Exhaust 'puff' occurring, any ideas of cause?

[Jocklandjohn]

200tdi

Start engine, let it warm for a spell and drive off. I'm intially downhill for a few hundred metres from the house, then onto flat road where I can accelerate, usually in 2nd. When I do this the engine *feels* like its got a rev limiter when I accelerate and is not willing to rev beyond a certain point then suddenly there's a POOF and a burst of black smoke exits the exhaust and immediately the revs are 'free' and I can see and feel the rev counter needle bouncing up and down with throttle stabs. After it does this 'cough' of smoke it runs smoothly and fairly cleanly but prior to it doing it it feels very asthmatic. This happens every time I start it after its been sitting for a bit, or after taking it out for a run and parking up for half and hour or so.

What might be the cause? Is it a fuel pump issue? Might the fuel pin/boost pin/diaphragm be sticking in the bore? It 'feels' like its needing the turbo boost to build sufficiently to 'clear' whatever is causing it, but thats guesswork on my part. What does happen is that if I dont give it that initial real push of revs to clear it, it runs with much less vigour, like its got fuel starvation.

All the gubbins around the engine has been renewed - tank a few years ago, fuel lines as well (feed & return), fuel filter  replaced, injector nozzles renewed and injectors overhauled, and a new Delphi lift pump fitted a few months ago. Boost pipe was renewed as well from turbo to fuel pump with quality stainless braided pipe.

After it 'clears its throat' it runs really nicely so its not a major issue but I'd like to narrow down the likely causes. Any suggestions welcome.

 

 

[Snagger]

It sounds a lot like something sticking inside the injection pump, possibly through gumming up and possibly through corrosion.  I’d try running a fairly strong dose of cleaner through it.  I found Forte diesel system cleaner pretty effective in the past.

[Jocklandjohn]

6 hours ago, Snagger said:

It sounds a lot like something sticking inside the injection pump, possibly through gumming up and possibly through corrosion.  I’d try running a fairly strong dose of cleaner through it.  I found Forte diesel system cleaner pretty effective in the past.

Cheers Nick will give it a go. Looks like I can get it locally too which is good!

Thank you!

[Nonimouse]

If that doesn't work, run 200ml of two stroke oil per tank for a few months

[fmmv]

I have had a similar experience to the OP's. Our street is steep downhill, then level to a T junction where you have to climb up reasonably steeply again. So initially you need next to no throttle, till the T. Then the engine has to actually work, and like you, we had initial hesitation, then some smoke and splutter and after that all seemed to be OK, not even every time. This is on a 300. I admit I treated it as "it's OK now , let's just pretend that didn't happen for now" and put it on the todo list. For separate reasons completely I swapped the turbo (went VNT)  and the problem went away, and has been gone for years. I can't say for sure therefore what it was, I may have inadvertently fixed it while swapping turbos, or it may have been the turbo itself.

When I looked at the old turbo having got it off,  the compressor vanes had been rubbing the scroll, just slightly ( I knew it had had a good innings) . So maybe it didn't spin properly till the oil pressure had lifted it clear of the scroll, and it could spin freely, and that was my hesitation clearing. But that's a maybe, I have no definite idea what was causing it. Your smoke is black so that suggests over fuelling or shortage of air for some reason. Or maybe it could be an injection pump issue, something sticking in there.  I think there is a device within the FIP that gives it full fuel for cold start, hence the puff of black smoke on startup - maybe that is sticking. If you have a boost gauge or could temporarily plumb one you could see if the boost when it's cold matches what it is when you do the same journey when it's running Ok, so that would help eliminate the turbo side. Can you get it to 'cough' just stationery when cold or does it have to be moving? Might be worth taking the diaphragm off the top of the pump and making sure the pin that bears against the boost pin can move easily (mark position of diaphragm and return to same) as they are known to stick, it's only 4 screws.

 

Just another thought... does this only happen when the weather is cold?

Edited December 4, 2023 by fmmv

[Jocklandjohn]

2 hours ago, Nonimouse said:

If that doesn't work, run 200ml of two stroke oil per tank for a few months

🙂  Been doing that anyway after the fuel pump service I had a some years ago where the newly serviced pump jammed *in the Bosch shop* but they did not realise it had happened during their pst-overhaul testing. It took a year to remedy and the fault was the horizontal pin jamming against the vertical diaphragm/boost pin. They'd never seen that before, but a few months later told me they'd had another pump same vintage as mine in for service and they doscovered it had exactly the same problem. They postulated the cause having something to do with the low sulphur diesel causing a lack of lubrication. When researching this later I saw a comment on here to use 2-stroke so I've been doing that ever since.

