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Discussion Starter · #1 ·
Alright guys. I haven’t posted here in years. Due to me always knowing how to fix my own cars. But this time? Definitely going to need some thoughts and insight to see if this can be figured out. All of your help will be greatly appreciated.

So cylinder 5 misfires on cold starts.
once car is warm runs totally fine. Here’s what I’ve done so far.

replaced spark plug, ignition coil, injector. Found vacuum leak on throttle body on that cylinder. Fixed that also. Replaced ionic sensors on both banks. I’ve also done a leak and compression test and it was perfect.The only code I have is misfire cylinder 5. Nothing else. I’ve also swapped plugs, coils etc misfire did Not follow.

the only thing I can think of at this point. Is vanos solenoids on that bank. They’re the originals. I have not performed a vanos test yet. But that’s my next step. I’ve attached the leak and compression test as well.
So any idea would be great!
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293 Posts
Discussion Starter · #6 · (Edited)
That's exactly what I did and swapped one at a time. No misfire followed.
I do have the BMW specific codes. I will have to find those at a later time since I'm no where near them. I will report back with those.
Throttle is functioning fine. When I ran an autel computer to it. I looked at my injectors and they were firing fine. I also looked at fuel pressure etc etc.
The ONE thing I noticed before the injector was replaced is that it acted DEAD completely. It wasn't even working at all.

I have not taken the valve cover off to inspect the valves ( I believe that would be a good next step as well?

One at time:
Swap ignition coil.
Then spark plug.
Then injector.

If misfire doesn't follow, you have a problem limited to that cylinder, possibly with the opening and closing of the valves.
A misfire is detected using the ionic modules. That means, the quality of combustion is not as expected. Is the throttle sticking, working?

Do you have the BMW specific codes? or is the misfire read off from an OBD2 device ?

Check dme output for cyl 5.
As far as I saw when I connected my Autel yes. But I can certainly check again and post what I see for you guys.

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Discussion Starter · #8 ·
I haven't used a scope to inspect yet. GOOD idea! I will do that as well.
Yes the fuel filter and pump are fairly new and in good working condition. My fuel pressure has no issues.
And when going over 100mph when the other fuel pump goes into effect also is reacting as it should.

I've new vanos solenoids sitting here and will do that next just because mine are the originals and I have an 06 M5.
I know that these can cause SO many weird issues.

But I think once I pull the valve cover off ( I've never done that yet since the gasket has NEVER leaked and it's also original )
I should be able to see as much as I need mechanically.

My thoughts right now are a few issues probably causing it. Vanos solenoids. And MAYBE a bad valve spring.
Its just the whole car running COMPLETELY fine when warm is what throws me off.

Ever looked with a scope into the cylinder? Wondering if there are excess carbon deposits on the pistons for hot spots etc.
With little confidence it's the cause, fuel pump/filter change? I would expect to see a low fuel pressure code if that were the cause hence low confidence but asking for completeness.
Not having any other codes leads me to think mechanical (eg, carbon deposits) that done have direct sensors to detect deviation from 'normal'.


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293 Posts
Discussion Starter · #11 ·
You may have hit the nail on the head… I know my cats are bad. I smell them lol. No codes from them though for years. UNTIL a week ago. I got these ones. I cleared the codes and they haven’t came back.
P0430 and P0420 Could this be it!?

I also noticed earlier when I was driving in realpt Low rpm it gives a little sputter feel. But on wide open throttle… again car runs fine.

Three things come to mind to check before committing to pulling the valve cover. You mentioned it runs fine when warm and even at high RPM so I doubt it would be a valve spring or a VANOS solenoid (although I'd be willing to bet your solenoids fail the test)
1) Scope the cylinder like what @amesser325 said. Look down both the spark plug hole and throttle body.
2) Check the wiring for both the ignition coil and the fuel injector
3) Since it runs fine when warm it sounds very similar to symptoms I had a few months ago. I had misfires on cylinders 2, 3, 4, and 5, so all on bank 1. But on bank 2 I only had a misfire on cylinder 7. It had only been a year since I replaced all the plugs and coils so I was fairly confident it wasn't any of that. The key difference is that I had some catalyst codes and the misfires were pretty specific stating "DME: Misfire impairing exhaust emission, cyl. X" which was code 002B46 for cylinder 5. When you get a chance let us know the exact code you're getting.

