BMW M3 Forum (E90 E92)

BMW Garage BMW Meets Register Search Today's Posts Mark Forums Read


Go Back   M3Post - BMW M3 Forum > E90/E92 M3 Technical Topics > Mechanical Maintenance: Break-in / Oil & Fluids / Servicing
 
GTB Performance
Post Reply
 
Thread Tools Search this Thread
      10-24-2013, 10:48 AM   #1
Infuzion
///M Car Pusher
 
Drives: 2008 E92 M3 6MT
Join Date: Jul 2013
Location: East Coast

Posts: 45
iTrader: (0)

Backfire through Intake?

As the title states, I'm having a backfire through my intake on a COLD START only. This only happens when the car has been parked for the night and has cooled down to ambient temperature.

Two days ago, I woke up and started my car to let it warm up before heading into my attorney's office for some paperwork. The car was making some awkward "popping" almost like creating a vacuum noise in the car and it threw itself into limp mode not too long after. I let the car warm up for about 20 minutes in limp mode (increased idle) and restarted it. Lo and behold, it cleared the limp mode, and the car restarted and ran and drive perfectly fine. I decided to take it over the my parent's house and crash over there to see if my dad (mechanic) could replicate/figure it out during the next start.

We woke up this morning, and I fired the car up. Exact same thing. He explained it was severely backfiring through the intake, but had no idea how fuel would be getting that high. I decided to post it up on here in hopes that anybody would be able to help me out. I'm hoping it something like a sensor I could replace or anything, because I'm scared to drive the car as-is.

It's a 2008 E92 M3 6MT with ~77.5k miles. The car's ran amazing before this, aside from a low fuel pressure sensor and an O2 sensor, and I don't want to risk damaging this car. I'm hoping it's something I can do myself or on the weekend, though. I have a government job and during the government shutdown they postponed my yearly bonus so I can't exactly afford to pay BMW to fix it (unless they're willing to wait for payment until early/mid November).

I tried using the search button, but couldn't find anything; nor could I find it on Google. Sorry guys!! I appreciate all the help in advance!!

Thanks!!!
Infuzion is offline   United_States
0
Reply With Quote
      10-24-2013, 05:16 PM   #2
kenwelch
First Lieutenant
 
Drives: 2008 E92 M3 M-DCT
Join Date: Dec 2006
Location: Mission Viejo, CA

Posts: 390
iTrader: (0)

You need a way to pull stored codes (DTC's) since having the limp mode.

Your Dad should be able to name a number of things that could cause a lean backfire into the intake. But tripping on the actual problem with out the right tool could make for a very long diagnosis. The codes should be able to point a technician in the right direction.

Wiki:
"A fuel-injected engine may backfire if an intake leak is present (causing the engine to run lean), or a fuel injection component such as an air-flow sensor is defective."

http://en.wikipedia.org/wiki/Back-fire
kenwelch is offline   United_States
0
Reply With Quote
      10-24-2013, 10:13 PM   #3
Infuzion
///M Car Pusher
 
Drives: 2008 E92 M3 6MT
Join Date: Jul 2013
Location: East Coast

Posts: 45
iTrader: (0)

Thanks for the reply!

I took the car up to Advance Auto today and had them scan it and it pulled up several codes:

Cylinder #1, 2, 3, 4, 5, 6, 7, 8 Misfires
Fuel Rail Pressure Sensor Low
Oxygen Sensor Error (Not sure of the actual code for it, the guy was in a rush sorry!)

Those were the codes that it threw, and I'm actually almost certain that the O2 sensor is still covered under the 80,000 mile emissions warranty. Aside from that, the Fuel Rail Pressure Sensor Low concerns me as I'm not sure which sensor is going bad. I know that we just replaced the one that I made a DIY on, so I'm wondering if it's the one directly behind where it takes intake from the hood (much simpler to replace!).

I appreciate your help, and any other assistance and/or guidance is more than welcome.

