Matt Harwood Posted November 19, 2002 Share Posted November 19, 2002 I'm hoping some of you techy guys can help here. I don't know if I have a problem or not... Recently, I have become more aware of what I think is turbo stalling. If I were to pull out of a junction sharpish, (or overtake something), if I then back off the throttle a little at around 3500 rpm, the autobox changes up a gear and I get a deep drone from the exhaust. At the same time, the turbo pressure drops to around zero. This only lasts about a second before the boost pressure stabilises, the drone fades away, and I can feel the engine is ready to go again. Does that make sense? - I assume it's not supposed to happen as I believe this is not good for the turbos. Any suggestions? Quote Link to comment Share on other sites More sharing options...
Guest Martin F Posted November 20, 2002 Share Posted November 20, 2002 Matt, can you remind us of your mods. Quote Link to comment Share on other sites More sharing options...
Matt Harwood Posted November 20, 2002 Author Share Posted November 20, 2002 No probs. I can't say when I noticed this started to happen though. The car is a 94 TT auto J-spec. Decatted, (both) with restrictor plate TRL VFCC HKS Hiper HKS R-type intercooler and hardpipes Iridium plugs TRD panel filter Blitz boost controller It was definatly doing it before these mods. Walbro high pressure fuel pump FSE fuel pressure regulator HKS SSQV Any clues? Quote Link to comment Share on other sites More sharing options...
Induction Posted November 20, 2002 Share Posted November 20, 2002 Matt I've noticed similar things and was also wondering what was the cause. On an overtaking move I sometimes have a situation where the 'box changes up whilst on full boost and the power seems to drop for half a second, almost like the engine is catching a breath, then it comes back and keeps going. This doesn't always happen, most of the time the engine delivers a fairly smooth and constant stream of power during the change. Jules Quote Link to comment Share on other sites More sharing options...
Matt Harwood Posted November 20, 2002 Author Share Posted November 20, 2002 That's it exactly, although I only get it as I back off the throttle slightly. - If you have a boost gauge, you'll notice that the boost drops off to zero before things return to normal. Glad I'm not the only one Quote Link to comment Share on other sites More sharing options...
Guest Martin F Posted November 20, 2002 Share Posted November 20, 2002 Well it's a little hard to diagnose these sorts of things without experiencing it. But my guess would be the HKS BOV or a boost leak. I know you say this was happening before you fitted the BOV, but the description you give seems like a BOV that's not reacting properly. Bit hard to do at a distance. Quote Link to comment Share on other sites More sharing options...
Guest Martin F Posted November 20, 2002 Share Posted November 20, 2002 I wonder if it's something to do with the TRAC butterfly closing on shifts. Quote Link to comment Share on other sites More sharing options...
Matt Harwood Posted November 20, 2002 Author Share Posted November 20, 2002 Originally posted by Martin F I wonder if it's something to do with the TRAC butterfly closing on shifts. Now that sounds possible. I have a throttlebody without the butterfly. It only takes a few minutes to change... I'll give it a go... Quote Link to comment Share on other sites More sharing options...
Matt Harwood Posted November 20, 2002 Author Share Posted November 20, 2002 Originally posted by Martin F Well it's a little hard to diagnose these sorts of things without experiencing it. But my guess would be the HKS BOV or a boost leak. I know you say this was happening before you fitted the BOV, but the description you give seems like a BOV that's not reacting properly. Bit hard to do at a distance. I fitted the HKS one as a suggestion to cure the problem. I've been told that the BOV can be adjusted but I don't think this will help as the problem happens while I'm still on the throttle. Quote Link to comment Share on other sites More sharing options...
adi Posted November 20, 2002 Share Posted November 20, 2002 The deep 'drone' from the exhaust sounds to me like the gearbox retarding the ignition, as it should do, and sounds like normal operation to me. The exhaust note normally drops, 'farts' a bit, and then goes back to normal after the gear change. Theres always going to be some release of boost pressure between shifts.. generally its not noticeable, but with an aftermarket BOV it may be exaggerating it a bit. Dont forget that the gearbox retards the ignition.. you cant expect the turbo to still be producing max boost during this. Your description sounds like normal operation. On an auto i'd personally stick to the stock BOV, as autos do funny things to boost pressure when changing.. probably most aftermarket BOV's are made for on/off boost pressure that you get with a manual. PS im probably technically incorrect, but it kinda makes sense.. i think, maybe... Quote Link to comment Share on other sites More sharing options...
Adam W Posted November 20, 2002 Share Posted November 20, 2002 I don't want to start a rumour here about em, but I'm sure I've read before that FSE valves are unreliable - can anyone back me up on that? Loss of power could be a mixture problem - my car felt godawful as I came on and off boost a while back, it turned out the pressure hose to the fuel pressure regulator had blown off and fuel pressure wasn't increasing with boost. Quote Link to comment Share on other sites More sharing options...
