Don'ts and Don'ts of Running an Atmospheric BOV

[Spec83]

Not sure if this should be in ECU/Tech or here since it's related to GTI's, Anyway...

Just a word of warning if you are planning to use an atmospheric or semi-atmospheric BOV on you Polo GTI (or 1.8t for that matter). I recently had the ECU re-tuned and not long after fitted a Turbosmart Kompact dual-port bov as a replacement for the stock diaphragm diverter valve.

I set the dual-port onto the hardest setting with 50% of the flow on closed throttle going to atmosphere and 50% recirculated back into the plenum. No check engine warnings were displayed and the car only displayed the occasional backfire on closed throttle so I thought I was sweet... But there were much bigger problems brewing as indicated by the VAGCOM readings...

I started to notice that timing and boost were being pulled by the ECU at ~4-4.5k in 3rd and 4th gear quite often (I thought it was the ambient temps being QLD summer) but merging onto the freeway Thursday I heard the dreaded 'tap tap tap' of detonation. I lifted the accelerator and began to do some more testing and every time I would hear a 'tap tap tap' then the ECU would cut the boost and timing.

I had Jimmy do some logging when the car was serviced on Saturday and he noted that the timing and boost were being retarded significantly in the load gears (3,4) but we could not figure out the exact cause. He seemed to think it was air fuel mixture as everything else checked out fine.

As only the BOV had been changed since the ECU tune, I removed the trumpet and blanked the atmospheric part off. All of a sudden the car pulls hard and clean in all gears right through to redline.

In the end, the problem seems to have been that the A/F ratios were rich-as on the 1-2 and 2-3 gear changes as half the air was exiting the system through the BOV (as correctly detected by O2 sensors in the exhaust) so the ECU leaned the mixtures off to compensate, resulting in knocking in the 3rd and 4th (load) gears as the ECU tried to figure out what the hell was going on!!! This all but sent the car into limp mode.

It was only a bit of luck and the ECU's knock sensors that saved me from splitting a piston or something worse.... So you have all been warned, don't use an atmospheric or semi-atmospheric BOV on these engines!!!

Jimmy or others, please feel free to elaborate some more if I have left anything out!!

[noone]

Good info. I believe the Forge one only was 30 or 40 % atmo when split, did not run it split for long, but didn't have any issues that I saw / felt.

[Blitzen]

Yeah, the Forge allotted DV was apparently designed just for the VAG motors, and it is a 30%/70% split between atmo and recirc... I ran one for over 18 months and never had a drama with it.

[Chuck]

i have a forge valve...if i wanna make it full recirc, once i have replaced the trumpet with the plug, which way tdo i tighten the adjustment??

[noone]

The adjustment is for the boost pressure, not for change to circ. From memory I have mine 38 clicks clockwise from fully anti clockwise (lower boost).

[Pommie]

That sounds just like my pinging problem, I to have a BOV going half/half - I will change mine to full recirculating and see if it's any better.

[Pommie]

Bugger - I tried it but never worked for me, looks like I'll have to put my hand in my pocket

[hazrd]

hmmmmmm

have just closed mine off for now, never really had a problem, but the last thing i would want is detonation lol

[WHTPOLOGTI]

Had mine set up at 30%/70% split between atmo and recirc. Ran ok for about a week. Then all of a sudden kept going into limp mode as soon as i hit boost. I then put the plug on and removed the trumpet. After that boost came on nice and hard. I was getting a error code when running diagnostic tests so removed it all together

NOW FOR SALE $140 pick up in south/eastern suburbs melb

[Jmac]

Guys this was pulling up to 10 degrees of timing, third gear was real bad, hard to describe really but in theory the (missing air) that you dump to atmosphere upset the apple cart, 02 sensor i reckon detected this and leaned her off and as you progressed though 3rd and loaded it up it was already lean and the timing pull went haywire. i call it Warranty mode, Ecu went into warranty mode. Anyway now that the system has the recirc air now its a wee strong Polo again.
Doent upset the Jap cars like that but just look at the next white Skyline you see, bet you the bar cover is covered in soot. recirc air goes to atmosphere and the mix gets richer. 1.8T just too smart. They just dont like dumpers. Some do get away with it but i would opt for strong piston type Divertor any day on the 1.8T
Laters
Jmac