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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Mechanical Maintenance: Break-in / Oil & Fluids / Servicing / Warranty > HOT start misfire



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      05-25-2019, 09:45 AM   #1
BadContrakt
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HOT start misfire

Been reading and reading and searching all over the internet to see if anyone else has a problem that fits mine exactly, and I've found one that seems to be very very close to what's going on with my car here which he resolved with injectors. I really would like some input before I purchase injectors based off of one guy's post.

If the car is full operating temperature and I park. Shut down. And turn it back on, it goes as follows:

Fires up in one or two cranks - very fast
RPMs stable out to ~800-850 after the engine fired - normal operation - smooth idle
7-10 seconds of smooth idling at ~800-850 goes by and the RPMs slowly fall and the engine starts to feel shaky
RPMs fall to 450-550 fluctuating with rough misfires for about 7 seconds
Engine seems to finally catch its breath
RPMs then SURGE way up to 1000 maybe even 1100 smoothly and then smoothly fall down to normal 650 RPM idle
Engine runs great. No hiccups no stutters no misfires after the initial stumbling
Wide open throttle pulls hard and smooth. Normal driving around town is smooth.

The reason I struggle to believe this is a leaky injector issue is because I can shut the car off and literally 3 seconds later, turn the car on, it does this. Every. Single. Time. I don't get a gassy smell. I don't get white smoke from pipes. I get pretty good gas mileage (24mpg) too.

Last edited by BadContrakt; 05-25-2019 at 10:20 AM..
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      05-25-2019, 03:49 PM   #2
arkie6
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Here is another thread on the subject that I started:

https://www.e90post.com/forums/showthread.php?t=1459075
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      05-28-2019, 02:14 PM   #3
BadContrakt
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Quote:
Originally Posted by arkie6 View Post
Here is another thread on the subject that I started:

https://www.e90post.com/forums/showthread.php?t=1459075
Arkie, I actually saw your post after posting this thread - based on both of your guys' findings, I ordered 6 brand spanking new index 12 injectors from FCP and will be replacing them this weekend. I'm pretty sure that will be the fix for my chronic post-startup misfire lol

I'll be sure to report back here for documentation purposes
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      06-10-2019, 10:59 AM   #4
BadContrakt
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Update:

Injectors got here and I was about to replace all 6. Before-hand though I wanted to double check my downpipe job before I replaced them, as, all of this started after replacing downpipes.

Turns out the BMW master technician I had with me (sarcasm only slightly intended) swapped my O2 sensors front to back and back to front. Swapped the plugs and no symptoms and beautiful cold start idle and hot start idle. 100% fixed. I'll be swiftly returning those injectors, clips, and seals and saving almost 1400 dollars. Turns out my intuition was correct. I didn't really believe this was an injector issue. Dodged that bullet for now!

Last edited by BadContrakt; 06-10-2019 at 11:14 AM..
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