Boost Problems, what next? (video)

[montez]

I am still having problems reaching full boost with the homefrys map

I though that I had found the leak today as there was some air leaking from the n75 valve, stopped the leak but the problem is still there.

The car tries to boost to the 1.4 bar when pulling in 4th but then snaps back to about 1 - 1.1 bar

The car also drops down to mechanical boost for a few seconds after a gear change at high revs as you can see in the video here http://www.youtube.com/watch?v=51s8aKTEMBM (sorry about the quality but it gets the idea across)

I have run vagcom with no faults found and boost leak tested with a compressor between the metal intake pipe at the top to the MAF pipe on the air box with the metal breather pipe blocked off.

I now cannot see any boost leak at this side of the engine but am guessing a leak is causing my problem. What is my next step to sort this out?

(I also reset the ecu after finding the last leaks.)

[AndyP]

Try taking the 3 vac lines off the back of the inlet manifold and pressure test them. Use a blowgun like this

http://cgi.ebay.co.uk/Air-Blow-Gun-A...-/290449062524

Just press it onto the end of the vac line and see if you hear a leak.

[UrS4boy]

Jeez. Get a real boost/gauge with numbers, not something you stole from a Volvo.

And have somebody else hold the camera. Can't see anything useful with all that bouncing.

BTW, looked normal to me.

[montez]

Yeah i know the camera man was poor but you can see how it holds on mechanical after gear change, surly there should not be a massive lag on boost between gear changes, i am just wondering if my spring on the diverter valve is too high but it was recommended by Forge Motorsport.

I have tested the three lines on the back of the manifold and there was a slight leak on the one going to the rear diff line. That is now sorted and i took it for a test run.

The car is again boosting up to 1 goes up to 1.4 and backs of to 1 very quickly.

As for the boost gauge it is all i could afford at the time, it does has numbers, it is just bad camera man!!

[UrS4boy]

Yeah i know the camera man was poor but you can see how it holds on mechanical after gear change, surly there should not be a massive lag on boost between gear changes, i am just wondering if my spring on the diverter valve is too high but it was recommended by Forge Motorsport.

I have tested the three lines on the back of the manifold and there was a slight leak on the one going to the rear diff line. That is now sorted and i took it for a test run.

The car is again boosting up to 1 goes up to 1.4 and backs of to 1 very quickly.

As for the boost gauge it is all i could afford at the time, it does has numbers, it is just bad camera man!!

1. Replace Forge valve with OE style plastic 710N Bypass Valve and report back changes/improvements. This will give us a base line and take the Forge spring out of the equation. Have a read on this:

http://forums.quattroworld.com/s4s6/msgs/20994.phtml

2. Do we have any idea of what hardware/software level you are running? 1.4 Bar is 20.3 psi (relative) which is about normal for a Stage 1 level of chip s/w with the OE 250 kPa (2.5 Bar) MAP sensor and OE K24. 1 Bar is 14.5 psi, which for a stock K24, isn't a bad holding level.

3. I have looked at that video several times and there isn't one frame that it is in focus so we can read the numbers. This is the best there is (enlarged - still can't be read):

[montez]

1. I replaced the forge valve with the original and tested the, I am getting the same results at about .1 of a bar less as there is a slight leak from the casing.

2. The car is running one of the S2Central the home fry ecu's and should be hitting 1.4 bar of boost and has one of the heavy duty n75 valves http://www.s2forum.com/forum/showthr...&highlight=n75 but apart from that is standard.

3. I have uploaded some new videos filmed by a better cameraman on a smoother road, videos where filmed with oe dv in place, with forge the same happens at fractionally higher bar (just skims the red on gauge in 4th)

This shows gear change from 2nd to 3rd at 6500rpm you can see in second it tries to go up to one bar then backs off a little, then after the gear change it holds mechanical boost for a few seconds before the boost kicks in, you can really feel the power loss in the carhttp://www.youtube.com/watch?v=T32iEMWzLDU

This shows running from 4th gear from about 2000rpm to 4500rpm on the flat, it should be holding about 1.4 bar http://www.youtube.com/watch?v=cQ8H8IEEe84

[simon20vq]

What do I know but have you connected the n75 the right way?