58 minutes ago, fmmv said:

I have had a similar experience to the OP's. Our street is steep downhill, then level to a T junction where you have to climb up reasonably steeply again. So initially you need next to no throttle, till the T. Then the engine has to actually work, and like you, we had initial hesitation, then some smoke and splutter and after that all seemed to be OK, not even every time. This is on a 300. I admit I treated it as "it's OK now , let's just pretend that didn't happen for now" and put it on the todo list. For separate reasons completely I swapped the turbo (went VNT)  and the problem went away, and has been gone for years. I can't say for sure therefore what it was, I may have inadvertently fixed it while swapping turbos, or it may have been the turbo itself.

When I looked at the old turbo having got it off,  the compressor vanes had been rubbing the scroll, just slightly ( I knew it had had a good innings) . So maybe it didn't spin properly till the oil pressure had lifted it clear of the scroll, and it could spin freely, and that was my hesitation clearing. But that's a maybe, I have no definite idea what was causing it. Your smoke is black so that suggests over fuelling or shortage of air for some reason. Or maybe it could be an injection pump issue, something sticking in there.  I think there is a device within the FIP that gives it full fuel for cold start, hence the puff of black smoke on startup - maybe that is sticking. If you have a boost gauge or could temporarily plumb one you could see if the boost when it's cold matches what it is when you do the same journey when it's running Ok, so that would help eliminate the turbo side. Can you get it to 'cough' just stationery when cold or does it have to be moving? Might be worth taking the diaphragm off the top of the pump and making sure the pin that bears against the boost pin can move easily (mark position of diaphragm and return to same) as they are known to stick, it's only 4 screws.

 

Just another thought... does this only happen when the weather is cold?

I fitted a VNT last year - it has made a huge difference. I have a boost gauge and all looks normal - only indicator of the oddness is the EGT gauge which shows higher EGT before the 'cough' and lower afterwards. I have not had a decently running van for years - I only found the cause a month or so back. Because I had a 19J/2.5TD originally and now a 200tdi I was still using the old passenger side vertical air filter, which worked ok. But. But the intercooler lower pipe exits there and has had to snake around the legs of the air filter can and this was putting pressure on some alloy piping further along and there was a cracked weld in an elbow there that was not at all obvious. When idling it all looked ok but under pressure when driving the seam would open and boost was lost. It took ages to discover it and only did so after pulling all the piping out, cleaning it and replacing and it then discovered that however bad it had been before it was now running much worse than that! Reason was the snaking through the air cleaner legs was a tad diferent this time when I reinstalled at after cleaning it all and this was putting even more pressure on the dodgy seam allowing it to open more easily under boost. Now its been replaced, a Donaldson filter fitted on the other side with a nice big pipe to the turbo and a clean run out of the intercooler lower pipe to the manifold and its now running like a champ. And this 'puffing' issue has revealed itself!

The problem does not seem related to cold weather. I'll have a poke at the boost pin and see whats afoot, I have had the top off recently and it seemed to be ok but will take anothrt look.

I'm sticking some injector cleaner through it later today so I'll see what that does. Its warming up off the diesle heater just now so I'll see what revving and boost does WITHOUT having started it from cold using the engine alone (we're still sub-zero so the eberspacher is a kinder starting option for the old engine!).

Thanks for the advice.

Edited December 4, 2023 by Jocklandjohn

[vulcan bomber]

14 hours ago, fmmv said:

I have had a similar experience to the OP's. Our street is steep downhill, then level to a T junction where you have to climb up reasonably steeply again. So initially you need next to no throttle, till the T. Then the engine has to actually work, and like you, we had initial hesitation, then some smoke and splutter and after that all seemed to be OK, not even every time. This is on a 300. I admit I treated it as "it's OK now , let's just pretend that didn't happen for now" and put it on the todo list. For separate reasons completely I swapped the turbo (went VNT)  and the problem went away, and has been gone for years. I can't say for sure therefore what it was, I may have inadvertently fixed it while swapping turbos, or it may have been the turbo itself.

