25 replies to this topic

[james4563]

I'm sure there is something wrong with my vxt. I have this problem wher when boost reaches around 13psi the turbo seems to stall really badly, which makes the engine jerk quite a bit and unsettles the car. The stalling generally results in a lose of boost as well obviously. However, I feel that it isn't true on boost surge for two reasons, 13 psi is not much more than standard vx boost level and if plant my foot wide open throttle then it doesn't do it at all. I've done a lot of experimenting with the recirculation valve and replaced so many vacuum lines and I've tried running without the inlet BCS to rule that out. I've also ran a electronic boost controller to rule out the turbo BCS and still the same issue is present. I know at stage4 the power becomes very on/off but it never used to feel like this and it seems to me that something is wrong. Even running at 14psi which much be like stage 2 tune levels the flutter is so terrible and makes for a horrible drive. I did a long drive on the motorway last night and pulling out into the outside lane to takeover (in 5th) with very gradual thottle just results in a massive flutter and the car like bogging down and feeling really rough. The issue is present in all hears though at the same level of boost I have experimented with the spring in the forge DV to which seems to not affect said fluttering at all. I've even run with the red spring and have the same problems. Is there other things that can cause this to happen?? Maf or anything like that cause problems like this? I've had turbo cars before and never had this kind of problem.

Edited by james4563, 11 November 2017 - 11:13 AM.

[Ormes]

Probably going to expose my incomplete understanding here but...

 

Stuck penny valve, knackered actuator, or knackered boost control solenoid (actuator control).

 

Does not feel like a DV issue to me.  You are, I assume, open throttle at the point at which the turbo flutters, so my logic says the DV should just be closed at this point.  If it was open, I assume you'd just be dumping boost rather than stalling the compressor?

[james4563]

Could be the penny valve I guess. I have a turbo smart actuator which is set at about 10psi I think. I'll remove it and check the penny moves freely. You are right that the DV shouldn't open because I am on throttle. Not wide open throttle, but gradual. If I do just boot it and go wide open throttle it doesn't flutter. Does yours ever flutter ormes?? Did I read that you added a dv30 Bailey's DV??

[Ormes]

Years ago I did suffer intermittent surges, probably couldn't hear a flutter as I was running a standard intake. Usually occurred in higher gears (4th & 5th) when transitioning between WOT and part throttle, but the surge would always occur when reducing throttle input. You seem to suggest a flutter at constant throttle which suggests boost control rather than DV? Over time I've improved the symptom significantly through changing both solenoids, replacing the rubber recirc with a forge, changing most intake and exhaust pipework and remapping. It now happens very rarely and is far less vicious when it does. I think Nev has a DV30. I bought a forge equivalent but never fitted it in the end. Good luck. Not sure where you are but let me know if you are close and want assistance and a car to swap bits off.

Edited by Ormes, 11 November 2017 - 05:34 PM.

[james4563]

Which spring do you run in your forge DV? I'll check the penny and then I'll look maybe at the solenoids as they are pretty cheap. I'm located near Southampton btw, where are you?

Edited by james4563, 11 November 2017 - 06:15 PM.

[Ormes]

I recall I used the green spring when the car was in a standard state of tune, and moved to a yellow spring with the Stage 2 remap.

 

I am in Corsham, Nr. Chippenham, Wiltshire.

[Nev]

I have experimented with the spring in the forge DV to which seems to not affect said fluttering at all. I've even run with the red spring and have the same problems.

By this, do you actually mean the Forge rercic valve? As a DV can cause at least 2 issues I know of...

[Nev]

I did a long drive on the motorway last night and pulling out into the outside lane to takeover (in 5th) with very gradual thottle just results in a massive flutter and the car like bogging down and feeling really rough. The issue is present in all hears though at the same level of boost  

 

If this is true then your engine is unable to "swallow"/"consume" the boost that the turbo is pushing out. This is highly irregular. My first thought would be to check your cat and exhaust silencer has not collapsed causing high EBP.

 

 

[james4563]

I meant DV as in diverter valve, it's the one at the standard OEM location but a forge aftermarket one. Not talking atmospheric dump valve. I had wondered about what you mentioned with the too much boost for the engine, but it's fine at wide open throttle, obviously the throttle plate is open more then. It is possibly just too much boost for the amount the throttle plate is opened?? I mean 0.9 bar isn't much though. As far as I am aware the exhaust/cat are fine. I just had mot and passed without issue. No rattles or anything either from the exhaust. It's an aftermarket one but I've not idea what make, MBR didn't know either. I'm at a loss with this now lol.

