23 replies to this topic

[Graeme Lambert]

Okay, Took the VXT out for a short drive to pick the G/F up from School (she's a teacher before anyone gets smart!) and noticed a lack of power in the 3-4,000rpm area. Now i've read up plenty on this infamous flatspot, but does anyone have any rolling road graphs or suchlike to show what is happening? Specifically i'm curious what happens to the boost at this point? My VXT is standard (as far as i know - having just bought it a couple of weeks ago), save for full Larini system but it does have a boost gauge fitted. Anyway, when flooring (as in full-throttle) the boost peaks about 10-12psi around 2,000rpm and backs off to about 8-9psi up until 3,000rpm. At this point it decreases, to around 2-3psi i reckon (may actually be even less - almost no boost at all) and the car feels like it hits a virtual brick wall. By 4,000rpm it is picking back up again and the next couple of thousand RPM see's the boost increase once more. Having chopped in a modified Saab turbo with gobs and gobs of mid- range boost it's not only a strange feeling, but a disappointing one as well. It's severe enough that even my girlfriend can feel it from the passenger seat So is this the flatspot issue, or is there something else the matter? Have read about and thought of; Dump valve releasing the boost (though why only at 3-4,000rpm?) Intake pipe collapsing (standard one fitted i think) Weak actuator (though again why at same point, and where flatspot is traditionally?) There's no smoke from the turbo, and no particularly strange noises (though i don;t have much reference apart from the 18 year old Saab turbo...) I need to test out what happens under a 50-75%throttle to see if the same symptoms appear but haven't had the chance yet. Not sure if that will make a difference? Further info: it's always run on BP ultimate or Optimax/V Power and it certainly happens in 3rd and 4th gears (not dry enough to try 2nd) In the meantime, peoples thoughts and tips on how to diagnose would be appreciated. Cheers, G

[p4cks]

I always understood it was the pre-cat being restrictive, as the 'flat spot' area is where the measurements for the EU emissions figure is taken. It's the manufacturers purposely restricting the emissions so that it passes these regulations. It happens a lot, and not exclusive to the automotive industry.

[siztenboots]

standard z20let turbo, some nasty texaco 95ron that was the only petrol garage for miles, on a hot summers day.

the map is a courtenay stage 3 from 2007, as you can see nice overboost , the turbo can't really flow enough at the top end for big bhp figures but the low and mid range torque is very useful on road and track.

[spuk87]

Anyway, when flooring (as in full-throttle) the boost peaks about 10-12psi around 2,000rpm and backs off to about 8-9psi up until 3,000rpm. At this point it decreases, to around 2-3psi i reckon (may actually be even less - almost no boost at all) and the car feels like it hits a virtual brick wall. By 4,000rpm it is picking back up again and the next couple of thousand RPM see's the boost increase once more.

2-3psi doesn't sound right at all to me

[walkes]

It's just a crap mapping imo..... orignially had a stage 1 remap only and made the car more driveable.... stage 2 sits year eyeballs into sockets a stage 3 feels like you have sh** yourself.... Personally stopped at a stage 2.

[Graeme Lambert]

Anyway, when flooring (as in full-throttle) the boost peaks about 10-12psi around 2,000rpm and backs off to about 8-9psi up until 3,000rpm. At this point it decreases, to around 2-3psi i reckon (may actually be even less - almost no boost at all) and the car feels like it hits a virtual brick wall. By 4,000rpm it is picking back up again and the next couple of thousand RPM see's the boost increase once more.

2-3psi doesn't sound right at all to me

Nor me either, which is why i'm interested to see if anyone has a graph (preferably with boost plot) of a standard car.

Can't help feeling it must be something else apart from just the mapping/flat spot. Which is why i was wondering if it was intake pipe, dump valve or actuator arm.

As long as i haven't bought a pup

G

[snotvomit]

2-3psi doesn't sound right at all to me

Nor me either, which is why i'm interested to see if anyone has a graph (preferably with boost plot) of a standard car.

Can't help feeling it must be something else apart from just the mapping/flat spot. Which is why i was wondering if it was intake pipe, dump valve or actuator arm.