When I looked at the old turbo having got it off,  the compressor vanes had been rubbing the scroll, just slightly ( I knew it had had a good innings) . So maybe it didn't spin properly till the oil pressure had lifted it clear of the scroll, and it could spin freely, and that was my hesitation clearing. But that's a maybe, I have no definite idea what was causing it. Your smoke is black so that suggests over fuelling or shortage of air for some reason. Or maybe it could be an injection pump issue, something sticking in there.  I think there is a device within the FIP that gives it full fuel for cold start, hence the puff of black smoke on startup - maybe that is sticking. If you have a boost gauge or could temporarily plumb one you could see if the boost when it's cold matches what it is when you do the same journey when it's running Ok, so that would help eliminate the turbo side. Can you get it to 'cough' just stationery when cold or does it have to be moving? Might be worth taking the diaphragm off the top of the pump and making sure the pin that bears against the boost pin can move easily (mark position of diaphragm and return to same) as they are known to stick, it's only 4 screws.

 

Just another thought... does this only happen when the weather is cold?

There's nothing on our version of the Bosch VE to help with cold starting. 

[Giles]

23 hours ago, Nonimouse said:

If that doesn't work, run 200ml of two stroke oil per tank for a few months

I was talking to an old-school Bosch pump rebuilder in Germany t'other day and he also recommended 1% cheap engine oil with every fill .... Think I might do this ...

[Maverik]

I installed a VNT back in 2020, it seemed to run ok for 10 months, but then when starting it up, I found something was "sticking" - symptoms where no power or rev's, a good bit of smoke and spiking boost pressure, it would then suddenly pick up, the pressure would "pop" back to the max pressure and all was well in the world.

Quite simply this drove me loopy trying to figure what was going on, I stripped the VNT cleaned rebuilt, made up a test rig- replaced the VNT vane pressure modulator, tested all lines for blockages, replaced injector pump for overhauled unit... I even replaced the engine for a turner short block and rebuilt the whole thing -  I simply exhausted testing and inspecting pretty much every related component and I didn't find the reason.

For sanity reasons I swapped the VNT turbo back out for a new garret standard turbo and just went back to some basic pump tuning and worked on making a nice intake and exhaust set up.

I wasn't very happy with the VNT set-up even without the "sticking" issue, in my opinion, you just cant control the air to fuel ration precisely enough on a 200tdi using mechanical means, to have a nice smoke free experience. 

So unfortunately not a lot of help, but I never got to the bottom of the weird symptoms. 

Quite an expensive endeavour.

[Jocklandjohn]

Warmed it up with the eberspacher yesterday. Gave it a rev at ignition startup and got the normal slight haze of smoke, then down hill and onto flat and accelerated and there was no detectable puff. Picked up Forte Diesel System cleaner later on and got a bit of a puff on acceleration after it had sat for a while in town. The cleaner is in and I'll see what difference it makes after a thorough scrub through with it. Seems the static rev up after pre-heater warmup might have had an effect.

[Jocklandjohn]

1 hour ago, Maverik said:

I installed a VNT back in 2020, it seemed to run ok for 10 months, but then when starting it up, I found something was "sticking" - symptoms where no power or rev's, a good bit of smoke and spiking boost pressure, it would then suddenly pick up, the pressure would "pop" back to the max pressure and all was well in the world.

Quite simply this drove me loopy trying to figure what was going on, I stripped the VNT cleaned rebuilt, made up a test rig- replaced the VNT vane pressure modulator, tested all lines for blockages, replaced injector pump for overhauled unit... I even replaced the engine for a turner short block and rebuilt the whole thing -  I simply exhausted testing and inspecting pretty much every related component and I didn't find the reason.

For sanity reasons I swapped the VNT turbo back out for a new garret standard turbo and just went back to some basic pump tuning and worked on making a nice intake and exhaust set up.

I wasn't very happy with the VNT set-up even without the "sticking" issue, in my opinion, you just cant control the air to fuel ration precisely enough on a 200tdi using mechanical means, to have a nice smoke free experience. 

So unfortunately not a lot of help, but I never got to the bottom of the weird symptoms. 

Quite an expensive endeavour.

Ah yes I recall that episode, and you mentioning it, and the various attempts to resolve it. I take it the standard turbo you reverted to (with other alterations) has enabled a better outcome?

