[JamesM3M5]

Got an interesting case. 2008 335Xi 6MT, stock, 62k miles.

6th gear, 1500-2000RPM cruising (50-60MPH), floor the throttle, it is quite slow, then half engine light comes on the display and 30FF code is stored. The engine feels fine, but the turbos seem a tad bit laggy. The engine pulls to 7000RPM just fine under boost, no underboost codes when driving normally or hard. It only does this in 6th gear, low RPM, sustained high load.

I have checked the following:

Full boost pressure test from turbo outlets to motor - no leaks
Found bad boost control solenoid, replaced
Updated programming in ECU with factory new software (don't know the BMW version)
Checked for carbon deposits - minimal, not enough to hinder performance
Full vacuum system check - holds 25inHg vacuum for 20+ mins, no bad lines or cracked accumulators.
WG actuators move smoothly, completely shut by about 7inHg. Tested cold and hot. Already seen one car with a bad turbo, WG shaft was binding in the turbine housing due to excessive wear.

I do not have a BT tool to check operating parameters. The Autologic doesn't tell me anything about boost or wastegate duty cycle, so I'm at a loss.

Final step is to pull the downpipes and inspect the turbines and shaft play / pull turbos. Turbos are silent, build boost just fine in any other gear, and the car accelerates like a stock 335Xi (not that fast). Compared to my E92 335i, the turbos do have a bit of lag, and the car is overall a tad bit slower, but that could be partially due to the Xi drivetrain.

I'm trying to figure this one out without the time and expense of pulling the turbos to find nothing wrong.

Anyone have any ideas?

[rader1]

James, why not invest in a BT? I'm suprised you don't have one. Maybe you should install a vaccuum boost gauge, just to check and confirm boost.

[bv1]

If you haven't already check the vacuum lines behind the oil filter housing.

[litz4244]

On the thick vaccum line from the vaccum pump to the booster there is a tiny vaccum line that tees off to the rear for the vaccum flap for the exhaust. See if thats torn. I seen a 535 with the exact same problem whoever did the high pressure pump recall torn the line.

[Joshboody]

vacuum canisters: Pull solenoid input, plug it, and use vacuum pump at the 3.5mm hose start behind the oil filter... see if you loose vacuum.

Test the vacuum to the WG by pulling solenoid outlets, plug one, and vacuum pump on the other.

what about vacuum pump... I get 17" from each solenoid at 60% DC. But newer software probably leaves WG open.

[Joshboody]

Originally Posted by litz4244

On the thick vaccum line from the vaccum pump to the booster there is a tiny vaccum line that tees off to the rear for the vaccum flap for the exhaust. See if thats torn. I seen a 535 with the exact same problem whoever did the high pressure pump recall torn the line.

+1 good one... never would have thought of it.

[Z3->WRX->335]

I've heard the vacuum line is often the culprit. I get the same code when I run Cobb Stage 1. I still haven't been able to figure it out so the AP has been sitting in my desk for months.

I've heard one or two people mention that they upgraded their DV's and the 30FF went away...

[litz4244]

Originally Posted by Joshboody

+1 good one... never would have thought of it.

Thank you sir. I have seen so many crazy problems with these cars its not even funny. Also like everybody else stated check the vaccums lines that tee off that vaccum pump line to the booster taht go to the waste gate soliniods for tears. Anything on that circuit off the vaccum pump will cause it. And you wont see it with a boost leak test if its on that circiut due to it not being completey seperate circuit for the intake system.

[JamesM3M5]

Forgot to mention that I've tested the vac pump and all related lines. The system holds vacuum for 20+ minutes. Vac pump pulls down to 25inHg within a few seconds of running at idle, holds 25 at all RPM levels. Checked for perforated or burned lines, cracks in the accumulators, nothing!

I made two caps last night on the lathe for the turbo outlet pipes, one with a fitting to pressurize the entire intake tract minus the turbos. I can push 15+ psi with only a little hiss from the crankcase due to ring blowby.

[litz4244]

Originally Posted by JamesM3M5

Forgot to mention that I've tested the vac pump and all related lines. The system holds vacuum for 20+ minutes. Vac pump pulls down to 25inHg within a few seconds of running at idle, holds 25 at all RPM levels. Checked for perforated or burned lines, cracks in the accumulators, nothing!