As long as i haven't bought a pup

G

I get the same thing in mine. The first time it happened, I thought it was fuel starvation or something.

Loads of power up to about 3200 RPM, then it's almost like I've come off the throttle, then loads of power again from about 4200 onwards. I'm considering a remap just to get rid of it - I don't really want more power but it would be nice to have smoother delivery.

[Graeme Lambert]

2-3psi doesn't sound right at all to me

Nor me either, which is why i'm interested to see if anyone has a graph (preferably with boost plot) of a standard car.

Can't help feeling it must be something else apart from just the mapping/flat spot. Which is why i was wondering if it was intake pipe, dump valve or actuator arm.

As long as i haven't bought a pup

G

I get the same thing in mine. The first time it happened, I thought it was fuel starvation or something.

Loads of power up to about 3200 RPM, then it's almost like I've come off the throttle, then loads of power again from about 4200 onwards. I'm considering a remap just to get rid of it - I don't really want more power but it would be nice to have smoother delivery.

Reassuring to hear it's not just mine...
Do you have a boost guage - do you know what is happening to your boost?
Would be good if i can persuade an experienced VXT'er to come out as a passenger to give their opinion (promise i'm not a nutter).

G

[Duncan VXR]

2-3psi doesn't sound right at all to me

Nor me either, which is why i'm interested to see if anyone has a graph (preferably with boost plot) of a standard car.

Can't help feeling it must be something else apart from just the mapping/flat spot. Which is why i was wondering if it was intake pipe, dump valve or actuator arm.

As long as i haven't bought a pup

G

I get the same thing in mine. The first time it happened, I thought it was fuel starvation or something.

Loads of power up to about 3200 RPM, then it's almost like I've come off the throttle, then loads of power again from about 4200 onwards. I'm considering a remap just to get rid of it - I don't really want more power but it would be nice to have smoother delivery.

Reassuring to hear it's not just mine...
Do you have a boost guage - do you know what is happening to your boost?
Would be good if i can persuade an experienced VXT'er to come out as a passenger to give their opinion (promise i'm not a nutter).

G

If you end up coming round my way, can take you out in a stage 2 prepped car and stage 4 but agree stg2 more than enough will less comp for on road manners

I would never run a stage 4, stage 2, 5 or Tsi power

DG

Oe has a def flat spot but should not be that bad? Would need to go out in it to confirm fully but std map is a bit pants imo

[KurtVerbose]

the 'flat spot' area is where the measurements for the EU emissions figure is taken.

That's right, 4000rpm. Think it's noise rather than emissions though.

Bikes suffer from it too. All remaps seem to be able to fill the hole in.

[Graeme Lambert]

If you end up coming round my way, can take you out in a stage 2 prepped car and stage 4 but agree stg2 more than enough will less comp for on road manners

I would never run a stage 4, stage 2, 5 or Tsi power

DG

Oe has a def flat spot but should not be that bad? Would need to go out in it to confirm fully but std map is a bit pants imo

I expect i'll go for stg2 at somepoint, but for now i want to make sure it is running correctly as a standard car. So in the meantime it sounds like i need to track down what is making the boost drop by so much...

If this really is just a fault of the map, then i cannot believe that any automotive engineer would sign this off.

G

[siztenboots]

If you end up coming round my way, can take you out in a stage 2 prepped car and stage 4 but agree stg2 more than enough will less comp for on road manners

I would never run a stage 4, stage 2, 5 or Tsi power

DG

Oe has a def flat spot but should not be that bad? Would need to go out in it to confirm fully but std map is a bit pants imo

I expect i'll go for stg2 at somepoint, but for now i want to make sure it is running correctly as a standard car. So in the meantime it sounds like i need to track down what is making the boost drop by so much...

If this really is just a fault of the map, then i cannot believe that any automotive engineer would sign this off.

G

I think we might need to check the vacuum hoses for any leaks and it might be a good idea to replace the boost control solenoid and the spring pre-load on the actuator.

[Duncan VXR]

If you end up coming round my way, can take you out in a stage 2 prepped car and stage 4 but agree stg2 more than enough will less comp for on road manners

I would never run a stage 4, stage 2, 5 or Tsi power

DG

Oe has a def flat spot but should not be that bad? Would need to go out in it to confirm fully but std map is a bit pants imo

I expect i'll go for stg2 at somepoint, but for now i want to make sure it is running correctly as a standard car. So in the meantime it sounds like i need to track down what is making the boost drop by so much...

