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Bogging Down For 3-5 Seconds On Downshifts Only

rondofj

By rondofj,
in Engines & Forced Induction

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rondofj Veteran

rondofj

Posted
Posted (edited)

Hey guys, hope you all having a good weekend, well heres my problem again which I mentioned in my past thread 'Restriction in Exhaust' but decided to create a new specific thread for it.

R34GTT running Precision 5558 @22psi on 98 with support mods, Z32 afm, Power FC, EWG off housing, stock plumbed back BOV etc.

Problem- bogging down big time down and losing 50-60% power for 3-5 seconds when downshifting ONLY. Doesnt happen in regular driving, boosting, upshifts. Didnt happen at all with my previous Nistune, exact same setup all else.

Diagnosis- went for a drive with Yavuz the tuner and he finally managed to detect what is causing it- the map tracer in the power fc commander drops 5-6 cells down during this period. He said the Z32 during this point is seeing a big voltage drop or something I dunno, and hence metering the wrong or extra airflow to the ecu which is dumping extra fuel and/or retarding timing since its thinking its seeing 15psi instead of 5psi.

Couldnt be a faulty Z32 since its only under this specific condition it happens and it didnt happen with Nistune/ same all else. He said Nistune has the filters to iron this out, whatever he meant, and they have been through my current Pfc tune three times and absolutely confident that it cannot be made better - and I agree, from driving experience, apart from this downshift issue. The only other possibility according to Yavuz is the famous n dreaded BOV recirculation issue blowing air at the afm. He had a look at my piping and said the entry angle of my bov return into the intake isnt optimal at 90 degrees and should be pointed back at and closer to the turbo intake. Have attached pics here, what do you guys think?

Scotty once mentioned it could be the CAS too, and I think he could be right also. Dont have one to try though..

Another thing with the Gizzmo IBC-R ebc I installed, boost goes up, down, up, down, up, down everytime - what causes that- have no leaks and gain is low around 10 with duty at 58, overboost at 22.5psi. Goes from 22-18/16psi back n forth.

post-49401-14021849931931_thumb.jpg

post-49401-14021850060278_thumb.jpg

Edited by rondofj
scotty nm35 Grand Master

scotty nm35

Posted
Posted

That fault is most likely the BOV return, it gives the AFM a lower voltage for a second on back off if the air flows back up the intake. It took me quite a while to work out the correct angle to return the BOV for my intakes.

You can buy a new CAS easily from Amayama, there are knock off ones on Ebay, but I wouldn't recommend them.

  • Like 1
jet_r31 Mentor

jet_r31

Posted
Posted (edited)

Still doesnt work on some cars, scotts intake was no good on mine, no matter what i did it f**ked around, randomnly stalled, hiccups of decel ,tried everything, but even tuning around it was just covering up a polished turd. AFM now in cooler pipe, its a totally

different car..autos are far worse for the problem though

cheers

darren

Edited by jet_r31
rondofj Veteran

rondofj

Posted
  • Author
Posted

Afm in cooler pipe means high boost blown thru afm = bad/damaging? Or isnt it. One other thing is, during the BOV recirculation into the turbo, the afm hasnt measured this air hence the turbo is pumping more air into the motor than measured thru afm/intake = lean/danger?

scotty nm35 Grand Master

scotty nm35

Posted
Posted

First time I have heard any bad feedback Darren, shame you didn't bring it down so I could inspect what was causing it, Were you using the stock airbox?

Personally I don't like putting the Z32 in the cooler pipe... Actually, I don't like AFM's at all. :P

scotty nm35 Grand Master

scotty nm35

Posted
Posted

Afm in cooler pipe means high boost blown thru afm = bad/damaging? Or isnt it. One other thing is, during the BOV recirculation into the turbo, the afm hasnt measured this air hence the turbo is pumping more air into the motor than measured thru afm/intake = lean/danger?

The AFM would need to be after the BOV Ron, otherwise you are right, it would run like crap... Rich as buggery.

rondofj Veteran

rondofj

Posted
  • Author
Posted

Nope u didnt get me, I meant as in stock setup with afm behind air filter, when the bov recircs into the turbo, the afm isnt measuring this air ( its only measuring air sucked thru the filter) so really the turbo is pumping more air than measured= lean :\

jet_r31 Mentor

jet_r31

Posted
Posted (edited)

First time I have heard any bad feedback Darren, shame you didn't bring it down so I could inspect what was causing it, Were you using the stock airbox?

