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      11-11-2019, 11:29 PM   #1
The Blimp
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N55 Saga

I thought that the N55 would be a much easier engine to live with after having two N54 powered cars over the years, but I think I was greatly mistaken.

I moved to a N55 a couple of months ago, hoping that the trade off with lower engine power potential against better reliability would be a smarter outcome but it has been a bit of a pain so far. I'm starting this thread to welcome advice and suggestions, but also to document problems and solutions for other owners that might face the same challenges.

Initial purchase
The N55 I picked up was a 10/2010 build with 68,000kms on the clock. It ran fine when I inspected it and had no codes when scanned. Had a full service history but there were a few issues that I could see such as the oil temps reaching 120-125c and the battery not being coded to the car.

I immediately changed the oil and filter. In hindsight I wish I had run a cleaner additive first such as the Liqui-Moly detox but might do that in the next 1,000kms (I've put 4,000kms on the car so far).

The oil change saw the oil temps never go above 110c, so its likely that the previous oil had been there for some time (too long).

I coded the battery to the car as it was giving the increased battery discharge' code at start up. The battery was replaced in mid-2016 so Im not sure there would be any ill effects of not having it properly coded for so long.

The PCV vent hose had cracked and I had a replacement one that I got with a secondhand intake system off eBay ($50).

I also replaced the ignition coils with Delphi coils from FCP Euro, as well as fresh Bosch branded plugs (ZR5TPP33S) that I got on special from supercheap. Engine ran fine after this until...

Limp Mode Event #1 - Resolved
Not long after changing oil, plugs and coils, I was hit with a half-engine limp mode. Power was indeed reduced and I did literally limp it home. Upon reading the codes:

2C56 - Boost Control, Pressure Too High
2C58 - Boost Pressure Deactivation
36C9 - Internal DME Fault

Researching the issue it appeared that the culprit was a dead/dying boost solenoid. This was replaced with a Pierburg branded version and all was running great again - in fact better than before.

Idle issues - Ongoing
The more familiar I got with the car, I started to notice that there is a rough vibration at idle, which will get worse if the AC is engaged. It can easily be felt through the steering wheel and pedals, like a fish pulling on a line.

It will also idle-hunt when stopping at the lights or putting into park.

I inspected the engine bay and noticed that the tensioner pulley was moving quite a lot. So I replaced it with a new one. which reduced the movement but didnt have any impact on the idle. I also inspected the crank pulley/harmonic balancer/vibration damper and other pulleys and couldn't see any issues. There isn't any apparent wobble.

Upon researching this issue further I read that the earlier N55s (late 09 to 2011) had a similar issue being caused by an early DME software version. Updating to the latest DME software can potentially resolve the idle problems, which is the next course of action.

If updating the DME doesn't improve this, other culprits might be the VANOS solenoids being dirty/dying (about $450 to replace both), or the PCV system failing and there being an internal vacuum leak (apparently not uncommon with the integrated N55 PCV) - an expensive item to replace.

Still sorting this one out

Limp Mode Event #2 - ??
After driving with some gusto and then parking for a little while, upon restarting the engine it immediately entered a half-engine limp home mode. After pulling over and scanning the DME it was the following:

2BF8 - Rail Pressure Sensor, signal; Permanently stuck
2C01 - High fuel pressure, Pressure too low.

I cleared the codes and they haven't yet returned but I haven't actually given the spurs to the car since so I am not sure if it will return.

Researching this issue it could be (hopefully) just the rail pressure sensor needing to be replaced (which I have ordered from FCP Euro).

If it isn't the sensor, then I guess the HPFP will be the next culprit but I still haven't had any classic long cranks or anything like that so I'm leaning towards the sensor being on its way out.

Fuel Economy - Ongoing
When I first purchased the vehicle I didnt notice any issues with the fuel consumption, however since I have been diagnosing issues I have notice that consumption is up around 20l/100km.

I looked for a vacuum leak but couldn't see anything out of place. I inspected the MAF sensor and noticed it was quite dirty and there was some oxidation on the metal tab and resistor, so I replaced it with a VDO branded one (again from FCP Euro) hoping that it would resolve the issue (and maybe the idle problem too). Alas this did not improve anything and I'm back to the drawing board on this one - it could be multiple things. I am trying to get ISTA to run on my laptop and so will hopefully get to run some proper diagnostics.
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      11-12-2019, 07:08 AM   #2
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Firstly - unless your pockets are deep, stop firing the parts cannon and invest in some diagnosis.

