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Question About the Diagnostic Process (BMW Car)


Mike

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I admit that there are many things in this world I don't understand, and one of those is the diagnostic process. I'll tell my story and ask those of you who are in the know if this makes sense (I'm not saying it doesn't; it just leaves me confused). Here's the background:

 

A couple of months ago I bought a used CPO BMW 535xi. Nice car . . . really fantastic to drive. For those who don't know the model, it's an AWD sedan with BMW's twin-turbo direct-injected 3.0 six-cylinder engine (the "N54"). Unfortunately, the High Pressure Fuel Pump (HPFP) has been the Achilles' heel in these and other N54-equipped cars. They've improved the HPFP design and have upped the HPFP warranty to 10 years/120k miles. Most of the cars that have had the HPFP replaced run fine and don't have any problems afterward, but a small number have repeated issues. Often, when replacing the HPFP, the injectors are tested and replaced. I was actually happy to learn from the salesman that the HPFP and injectors for cylinders 1,3,4,5 & 6 had been replaced (note which one wasn't, for later reference).

 

So, that's the background; this is my story: After a few weeks I began to have an occasional cold start problem. My OBD-II code reader told me it was a #2 cylinder misfire (code P29CE). The car would run like hell until I reset the code, then everything was fine. After this happened a few times, I took it to the dealer. They had it for a while, and determined that the cause was likely the #2 coil pack. The plugs were changed, but I'm not sure when--it might have been at this time, or it might have been about 5,000 miles ago, when the HPFP and most of the injectors were swapped.

 

Things were good for a couple of weeks. Though the cold starts seemed a little rough, I didn't get any check engine lights or misfire codes until it happened again a few days ago. Again, checking the codes, I saw that it was a cylinder # 2 misfire. Back to the dealer. They let the car sit overnight and did a cold start this morning. I don't know if it activated the check engine light, but they did confirm a cylinder #2 misfire. I understand that this misfire code (P29CE) is generally attributed to one of three things in the N54 engine: the coil pack, the spark plug, or the fuel injector.

 

Now, here's the part I don't quite get. My intuition would be this: There are three components that generally cause this code to be thrown. Two of the three are pretty much new. The third--the fuel injector--is the only one of six that didn't test bad a few months ago and was not replaced. My reaction--and maybe this is telling--would be to replace the injector on the assumption that it's the likely culprit. However, the service adviser, a heck of a nice guy who rides motorcycles, tells me that instead they're going to swap all the components on the #2 and #3 cylinders, to see if the misfire moves to the #3 cylinder with those components.

 

Really, while I'm not sure that I'd do this, I'm glad--overjoyed, actually--that they're being so thorough. I suppose that if the misfire stays at #2 or moves to #3 will tell them a lot, and it should permit them to definitely determine if it's one of this evil trio of components that's the problem or if it lies somewhere upstream.

 

So, I'm not complaining. I'm just, uh, lacking in understanding if this makes financial sense for BMW. The injector retails for about $130-$140, so it certainly costs them less. The cost of relocating these components, buttoning up the engine and retesting--which will have to wait until tomorrow, when the engine is stone cold--would seem to be more. Again, I'm pleased with the thorough attempt to isolate what's going on here, but my admittedly amateur instinct would be to simply replace the injector and see if that cleared things up.

 

How do those of you with real mechanical skills feel about this?

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Dennis Andress

Either approach, swapping the parts with #3 cylinder or just replacing the #2 injector, would be a good course of action. If it were a car I was familiar with then I'd be comfortable just replacing the injector. If not, then I'd prefer swapping the parts because if the problem does indeed follow the injector -- to the #3 cylinder -- then I could assume the rest of #2 cylinder is healthy. Short answer: If the problem moves to #3 then the tech has confirmation that replacing the injector is the right thing to do.

