used 335i has no power

[Runway9]

I just bought a used 2007 335i and I think the turbos aren't working. Runs good at low speeds but when i go WOT it pulls to 3500rpm and then losses power and stops accelerating. It feels like the turbos never kick in. How can I check if the turbos are working?

[154e90]

1. Have you scanned for any codes or have you seen any half engine signs?

2. If you pull off the vacuum hose that goes over the intake filter box, do you hear a whoosh as air enters the system? Cars with no vacuum leaks will do this long after a car has stopped.

3. If you rev the car at idle to 3000rpm and immediately come off throttle, do you hear a rattling sound as rpm drops?


Edit: attached photo of the line I'm talking about.

[Runway9]

Thanks 154e90

I don't have a code reader, but the engine malfunction 1/2 motor symbol does appear on the dash. I don't don't hear any rattling sounds from the engine at all. I"ll try the vacuum line test.

[154e90]

I should have been more specific with regards to time. A car with good vacuum lines will have vacuum well over an hour after the car is shut off. A car that has vacuum 10 minutes after the car shuts off should also have good enough vacuum lines to properly control the turbos, even if there is a small leak.

Here's a description of how the system works. I don't know how familiar you are with the car, so forgive me if this is oversimplified.

Vacuum:
The engine generates vacuum when it runs at low throttle body angles. The engine does not generate vacuum when it is at high or wide open throttle, so the vacuum canisters were added to hold a vacuum reserve under high load, when none is being generated. The vacuum supplied to the canisters comes from the brake booster line (the one I asked you to unplug). This vacuum is supplied to the vacuum canisters, the boost solenoids, and then the wastegate actuators, in that order. If there is a cracked line, there may not be enough vacuum to let the components work as intended, as air is entering the system and turning the vacuum into regular atmospheric pressure. If you unplug the line and hear nothing, then there is a leak that already let all the air in beforehand.

Edit: The N54 has a vacuum pump so that the car maintains vacuum all the time regardless of what the engine is doing. If it used intake manifold vacuum, you would get boost in the vacuum lines during WOT and have all sorts of issues. the canisters are there to have an additional vacuum reserve at high altitude. The statements I made about engine vacuum before are valid for NA engines without vacuum pumps.

The wastegates:
The turbos have a normally open wastegate flap that is only closed when vacuum is applied to the wastegate actuator. This flap lets exhaust gasses bypass the turbo so the car creates no boost. When vacuum is applied to the wastegate actuator, the flap closes and exhaust gasses are forced through the exhaust turbine, which spins the compressor wheel, which makes boost. The rattle sound people often hear is this flap rattling against the bypass port it seals off. This is fixed either by adjusting the wastegate actuator rod, or fixing an issue with vacuum supplied to the wastegate actuator.

Boost solenoids:
The boost solenoids have an input vacuum line and an output vacuum line. The input line connects to the vacuum canisters. The output line connects to the wastegate actuators. These are controlled by the computer using a square wave signal. This turns the solenoids off and on really quickly. This connects the wastegates to the vacuum lines and disconnects them very quickly. The duty cycle or "% on time" of the signal from the ecu to the boost solenoids controls vacuum pressure to the wastegates, which controls how closed the flap is, which directly controls boost.

If your car has a massive vacuum leak, the wastegate actuators will never move and you will never have boost. This is why you are checking if the brake booster line holds vacuum.

[JDStrickland]

Danger Will Robinson, danger.

I hope you paid a discounted price for this car because the turbos are costly to replace/repair.

[White94RX]

A proper diagnostic scan is usually the first step in fixing any BMW. Especially when the reduced power and check engine light comes on. Your car can tell you what is wrong.

[Runway9]

I was totally wondering how it all worked, that is awesome thanks 154e90 . I think I might have a vacuum leak. there was no vacuum left immediately after i turn off the engine. I guess I will be buying a vacuum tester. I didn't pay much for the car ($2300 CDN), knowing it needed some work. I just hope the turbos are good. thanks again.

[154e90]

Here's the tester I have. It's useful both as a gauge and as something that can generate vacuum to test lines. You should be able to find this in Canada easily somewhere. It has adapters to plug off and connect to the lines you need to test.