The idle issue with the AC on or coming to a halt is a well known issue and I am going to assume yours is a DCT as I've not heard of it affecting manual cars. edit: Missed the bit about putting it into park. The software update addresses this issue. There are several threads on the forum about this including one very detailed one which details one owner's battle.

What was the service history like? It sounds like the previous owner was never fussed about it or the car rarely saw a dealership. Has it had all the recalls done? (junction box cable, driver airbag, VANOS?).

Is there any tune or piggyback installed?
20L/100km is ridiculous. Mine averaged around 11.5. Still crap for a 3L motor.

You should also reset the adaptations after installing a new MAF sensor.

Last edited by juld0zer; 11-12-2019 at 07:15 AM..
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      12-02-2019, 09:15 PM   #3
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Update: flashed the DME with latest N55 software. It improved its behaviour when driving and idling but still has something (or things) wrong.

Got inpa to work but as there is only a German language version for n55 itís hard to use. Did a rough running test and it appeared all was within tolerances at idle (though I still canít find definitive info on what the figures mean and how the test should be performed - which makes diagnosis difficult).

Idle
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When I increased revs to ~3000rpm+ the thresholds were exceeded on cylinders 1, 3 and 4.
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I posted this over in the main N55 sub forum and the Oz FB page for advice as I am unsure what these values mean.

I swapped coils between cyl. 2 and 3 but it made no change to the values in inpa.

I am leaning towards the injectors being clapped out as the plugs and coils and basically new. No current fault codes.
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      12-02-2019, 09:25 PM   #4
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Quote:
Originally Posted by juld0zer View Post
Firstly - unless your pockets are deep, stop firing the parts cannon and invest in some diagnosis.

The idle issue with the AC on or coming to a halt is a well known issue and I am going to assume yours is a DCT as I've not heard of it affecting manual cars. edit: Missed the bit about putting it into park. The software update addresses this issue. There are several threads on the forum about this including one very detailed one which details one owner's battle.

What was the service history like? It sounds like the previous owner was never fussed about it or the car rarely saw a dealership. Has it had all the recalls done? (junction box cable, driver airbag, VANOS?).

Is there any tune or piggyback installed?
20L/100km is ridiculous. Mine averaged around 11.5. Still crap for a 3L motor.

You should also reset the adaptations after installing a new MAF sensor.
Thanks for your reply

All recall work was done prior to my purchasing of the car. It has been serviced by bmw dealers up to 40k km and then by a euro specialist in eastern suburbs of Sydney - however Iím sure they did the standard bmw service intervals.

No jb4 is attached and doubt previous owners had one installed (but can never be sure).

Without specific codes itís hard to properly diagnose what is happening. I think the dme is ignoring rough running as inpa testing appears to show that things arenít quite right.

I donít want to spend money if I donít need to but I think it is obviously a hardware problem.
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      12-03-2019, 02:29 AM   #5
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Ok, I’ve done some more research and discovered that I shouldn’t have used the throttle during the rough running test (not that there are instructions for this stuff - at least not easily accessible).

It measures idle performance and I’m (guessing) that cylinders 3 and 4 are the most efficient when given revs as they are right behind the throttle body.

Anyway, any result at idle that is beyond -.5 means the injector is toast and is leaking at idle. So from my previous screenshot I can see that cylinder 1 is in excess of this and must have its injector replaced.

That’s some progress anyway
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      12-03-2019, 07:11 AM   #6
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Nice work mate... diagnosis is always the hardest task
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      12-06-2019, 06:59 AM   #7
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If you have access to ISTA, try an adaptations reset. I don't recommend doing it in INPA because it can cause some cold start issues on some DMEs.

For the fuel pressure issue you need to monitor the target vs actual pressures at idle and under load. Keep in mind that unlike the N54, this motor has no LP fuel sensor so the rail pressure sensor has sufficient resolution to monitor the low pressure system also.

What other fault codes do you have?
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      12-06-2019, 09:03 AM   #8
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      12-06-2019, 04:38 PM   #9
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I've managed to do a bit of diagnosis work with logs and INPA functions.

Fuel pressure is never below 700 and isnt a problem at idle or at WOT. Boost is fine and WGDC is within spec.

Rough running analysis shows that all cylinders are way out of tolerances over a 10 second period when the engine is at operating temp, most dip between -2.0 to +2.0 but cylinder 4 went over 4.0. The DME cannot balance them. LTFT and STFT show that the DME is always pulling fuel but for some reason no CEL is being raised. O2 sensor voltage is always around 1.45v (2.0v is ideal) indicating the rich condition but still no code, which is worrying in itself.

