Tire Question

[BlueBMW]

That wouldn't be a bad system SoZ.  Some dealerships have formed "diagnosis teams" which are just there to take care of particularly challenging diagnosis problems.  Once they determine what they think needs to be done they give it back to the tech or team where it originated and they perform the fix.  I pushed for these sorts of arrangements for a long time but it was always opposed by the high hour turners.  They didn't want to pay a portion of their hours to support a diagnosis team like that.  Their system of avoiding diag problems and just churning the hours was threatened by such a system.  Management didn't like the idea much either since they were concerned with individual technician productivity numbers.

Sadly some of my most satisfying days as a technician were solving super challenging problems.  Though one car got me really good...

2011 BMW X5 with the twin turbo V8.  Had an intermittent stumble and eventually would post a misfire fault.  I went through EVERYTHING on this car.  By the end we had done the following to it:

Approximate costs shown:
Spark Plugs  $400
All Fuel Injectors (the pricey direct injection units!)  $1600
Both High Pressure Fuel Pumps $1400
All Intake seals $400
All Ignition coils $900
Cylinder compression and leakdown $700
Engine Computer $1400
Software Update / Reprogramming (3 times) $600
Dropped engine and performed carbon cleaning on the valves (You had to drop the engine for this) $2600

All that at it still wasn't fixed.  BMW was stumped, I was stumped.  Finally we pulled the cylinder head on the bank that had the fault.  Sent it off to BMW for analysis.  They sent us a new one back and said the injector bore on the cylinder that was misfiring was out of tolerance.  Apparently when the injector fired it was pushing itself too far back up its bore and then not delivering the fuel correctly at that position.  So basically $10,000 in repairs and then finally needed a cylinder head (a $6800 part plus another $1700 labor)  BMW ended up covering all of it since they couldn't help figure it out until the end.

That twin turbo V8 is easily the hardest BMW engine to work on except maybe the diesel 6 cylinder.  That car broke me.  No one had ever seen that issue before though.  Apparently its becoming common on those engines now.  Though I can say I'm super quick at taking everything apart on that engine now.  I only took the intakes apart maybe 40 times during that diagnosis.  It took us two months to fix it.

My Nemesis:

[Zero_Gamer]

I would have never guessed this thread would generate this much activity lol

[wildfruit]

Why are BMW's V8 engines so terribly unreliable compared to their almost bulletproof straight 6 variants?

[SignOfZeta]

BMW:

I had a similar diagnosis to a totally different problem. Long story short, actual cylinder volume and injector depth is crucial nowadays. Even something as minute as a copper washer of incorrect thickness can made a DI engine f*ck up.

I know this because at work (engineering lab, not a shop) we had an incorectly machined head and and we fixed it by sanding down a washer. This was a cheap American SFI V6 (yes, they still make them) where we had installed pressure transducers in all the cylinders and one showed a trace absolutely in line with the other cylinders but at all points lower pressure. Nobody could figure it out until we had a guru from elsewhere in the company who eventually determined that the bore depth for the TD was wrong (not usually present, had to be machined by hand), in comes the sanded down washer. Being a guru he was able to tell us exactly how thin to make it to .001".

Btw, my TDI has pressure transducers in the glow plugs so maybe newer high end engines have adopted this as well. It would be way more helpful than just crank angle and while it's an outrageous expense we're talking about cars that depreciate more in their first year than the cost of the average car so f*ck it.

[NightWolve]

Anyway, I had a weird/dangerous experience not that long ago worth pointing out on the subject of the importance of checking your tires from time to time, at least visually! My brakes were going out and I had to keep pumping the pedal to achieve slow down as I was going to a MicroCenter store pretty far away from me in another city!

It was pretty WTF cause I had changed everything myself over the years, the brake lines/pipes, calipers, hoses, drum shoes, drum pistons, etc. and it worked fine for years, so I was pretty upset! The car pretty much runs on mostly AutoZone/AdvanceAuto parts!

So, I stopped the car in a parking lot before getting there, popped the hood and noticed I had full brake fluid which left me not really knowing what the hell was going on (was thinking maybe the booster was finally going bad maybe)...

Well, I got to my destination safely by going slow and pumping the pedal as mentioned, parked, got out and somebody saw my front passenger-side tire was extremely deflated so he pointed it out to me. I was like, "Oh, thanks, f--k, so maybe that's why?!?!" A gas station was across the street, so I refilled it there for some quarters because I didn't have my supply box which had my 12VDC car light/air compressor in it. Sure enough, brakes worked fine again, so WTF ??

I never heard of this behavior due to low tire pressure or practically a flat tire... Never happened again as I try to remember to do visual tire checks, but I don't trust the car like I used to... I'm tired of looking at the rust anyway, so I'll be looking for a new one in the near future and will likely switch to a manual transmission also.

Hey guys, I wanted to update this when I got a chance... I figured out why my brakes were failing after driving around for a few miles on the highway and it's a safety tip worth mentioning...

So, long story short, last time I rebuilt my drums 8 years ago, the frame I had to get from a junkyard had the metal components to enable the star wheel to tighten the brake shoes when you pull the parking/e-brake up and down... I used to use that to keep 'em tight thinking that was a good idea... Well, it wasn't. For some reason, only the right side overtightened and before this happened, I was hearing lock noises on that side for about a month and was intending to have a look, well, check it out (nasty overheat, cracked the padding, ruined the rubber paint job I did, etc.):




Scenario: You drive fast for a few miles on the highway, the shoes would heat that drum up rapidly, I mean, it was burning hot if you'd touch it, the wheel cylinder with brake fluid absorbs some of that heat, enough to evaporate DOT 3 brake fluid, AKA Fluid Vaporization, next thing you know, you're having to pump the brakes, the pedal goes all the way down and you're not stopping...

Anyway, those are the before photos. I got new brake shoes under lifetime warranty with my AutoZone account since I bought a pair 8 years ago. Bought a new spring set as well for $12, but the nightmare scenario where the bleeder valve was seized occurred, it broke on me, so spent another $13 for a wheel cylinder, and $5 for a copper/nickel brake line 12" in length because I want the corrosion protection and it broke too... I had all the needed grease and anything else needed, and got this done in October, so the car was set for winter, just was too busy to stop by and share the story.

ProTip: You can buy newer DOT 4 fluid for a few more bucks, and add about 50 degree more overheat protection. I'd do it if you've got an older car that still runs on DOT 3. Another thing I learned.

Well, FYI to any car buffs... Drive safely... Don't be me!

Oh, I should also mention I eliminated the metal component to auto-tighten the brake shoes with the parking brake... Each shoe is 1/4" of material, at best you lose a half inch on each side when it wears out, so your brake pedal would only go down about an extra inch as they come close to the end of their life... I'd rather just tighten manually from behind the drum with the car jacked if ever needed.

Another detail, I didn't know much about cars when I originally got it in '98 and eventually had a case where they wore out and ruined the steel drum, so those had to be replaced too way back... But yeah, car's been braking fine now, problem solved! It was quite bothering as there was no leaking fluid, so you wondered what the hell was going on, thinking the power brake booster was maybe going bad or the hoses were weak...

[blueraven]

Glad your car is fixed, Nightwolve. I had a similar problem with my Honda recently. Bad hardware and a leaking wheel cylinder.

And BMW, You're spot on about the BMW school. Not that I ever worked for them, but went through a similar situation when I got trained at WyoTech, and then went to work for a shop.

Because they don't care.

For the win.