I just did an experiment with a new air intake on the other side from the existing original one using a Donaldson canister. From the wing a 100mm inlet reducing to 76mm pipe to the filter, then reducer 76-60 and 60mm silicone flexi pipe to turbo inlet. Big improvement on previous, but it still felt a little restricted. So I swapped the reducer out of the canister outlet, ran 76mm flexi pipe to the turbo instead of 60mm and put the reducer at that end so reducing 76-60 into the turbo. There is a very noticeable difference with the latter, wider pipe. The intake noise is distinctly 'burbly' and it pulls really well but the interesting thing was a reduction of EGT in certain situations, particularly on the flat in 5th at 50mph, of between 80-100deg compared o the narrower pipe which was a real surprise. And with it a much better high gear roll-on with negligible black smoke. Which is a major improvement on previously.

[Maverik]

42 minutes ago, Jocklandjohn said:

Ah yes I recall that episode, and you mentioning it, and the various attempts to resolve it. I take it the standard turbo you reverted to (with other alterations) has enabled a better outcome?

So in my opinion I don't think VNT suits a 200tdi.

With standard turbo, some Inlet/Exhaust improvements, a Dynamic adjuster ring, and a tweak to the boost pin, I've got a day to day drive that is pokey enough to keep up with motorway traffic and be quite fun to drive. Unfortunately  I think I have higher expectations out of a 200 hence why I'm always a tad disappointed with them, especially when towing. 

[vulcan bomber]

3 hours ago, Maverik said:

So in my opinion I don't think VNT suits a 200tdi.

With standard turbo, some Inlet/Exhaust improvements, a Dynamic adjuster ring, and a tweak to the boost pin, I've got a day to day drive that is pokey enough to keep up with motorway traffic and be quite fun to drive. Unfortunately  I think I have higher expectations out of a 200 hence why I'm always a tad disappointed with them, especially when towing. 

Out of interest, how was the VNT controlled?

[Nonimouse]

I've yet to hear of someone who hasn't had issues with 200tdi/VNT.  No doubt it has worked for some people....

[Maverik]

On 12/6/2023 at 9:52 AM, vulcan bomber said:

Out of interest, how was the VNT controlled?

Boost pressure, which is the downfall in my opinion, its just not accurate enough.

Recently noted that alive tuning now use a digital controller on the vnt they put on their td5's turbo upgrades, makes a lot of sense. With accurate tuneable fueling and air, you can make it work very well.

[reb78]

On 12/6/2023 at 10:15 AM, Nonimouse said:

I've yet to hear of someone who hasn't had issues with 200tdi/VNT.  No doubt it has worked for some people....

I am sure I spoke to Pete Bell years ago and he pretty much said not to bother. It was mostly around the fact that I wanted more top end. I have what I want at the bottom end which is where the VNT is most effective. Trade off with more top end is that you would need a bigger turbo and if it is not VNT I think that would have an effect at the bottom of the rev range. So I think what we need for both is a bigger VNT turbo that is properly controlled...

[reb78]

On 12/5/2023 at 10:44 AM, Jocklandjohn said:

Warmed it up with the eberspacher yesterday. Gave it a rev at ignition startup and got the normal slight haze of smoke, then down hill and onto flat and accelerated and there was no detectable puff. Picked up Forte Diesel System cleaner later on and got a bit of a puff on acceleration after it had sat for a while in town. The cleaner is in and I'll see what difference it makes after a thorough scrub through with it. Seems the static rev up after pre-heater warmup might have had an effect.

I don't know if this helps, but its almost as if there is incomplete combustion until you get going? I say this as I can get something like your signs if I am running on SVO and I mess around for too long with the engine idling when cold. I try not to do it but on the odd occasion where I do (hitching up a trailer or something), when I do then go to pull away, I create a smokescreen like battleships used in WW2 to mask their exact positions from enemy ships, and then when that clears it runs absolutely fine. I imagine this is burning off unburnt fuel. Its bad for the engine so I avoid situations where it happens when on SVO and try to just start and go (initial run if from home is straight up a 1 i n6 road for a mile so its warm by the top) but occasionally its not possible to start and head straight off.

[vulcan bomber]

6 hours ago, reb78 said:

I am sure I spoke to Pete Bell years ago and he pretty much said not to bother. It was mostly around the fact that I wanted more top end. I have what I want at the bottom end which is where the VNT is most effective. Trade off with more top end is that you would need a bigger turbo and if it is not VNT I think that would have an effect at the bottom of the rev range. So I think what we need for both is a bigger VNT turbo that is properly controlled...