Either the plugs, coils or injectors are defective. Plugs and coils are new, and the symptoms existed prior to replacing them so that really leaves injectors. I have arranged to get them all replaced but it wont be until early January. So until then I am not sure if I should drive the car normally or leave it until they can be replaced.

No codes makes me think that the issue is within tolerance for BMW but the stories of ruined N55s due to injector leaks scares me (I have read so many threads on here about this trying to figure all this out).

The oil in the motor is 3,200kms old and with leaking injectors I am suspicious that it will be diluted with fuel. So I plan to change it asap but not sure if its safe to drive without risking damage.
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      12-08-2019, 09:07 PM   #10
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I managed to pick up a genuine BMW VANOS solenoid for $200 shipped a few weeks back.

I was interested to test whether replacing the intake solenoid would have any affect. So on the weekend I swapped it out and it indeed improved the situation a great deal. I was contemplating removing and cleaning the exhaust one but will just replace it with a new one down the track.

Before there was surging idle for a second or two, between 600 to 900rpm when shifting from P to R or D, coming to a stop at lights, and whenever turning the wheel full lock. This is now gone completely. Updating the DME and changing the VANOS has made a big impact, however the shaking from the leaking injector(s) is still present of course.

Fuel economy has also improved since the solenoid was changed. From getting up to 20l/100km down to 15l with about 200km of the same driving style.

Once I get this sorted I can finally get around to mods and tuning, which I had hoped to have already done by now.
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      12-08-2019, 09:57 PM   #11
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Quote:
Originally Posted by The Blimp View Post
I managed to pick up a genuine BMW VANOS solenoid for $200 shipped a few weeks back.

I was interested to test whether replacing the intake solenoid would have any affect. So on the weekend I swapped it out and it indeed improved the situation a great deal. I was contemplating removing and cleaning the exhaust one but will just replace it with a new one down the track.

Before there was surging idle for a second or two, between 600 to 900rpm when shifting from P to R or D, coming to a stop at lights, and whenever turning the wheel full lock. This is now gone completely. Updating the DME and changing the VANOS has made a big impact, however the shaking from the leaking injector(s) is still present of course.

Fuel economy has also improved since the solenoid was changed. From getting up to 20l/100km down to 15l with about 200km of the same driving style.

Once I get this sorted I can finally get around to mods and tuning, which I had hoped to have already done by now.
Been following your thread out of interest... this is a great breakthrough!
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      12-08-2019, 09:58 PM   #12
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Back when you were in the game with your N54 the N55 was largely deemed more reliable due to being newer and BMW had redesigned quite a few things differently but alas now they're older and have a few kays on them they also suffer from quite a few reliability issues and alike the N54, the N55 has a few inherent design weaknesses (thankfully wastegate rattle isnt one of them!)

Did you screen your vin # to ensure it has had the vanos bolt recall done?

https://www.productsafety.gov.au/rec...09-2012-series
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      12-08-2019, 11:30 PM   #13
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Quote:
Originally Posted by DR-JEKL View Post
Back when you were in the game with your N54 the N55 was largely deemed more reliable due to being newer and BMW had redesigned quite a few things differently but alas now they're older and have a few kays on them they also suffer from quite a few reliability issues and alike the N54, the N55 has a few inherent design weaknesses (thankfully wastegate rattle isnt one of them!)

Did you screen your vin # to ensure it has had the vanos bolt recall done?

https://www.productsafety.gov.au/rec...09-2012-series
Yes, checked the recalls before purchasing it - all had been done.

If I had the choice again I probably would go with an N54 again, but learning about this engine is interesting.
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      12-09-2019, 09:34 PM   #14
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Correction

Perhaps others on here already knew this but my previous post stating that the lambda voltage of 2.0v is ideal is actually correct for the n54, but not for the n55.

This is because the other N series 6 cylinders n52,53 and 54 use Siemens dme, with the n55 using Bosch. Apparently Bosch has an ideal lambda value of 1.5v, which means my issues arenít quite as bad as initially suspected.

My lambda readings were between 1.396 and 1.475v over a 30 second period at idle, which is only 2-7% under the ideal (much better than the ~30% I thought before). So itís rich, but not that rich.

So I am now assuming that no codes are coming up as itís not that extreme, though LTFTs show that the dme is pulling 25% fuel at times which I thought would definitely throw a code.

Anyway, I thought it best to correct myself as I go along. Iím not a mechanic so itís all a matter of learning from scratch for me. That said, I had taken the car to 2 workshops (one general and one euro specific) and neither could work it out. I think itís common these days for fault codes to do 90% of the work, so no codes = no idea.
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