surge from a steady speed. That's got to point at something?

 

Well, for the moment it's a mystery...

Hi All, and sorry for long delay in posting more on this.

 

SOLUTION FOUND YESTERDAY - Woohoo!

 

.....with many thanks to DARKSIDE DEVELOPMENTS of Barnsley.

 

Not that it didn't test them. After 3.5 hours they admitted "We don't know what the cause is; we've never seen symptoms quite like this before".

 

But they didn't stop there: "Our best guess at this stage is a faulty ECU. We'll dig out a used one that will be suitable for your engine, connect it up and see what happens to the symptoms".

 

Result: Sorted!

 

They went on to transfer all the relevant data from the original ECU to the replacement one (for which they'd only charged me £30!) and job done.

 

But there's more: I was liking it on the Dark Side (everyone's dressed in black and speaks in a strange tongue, unfamiliar to Suffolk folk) and decided to blow the cash saved on a new ECU on a re-map. According to DD's s****y dyno rig the car now makes no less than 186hp (c/w the original 140. when new) but with no loss in drive-ability that I noticed on the 188 miles back to Suffolk from Barnsley. And they say I shouldn't notice a significant impact on MPG once I've stopped exploiting the pull from the black holes that open up when I depress the throttle....

 

I'm particularly impressed with DD because they noticed and rectified two unrelated faults along the way (very slight coolant leak and EGR cooler leak) and ran through a long list of tests before letting themselves get into 'best guess' territory. Their hourly rate is also less then half that of a franchised VAG dealer.

 

I've never had a vehicle with such a long-running issue, or been so pleased to get it resolved. This one had been past an official VAG dealer and much respected local garage with no solution in sight. I was left with the options of continuing to blindly replace parts, or stick the car on eBay to get what I could for it.

 

By all accounts this was a pretty rare fault (loads of power when you don't want it), but thought I'd bring you all up to date in case someone else might get the benefit at some point.

 

If nothing else, you know where to go for top diesel diagnostic/ tuning advice: Darkest Barnsley (it wasn't at all scary when I was there, but who knows what happens after dark.....).

 

Cheers

 

KimT

Nice one when you get a result!

Further to my last post: To the best of my knowledge Darkside's Dyno is great!

 

So don't get (completely) the wrong idea from the four asterisks!

 

The word I actually used was (in reverse) 'yknaws', but the system took exception to the middle four letters and substituted asterisks, which had completely the wrong effect.

 

Sorry Darkside - No offence intended!