Personally I don't like putting the Z32 in the cooler pipe... Actually, I don't like AFM's at all. :P

I don't like it either, but its better then my wife having a accident from random stalling, and ive spent enough on a family car i now rarely even drive to

get rid of afm.i didn't have stock airbox, i have a pod in a big airbox i made.

I could get it not to stall through tuning but this is the thing. If youve never driven a stocky and drove it, you would think its ok, but after driving

stockys you can tell the way it returns to idle and its general manners thats its not as nice.

i shifted the afm and didn't tell wife, after 3 days she asked what i had done to car as it now drives so nice. i'll guess ill just have to make cleaning the afm meter another service job during oil changes.

Seems to be more of a problem with autos. I even changed blow of valves, 2 stock ones, turbodumb one, then spring changes ffs.

and those stupid turbodumb ones are meant for R33 rb25's, they are a different height to standard

cheers

darren

Edited by jet_r31
rondofj Veteran

rondofj

Posted
  • Author
Posted (edited)

My problem is funny because it happens kinda off boost as well ( when theres no BOV recirc), say shifting from 3rd to 2nd at 3000rpms you get this bogging but milder, the more load/boost its under, the more pronounced- but why only during downshifts..?

Edited by rondofj
rondofj Veteran

rondofj

Posted
  • Author
Posted

Thats what I told them but they have been through the tune thrice and massaged it as best as they could, Yavuz said theres not much else they could do to the tune to make it even better.

scotty nm35 Grand Master

scotty nm35

Posted
Posted

What about the surge, is it only when you boot it? Does it happen with a full tank?

I still think its the bov return though. Does it happen if you block the BOV with a coke can?

Ben C34 Grand Master

Ben C34

Posted
Posted

If it didn't happen with the nistune and only happens with the power fc it is surely tune related.

Such a shame you ditched the nistune for no real gain, especially as they will be releasing flex fuel for the r34 ecu in the near future.

rondofj Veteran

rondofj

Posted
  • Author
Posted

Lol at coke can. Havent had coke in ages mate. Might try that trick though. Dont know about surge, yeah happens with full tank n yes when you boot it after downshifts.

BUT, if you wait a second or two after downshifting or if you very gently stab the pedal after thge downshift, it doesnt happen or you dont feel as much- depends on the load and time/nature of stabbing the pedal.

Tune related- yeh Yavuz said nistune has inbuilt filters to iron this out/tune around it but powerfc doesnt have anything they could adjust as they've fine tuned it a fair bit

  • 2 weeks later...
rondofj Veteran

rondofj

Posted
  • Author
Posted

Update - blocked off stock bov with a pepsi can block-off plate under gasket.

Result- it drives so much crisper, smoother and significantly more down low power/torque now, its amazing - boost comes on very fast (electronic boost controller duty 55 for 22psi, before it took duty 67 for 22psi) - and also much quicker to rev out 3rd to 7000 rpms whereas before it took a long time to reach 7000rpms+. Basically drives the way it should. And yes now I get that expected and unwanted gay sound - a loud flutter/bang when shifting under load.

All this leads me to believe there was a boost leak in my bov before - am I correct?? Also explains massive boost drop-off at high rpms from 22 to 12 or 13psi which is my EWG spring rate. And fluctuating boost.

AND - the huge lag/ 60% power loss on downshifts is almost all GONE. Yesss.. Chirps tyres under downshifts which it didnt do before. Extensive testing shows there's still a wee bit of lag (say 10% down on power) for half a second or 1 second - very minor and sometimes not noticeable at all. Maybe cos the air charge/boost is now slowed down a bit when releasing the throttle from the backflow since the bov is now blocked. But all in all a positive experience.

So do I keep it this way or get a new bov gasket, revert back to the way it was and relocate afm in cooler piping or change my bov intake entry angle in my intake (fabrication) ?

cheers Ron

Ben C34 Grand Master

Ben C34

Posted
Posted

Smash my bov? ah no.. ;)

Ok don't smash it. Caress it with a hammer.

Like I said to increase the spring preload.

It fixed my bov leaking which is your current Issue

Also block up the little hole with a m5 grub screw.

or think about it for weeks and do nothing. Doesn't bother me.

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