Is it a boost leak or just a bad boost solenoid?

[WedgePerformance]

In the past month I have been testing pump / meth on my Pure Stage 2 car and started to notice my boost taping off. I was running a map that should have been pushing 21 psi without issue, but I was only hitting 18. Two week later 13 psi. Normally if you had a boost leak and you were dropping almost 10 psi you would hear the leak. I didn't hear anything other than my turbo spooling and logs showing 90% wgdc and only 11 psi to show for it on a Pure Stage 2 turbo.

Last weekend I checked my clamps and all was good so today I bought a new boost solenoid. Install took 20 min because I removed the intake inlet so I had room to work. I still dropped the F'n bottom nut trying to install the solenoid. Murphy's law...

Good news... It was the solenoid and my car is boosting harder than it has ever boosted. Actually need to turn things down a bit. So before you go pulling your car apart looking for a boost leak, do yourself a favor and spend the $ to buy a new boost solenoid. It's a simple fix...

[sean5000]

Thanks for the post! Did you ever have any codes come up? Every once in a while my car gets all pissed off and jumps into limp mode. I have to stop and restart to get rid of it. Had my laptop on one occasion and it came up as an exhaust leak? Haven't had time to dive into it just yet... I know there's a possibility of a boost leak as I slapped together a tube to the intercooler as the cx racing piping wasn't even close lol

[WedgePerformance]

Originally Posted by sean5000

Thanks for the post! Did you ever have any codes come up? Every once in a while my car gets all pissed off and jumps into limp mode. I have to stop and restart to get rid of it. Had my laptop on one occasion and it came up as an exhaust leak? Haven't had time to dive into it just yet... I know there's a possibility of a boost leak as I slapped together a tube to the intercooler as the cx racing piping wasn't even close lol

No because I disabled underboost. You would be surprised at how many cars out there are 1 to 3 psi low at 6000 rpm due to an old boost solenoid. It's $125 to $150 depending on where you get it. It's an easy DIY replacement. two 10mm nuts, harness connector and two vacuum hoses. It should be a common replacement just like coils. If you have 50k mile or 80k km and it hasn't been changed, change it.

[ianc]

How does one properly test this component instead of just throwing money at it? Sounds like it's a progressive failure...

ianc

[WedgePerformance]

Originally Posted by ianc

How does one properly test this component instead of just throwing money at it? Sounds like it's a progressive failure...

ianc

It's an inexpensive part. In my opinion if you have a decent amount of miles and you feel your wgdc is high and you're not making enough boost, replace it.

But... I also understand your point so my recommendation is Google it because there are lots of YouTube DIY's.

I also want to say that I'm not sold that the testing works because in my case the solenoid still worked, but it was progressively getting worse. Like others, I just assumed it was a boost leak and spend several hours pulling stuff apart. My next option was pressure testing. Time is $ and to me spending $150 to just replace it was a much easier solution than wasting my time trying to decide if it was the issue.

[velociti]

For the past year, my car hasn't been pulling as hard as it had despite my running a JB4. It wasn't boosting consistently, felt "dead" after about 3,000 rpm, and I attributed this to the JB4 because it seemed to happen so gradually. So I ditched the JB4 and did a custom Wedge tune via MHD...only for that to feel similarly. Dead, flat, no pull whatsoever. I was boosting around 7psi or so, but apparently that's not enough of a drop to throw a code, which I never threw.

I knew the boost solenoid was a possible culprit but figured it could also be my vacuum lines or something on the intake track (which I spent quite a bit on for a smoke test at my local shop). Based on this post, I bought a Pierburg equivalent of the BMW part for $90 from ECS (#11747626350) since I read that the N54 part worked just fine on the N55. Installed it this afternoon, and lo and behold, I have my boost back. The hardest part was getting the vacuum hoses off which took me using a pick tool to loosen them up, though the nuts are a bit of a pain to get off and back on. Should take no more than 20-25 minutes.

