Fuel injector problem - 2008 BMW 335xi

[JD!]

I just bought an absolute dumpster fire of a 2008 BMW 335xi. After replacing two leaking injectors, I still have a slight idle unsteadiness and occasional misfire on one of the cylinders (not enough to set a code but I've isolated it with live data) which I assume is a fouled up injector based on the state of the others. It doesn't leak and it runs fine off idle. All new spark plugs and I've isolated the problem away from the coil pack.

I've used various fuel system cleaners in the past and haven't noticed any difference in how my car runs, just a feel-good preventative maintenance item. Everyone's seen the rave reviews for fuel additives and how they can cure all sorts of ailments, but of course, a lot can be chalked up to the placebo effect.

Personally speaking, have any of you ever had a verifiable issue (like an occasional idle misfire) that has been fixed with a fuel system cleaner? Should I just bite the bullet and replace this injector already or do I have a shot at salvaging it with something like Techron or SI-1?

 

[Cujet]

My Old clunker 2003 Jag X-Type with 250K miles dropped a cylinder on a 2000 mile trip last month. I purchased 2 bottles of Techron and one bottle of Seafoam fuel system cleaner. Of course, it was not a bad injector, it was a coil failure.

After getting home, I pulled the V6's complex intake manifold to access the coils and change the plugs Which gives an awesome view of the parts. The valves and ports were spotless, not a hint of carbon or discoloration. I could see green marking paint on the valve seats! The pistons were clean with zero carbon buildup, especially the one not firing, which was bare bright aluminum in places.

Having pulled the intake a few times I remember the ports and valves being quite dirty last time. And I considered using solvent to clean 'em, but did not.

Also of note, the X-Type did have a sticking injector 50K miles ago, and using Shell 93 and some techron cleaned it up, no problems since. Yes I did also add MMO, just in case the oil helped lube the injector. The MMO did not seem to help. You do what you have to when 1300 miles from home.

On my Jag F-Type sports car, the direct injectors are known to stick. Owners swear by Redline S1. I use it before every oil change.

 

[Astro14]

If it is truly the injectors - I would pull them and have them rebuilt. No eBay or Amazon knock off parts - you know they're the right part because they came off the car. It's about $17 an injector to get them done. Honestly, a bargain, and this company has done several sets of mine with great results.

https://hurstinjectorservice.com/

 

[RallyXaDSM]

Yep, had very strong results on two old neglected cars with BG44K. After that I started using Techron or SI-1 at least once per year in whatever I was driving.

 

[JD!]

If it is truly the injectors - I would pull them and have them rebuilt. No eBay or Amazon knock off parts - you know they're the right part because they came off the car. It's about $17 an injector to get them done. Honestly, a bargain, and this company has done several sets of mine with great results.

https://hurstinjectorservice.com/

Interestingly, there are no aftermarket injectors for these. The "refurbished" or "new" ones for sale are just recycled old injectors with a new Teflon stem seal and the part number repainted. There is a single Siemens/VDO plant in Italy that has, since they started being produced around 2006, built these. Thus, new prices are insane: $2800 for a VDO branded set of six, $4600 for a BMW branded set. Additionally, they are laser welded, and thus non-rebuildable. Cleaning prices for these to be properly 2,000psi leak tested and flushed are more expensive than a used injector (and more expensive than cleaning port injectors) and the process is often fruitless as far as restoring proper flow based on reports I've read online.

I read some comments from one of the guys who designed these and they are little technical marvels, extremely precise and capable of some very neat fuel economy tricks in the European market where the NOx standards are less ambitious. But holy moly are they a nightmare. BMW switched to regular solenoid-type injectors in 2011 for good reason.

At the moment I have three spare injectors I've acquired over time. One I know for sure flows good and leak-free. What's stopping me from replacing the bad one is that this car is running all Index-11 and Index-12 injectors, the two latest and most valuable injector revisions, and my spares are Index-01, Index-07, and Index-08, not known to be terribly troublesome but miss some of the latest fixes like a revised thermal compensator oil and internal microfilter. BMW has advised against mixing 11/12s with lower revision numbers. So if I can salvage this troublesome Index-12 I'd be very happy! Tossing two in the scrap pile this month was already a bit of a heartbreaker.

 

[perkz]

If it is at idle, clean the throttle body. If at cruise, double dose techron for 2 tanks. If that doesn't work, look at slow O2 sensor or injectors. If scan tool show less than 10% negative trim, you can just live with it.

 

[Marcozi]

How does it idle?

 

[JD!]

How does it idle?

Idle is the only time the problem manifests, which makes sense for a fuel injector issue. It runs great from light load to full boost. Looking at the misfire counter it's only misfiring on cylinder 4 which, to me, rules out a more systemic issue.

I have run through about a half a tank with Techron by now and it hasn't been any better. Think I'm probably going to bite the bullet and dip into my injector stash this weekend.

 

[Marcozi]

Idle is the only time the problem manifests, which makes sense for a fuel injector issue. It runs great from light load to full boost. Looking at the misfire counter it's only misfiring on cylinder 4 which, to me, rules out a more systemic issue.

I have run through about a half a tank with Techron by now and it hasn't been any better. Think I'm probably going to bite the bullet and dip into my injector stash this weekend.

It sounds like a vacuum leak. The only way to find all of the vacuum leaks is to have the engine professionally smoke tested. Try www.bimrs.org to find a reputable indie shop that specializes in bimmers in your area.

 

[JD!]

