Exhaust 'puff' occurring, any ideas of cause?

[vulcan bomber]

Is it an air related problem? Smoke suggests not enough air. Something often miss understood is that Boost pressure doesn't necessarily mean you've got enough volume of air.... If you have the boost pressure then your injection pump will fuel for it, but you might not have enough flow to actually ha e enough air to burn all that fuel.

[fmmv]

Or following on from that, maybe there is some exhaust obstruction that clears

[Jocklandjohn]

19 minutes ago, vulcan bomber said:

Is it an air related problem? Smoke suggests not enough air. Something often miss understood is that Boost pressure doesn't necessarily mean you've got enough volume of air.... If you have the boost pressure then your injection pump will fuel for it, but you might not have enough flow to actually ha e enough air to burn all that fuel.

I understand your suggestion. I wondered if the boost pin was 'sticking' in the bore and therefore slow to respond to the building boost, so had a look and it was moving freely, but I gave it some light grease anyway. So it's definitely moving correctly - however as far as the AMOUNT of boost - well thats showing on the boost gauge as the correct max psi as per its operating spec. so I'm assuming thats ok too.

What puzzles me is the 'strangled' initial performance - poor acceleration and not revving freely, then hit second gear and give it some more acceleration and it invariably goes POOF throws a cloud of black smoke out the back and then revs freely and runs like a champ. Until I stop and park. Then the whole process gets repeated.

[Jocklandjohn]

2 minutes ago, fmmv said:

Or following on from that, maybe there is some exhaust obstruction that clears

What might be able to cause a repetitive situation as I describe above? Something in the pipework that gets 'shoved' aside with pressure? It's not an occasional thing, it's happening with virtually every run, coughs a giant POOF and clears then runs ok until I stop again, and then it repeats on starting again! 

[fmmv]

I think @vulcan bomber made a good point, just because you have boost, it doesn't mean the air is going in, hence the black smoke. Whatever it is resets itself somehow with the engine off. Something must be affecting the flow of air through the engine somewhere.But we can only guess from afar. You could try running without non-essential things temporarily, eg exhaust beyond the first joint, or air filter and see if it has any effect.

[David Sparkes]

There is a lot of reliance being placed on 'the boost pressure is OK'.

Where, in the induction system, is this boost pressure being measured?
The turbo outlet?
Before or after the intercooler?
The inlet manifold itself?

I feel this should help indicate whereabouts the 'temporary' blockage is, that is being cleared by the POOF events.
Obviously I am accepting that the black smoke shows 'not enough air', or 'too much fuel'. While both events will cause black smoke, the physical causes will be different.

Regards.

[Jocklandjohn]

6 hours ago, fmmv said:

I think @vulcan bomber made a good point, just because you have boost, it doesn't mean the air is going in, hence the black smoke. Whatever it is resets itself somehow with the engine off. Something must be affecting the flow of air through the engine somewhere.But we can only guess from afar. You could try running without non-essential things temporarily, eg exhaust beyond the first joint, or air filter and see if it has any effect.

Yes thats a good suggestion. As an indication of the issue - with the old turbo (and duff intake pipe with the crack which was losing the boost between intercooler and intake manifold) I could get the giant puff of black smoke and a partial improvement. This needed a lot of revs and speed to achieve.

With the new turbo and new properly sealed intake pipes the same issue occurs but (I'm guessing here) is more easily 'overcome' at lower speed/revs because the system is intact and the pressure increased so overcomes whatever is at fault. Does that sound like a reasonable assumption? And if it does, what does that point to?

 

1 hour ago, David Sparkes said:

There is a lot of reliance being placed on 'the boost pressure is OK'.

Where, in the induction system, is this boost pressure being measured?
The turbo outlet?
Before or after the intercooler?
The inlet manifold itself?

I feel this should help indicate whereabouts the 'temporary' blockage is, that is being cleared by the POOF events.
Obviously I am accepting that the black smoke shows 'not enough air', or 'too much fuel'. While both events will cause black smoke, the physical causes will be different.

Regards.

Thanks for your input David, good points. The boost gauge is T'd off the turbo outlet, so you're right thats not necessarily a good indicator of what's happening further down the system. I wondered about the thin pipe from turbo to compensator on top of the injection pump so replaced that with a good quality alternative in case of delaminating in the old one, but its not really improved it. 

Might some issue with the spill return lines cause this? I renewed the tank feed/return pipes, and some years ago did the small pipes between injectors on the spill rail but perhaps something causing a partial blockage inside one of the metal components?

[fmmv]

Do you get a poof if you switch off after a run so it's unpoofed, then restart, or do things have to cool to get one?

