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///M3 Forum
The BMW E46 ///M3 is the M version E46 and puts out an amazing 333 HP and 262 lb-ft of torque at stock specs! There are an amazing amount of modifications for both the coupe and convertible models so read up and get started modifying your cars today!

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Old 10-30-2015, 01:57 PM   #1
Hobohunter
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Join Date: Aug 2010
Location: Pasco, WA
Posts: 187
My Ride: 2001 M3
Rough Start when cold

I'm having a rough start when the car has been off for more than a few hours. The car usually manages to start successfully the first time I try but occasionally will require a second try. When it starts, it starts rough, very shaky and sounds like death, for a few seconds and then it goes to a smooth and perfect idle and sounds great.

Things I've replaced already:
Fuel Filter(OEM) about six months ago, less than 2k miles since then
Fuel Pump about a month ago, with OEM
Valve Cover Gasket, replaced two weeks ago after doing the Beisan Systems Vanos pump disk, seals, and solenoid pack replacements.
Spark plugs and ignition coils about six months ago.
All 4 O2 sensors replaced with OEM when I got my exhaust headers returned to stock.
I put in a stock OEM intake to replace a poorly made home built cone filter rig.
Battery replaced about six months ago.

I suppose I'll try replacing the fuel pump relay, but I can't really see anyway for that to be the cause of my rough start.
There are absolutely no codes and I don't experience any stalling or loss of power/responsiveness.

I must be missing something to check/replace but I just can't think of what.
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Old 10-30-2015, 02:42 PM   #2
ALPIN3
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When was the last time you had a valve adjustment?
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Old 10-30-2015, 02:56 PM   #3
Hobohunter
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Quote:
Originally Posted by ALPIN3 View Post
When was the last time you had a valve adjustment?
Forgot to include that in my list. I checked them all during my Vanos work. All solidly within the prescribed band.
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Old 10-30-2015, 07:24 PM   #4
Incog45
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Have you thought about the fuel pressure regulator? I'v had same problem before, I replaced the filter and regulator and it fixed it.
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Old 10-31-2015, 09:16 AM   #5
Hobohunter
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Quote:
Originally Posted by Incog45 View Post
Have you thought about the fuel pressure regulator? I'v had same problem before, I replaced the filter and regulator and it fixed it.
I think that'll be my next thing to try. For some reason I had it in my head that the regulator was integrated with the filter, I think that must be a misconception from the non-M E46 I had recently.
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Old 11-01-2015, 09:21 PM   #6
tacomeat1
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And you're sure it's not just the normal cold-start procedure the cars does on its own?
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Old 11-02-2015, 07:35 AM   #7
Hobohunter
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Quote:
Originally Posted by tacomeat1 View Post
And you're sure it's not just the normal cold-start procedure the cars does on its own?
Pretty sure. I didn't have this issue on the '02 M3 I used to own. Something's not functioning correctly with this one.
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Old 11-02-2015, 11:36 AM   #8
Commando
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I'd have a look at cleaning the idle air controller. Also look into the throttles, make sure they are all closing properly and synchronised. I use a carb balancer to measure the flow through each inlet.
Injectors that are not giving a good spray pattern is another possible cause.
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Old 11-02-2015, 01:06 PM   #9
Hobohunter
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Those will be a good next step to check after I get the fuel regulator swapped.
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Old 11-09-2015, 08:52 PM   #10
Hobohunter
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Got my new fuel pressure regulator in the mail yesterday and got it installed this morning. Seems to have fixed my rough start issue.
I pulled the fuel pump fuse and then started the car to get the lines depressurized and the car only caught and sputtered twice. I helped a friend replace their fuel filter a few weeks back and his car started and ran for several seconds before his depressurized. It seems like my fuel pressure must have bled back through the regulator whenever the car sat still for more than a few hours, causing my rough starting.
Thanks to Incog45 for mentioning the regulator, I likely wouldn't have remembered that it's a separate component on the M3 and would have been chasing other leads to figure it out. Thanks for the other replies as well guys, I appreciate the help.
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