[UrS4boy]

1. The OE BPV should not leak, even slightly

2. Was the homefries "fried" to take into account the "heavy duty" non-stock, non-Eaton N75? If not, there's your issue. If is was, talk to Paul or S2bo about the s/w and the WGFV. Personally, I don't think there is anything wrong with the OE Eaton N75, e.g. the "H" or the "K" versions. I would go back to an Eaton WGFV.

3. Better video (thanks). Have you proven 100% that you do not have a boost leak somewhere, i.e. by pressure testing from the turbo outlet to the throttle body? I know you don't have an AAN but here are my thoughts on what needs to be blocked off during such a test (no more than 1 Bar is needed):

[montez]

1. The casing was slightly damaged to the oe valve and was verified to be leaking with pressure test with the compressor.

2. From reading up on the Heavy duty WGFV I can see that it works fine with the home fry ecu and no other people have had any problems. I tried swapping to my original valve but as I remember the unit is completely dead, hence why i ended up with the new unit.

3. I have tested the system up to 1.5 bar blocking off the intake pipe at the maf the intake pipe at the throttle body and blocked the pipe to the engine breather. I checked the pipes, connections and inter-cooler with soap and water for any leaks. I also tested the system going into the throttle body pressurising the intake manifold I found a small leak on part of the breather system by the valve for the carbon canister.

I will put the original n75 back on the car so I can drive it and put the dv back in with the lowest rating spring.

[montez]

I have also just pressure tested it the way you suggested in your diagram before putting all the parts back on and it is holding 1.7 bar of pressure fine. There are no leaks in the intercooler or the connecting o ring.

[montez]

I have now cleaned the maf + connectors which has made the idle a little bit smoother, I have also disconnected the MFTS to see if that is making any difference. I will take it for a quick run when the traffic has died down to see how it is boosting now.

[montez]

I am quite certain there are no boost leaks now but the car is still going up to about 1.4 bar for a split second then backing off to 1 when accelerating. As well as this it is still dropping back to mechanical boost after gear changes. I have managed to get the car up to 1.4/1.5 on the gauge for the first time now going up a long hill in 4th gear at about 3500 rpm.

I am thinking that at highest rpm on a gear change the wastegate is open at its fullest, if it is at all sticking a little when i change gear i will continue to get low or mechanical boost until it gets to the correct position. Is this possible or am i way off the mark?

[montez]

I have just checked the wastegate spring and was not sure if the perch was at the right height it is supposed to be at 25mm but the ledge was at 20, I have some spacers from an old superchip modded wastegate which I have put in and it has slightly changed the problem. The boost now comes in harder and holds better than previous especially considering the outside temperature, and now when I change gear the boost instantly comes back in which it was not doing before then drops then comes back in again.

Am i going along the right lines with the wastegate, I changed it when i got the car to get rid of the superchip setup I replaced it with an AAN wastegate but I thought the spacing where all the same?

P.s all the other wastegate caps which I have seen have the top perch allen bolted into place, mine did not??

[S2central.net]

maybe the WG was mangled before... try unplugging the N75 and driving the car... should see ~0.4bar max boost that is derived by the WG spring on its own... you can go a little stiffer than that and stay within adaptation limits of the ECU but you cannot go mad with a monster spring.

Have you double checked the DV is oriented the right way ?

Have you checked the WG diaphragm isnt leaking ?

[montez]

I have checked both the wastegate diaphragm and that the dv is in the correct orientation, like i said spacing the spring by 5mm has made the car spool a lot quicker and pull harder but i am still getting mechanical boost after a gear change.

I am really stumped as to what it can be as checked about every sensor going now and have no boost leaks, and turbo seems fine.

It does not seem as if the turbo is stalling at gear change but the car is boost cutting back to wastegate spring boost.

Do you think it could be detecting knock at high rpm and and boost cutting at the gear change, you can change gear up to about 4500/5000 rpm and the car will boost ok in the next gear.

Have spent hours reading the forum and cannot find anyone with the same symptoms