If this really is just a fault of the map, then i cannot believe that any automotive engineer would sign this off.

G

I think we might need to check the vacuum hoses for any leaks and it might be a good idea to replace the boost control solenoid and the spring pre-load on the actuator.

good start Steve, you know the suspects

DG

[moospeed]

As long as i haven't bought a pup

G

I don't think you've bought a pup G. When Whippet took me out on the test drive of my future toy I think we were less than a couple of miles in before I said "well, you can definitely tell this was mapped at Flatspot City". As you know, mine is standard with just the larini backbox.

I had the same thoughts about the intake pipe collapsing slightly but when I asked elsewhere it seems that people weren't fitting the pricey alloy pipes to fix this issue.

I'd say that mine has that dip just below 3k and starts to get back on it properly just under 4k. As mentioned, it's almost as if your foot has slipped slightly off the throttle. I always had it in mind to go for a mild map but I may well lose the pre-cat beforehand anyway so I'll let you know if it makes a difference. It won't be for a little while yet though - got some other bits to do on it first.

Part of the problem is that now you've driven it a few more times (probably more than I have with mine now) you've gained enough familiarity to spot the niggles and focus on them. A condition curable with money

[hairy]

Curves from TIS, so just a mapping issue[attachment=22714:00031319-torque and output curves.pdf]

[snotvomit]

Curves from TIS, so just a mapping issue[attachment=22714:00031319-torque and output curves.pdf]

Very informative. I must arrange remap.

[Cookies220]

I have discussed this with John from CMS. He told me that in standard map, the ECU overboosts at low revs to give the car some low down pulling power, but it's not sustainable hence the reason why the boost backs off at around 3 - 4 k. It then winds back up over 4k. This gives the impression of a flat spot. If you have a boost gauge installed you'd see this overboosting in action.

[spuk87]

I think most people are aware that there is a flat spot there and it is for the reason as cookies220 has said above, however there is no way it should be dropping to 2-3 psi. It should be overboosting then drop to just below the 'steady' boost level and maintain around that sort of level with a slight decrease as the revs go up to the redline. Something is definitely right if it's dropping that low.

[Graeme Lambert]

Update: Just been out for a drive in the car. It didn't happen all the time today, though it did most times. On part throttle i can almost drive through it, but full throttle it's almost always there. It's hard to diagnose on my own, trying to look at the boost gauge and accelerate hard on the wet roads! However, the boost does actually drop off completely. Think i need to double check that the boost gauge registers Zero pressure when the engine is off, just in case it's not properly accurate. I do have plenty of vacuum though, around -25psi when idling, which seems pretty healthy to me. One thing i did notice was the car makes a bit of a wheezing noise when boosting. Given my vacuum levels on idle I'd be surprised if this was split or holey hose, as i would have thought this would have affected the vacuum at all times? Unless of course the hole/split was only actually opening under higher boost pressure (hence why it always happens more under full throttle?). Also, would the ECU not detect this air leak and throw an EML? My thought was that it might be the dump valve maybe? Strange that it always happens at the same spot as the usual flat spot though. One other thing - it has been raining a lot recently, and the car has been outside without a water ingress cover or car cover. There's no misfiring or problems starting etc so not sure if this is relevant? On a plus note, i did fix my innoperative screenwasher today! G

[Vespa]

I would check the Intake pipe hasn't perished and/or collapsing under boost as this would cause the drop in boost you're talking about. When you put your foot down the turbo will spool up and cause high vacuum in this pipe, mine used to collapse and then sprin back into shape higher in the rev range when our little turbos can't maintain that level of boost. The other thing that seems to be a problem for some people are the boost solenoids and well worth changing as they're not so expensive from autovaux. If the diaphragm in the recirc valve is split I doubt it would create the symptoms you've mentioned. If a vacuum pipe had split or come off you would loose boost across the whole rev range. Have you done the airbox mods? This may help with intake pipe collapsing and is free