If your misfire is the code in #3 then the remedy is to gut the cats and get a tune :cool:
not familiar with the term SAP? Sorry. What do you mean? I will answer.

Dead cold like when the SAP runs?

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Discussion Starter · #18 ·
I have no SAP codes. The fuel injector in cyl 5 was never leaky and I only replaced it due to this issue.
I see vapors coming from exhaust on start-up just fine. Assuming SAP works. I swapped the injector into cyl 1. Misfire did not follow.

SAP = Secondary Air Pump. SAP gets kicked off on cold starts only, to pump air into the exhaust headers, and burn the extra fuel that is injected into the cylinders and into the catalytic converters to heat them up quickly.

Is the fuel injector in #5 leaking by any chance? Can you take out the rail and crank the car and see how they spray ?
They are definitely bad. It isn't the smell of gas. It's the smell of rotten eggs when WOT and always going over 100mph.
Although I don't get codes for them often. Maybe like twice in the past 6 months?

It does however smell like gas on start up. But I've had this car from almost 11yr and it's always smelled like that?

Negative ! Cats do not go bad. The smell of gas means your Secondary Air pump may NOT be working, so you get misfire only on cold ! Tada !

Do this: early in the morning, start the car, you should see water vapor coming out the exhaust , thick white "smoke" that is purely water vapor. If you don't see this, there is a good chance your SAP is dead and not blowing air.

Yeah no SAP codes at all.
And I wouldn't count vanos solenoids out. I've had misfires and timing issues caused by solenoids before on another car.
After solenoids were replaced. The car idled PERFECT and the startup was smooth as butter.
Being that I did leak/compression test I would assume it should show a bad spring.

I have no reset adaptations though.... I could do that.

No sap code? Not sap then.

Given you've cat codes and seems you've already covered plugs, coil, injector and ionic module I'd look at valve springs or wiring or resetting adaptations. Start with easiest (adaptations). And post the bmw codea you're getting.

Vanos is not cylinder specific so can't be that.
Yes after the car is warmed up. I restart it and the issue goes away completely. And the check engine light goes off.

That cylinder read little low 79 psi to the minimum which is 6 bar=87 psi.
Have you compared it to the other cylinders?.
Other than that I would think of valve spring/lifter issue.
Do you restart the engine after cold start for the engine to run better?.
That's what I think to. leak down would show if spring / valve issue.
No I have not checked the coil harness yet. Reason being when I'm watching all coil reactions on the computer they look fine.
On startup and idle and when warm...

What about the injector and coil harnesses? Leakdown would have confirmed the valve springs if they're in the range.

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293 Posts
Discussion Starter · #20 ·
It'll misfire and idle really rough until it's basically warm. So 8-10mins? restart car after that and all is good. Idles smooth, no more misfires, runs good.
This is truly a needle in a hay stack. That's why I came here to get some helpful thoughts from everyone.

You fixed yours correct? what was it?

Interesting that you get a check engine light... Or maybe interesting that I did not. How long do your misfires last during a cold start? Mine were only ever less than 5 seconds as the RPMs would bounce quickly then smooth out around 1200. Then after another 5-10 seconds start steadily dropping to a normal idle.

Either way, when restarting the engine warm I had no issues either.

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Discussion Starter · #22 ·
Yeah measurement was cold. And the pic is misleading taken at an angle it was actually at 82+
All other cylinders were identical.

I have not done the test when fully warm. Good call.

Mine was fixed by gutting the primary cats and getting a tune, so I can only assume the misfires were due to clogged primaries.

This is WAY longer than any of my symptoms persisted so I don't think we're comparing apples to apples anymore. @platii mentioned your compression seems low compared to spec.
What do your other cylinders measure?
Was that measurement taken cold?
Could you measure it warm and compare?
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