It sounds like a vacuum leak. The only way to find all of the vacuum leaks is to have the engine professionally smoke tested. Try www.bimrs.org to find a reputable indie shop that specializes in bimmers in your area.

N54 uses speed density, so any air leaks up to the manifold won't affect running at idle. Additionally, air issues would theoretically cause rough running on all cylinders, not just #4. I have a smoke tester but it would probably be a waste of time. Holds boost fine.

 

[97prizm]

Idle is the only time the problem manifests, which makes sense for a fuel injector issue. It runs great from light load to full boost. Looking at the misfire counter it's only misfiring on cylinder 4 which, to me, rules out a more systemic issue.

I have run through about a half a tank with Techron by now and it hasn't been any better. Think I'm probably going to bite the bullet and dip into my injector stash this weekend.

I'm getting a slight tick at idle on my cavalier. How do you figure out which injector is the culprit while plugged into a scanner? I have an old Snap On bluepoint obd2 scanner.

 

[JD!]

I'm getting a slight tick at idle on my cavalier. How do you figure out which injector is the culprit while plugged into a scanner? I have an old Snap On bluepoint obd2 scanner.

I'm not sure which extended PIDs you might have access to on the Cav, but my 335i has a lifetime misfire counter for each cylinder. In my case I'm able to watch all six cylinders and see that every time I feel a stumble, the cylinder 4 counter ticks up an additional misfire. I swapped the coil packs and spark plugs so in my mind it's most likely an injector given that it doesn't misfire in any other load range.

I suppose if you're dealing with an unusually noisy injector, you might have better success using a stethoscope or putting your ear to a long flathead screwdriver to listen to each individual injector.

 

[D60]

I swapped the coil packs and spark plugs so in my mind it's most likely an injector given that it doesn't misfire in any other load range.

I suppose if you're dealing with an unusually noisy injector, you might have better success using a stethoscope or putting your ear to a long flathead screwdriver to listen to each individual injector.

So how much work to move that injector and see if the problem follows? (I don't know)

 

[JD!]

So how much work to move that injector and see if the problem follows? (I don't know)

Not much, but the Teflon combustion chamber seal is one time use and $9 each if I buy it locally. As soon as I get done with all of this suspension work I'll just toss in a spare and see if it cleans up my idle.

 

[demarpaint]

Reach out to @Trav you won't regret it!!

 

[dfarr67]

Why would you replace two of the set- you're wasting your time.

 

[D60]

Not much, but the Teflon combustion chamber seal is one time use and $9 each if I buy it locally. As soon as I get done with all of this suspension work I'll just toss in a spare and see if it cleans up my idle.

Leakdown? Just trying to think of ways to diag an individual cylinder

 

[BMWTurboDzl]

I just bought an absolute dumpster fire of a 2008 BMW 335xi. After replacing two leaking injectors, I still have a slight idle unsteadiness and occasional misfire on one of the cylinders (not enough to set a code but I've isolated it with live data) which I assume is a fouled up injector based on the state of the others. It doesn't leak and it runs fine off idle. All new spark plugs and I've isolated the problem away from the coil pack.

I've used various fuel system cleaners in the past and haven't noticed any difference in how my car runs, just a feel-good preventative maintenance item. Everyone's seen the rave reviews for fuel additives and how they can cure all sorts of ailments, but of course, a lot can be chalked up to the placebo effect.

Personally speaking, have any of you ever had a verifiable issue (like an occasional idle misfire) that has been fixed with a fuel system cleaner? Should I just bite the bullet and replace this injector already or do I have a shot at salvaging it with something like Techron or SI-1?

Throw in some Si-1 and then drive the car. Worry if it throws a code. On an old, likely previously tuned, BMW I6 a misfire can be attributed to a crack in the cylinder head or between cylinders. Piezoelectric injectors are pricey but really cool at 7 pulses/sec vs the 5/sec from solenoid.

 

[goblin]

Our n54 engines (ths 335i included, me think) use super expensive and super fragile piezo injectors that have only been fixed (supposedly) in their 12th itteration (index 11/12). Index 11/12 can not/should not be mixed with earlier ones on the same bank (cyl 1-3 and 4-6) and in general they are a science on their own to source for a decent price (basically a forever hunting in junkyards, buying full sets).

Also, no matter what - they have to be coded/calibrated after install. Coding is usually done with a dedicated cheap laptop running ISTA (ISTA should be relatively straightforward to source for free if asked nicely on the correct thread on bimmerfest), or with the excellent BimmerGeeks ProTool app available for Android.

ProTool requires either a good quality cable, or one of the good WiFi OBD adapters, or their own dedicated BlueTooth OBD adapter (for BT, only theirs will work).

 

[JD!]

Throw in some Si-1 and then drive the car. Worry if it throws a code. On an old, likely previously tuned, BMW I6 a misfire can be attributed to a crack in the cylinder head or between cylinders. Piezoelectric injectors are pricey but really cool at 7 pulses/sec vs the 5/sec from solenoid.

Thought about deeper issues but I imagine if I had something internal, I'd notice other symptoms. The car runs fantastic as soon as you hit the gas. No hesitation, misfire codes, smoke, cross-contamination, or anything besides a slightly shaky idle. It makes sense in my mind that if an injector has an undesirable spray pattern, it would be most noticeable when it's outputting the least fuel.

Agree on the piezo injectors, they are quite neat and I enjoyed reading up on the cool tricks they can do in the Euro market with stratified injection. I always noticed how smooth my N54s ran (back when I had nice ones).