Thanks again!!!
Infuzion is offline   United_States
0
Reply With Quote
      10-25-2013, 08:54 AM   #4
bandit408
New Member
 
Drives: 2003 ZHP
Join Date: Nov 2011
Location: MPLS, MN

Posts: 8
iTrader: (0)

Check your actual fuel pressure first! When an engine is cold it requires more fuel. If the the fuel pump is weak, either pressure or volume, it will cause the lean backfire.

One thing about code readers at parts stores. All it does is tell you which circuit the computer is seeing the problem in. The problem could be 4 different things.

1. a problem in the computer
2. a problem with the wiring
3. a problem with the sensor/actuator
4. a mechanical condition causing the sensor/actuator to go out of range

To be honest the most mis-diagnosed part on a vehicle is the oxygen sensor. if the fuel volume is low you are going to see it as a cold start issue first (at least up here in Minnesota). This is usually associated with misfire codes and oxygen sensor codes. After you check fuel pressure/volume and if it is in specification I would do a smoke test on the intake. I have seen quite a few intake gaskets fail and cause this also. The unfortunate part is the old way of using propane or brake cleaner to find the leak does not work as well as in the past. Google homemade smoke machine and build one. I did it for $20.
bandit408 is offline  
0
Reply With Quote
      10-26-2013, 09:55 AM   #5
Infuzion
///M Car Pusher
 
Drives: 2008 E92 M3 6MT
Join Date: Jul 2013
Location: East Coast

Posts: 45
iTrader: (0)

Awesome I'll have to try that! Hopefully it's nothing too serious, but in terms of the air/fuel ratio, shouldn't the computer figure that out rather quickly when the car is started? Or could the possible intake gasket failure be causing serious issues with it?

Thanks again for your replies and it does mean a lot!
Infuzion is offline   United_States
0
Reply With Quote
      10-26-2013, 05:23 PM   #6
kenwelch
First Lieutenant
 
Drives: 2008 E92 M3 M-DCT
Join Date: Dec 2006
Location: Mission Viejo, CA

Posts: 390
iTrader: (0)

Quote:
Originally Posted by Infuzion View Post
Awesome I'll have to try that! Hopefully it's nothing too serious, but in terms of the air/fuel ratio, shouldn't the computer figure that out rather quickly when the car is started? Or could the possible intake gasket failure be causing serious issues with it?

Thanks again for your replies and it does mean a lot!
The computer can figure it out when it gets the correct information. The check engine light and diagnostic trouble codes help when the sensors are providing information the is "out of range". Being able to look at codes and live data help the technician locate the real problem. They can also utilize the BMW data base of known problems for the vehicle and codes stored.

Your random misfire on all cylinders will create O2 sensor readings that are not in range. The exhaust O2 readings are used to trim the fuel mixture.

The pressure sensor code could be the hint that will lead to finding the problem. But again being able to monitor the fuel pressure data with the engine running to see if it is within normal amounts helps with the diagnosis.

This is from the M3 Tech Info for the fuel system:
"There is now only one fuel pump (the M5 has two). This has a three-phase motor, which ensures sufficient torque across the whole pump speed range. The pump speed is used to provide the required fuel pressure of 3-6 bar, depending on the engine operating state.

A fuel pressure sensor sends its signal to the MSS60. The fuel pressure sensor is located behind the inner fenderwell. If the pressure sensor fails or there is a fault in the CAN bus and in the engine emergency program, the fuel pump is operated at full speed. In this process, the pressure is limited to 6 bar by the mechanical pressure sensor.

The signals from both tank fill level sensors are sent to the junction box and are forwarded to the instrument cluster via the K-CAN, where they are evaluated and displayed."
kenwelch is offline   United_States
0
Reply With Quote
Post Reply

Bookmarks

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -5. The time now is 01:14 PM.




m3post
Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
1Addicts.com, BIMMERPOST.com, E90Post.com, F30Post.com, M3Post.com, ZPost.com, 5Post.com, 6Post.com, 7Post.com, XBimmers.com logo and trademark are properties of BIMMERPOST