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the GDI injectors can be cleaned and flow matched. Your problem is probably unequal deposits and flow

 

Check this link

 

http://www.asnu.com/gdi.htm

 

I used to be affiliated with them, the stuff works. The mfg would rather sell $150 EACH! injectors than have a set cleaned AND flowmatched for $150-$200

 

I also understand that a small mound of deposits tend to build up on the piston where the injector squirts. You might get one of the heavy duty professional combustion chamber cleaning kits that meter in liquid for a time to really clear out the gunk.

 

GDI is new and there are sometimes some issues that not all mechanics have caught up with. Gas is not very good now either.

 

Rod

 

 

 

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That makes sense, Dennis. Just another quick question for anyone out there: I know that not every engine malfunction will trip the Check Engine light. Is it reasonable to assume that the dealer technician's more sophisticated diagnostic tools will be able to "see" a misfire or other malfunction, even if it's not serious enough to activate the Check Engine light?

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the GDI injectors can be cleaned and flow matched. Your problem is probably unequal deposits and flow

 

Check this link

 

http://www.asnu.com/gdi.htm

 

I used to be affiliated with them, the stuff works. The mfg would rather sell $150 EACH! injectors than have a set cleaned AND flowmatched for $150-$200

 

I also understand that a small mound of deposits tend to build up on the piston where the injector squirts. You might get one of the heavy duty professional combustion chamber cleaning kits that meter in liquid for a time to really clear out the gunk.

 

GDI is new and there are sometimes some issues that not all mechanics have caught up with. Gas is not very good now either.

 

Rod

 

 

 

Interesting stuff, Rod! It actually makes sense, even to me. This car had 39K miles on it and I can't know how it was driven or maintained (except that everything was done on time, per the BMW service records). I've long been a believer in using fuel system cleaners. Is this of any real benefit in direct injection engines?

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I imagine the dealership is concerned with following BMW's detailed diagnostic instructions so that they will get paid for their labor and any new parts (warranty reimb.). This would override any local inclination to just go directly to what they may suspect is the necessary repair. And in this instance they also would have to "explain" why the work BMW paid for earlier didn't quite fix the problem and now they need more $$ to really fix it. The explanations would benefit from always having followed BMW's diagnostic procedures. The "customer" doing the paying is BMW, not Mike and not the dealership.

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I imagine the dealership is concerned with following BMW's detailed diagnostic instructions so that they will get paid for their labor and any new parts (warranty reimb.). This would override any local inclination to just go directly to what they may suspect is the necessary repair. And in this instance they also would have to "explain" why the work BMW paid for earlier didn't quite fix the problem and now they need more $$ to really fix it. The explanations would benefit from always having followed BMW's diagnostic procedures. The "customer" doing the paying is BMW, not Mike and not the dealership.

 

That thought had occurred to me. I imagine that BMW may not as willing as I would be to act on a hunch.

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Mike, you know their is a recall for this issue? (I have the 335XI- same engine, cept' I have a Stage II juice box chip and wastegate bypass installed ;-)) Prior to the recall I had one or more injectors, coils and plugs replaced... only to have it happen again as well as the dreaded engine go into "safety, survival mode" when it can't get out of it's own way... of which I think is the major recall issue, software change to get rid of that "mode." It happened again within 6 weeks of the initial repair and my dealer just said" Were going to replace them ALL as well as reflash the software, due to the pump creating too high a pressure at start-up. (which they believe is the main culprit of the issue) Actually tomorrow it is going back for the recall as I guess a few things haven't been done.. I discussed this with the dealership as I thought everything HAD been done, but I think in my case it is just the software re-flash to get rid of that slow-poke safety engine mode.

 

Anyway, re: your issue.... BMW won't just green light every repait the mechanics want to do under warranty and I guess they are asking them to do this first before they will okay a complete injector fix.. I know.. doesn't sound like it makes much financial sense to me... but who knows what BMW is thinking??

 

BTW, I'm at about 360 to 380 HP, maybe 400 ft/lb torque... Yeah, IT"S FAST! ;-)

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