2012 F10 M5 - Strange Popping Sound

[LinusIT]

Hi

My car has developed a new issue and I'm struggling to figure out what it is. This sound only happened after I had my car washed yesterday, I didn't have the engine cleaned nor the bonnet open at the time so it may just be a coincidence. The sound only happens when pressing the accelerator, on idle or cruising at a steady speed you can't hear it. I've had my head in the bonnet listening and it sounds as though it's either coming from the turbo area or cylinder bank 1-4 (drivers side). I've done some diagnostics with ISTA-D and have misfire counters on cylinders 2 and 3 (count 1 for each), for some reason ISTA-D won't let me select/show the misfire counter for cylinder 1 so that may have counters as well.

I appreciate it's hard to diagnose an issue like this from a video but any clues/pointers would be massively appreciated.

Cheers

[SapphireM5]

That does not sounds good. Almost sounds like a rod knock. Can you get to a could plug while it's idling? I was going to say unplug one at a time and see if it still makes the noise. If it stops on one cylinder then you know which is hurt. GL bud.

[DTP1980]

That is really weird. It sounds like something that is pressure fitted is being pushed out under compression, then sucked back in under vacuum and repeating. Based on this, I'd go for something close to a cyclinder.

Personally, I'd connect a bit of tube to the end of a funnel and use it like a stethascope to isolate the area the noise was coming from.

And I'd be checking all the injectors were where they are supposed to be. Might want to check no water has gotten into a cylinder and it's not in fact trying to 'hydraulic' itself to death.

Other than that to start with, i'd swear it was an April fool's joke and you were trying to convince us you'd manage to convert you car to bubble power.

[LinusIT]

SapphireM5 That's a really good idea, the problem is getting to stuff with everything connected to make it run. Would unplugging the coil pack cause any engine damage whilst doing this test?

DTP1980 It's definitely an air type noise, know that sounds odd, sorry. When I first heard it I thought it was an engine knock and my heart sank but from listening with the bonnet open it's definitely air/pressure related. I hadn't thought of the tube and funnel idea. Someone else suggested taking the spark plugs out and turning the engine out to expel any water, which surprised me a lot but you're the second person to mention water. I wish it was a joke, at present I'm without my car

I'm picking up a set of plugs and filters tomorrow, hopefully will either know more or have solved it.

[LinusIT]

Fitted new plugs today but the noise still persists. I checked each bank for disconnected vacuum lines and anything out of place but couldn't see anything wrong at all. I'm pretty certain the noise is coming from the top of the engine now, although I'm going to try and locate it more precisely with a funnel and length of tube once I source them. I wasn't able to turn the engine over with the plugs removed, even after reconnecting both ecu's, the only thing left unplugged was the coil packs. I could take to a friends garage tomorrow and take the plugs out and blow the cylinders out with an airline. Would this be a good approach?

Spark plugs weren't damaged at all, just worn by the looks of it.

[LinusIT]

So after spending a few hours taking as much apart as I could without stopping it from being started I believe I've found the issue. Using a length of garden hose I've located the noise to be coming from injector 1 or 2 area, so I unplugged the coil pack for injector 1 and hey presto, the noise is gone. Swapped two of the coil packs around and did the same test and got the same results.

I replaced the fuel rail on bank 1-4 recently and noticed the screw holding those two injectors in was severely lose and subsequently injectors 1 & 2 wobbled quite a bit, maybe this is what caused the issue despite me tightening it up. I'm going to replace injector 1 and fingers crossed, the problem will be fixed.

[SapphireM5]

Originally Posted by LinusIT

So after spending a few hours taking as much apart as I could without stopping it from being started I believe I've found the issue. Using a length of garden hose I've located the noise to be coming from injector 1 or 2 area, so I unplugged the coil pack for injector 1 and hey presto, the noise is gone. Swapped two of the coil packs around and did the same test and got the same results.

I replaced the fuel rail on bank 1-4 recently and noticed the screw holding those two injectors in was severely lose and subsequently injectors 1 & 2 wobbled quite a bit, maybe this is what caused the issue despite me tightening it up. I'm going to replace injector 1 and fingers crossed, the problem will be fixed.

Hey bud glad your making headway, let see if I'm following you.

You switched coil packs and the noise stayed at the same cylinder?

When you unplugged the coil pack and ran the car no noise?

If the noise stops when you disconnect the coil and comes back when you reconnect it, injector is t your issue. It sounds like that cylinder is hurt.

Let me know about my questions. GL bud!!

[LinusIT]

I'm so glad as well, I was getting so frustrated with it cos it was hard to locate where the noise was coming from.

Switched coil packs on cylinders 1 & 2, exact same result.

Unplug the coil pack on cylinder 1 and the noise is gone.

[LinusIT]

I have found a second hand injector on eBay which I intend on buying, it's £40 which is far better than £240 from BMW. The one I have found on eBay is a different part number to the one I have fitted at present, basically a newer revision although not the newest.

Will it be ok to fit just this one?

[apexlocator]

Newer is ok, but you'll need to get it coded to your car

[LinusIT]

Awesome, thanks for that. I've got ISTA so coding isn't an issue

[DTP1980]

How fascinating. And the initial information suggested that this happened after you had washed it. So this was either a coincidence, or a very strange set of circumstances which caused it. Glad you got to the bottom of it.

One query on the second hand injector - it's good you can code it in, but if I'm not mistaken, it is possible to establish whether the injector is worn out or within tolerances. I'm just hoping you can check this out to avoid any future problems with that injector.

[LinusIT]

Fitted the new injector the other day and the noise has gone completed, I've never seen this before but hopefully this post may help others, should they have a similar issue. They key to find the noise was placing a length of garden hose down where the injector sits, located the noise extremely quickly.

I'm not aware of how to test petrol injectors. I know you can with diesel injectors to see if they are within tolerances. I did a test I found in ISTA but this only tests for leaking injectors by putting massive pressure in the rail and then monitoring it there after for 30 seconds.

Thanks for everyone's input

[Verneycoin]

Hi Linus!

I’m also experiencing similar issue as you. I have these strange sound coming out from the dashboard whenever i accelerate from gear 3,4 and 6th. 1,2,5 and 7th have no sound.

After looking at your post, i’m going to get the fuel injector changed and hoping that the sound will be gone too! Sick of that sound!

I have a question: is there any brand for the fuel injector? Only have to buy one right?
Noob at this. Just gotten this M5 ride two weeks ago!

[BeachM5nster]

did you leave the car with the person that washed it?