[Jocklandjohn]

2 hours ago, fmmv said:

Do you get a poof if you switch off after a run so it's unpoofed, then restart, or do things have to cool to get one?

Just in from town - here's how it went:

Warm engine for a few minutes at house, down hill onto flat, pull away, strangled performance then in 2nd or 3rd POOF and it runs lovely.

Stop  for fuel for 10 minutes and restart, sluggish out on to carriageway, give it welly and POOF it clears and runs lovely.

Train coming so barrier down. Stop. Engine off. Around 3 minutes before restart. Sluggish out onto main road in 1st and then into 2nd, sluggish as I navigate roundabout, onto straight dual carriageway and get into 3rd and accelerate and POOF it clears.

Stop for another 5 minutes, engine off. Restart, sluggish all the way through residential area w/loads of cars until I get to dual carriageway and get up a bit of speed and POOF it clears.

EVERY time I switch the engine off it reverts to slugsville! No cooling required!

Before I noticed the poof effect I was wondering what some days it *seemed* to run better than others and its basically down to me giving it sufficient revs to generate the POOF, if I don't its perfectly possible to bimble about in lower revs for miles with it 'strangled'. 

So it *seems* like its something that requires the generation of revs and boost pressure (and fuel demand) to clear. 

 

[Bowie69]

Have you checked all the inlet tract hoses for delamination? 

Did read through but didn't see it mentioned. 

[fmmv]

I do wonder about rhe exhaust. Years ago I gad a Cavalier Gsi 4x4 and the catalyst blocked  The early effects were like you are experiencing, eventually it blocked almost completely and brought me to a stop on the M58. The engine would tickover but no more. Not saying its totally relevant or you have a blocked cat, but it does sound something like.

I think it might also have something to do with the engine breather getting blocked and then clearing,  but I think that would make the engine smoky, can only suggest rooting round till you stumble on it. I don't think the leak offs are relevant but who knows, it'll be obvious when you pin it down.

[Jocklandjohn]

4 minutes ago, Bowie69 said:

Have you checked all the inlet tract hoses for delamination? 

Did read through but didn't see it mentioned. 

All brand new silicone, reinforced wire & alloy on the intake side to filter housing, then same to intercooler inlet, from intercooler onwards all new silicone and new alloy. Problem existed before fitting all this, continues now!

 

5 minutes ago, fmmv said:

I do wonder about rhe exhaust. Years ago I gad a Cavalier Gsi 4x4 and the catalyst blocked  The early effects were like you are experiencing, eventually it blocked almost completely and brought me to a stop on the M58. The engine would tickover but no more. Not saying its totally relevant or you have a blocked cat, but it does sound something like.

I think it might also have something to do with the engine breather getting blocked and then clearing,  but I think that would make the engine smoky, can only suggest rooting round till you stumble on it. I don't think the leak offs are relevant but who knows, it'll be obvious when you pin it down.

Entirely possible!

Exhaust is relatively new stainless, no cat. Might some packing in the muffler section flop about and cause this?

I also wondered about fuel lines whether a bend in the fuel lines somewhere could restrict fuel flow until I get more boost generated, then the increased sucking from the lift pump & injection pump allows the fuel pressure to 'open' the flow. Then stopping would allow it to restrict again?  Might this occur on the fuel return/spill rail side and have that effect?

[stevebus]

I had much the same problem and went down the filter line first, still poofing smoke, new lift pump, still poofing, Fip timing still poofing, so went down the air side of thing and started to cleans all the relevant pipes and found to my opinion to much oil in it all, cleaned my intercooler which I'm not going to say was rammed with oil but certainly more than there should of been and it all stopped, power back and runs like a train, after that I did replace the cyclone breather for a allisport one which definitely helped and been good since, I haven't read the whole post so someone might have suggested this already and if so sorry 

[Jocklandjohn]

20 minutes ago, stevebus said:

I had much the same problem and went down the filter line first, still poofing smoke, new lift pump, still poofing, Fip timing still poofing, so went down the air side of thing and started to cleans all the relevant pipes and found to my opinion to much oil in it all, cleaned my intercooler which I'm not going to say was rammed with oil but certainly more than there should of been and it all stopped, power back and runs like a train, after that I did replace the cyclone breather for a allisport one which definitely helped and been good since, I haven't read the whole post so someone might have suggested this already and if so sorry 

No, thank you, any help is useful, and thats a new suggestion! 

I did do an intercooler clean when I renewed all the pipework because I'd the whole front gubbins off and fitted a new radiator as well. What I also did was re-route the outlet from the cyclone through a small catch can before it goes into the air filter intake.  