Working on it.

[vulcan bomber]

12 hours ago, Maverik said:

Boost pressure, which is the downfall in my opinion, its just not accurate enough.

Recently noted that alive tuning now use a digital controller on the vnt they put on their td5's turbo upgrades, makes a lot of sense. With accurate tuneable fueling and air, you can make it work very well.

Correct, they just dont work off Boost Control, I have something in the pipeline.

[Maverik]

17 hours ago, vulcan bomber said:

Correct, they just dont work off Boost Control, I have something in the pipeline.

Oooooooo I did have a wonder as to adapting something alive was using, but that's as far as I got, you'd need some digital feedback from the fuel pump to make it all link up, EDC controlled 300tdi you might have some chance with.

I've still got the VNT turbo, a fair chunk of cash sat on the shelf.

[vulcan bomber]

On 12/13/2023 at 9:28 AM, Maverik said:

Oooooooo I did have a wonder as to adapting something alive was using, but that's as far as I got, you'd need some digital feedback from the fuel pump to make it all link up, EDC controlled 300tdi you might have some chance with.

I've still got the VNT turbo, a fair chunk of cash sat on the shelf.

Watch this space, it'll happen one day 

[Jocklandjohn]

On 12/12/2023 at 10:00 AM, reb78 said:

I don't know if this helps, but its almost as if there is incomplete combustion until you get going? I say this as I can get something like your signs if I am running on SVO and I mess around for too long with the engine idling when cold. I try not to do it but on the odd occasion where I do (hitching up a trailer or something), when I do then go to pull away, I create a smokescreen like battleships used in WW2 to mask their exact positions from enemy ships, and then when that clears it runs absolutely fine. I imagine this is burning off unburnt fuel. Its bad for the engine so I avoid situations where it happens when on SVO and try to just start and go (initial run if from home is straight up a 1 i n6 road for a mile so its warm by the top) but occasionally its not possible to start and head straight off.

Yes there's a bigh pooof of black smoke whih is obviously unburnt fuel, sluggish beforehand then after 'clearing its throat' its running pretty splendidly. I'm part way through a tank of Forte diesel/cleaner/additive/injector/fuel line degunger so I'll see what effect that has at cleaning things up.

On 12/12/2023 at 9:56 AM, reb78 said:

I am sure I spoke to Pete Bell years ago and he pretty much said not to bother. It was mostly around the fact that I wanted more top end. I have what I want at the bottom end which is where the VNT is most effective. Trade off with more top end is that you would need a bigger turbo and if it is not VNT I think that would have an effect at the bottom of the rev range. So I think what we need for both is a bigger VNT turbo that is properly controlled...

I remember quite a bit of discussion about all of this VNT stuff years ago on here. My need was for low speed oomph rather than top end, as the van is pretty heavy as is and even more so with full load of fuel and water, partner, dog and assorted tat, and occasionally bicycles hung off the towhitch carrier, and couple woith the 1:2 gearing.  Not doing a huge amount of motorway use, so its usually either plodding up and down on Highland single-track roads at 30-40mph or up and down on A roads in the 45-55mph range, which seems to suit the set up. I think I'll experiment with preheater warmup starts and engine idling warmup starts and see if theres a significant difference.

What I can say is that after solving the desperately poor running due to the dodgy intake pipe its running and pulling better than it has in years. So any other improvements are the cream on top of the icing on the top of cake!

[Bowie69]

To be honest, if your heavy and are mostly doing those speeds, depending on tyre size then you may find it much more enjoyable to drive with a 1.4.

[Jocklandjohn]

On 12/16/2023 at 12:38 PM, Bowie69 said:

To be honest, if your heavy and are mostly doing those speeds, depending on tyre size then you may find it much more enjoyable to drive with a 1.4.

I know what you mean. I had a 1.4 previously and it certainly gives lots of low down flexibility, but thought I'd try the 1.2 when I had the 200tdi overhauled. With the 1.2 5th is pretty much an overdrive, which I can use when I get on the other side of 50mph and it certainly eases back the revs. I'm on 235/85/16 so not anything overly sized. I'm not a regualr m.way/dual carriageway user but when I've had jobs in the south and had to go beyond Perth/Glasgow its come in handy having that taller gear. I guess the ideal is a 1.4 and overdrive!