I can share more info on how to test the lines/boost solenoids once I get off work.

https://www.amazon.com/dp/B0035533Q0..._HJRmFbH8D8DQ2

Sent from my SM-N950U1 using Tapatalk

[JDStrickland]

Google BMW N54 TURBO FAILURES

At one point there was (perhaps there still is) a class action lawsuit on this. Related but different is the High Pressure Fuel Pump.

[154e90]

A lot of dealerships replaced turbos because of worn wastegate arm bushings that would be fixed by rod adjustment. Even if the wastegate flaps are warped, you can have new ones welded in at a significant savings from new turbos.

I wouldn't worry too much yet.

Sent from my SM-N950U1 using Tapatalk

[154e90]

I'm not sure where you are with obtaining a pressure tester, but here's a starting point for testing.

Take the engine cover off to see the two lines that go from the vacuum reservoirs to the brake booster line. Test them by plugging one side with your finger or a vacuum plug and using the tool to pull vacuum on the other end.

Do the same with the lines that go from the vacuum reservoir to the boost solenoids. Test the reservoirs too. There can be hidden cracks. Be careful pulling the lines off. It's better to just cut the lines off carefully and replace them than break a $70 boost solenoid barb while trying to test $2 worth of hose.

Once those lines are tested or fixed, test the input vacuum to the boost solenoids. If that is good, test the output vacuum of the boost solenoids. You should see 10-15 inhg at idle and see 20+ when revved. The output lines are connected together once they leave the boost solenoids. I used the plugs and a T barb to send the output from one solenoid to one turbo at a time while measuring. If you have an active half engine sign the ECU won't command the solenoids to build boost, so restart the car If you need to.

You can test your wastegates individually too. Pull vacuum on each wastegate until you hear them clink closed. New wastegates will close at 6inhg or so. If they need more vacuum to close, they could use an adjustment. The back can be done easily, but the front requires removing the water pump, thermostat, and maybe the downpipes. Pulling downpipes gives you a chance to inspect the wastegate flaps for warping too. If they close with less vacuum than your boost solenoids output at idle and don't rattle, an adjustment isn't absolutely necessary as long as they close with less vacuum than your solenoids output at idle.

I can't recall ever seeing the hose that goes down from the connection you first tested to the block breaking, but you live in a very different climate than I do. It's worth pulling that hose to test it too.

If you still have the issue after verifying proper boost soleboid output pressure, you can replace the lines going out of the boost solenoids and Into the wastegate actuators. The wastegate actuator barbs are metal so don't be terrified of breaking them.

If the half engine sign pops up immediately upon startup, it is probably not a "30ff boost pressure too low" code. It may be a vanos issue that requires a scanner to diagnose.

Let us know how this goes. I can answer more questions if you have them. I can send pictures of relevant connections pretty easily because I have an n54 sitting outside a car in my garage at the moment.

[Runway9]

Thanks 154e90 [I]appreciate your insite here. I haven't bought the tester yet but I followed the lines from the solenoids to the actuators and they were broken at the actuators (front one was not connected at all). So I started dismantling the front area to get at the turbo. It looks like the inlet vanes are damaged. I'm not sure what would have caused it, but I think I need new turbos. I'm not sure about the rear one, I haven't gotten to it yet. I'm not sure if I want to get in to putting new turbos in this car?? what do you think?

[154e90]

Installing new turbos might be worth it if you can do It yourself, especially with what you paid for the car. Im not sure it's worth it to pay someone to install new ones. You could also consider rebuilding the turbos with new cores. The best option depends on the condition/mileage of the car. ECS tuning has a good guide available on YouTube if you're considering a diy

Do you have images of the damaged vanes? Sorry for the late reply.

[DJCHR1S718]

hey man i am having this problem where if i drive the car and pull of the brake booster line i dont hear any noise and my car is not boosting at all.

1. Have you scanned for any codes or have you seen any half engine signs?

2. If you pull off the vacuum hose that goes over the intake filter box, do you hear a whoosh as air enters the system? Cars with no vacuum leaks will do this long after a car has stopped.

3. If you rev the car at idle to 3000rpm and immediately come off throttle, do you hear a rattling sound as rpm drops?


Edit: attached photo of the line I'm talking about.