I did read a shedload of stuff about "should the cyclone breather outlet be plumbed in before or after the filter" and went before as thats the way it was as standard. The bottom of the cyclone still vents the oil to the sump as normal.

[stevebus]

Just for the record mines a disco 200 and my breather goes in after the filter and like you say the bottom exit goes back to the sump, I did this all a year or so ago and to be honest it's just started to blow a bit of black smoke again now but no poofing for want of a better word and I think before winter gets here I might clean it all again. The other thing is, and I don't how true this is, I do use supermarket fuel, some say its not up to the same par as let's say Shell or Esso but it's good deal cheaper, whether that has any adverse quincey quonces on the state of play I don't know.

[Jocklandjohn]

Just now, stevebus said:

Just for the record mines a disco 200 and my breather goes in after the filter and like you say the bottom exit goes back to the sump, I did this all a year or so ago and to be honest it's just started to blow a bit of black smoke again now but no poofing for want of a better word and I think before winter gets here I might clean it all again. The other thing is, and I don't how true this is, I do use supermarket fuel, some say its not up to the same par as let's say Shell or Esso but it's good deal cheaper, whether that has any adverse quincey quonces on the state of play I don't know.

Cheers. I had poor running with supermarket fuel (Tesco) and switched to branded stuff and it seemed to prefer it. Managed to upload a short video of the problem. It's sideways because my son was holding his phone out the window. It shows us coming down a short hill onto the flat, then onto the main road and immediately going uphill. I go into first and pull out and have black smoke, then into second and its still smoky both grey/white and black then the puff (thats not the biggest I've seen but its typical) and then it has cleaner running and is actually pulling like a train from its previous very sluggish performance. 

 

 

[stevebus]

Yes fella, exactly that, I haven't got the white/grey smoke I only have that once I've done the warm up in the morning and pull down my lane maybe half mile, that would clear then I had all the poofing bit once I'd put my foot down, but I was close to running temperature, like I say, for me it was the air intake side of things, I'm definitely going to follow this with interest, and I'm only sorry I didn't see it the post months ago, all the best

[Jocklandjohn]

1 minute ago, stevebus said:

Yes fella, exactly that, I haven't got the white/grey smoke I only have that once I've done the warm up in the morning and pull down my lane maybe half mile, that would clear then I had all the poofing bit once I'd put my foot down, but I was close to running temperature, like I say, for me it was the air intake side of things, I'm definitely going to follow this with interest, and I'm only sorry I didn't see it the post months ago, all the best

Thanks for the help (everyone!) - I'm slowly narrowing down possibilities so at some point I'll end up finding the culprit!

[hurbie]

i would say it's way overfueling , or a serious lack of air to go with the fuel .... the're not ment to smoke this much ....

[Jocklandjohn]

8 hours ago, hurbie said:

i would say it's way overfueling , or a serious lack of air to go with the fuel .... the're not ment to smoke this much ....

Yes, I agree. But it only does that initially, then after it goes POOF it runs much cleaner, smoother and far more powerfully. 

Whatever is causing this must be very far from obvious!

[rusty_wingnut]

Check the pin that runs on the boost pin (under the big diaphragm) is not sticking. Lift the pump top and remove the diaphragm and boost pin. You'll see a smaller pin that is protruding, give it a little light oil.

Edited August 29 by rusty_wingnut

[92a]

Just a thought have you tried removing the fuel filler cap before you start the engine / do your testing ? I don’t know if they are supposed to be vented or not ? 

[Eightpot]

Are you confident your pump/cam timing is set up accurately?  In the back of my mind I'm thinking bosch VE pumps have a cold start device which temporarily advances timing a few degrees on startup. Couple that with slightly advanced timing and it may promote black smoke for a short time.

[Eightpot]

4 minutes ago, 92a said:

Just a thought have you tried removing the fuel filler cap before you start the engine / do your testing ? I don’t know if they are supposed to be vented or not ? 

I'm also thinking it could be something daft in the fuel system - I had a real headscratcher once caused by a tiny plastic ball that somehow got in the fuel tank getting sucked up the pickup pipe and slowly strangling the engine. It would disappear for a bit every time the engine was stopped. Opposite problem but a fuel return line blockage might cause your symptoms.

[Snagger]

I have suspicions that the small horizontal pin that runs on the boost pin slope and transfers that boost sensing to the injection pump mechanisms is sticking in the casing.  I had that on a new 300 pump, and have read numerous similar accounts.  Mine was stuck solid and gave very sluggish performance.  Yours may be jumping out when enough boost occurs, seized but not completely solid.