[gde061]

Hi all - I have an E92 which was substantially modified by the original owner. It has a VRSF cold-air intake, tial BOV, catless downpipes, upsized intercooler... among other things. Turbos are OEM to my knowledge. Had a JB4 by previous owner, but that was removed. I owned this car for 3 years now. Overboost codes started appearing about 2 months ago. The boost pressure can thingies (I think they are called solenoids) are deleted, and it has the flapper out the back of the valve cover direct VTA.

For 2 years this car had misfire codes pretty regularly, but never an overboost issue. I had it walnut blasted, and one of the coilpacks also changed IIRC and the misfire problem started disappearing and then pretty much stopped entirely and I haven't had one in over 6 months. So I got optimistic and decided to get coilovers. During that episode, the car sat at the shop for over 2 months waiting to be worked on, and when the work was done, the starter had gone bad. I mention this because I suspect the issue on the overcharge code comes from the work done to get at and replace the starter.

After having the car back for a few weeks, I started getting the overboost error / limp mode. It seems to only happen when in 6th gear when downshifting into 5th at high speeds (not particularly high RPM's... maybe between 3K and 4K). But now it's to the point where I can pretty reliably reproduce the code with that drive pattern so I am confident it's not just an intermittent gremlin. It does not seem to happen, interestingly, when downshifting in lower gears at lower speeds (i.e., 4th to 3rd at similar RPMS / around 50 MPH - no code tripped).

My Internet research has turned up a number of possible causes:

1) bad boost solenoid (like I said, I think my car doesn't have those can things)
2) vacuum hose leak / sizing of vacuum hose
3) turbo waistgate problems (e.g., v-band obstructed)
4) bent pin on ECU

Now, on #2 above, a few months before I took the car for the suspension work, I started to notice that the "WHOOSH" of the BOV wasn't happening as much, sometimes not at all, even with what I'd consider aggressive shifting. So I took it to a shop (not the one that did the suspension + starter), and they diagnosed the issue to be (a) a bad BOV and (b) thy found a break in the pressure index hose feeding the BOV... so they cut out the small section with the crack and spliced that line back together. They didn't seem to interested in fixing the BOV and for this service they charge me around $200 for their labor. I disassembled the BOV myself and replaced the diaphragm. I discovered that the spring pressure (plain brown one) had been "boosted" a bit with a single flat washer. This is apparently pretty normal to get a pressure that is between the yellow and brown springs. I left the washer in there, as the car was doing well with that setup before. There was a noticable amount of carbon on the old diaphram seat, and the shop that did this work had explained that with a VTA setup, you get less hotside oil blowby into the exhaust manifold and normally those oils help to lubricate the BOV seat. Not sure if I buy that - that carbon came from something that was probably oil gasses, but whatever.

So getting back to point #2 above, one of the solutions some people suggest in some other posts is making that index pressure hose about 4" longer. That would be roughly the amount that was removed when they spliced out the cracked section of hose.

Attempts to find a shop in Ohio that knows how to work on this car with the mods has been very disappointing. So I really don't feel comfortable handing this off to a shop and saying, "run it down". They will probably have me replacing the turbos un-necessarily - I don't hear any waste-gate rattle, but what do I know?! If I take the car back to the guy who did the suspension, he's gonna tell me to convert back to an OEM intake (in fact, when I got the car back, his tech said - "It shouldn't run right without that flapper connected ... you should be getting codes all the time"... which is not true as I researched the VTA approach a while ago and it seems like a legit option if you don't mind the smell in the cabin, which I don't care about.)

All thoughts and insights are much appreciated.

[ky0u]

Just in regards to your #1 item, the boost solenoids are not the "can things". Those are just the vacuum canisters. They sit in between the main vacuum line and the solenoids. The solenoids themselves are located on the hotside of your engine near the VC/Head seam. They look like this:

[gde061]

Originally Posted by ky0u

Just in regards to your #1 item, the boost solenoids are not the "can things". Those are just the vacuum canisters. They sit in between the main vacuum line and the solenoids. The solenoids themselves are located on the hotside of your engine near the VC/Head seam. They look like this:

Thanks for setting me straight on that. Like I said, what do I know... here's what the old Internet has to say about those canisters:

"They accumulate and hold vacuum/air to be used on both turbos. The factory plastic N54 boost vacuum tanks tend to leak and cause problems. If vacuum can't be stored the wastegates will not function, leading to common low boost or overboost faults."