I made two caps last night on the lathe for the turbo outlet pipes, one with a fitting to pressurize the entire intake tract minus the turbos. I can push 15+ psi with only a little hiss from the crankcase due to ring blowby.

Where all did you check vaccum at? I assum and the pwm solinods and the canisters. Did you also check in the rear of the car by vaccum flap? In the trunk there should be a solioniod with a vaccum line that comes for the engine bay to that then to the flap. I would check it back there just to make sure.

[litz4244]

sorry about the spelling I was typing to fast.

[litz4244]

Do the wastegates rattle?

[E90SoFlo]

I have the 30ff code currently and I'm awaiting new DV's. I will update when I get them installed.

[JamesM3M5]

Just to be sure, I checked vacuum at the accumulators. I have the system fully closed, all lines hooked up (booster, rear exhaust flap, etc), and a manual vacuum pump connected. I pulled 20inHg on the system and waited - no drop.

I also have a lead to connect to the solenoids. With the crossover hose pinched down (since I only have one lead, can't acutate both solenoids at the same time), the WG actuators move smoothly and pull fully shut many cycles before I have to manually pull the system down again. Checked both front and rear acutators and solenoids. I did find a bad rear solenoid last week, but the problem persists.

If the rear exhaust flap hose were leaking, I'd see that in the tests. It is indeed hooked up and undamaged.

[Joshboody]

maybe its the combination of load, available vacuum at the low rpm, and these WG requiring more DC then typical. Have you teed off a vacuum gauge and watched it inside the car while driving?

[JamesM3M5]

Originally Posted by Joshboody

maybe its the combination of load, available vacuum at the low rpm, and these WG requiring more DC then typical. Have you teed off a vacuum gauge and watched it inside the car while driving?

That was going to be the next step. I have had the damn thing apart a few times now, and I'll have to put the charge pipe back on the turbos to have another go.

Odd thing is that the vac pump pulls 25inHg - 5 more than my manual pump - very quickly, at idle speed.

[JamesM3M5]

Other odd thing is that someone has been in here before. The 4 Torx screws that hold the solenoid mount / heat shield to the side of the head were loose. The left radiator mount is also loose and allowing the radiator to hang down. This car is weird.

[MDORPHN]

For us amateurs, it's interesting to see how you're going about diagnosing this.

I hope you keep us posted!

Thanks.

Neil

[JamesM3M5]

OK, so now I think we have a weak turbo:

I ran two vacuum gauges: one at the source from the vac pump, one after the solenoids. For those who do not know, the solenoids run in parallel - there is no controlling individual turbo wastegates with this system. There is a hose that connects both of the control sides of the wastegate solenoids. Both WG actuators move the same.

So the source vacuum was the control (constant 25inHg), and the post-solenoid gauge tells me what the solenoids are doing to control vacuum at the WGAs. Previous testing shows the WGs are closed at 7inHg. Any vacuum source over that holds the WG shut tighter.

Cruising: 14inHg (WG shut)
Increased torque demand: 20inHg (WG held tightly shut)
Boost onset: Sudden drop to 6-7inHg, modulates boost at this range to prevent overshooting boost target
Overrun (lift throttle): 14inHg

This car has a problem at low RPM, 6th gear, high torque demand:

1700RPM cruise, 6th gear: 14inHg
Depress pedal to the floor: 20inHg
Wait 5+ seconds, poor acceleration: holding 20inHg
After 7+ seconds, boost system deactivates: 5inHg
Release throttle: 10inHg
Full throttle: 5inHg

5inHg is not enough to shut the WGs, so this is how the ECU deactivates boost as a result of a fault. When you let off the throttle, however, it still behaves in the exact same manner by shutting the WGs (for exhaust noise?).

So I think we have a defective turbo - either it sucked in debris and damaged the compressor wheel (this car must have been previously modified, too many signs point to it), or has a melted/damaged turbine wheel. I have half a mind to scope the cylinders to check piston crowns and bores for detonation or other major issues. But damn, this thing runs seemingly OK unless you do the above process.

[B_davis]

STETT CP + Forge DVs fixed my 30FF problem

[Jeff@TopGearSolutions]

James, who does WOT in 6th gear at low RPM? Downshift!

[Joshboody]

bypass one of the solenoids so it's getting direct vacuum and use only 1 solenoid, reset adaptations... may fix the code.

btw, my WG seem to fully close at closer to 15", but I don't remember exactly... this is using a vacuum pump.