Bottom line, if anyone's down on boost, isn't throwing a code, and hasn't replaced this thing yet (40k miles on mine), start here and see if it fixes the issue. Big thank you to Wedge.

[ianc]

Thanks, good info here. I'm at 60k, running a Cobb tune and logged 15 pounds of boost late last year, so I'm probably ok because the car still feels like an animal to me. ;-)

Would still be nice to be able test the part to see if it's in spec or not though...

ianc

[tjswarbrick]

3 times in the last couple months, I have had no boost, but no codes.
Next day boost was back. 70k miles.
After second time I pulled off the JB+ expecting that must be the culprit.
Then it happened again today.

Is this a likely culprit?
P/N 11657601058?
Do I just need one on a 2012 N55?
Online, I only see electrical connection on this guy - no nipples for vacuum lines.

(I have the aluminum ER charge pipe. When first installed over a year ago I didn't tighten the clamps down enough and went into limp mode. Only other time I've seen limp mode was 105deg F day running freeway speeds with A/C got stuck in stop-and-go for 20 minutes.)

Thanks for the direction! I've been kinda lost.
If it works, I'll see about re-installing the JB+. I do miss the extra urgency in midrange pull.

[juld0zer]

Even with BMW diagnostic software, troubleshooting this component can sometimes take you in circles especially if you are tuned. Basically the test is not thorough enough and like others said, they can fail progressively. ie. not throw a fault code or register any anomalies except the car just feels lazy compared to a good example. The solenoid is still functional, but might have delayed response resulting in under or overboost.

I'm examining them as i replace them. The gauze filter underneath the detachable covers are usually soiled in black sooty particles. One day i will test a cleaned one.

Also, just a reminder that rocker covers are extremely expensive if you happen to break a nipple off an N55 one. Be careful as the temptation to yank or wriggle the stubborn hoses off might lead you to a date with Mcguyver.

[tjswarbrick]

Thanks for the pointers!

Last night and this AM, the boost is back.

Is this intermittent action typical of a failing boost solenoid, or should I be focusing elsewhere?

[BoosTonian]

Any other signs of this failing besides low boost?

Reason I ask if cuz when I floor it, it feels like the car boost climbs..then drops off and starts climbing again..feels like something is "closing" or maybe opening all the way which is causing the car to reboost.

Best analogy I have is like climbing stairs, suddenly dropping a floor and climbing the stairs again.

[ianc]

Would be very interested to hear any feedback on whether cleaning them is effective or not Juld0zer?

I might be a cheap bastard, but to me $150 is not inexpensive. Not inexpensive enough to do on a hunch anyway...

ianc

[BimmerAg]

Originally Posted by BoosTonian

Any other signs of this failing besides low boost?

Reason I ask if cuz when I floor it, it feels like the car boost climbs..then drops off and starts climbing again..feels like something is "closing" or maybe opening all the way which is causing the car to reboost.

Best analogy I have is like climbing stairs, suddenly dropping a floor and climbing the stairs again.

Do you have DTC on when this happens? Sounds like traction control cutting power to prevent wheelspin

[BoosTonian]

Originally Posted by BimmerAg

Do you have DTC on when this happens? Sounds like traction control cutting power to prevent wheelspin

Nope, does it when it's on or fully off

[BimmerAg]

Originally Posted by BoosTonian

Nope, does it when it's on or fully off

Would you happen to have any data logs of this happening? If it's not DTC, then it could be the DME closing the throttle in response to an overboost situation, which could be caused by the solenoid. A vacuum leak could also cause overboost.

[juld0zer]

Over here they retail for about AU$380 so it's not exactly something you'd want to break or replace on a regular basis.

I have heard mixed reviews on cleaning them using liquids or lubricating them with liquids. I know on the VAG forums it's quite common to take the N75 out and clean/lube them to restore perkiness. For some reason, this seems to kill our solenoids so i would advise against using any liquids or compressed air. All i did was wipe the black particles off using some rags and labelled it as a test mule for a rainy day.