Further investigation reveals some posts elsewhere on this site discussing the issue and concluding:"... they store vacuum and allow the wastegates to close faster than just using motor vacuum.... [f]or all you guys that say 'I deleted mine and it works fine'......you should run a log with them, and without. Although not a huge difference, the wastegates close slightly faster....and build boost slightly faster because of that."

So that would seem to indicate that without those cans, my wastegates would be staying open a bit too long and I might see an under-boost error, which isn't what I'm getting.

Also, had the car out today and did some more shake down: the problem does not appear on the downshift from 6-to-5 while cruising or decel, but on the downshift from 6-to-5 and stomp on the throttle to overtake as in a rapid pass on highway/track. Not sure if that is helpful, but from mechanics 101, it seems like maybe the BOV is closing too fast (or not openning up wide enough). I would say that, in layman's terms, after the diaphram replace on the Tial, the frequency of the "WHOOOSH" is back to normal, but it is more muted than it was before. In other words, it doesn't sound like a fighter jet blew by, more like a birthday balloon that went flying past.

[feuer]

Originally Posted by gde061

Thanks for setting me straight on that. Like I said, what do I know... here's what the old Internet has to say about those canisters:

"They accumulate and hold vacuum/air to be used on both turbos. The factory plastic N54 boost vacuum tanks tend to leak and cause problems. If vacuum can't be stored the wastegates will not function, leading to common low boost or overboost faults."

Further investigation reveals some posts elsewhere on this site discussing the issue and concluding:"... they store vacuum and allow the wastegates to close faster than just using motor vacuum.... [f]or all you guys that say 'I deleted mine and it works fine'......you should run a log with them, and without. Although not a huge difference, the wastegates close slightly faster....and build boost slightly faster because of that."

So that would seem to indicate that without those cans, my wastegates would be staying open a bit too long and I might see an under-boost error, which isn't what I'm getting.

Also, had the car out today and did some more shake down: the problem does not appear on the downshift from 6-to-5 while cruising or decel, but on the downshift from 6-to-5 and stomp on the throttle to overtake as in a rapid pass on highway/track. Not sure if that is helpful, but from mechanics 101, it seems like maybe the BOV is closing too fast (or not openning up wide enough). I would say that, in layman's terms, after the diaphram replace on the Tial, the frequency of the "WHOOOSH" is back to normal, but it is more muted than it was before. In other words, it doesn't sound like a fighter jet blew by, more like a birthday balloon that went flying past.

You have wastegate that is jammed up partially open/close. Probably your car feels slower/weaker and not building boost fast enough. Because the wastegate is not working the computer detects over boost but is actually under boosting.

[Saif2018]

Originally Posted by gde061

Thanks for setting me straight on that. Like I said, what do I know... here's what the old Internet has to say about those canisters:

"They accumulate and hold vacuum/air to be used on both turbos. The factory plastic N54 boost vacuum tanks tend to leak and cause problems. If vacuum can't be stored the wastegates will not function, leading to common low boost or overboost faults."

Further investigation reveals some posts elsewhere on this site discussing the issue and concluding:"... they store vacuum and allow the wastegates to close faster than just using motor vacuum.... [f]or all you guys that say 'I deleted mine and it works fine'......you should run a log with them, and without. Although not a huge difference, the wastegates close slightly faster....and build boost slightly faster because of that."

So that would seem to indicate that without those cans, my wastegates would be staying open a bit too long and I might see an under-boost error, which isn't what I'm getting.

Also, had the car out today and did some more shake down: the problem does not appear on the downshift from 6-to-5 while cruising or decel, but on the downshift from 6-to-5 and stomp on the throttle to overtake as in a rapid pass on highway/track. Not sure if that is helpful, but from mechanics 101, it seems like maybe the BOV is closing too fast (or not openning up wide enough). I would say that, in layman's terms, after the diaphram replace on the Tial, the frequency of the "WHOOOSH" is back to normal, but it is more muted than it was before. In other words, it doesn't sound like a fighter jet blew by, more like a birthday balloon that went flying past.

It's probably your Boost solenoids faulty, not the black cylindrical vacumn cannisters or cans as referred above.

