stalls on first start, then starts up fine

8900120d

Lurker
Apr 5, 2018
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when i start my car for the first time in the morning it stalls immediately, then it starts up fine and idles fine, there is no rough idle or anything noticeably odd.
This happens consistently for the past week.

its a 2011 e92 335i n55 FBO + stage 2 LPFP.

according to MHD, the rail pressure is 74.3psi before i try to start my car. i find it very weird that it ALWAYS stalls on the first start up and then the car runs fine after that.

i dont know about the history of the HPFP or if it was replaced in the past.
I have disconnected the Valvetronic as i was having issues with it (this shouldnt be the problem)

no codes (apart from valvetronic being disconnected)
 

doublespaces

General of the Army
Oct 18, 2016
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2009 E93 335i
Leaky fuel injector? My car would stumble on first start when I had a leaking cylinder 6 injector.
 

8900120d

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Apr 5, 2018
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I don’t get any error codes, once I start it the second time, it runs perfectly fine
 

doublespaces

General of the Army
Oct 18, 2016
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To me it just looks like your rail pressure is dropping because your engine is no longer running. Your HPFP seems fine IMO.
upload_2018-10-25_12-3-34.png
 

8900120d

Lurker
Apr 5, 2018
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That’s weird, it may just be injectors then, I’ll take it for a longer drive and hope some codes pop up.

Any recommendations on how I can test the injectors?

Thanks for your help :)
 

8900120d

Lurker
Apr 5, 2018
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It might be worth noting, i recently changed my valve cover gasket, and noticed one of the fuel rail lines was dripping from the top of the injector, fuel actually dripped into the spark plug well and damaged the coil. I’ve replaced the coil and removed all of the fuel rail lines, cleaned them up and refit them, and it wasn’t leaking anymore.

My question is, if one of the fuel rail lines was still leaking, would I have the issue I am experiencing now?
 

Bnks334

Lieutenant
Dec 1, 2016
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Leaky fuel injector? My car would stumble on first start when I had a leaking cylinder 6 injector.

https://datazap.me/u/8900120d/cold-start?log=0&data=3-15

Log attached for cold start stall, looks like rail pressure drops

good point on the injector. Fuel trims do look to be adding quiet a bit of fuel.
It might be worth noting, i recently changed my valve cover gasket, and noticed one of the fuel rail lines was dripping from the top of the injector, fuel actually dripped into the spark plug well and damaged the coil. I’ve replaced the coil and removed all of the fuel rail lines, cleaned them up and refit them, and it wasn’t leaking anymore.

My question is, if one of the fuel rail lines was still leaking, would I have the issue I am experiencing now?

it's possible dirt got into one of the injectors when you took the rail off
 

doublespaces

General of the Army
Oct 18, 2016
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Start by logging both fuel trim banks. This will give an idea of the amount of deviation you have.
 

NoQuarter

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Nov 24, 2017
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If you want to try injectors, my Son has a set he took out of his car. They worked great at the time he took them out. Index 9 I think.

Message me if you want to get in contact with him.

I also have some new index 12's on hand
 

8900120d

Lurker
Apr 5, 2018
22
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Ride
335i
If you want to try injectors, my Son has a set he took out of his car. They worked great at the time he took them out. Index 9 I think.

Message me if you want to get in contact with him.

I also have some new index 12's on hand

Thanks, I think n55 doesn’t have index 12 as they’re different injectors. Also I’m based in the uk haha
 

8900120d

Lurker
Apr 5, 2018
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335i
Quick update, I disconnected the MAF sensor and it seems to start up on first crank and it also idles a lot smoother!
Does this mean the MAF is definitely faulty?
I have tried to clean the MAF with electrical contact cleaner but it didn’t fix my issue
 

silverstreak18

Corporal
Jan 3, 2018
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Charlotte, NC
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2016 M3
MAF could be your issue. Try plugging it back in and confirming it stalls again before you replace it. Also the high lambda reading is normal, there is no fuel being burnt by the engine yet so its reading max lean. The same reading would occur if you coast down a hill with no throttle applied.
 

8900120d

Lurker
Apr 5, 2018
22
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Ride
335i
MAF could be your issue. Try plugging it back in and confirming it stalls again before you replace it. Also the high lambda reading is normal, there is no fuel being burnt by the engine yet so its reading max lean. The same reading would occur if you coast down a hill with no throttle applied.

Thanks for your response, I’ve tried plugging it back in and it stalls lol. Unplugging the maf definitely fixes the stalling issue.
But what about the fact that the maf readings look ok on the log?
 

silverstreak18

Corporal
Jan 3, 2018
126
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Charlotte, NC
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2016 M3
Ive seen stranger things happen on these cars. If I was diagnosing your car I would start with things that affect the motor as a whole. I would rule out plugs, coils, and injectors because if one was bad the motor would fire and you'd have a misfire or running issue of some sort. The maf is a possibility if for some reason the dme is getting a bad reading from it the first time you try to start it. Have you tried getting codes with INPA?