I have also tested an early F20 M135i valve on my E82 and it performed similarly, if not slightly less perky versus the stock valve. Never logged a fault.

Most commonly in my experience these valves usually cause overboost rather than underboost, but it can be difficult to reproduce. With the sooty filter in mind, i can imagine my theory might be supported as that filter is for the atmo port. ie. when de-energized, the valve opens the atmo port to vent vacuum. Guess what? The latest revision of the solenoid also has a much larger filter! It's about 20% bigger on the F10 one i most recently dealt with.

Vacuum leak would cause underboost irrespective of where the vacuum leak is in the wastegate control circuit. Unlike conventional wastegates which blow open, ours are pulled shut so the default position is open.

BoosTonian, if you are getting surging or pulsing I'd check the vacuum hoses and connections. The short hose from the rocker cover is known to get brittle with time and may not form a good seal. Also check the wastegate actuator using a Mityvac to see if it airtight, check also the vacuum tank in the rocker cover to make sure it is airtight. Carefully disconnect the vacuum supply connection on TOP of the rocker cover, inspect for engine oil contamination.

[iminhell1]

You know whats worse?
Having one failed and another doing all the work (N54).

I found this out the hard way. I was 6 hours from home, on track when mine failed. No warnings, no codes. Just an outright fail to make any boost. None of my previous logs showed anything wrong, boost targets where met and held, a little overboost on tip in (which I think is normal).


When upgrading parts, make sure you're doing so on known good parts.

[ianc]

I checked the Bentley, but didn't find much about this system. Let me just check to make sure I'm understanding correctly how these components work:

1) there's a full-time engine-powered vacuum pump which always runs and creates vacuum in the two plastic vac canisters on the front pass side of the engine compartment.

2) the lines on the tops of these vac canisters supply vac to the boost solenoids, which (when the solenoid is electrically energized), is passed through to the wastegates. As the wastegate is placed under vac, it closes and boost builds.

3) when the solenoid is not electrically energized, vacuum is bled off to the atmosphere rather than sent to the wastegates. The ECU decides the duty cycle to energize the solenoids according to what the current boost target is. A higher duty cycle provides more vac to the wastegates and hence higher boost.

4) both solenoids are plumbed in parallel for redundancy, and even if one (or its accompanying vac cannister) fails, the other is fully capable of supplying vac to the wastegates.

Correct so far?

ianc

- Edited to correct my previous misapprehensions, and to prove that I can count...

[juld0zer]

2 and 4 are incorrect. The wastegates are normally open. They are only closed when the solenoid valves are energised.

[ianc]

Hmm, seems like I forgot how to count. Where's number 3?

I understand the operation of the wastegates and how they require vac to close and create boost, but your statement seems to suggest that vac only passes through the solenoids when they're energized, rather than the reverse. Is that true? Thanks for the info..

ianc

[juld0zer]

That is correct, the vacuum builds up inside the reservoir tanks. The solenoid valves' atmo port allows the vacuum to be bled off to reduce or stabilise boost

[Dackelone]

Originally Posted by ianc

Thanks, good info here. I'm at 60k, running a Cobb tune and logged 15 pounds of boost late last year, so I'm probably ok because the car still feels like an animal to me. ;-)

Would still be nice to be able test the part to see if it's in spec or not though...

ianc

The OE vacuum hose(with fabric over them) do wear/fray and leak. I would look at all your vacuum lines for leaks. You can use a vacuum pump to check if they are leaking from one end. I would replace them with rubber BMW silicone, vacuum hoses. You can buy this from any BMW dealer by the meter.

N54's have two solenoids and a double vacuum reservoir, while N55 only have one Solenoid and one reservoir.

Perhaps these videos will help you find or show how to test the WG solenoids. They do go bad. But I think its more common for the hoses to wear out and leak.

Also... this thread might be a good read...
http://www.1addicts.com/forums/showthread.php?t=1293630