Induction Posted November 20, 2002 Share Posted November 20, 2002 I might try putting the stock BOV back on and see if it makes any difference. Jules Quote Link to comment Share on other sites More sharing options...
Matt Harwood Posted November 20, 2002 Author Share Posted November 20, 2002 Under full throttle it's fine. It only happens at part throttle, ie going from half throttle up to 3500 rpm then releasing to quater throttle, the box changes gear, boost goes from 0.6 bar to zero for a second, (if that), then back to about 0.3, (due to the less amount of throttle). While the boost has dropped you can hear a very prominent deep drone coming from the engine/exhaust before things rectify themselves. Could be my irratic driving style I suppose Quote Link to comment Share on other sites More sharing options...
adi Posted November 20, 2002 Share Posted November 20, 2002 Matt, that definately sounds like normal operation caused by the gearbox retarding the ignition.. its meant to do it to allow for smoother changes.. its not noticeable with a stock exhaust but a decatted or aftermarket exhaust willl make the noise. the change in the ignition timing will also drop the boost pressure. Is it less noticeable with the 'pwr' button pressed on the gearbox?.. this normally cancels the igition feature of the gearbox. Quote Link to comment Share on other sites More sharing options...
Matt Harwood Posted November 20, 2002 Author Share Posted November 20, 2002 Thanks Adi, something else worth trying. I was kinda hoping I didn't have a problem as such. All suggestions welcome Quote Link to comment Share on other sites More sharing options...
Doug Posted November 20, 2002 Share Posted November 20, 2002 Matt, have you tried it with the boost controller turned off. I had a similar effect on my old car when running with a bleed valve (I know they're not the same thing but they still fool the car as to what is really going on). Quote Link to comment Share on other sites More sharing options...
Matt Harwood Posted November 20, 2002 Author Share Posted November 20, 2002 Hi Doug, yep, still does it with the boost controller off, (although that's still 1.1 bar!) I drove home in 'manu' mode and I couldn't get it to do it at all. however, there was loads of rushour traffic around so I didn't really get a chance to put my foot down much. I'll try again in the morning Quote Link to comment Share on other sites More sharing options...
adi Posted November 20, 2002 Share Posted November 20, 2002 Manu mode and power mode will both stop the ignition from retarding.. although i cant remember if the mkiv box has a power button. Quote Link to comment Share on other sites More sharing options...
Dragonball Posted November 20, 2002 Share Posted November 20, 2002 Matt The same symtoms came up on the board some time ago - not much help I know - but was expalined as a natural function at certain revs with the pickup of the second turbo? Sorrry not much cop - but filed it away in the grey matter - may come back to me Cheers Paul:cool: Quote Link to comment Share on other sites More sharing options...
Alex Posted November 20, 2002 Share Posted November 20, 2002 Matt, I've always had this on my car....asked the question before aswell. I'll try to do it again tomorrow, but I think since I replaced my BOV with a recirc stock bov its stopped happening (as often as it did) I would guess its an air starvation/flow thing due to the loss of recirculation. Let me try it tomorrow and let you know. Mines a 6spd as you know and always used to do it at about the same RPM - I'd accelerate to a ton then ease off and the 'zust note drops suddenly. I apply the clutch let the revs drop - rev it up and hey presto the car sounds normal again.... It might be caused by the sequential system. IanC understands the flow etc quite well might be worth asking him to think about it. I think it is A turbo stalling. God knows how it effects egt's but I tend to "sort" the proble straight away to avoid issues! Quote Link to comment Share on other sites More sharing options...
Matt Harwood Posted November 20, 2002 Author Share Posted November 20, 2002 Originally posted by adi although i cant remember if the mkiv box has a power button. Is that like Michael Knights Turbo boost button Looks like you and Martin were on the right track. Isn't the power button the same as the manu button? Paul, I'm starting to think that its a common thing but my only concern was that I can't remember if it used to do it and I've become more aware of it recently. Perhaps more noticable due to the Hiper. Quote Link to comment Share on other sites More sharing options...
Dragonball Posted November 20, 2002 Share Posted November 20, 2002 Matt - is this the same Link ; Tecnical - One or two problems - Graham Rudd Paul:cool: Quote Link to comment Share on other sites More sharing options...
roboldham Posted November 21, 2002 Share Posted November 21, 2002 Originally posted by adi Manu mode and power mode will both stop the ignition from retarding.. although i cant remember if the mkiv box has a power button. "Power mode" - whats this? I dont seem to have this button on my VVTi? R Quote Link to comment Share on other sites More sharing options...
eyefi Posted November 21, 2002 Share Posted November 21, 2002 rob, it aint on a mkiv. Quote Link to comment Share on other sites More sharing options...
Doug Posted November 21, 2002 Share Posted November 21, 2002 Wouldn't this "power" mode be the equivalent of turning overdrive off on the MKIV? Quote Link to comment Share on other sites More sharing options...
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