Or your wastegates are shot as Freur said.

I just got an overboosting code when downshifting into 5th, getting my boost solenoids replaced, although my rocker cover is cracked and Index 1 injectors leaking, , welcome to N54 world. Getting it all sorted.

I'd recommend you start with Boost solenoids first if you have not changed them recently. Next step is probably a Turbo out job.

[PS2N54]

i had 30FF code on low rpm and downshifts (no other codes). the previous owner installed BOV without O-ring and didn't tighten the nozzle ports on chargepipe. no more 30FF

lucky for me he replaced boost solenoids and hoses trying to chase this problem. but iam going to redo the hoses anyways

[1Bad335turbopsi]

What about a 30FF low boost code what would cause that?

[Bimmer_Bro]

Originally Posted by 1Bad335turbopsi

What about a 30FF low boost code what would cause that?

A decent sized boost leak.

[1Bad335turbopsi]

Originally Posted by Bimmer_Bro

A decent sized boost leak.

Bad wastegates most likely.

[Bimmer_Bro]

Originally Posted by 1Bad335turbopsi

Bad wastegates most likely.

Which = a boost leak lol.
That's just one option though. You can still get that code with perfectly working waste gates and a leak somewhere else.

[1Bad335turbopsi]

Originally Posted by Bimmer_Bro

Which = a boost leak lol.
That's just one option though. You can still get that code with perfectly working waste gates and a leak somewhere else.

Did I mention that when I start my car it sounds like someone is beating on metal trashcans...lol...my wastegates are definitely trashed. I have smoke tested the car and have not found any known leaks.

[feuer]

Originally Posted by nzero

i had 30FF code on low rpm and downshifts (no other codes). the previous owner installed BOV without O-ring and didn't tighten the nozzle ports on chargepipe. no more 30FF

lucky for me he replaced boost solenoids and hoses trying to chase this problem. but iam going to redo the hoses anyways

Originally Posted by 1Bad335turbopsi

What about a 30FF low boost code what would cause that?

Thread is on 30 FE. Not 30 FF

[feuer]

Originally Posted by Bimmer_Bro

Which = a boost leak lol.
That's just one option though. You can still get that code with perfectly working waste gates and a leak somewhere else.

Thread is on over boost, fault 30 FE. Waste gate can get stuck in any given position, fully closed, fully opened, and anything in between.

[JR33S33S]

I've recently had new ghassan n55 remanded n55 motor installed , new dme , new wire harness new boost solenoid new BMW valve cover and valvetronics motor new crank cam and both map sensors all by a so called performance shop that seriously robbed me of over 20,000$ and car still has an over boost problem throwing car into reduced engine power mode ????? cats dme has just been flashed by a tune shop with multiple pulls and revised after revised tunes , all vacuum lines and components replaced , boost solenoid replaced , coils and plugs replaced all with genuine BMW parts from BMW , cars upgrades include stage 2 upgraded twin scroll single power turbo , downpipe, charge pipe , intercooler , jb4 tuner , full exhaust , brand new n55 motor and wire harness , brand new dme from bmw brand new bmw battery and fuel injectors yet car still has over boost upon hard acceleration putting car immediately in reduced power mode ????????? PLEASE IM DESPERATE IVE SERIOUSLY SPENT OVER 20,000$ AND LAST 2 YEARS TO CURRENT IN SHOP TIME , 4 DIFFERENT SHOPS AND OVER BOOST ISSUE STILL NOT FIXED ?????BOUGHT CAR 2 YRS AGO AS IT WAS IN ENGINE REDUCED POWER MODE AND KID WHO SOLDS TO ME SAID THAT WAS FROM TUNE IT HAD ? NOT KNOWING A DAMN THING ABOUT TUNED CARS I BELIEVED SELLER THAN 2 WEEKS AFTER DRIVING CAR , CAR BLEW CYLINDER 6 ALL WHILE HAVING THIS OVER BOOST ISSUE THAT NOW AFTER LAST 2 YEARS , NEW ENGINE , NEW DME , NEW SENSORS , NEW EVERYTHING BUT SAME UOGRADED TURBO AND SAME JB4 TUNER IS HAVING THE SAME OVER BOOST PROBLEMS! PLEASE ANYONE HELP IM DESPERATE !