Turbo Actuators

[Grumpyjohn1957]

Yet another of Grump’s stale discourses, turbo actuators.

This one starts off on a sunny Sunday autumn afternoon, shortly after Brunhilda had gratefully received her weekly spanking.
With cobwebs gone I’m just bumbling along enjoying the scenery listening to something classical when I encounter a set of temporary traffic lights. Duly pull up at the “wait here” board whereupon after several seconds of being stationary I hear a “bong” from the iDrive. The screen say’s Drivetrain (with picture of a spanner), you may continue driving etc, reduced power.
Bugger, methinks what’s going on here? Anyway, lights change, I drive off, and yes indeed, the cars gone into limp mode exhibiting a massive lack of performance. Gets home, consults the internet and quickly conclude that without a code read I’ll know nothing.

Monday afternoon comes around, I pop up the road to a local BMW specialist who plugs in his magic box. After several minutes of screen stroking and prodding the tech’ solemnly announces in his best funeral directors’ voice “There’s an electrical fault on bank 2 turbo actuator with the consequent loss of boost from both turbos”. I duly thank him, pay the bill, receive a hard copy of the report and drive home, albeit very slowly.

Concerned this might be expensive I ring Sytner. The cheerful young woman on the end of the phone proceeds to tell me they can’t even look at the car for best part of 4 weeks! After much begging, coercion and pleading she graciously finds me a slot only 3 weeks’ ahead. Convinced this will be a warranty job I book in.
Now because it says on the screen “you can continue driving” no one’s told me otherwise and the cars my daily, that’s what I had to do. (My alternative means of transport being shanks pony or the wife’s Focus when not at her golf club).
Not wanting to damage anything by continuing to use the car I embark upon some in depth research. The B5 N63 based engine & drivetrain is also used in the B7, B8 and XB7, so there’s a good few about. The whole lump is similarly packaged to that of 750iX / 550i / S63 engined cars. The exhaust manifold is stock N63 as opposed to the serpentine 8 into 2 arrangement of the S63 variant. Alpina have used Garrat MGT2259 turbos with bigger turbines than those of the M cars. (we owners appreciate the result)
My concern here was the actuator could be something totally obscure and available only from Alpina. Turns out not to be the case, so hoped it’s the actuator at fault which is a £750 easy swap part.
Standing the car overnight or letting it go to sleep temporarily cleared the fault. This allows it to drive normally for 10 minutes or so before throwing up the warning and going back into limp mode. Parking hot for a couple of hours causes a similar thing to happen but only gives about 5 mins of use before limp.

This behaviour suggested the actuator was being affected by heat soak. Eventually I found a video of an actuator being dissected for this very reason. It’s an amazingly simple yet complex piece of engineering, why the manufacturer chose to fuse the thing together as opposed to bolting it I don’t know, it renders it non repairable.
I couldn’t find anything regards what happens if an actuator suddenly faults and can no longer move. I can only presume it remains in its last position until power is restored. This struck me as not being good. A massive imbalance in bank pressures could occur were the engine to be revved. Is the ECU clever enough that should one actuator fail it adjusts the other to the same last known position? Don’t know, couldn’t find anything factual, information is pretty scant.
As I understand it the wastegate is closed at start up and remains so until the required level of boost for a given circumstance is reached. Opening / closing / incremental wastegate stepping being dictated by the ECU according to the various feedback’s when compared to the engine map. Remaining closed at low rpm/tick over allows the turbine to spin ready for instant load whilst creating minimal boost pressure. Conclusion on the basis of this? Run 99 octane, don’t go beyond 20% throttle opening and do not exceed 1800 rpm.

The above seemed to work quite well, the exhaust note is totally different though, it sounds like a proper bassy V8. Lots of quite loud growling and throbbing sounds from the rear as opposed to the normal whispering purr Fuel consumption at low speeds with stop/start motoring dropped at least 8mpg but cruising at 12/1500 rpm on the motorway still gave mid-30s. Luckily, most of the miles to be covered were motorway, so I thought sack it.

Finally, (today) the car got looked at and oh dear. The actuator isn’t faulty after all, it’s a cable fault somewhere in the rats’ nest of the engine bay. Shows up the wrong resistance apparently. I have heard of a cable routing issue between the gearbox and ECU resulting in a recall for some G30/31 and I’ve also found reports of valvetronic problems caused by similar cable issues over in the states.
One would of thought the harness to be modular so it’s a simple job to replace the appropriate limb in the event of a problem. However, this is where it gets crazy.

According to Sytner the whole engine wiring harness has to be replaced in it’s entirety. Due to being so crowded around the engine with lots of stuff inaccessible, the engine and gearbox have to come out!

Anyway, a harness on back order from Germany is 7-10 days. I reckon a day to drop the engine, ½ a day to replace the harness and a day to put it all back together. Perhaps with a further day on top to test and for the service manager to drive the car the long way round to his home under the guise of an extended road test.

I’m praying this is covered under the BMW insured warranty, they’ll be a lot of noughts in this bill for sure.

On the upside and now at 80K miles she’ll get a coolant refresh, I might as well have a new serpentine belt, transfer box and front diff oil service whilst it’s all on the floor. With the engine out the vibration damper is accessible and anything perishable that could prove awkward to get at later may as well get replaced at my expense. I don’t want an engine out job again for a very long time if ever again.

Should the warranty people say no, it will be BMR with a long, very slow drive down and a train ride home. Don’t think I’d trust anyone else to be honest, the cars too precious. I’ve already had a preliminary conversation and feel a lot better for doing so.
Fingers crossed warranty stump up.

[churchie386]

Good luck. Looking forward to a positive outcome.

[churchie386]

How much do you pay for a years BMW warranty on a B5 with 80K miles on the clock?

[Grumpyjohn1957]

Keep paying the monthly DD and have a full BMW service history it's good for 100k miles or 10 years. If you exceed the 100k and keep paying they will honour a claim. E.G gearbox falls out at 105k. After that? Goodbye. Various levels of cover available above and below mine. £89 pm with £250 excess.
Downside, any work must be done by a bmw dealer. Arguably, bank the premiums, cross fingers, use an indy.

[Grumpyjohn1957]

After 3 ¾ weeks finally got the car back, seems much quieter and smoother than pre issue. Not my imagination and entirely possible I suppose given various recalibrations were part of the job.
Eventually succeed in getting a copy invoice for the work done. Only a short section of wiring harness was required, not the whole thing as the service advisor kept suggesting. Again, did the engine come out as the advisor said it needed to? Don’t know, there’s a lot of hours showing on the paperwork.
The parts list consists of 300+ quid’s worth of cable, a turbo actuator and a plethora of nuts, bolts, clips and assorted oddments.
Seems the warranty rates vs retail rates bare no comparison, I’d be in perpetual penury had I paid this bill myself at dealer retail prices.

By way of celebration the now worn down to 2mm P. Zeros will be getting skipped tomorrow and winters refitted. Perfect excuse to go the long way home and destroy a few hills.