[SteveA]

Start by unplugging the MAF to see how it performs. It's a 10 second job and will eliminate it as a suspect for free.

[james4563]

Just unplug and take it for a drive? It'll be okay on boost without the mad plugged in???

[siztenboots]

MAF will not cause turbo stall / chatter , its the recirc valve  , possibly also clutch pedal switch / bracket

[Nev]

I meant DV as in diverter valve, it's the one at the standard OEM location but a forge aftermarket one. Not talking atmospheric dump valve. I had wondered about what you mentioned with the too much boost for the engine, but it's fine at wide open throttle, obviously the throttle plate is open more then. It is possibly just too much boost for the amount the throttle plate is opened?? I mean 0.9 bar isn't much though. As far as I am aware the exhaust/cat are fine. I just had mot and passed without issue. No rattles or anything either from the exhaust. It's an aftermarket one but I've not idea what make, MBR didn't know either. I'm at a loss with this now lol.

 

MOT or not, I'd still start with testing the exhaust especially as you have a non-OEM (ie probably cheapo cat). The easiest test I can think of would be to disconnect the downpipe from the main exhaust and insert a metal spacer into the joint, such that the joint is open by at least 1 or 2 CM to allow the gas to escape easily. Then take it for a short test drive (only short so the gas can't over-heat nearby things like the sump). Obviously it will be noisy and your EML might temporarily come on, but it would at least show you if the silencer or main cat is a restriction. This test (obviously) won't check that your pre-cat isn't the issue.

 

BTW a DV usually means "dump valve" in car parlance (which ambiguously usually implies to atmosphere, though it could also be back into the inlet tract). However our cars have a recirculation valve, which specifically implies the boost is re-entered into the inlet tract.

 

GL.

Edited by Nev, 14 November 2017 - 01:47 PM.

[SteveA]

Just unplug and take it for a drive? It'll be okay on boost without the mad plugged in???

 

Yes and Yes.

[SteveA]

MAF will not cause turbo stall / chatter

 

Chatter I agree but it certainly feels like stall with an enormous loss of boost. Worth eliminating as a quick and free test.

[Nev]

MAF will not cause turbo stall / chatter , its the recirc valve  , possibly also clutch pedal switch / bracket

 

Surely under normal conditions when accelerating in 5th gear (or indeed any gear except 1st) the recirc should be firmly closed to allow boost to rise, so turbo stall during this acceleration period should not be dictated by the RV. Once boost has reached whatever the map says then the waste gate is opened.

 

[siztenboots]

yes Nev, duty cycle on the wastegate actuator control solenoid, determines more turbine shaft energy captured to drive compressor wheel .

[james4563]

Steve I did try what you mentioned about the clutch pedal lifting it with my foot and it didn't make any difference. I'm going to check the wastegate movement later on, make sure it's not sticking at all. I'll also try a drive with the maf disconnected just to rule it out. Will look at what you've suggested too Nev, unfortunately that's not such a quick check.

Edited by james4563, 14 November 2017 - 02:18 PM.

[Nev]

Steve I did try what you mentioned about the clutch pedal lifting it with my foot and it didn't make any difference. I'm going to check the wastegate movement later on, make sure it's not sticking at all. I'll also try a drive with the maf disconnected just to rule it out. Will look at what you've suggested too Nev, unfortunately that's not such a quick check.

 

Yea, the test I suggested would take at least an hour or two unfortunately.

 

A sticky wastegate might possibly be the problem, but if it were really sticking closed then it would mean you see 20 PSI of boost, and as you haven't mentioned this symptom it seems an unlikely candidate to me.

 

The MAF is very unlikely to be the problem, people just mention it as it is a common culprit for other issues.  

Edited by Nev, 14 November 2017 - 03:31 PM.

[james4563]

It's a stage 4, and my boost gauge has actually logged peak boost of 1.7bar (~24.5psi), which is more than it should do. As a test I have run with a manual boost controller set at 1.1bar, the problem is still present with that setup. I did wonder if it's just on boost surge, however running at those levels of boost ~16psi I don't think it should surge. Otherwise all the people with stage 2 levels of tune would be complaining of the same issue.