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"Knocking" noise from Exhaust Manifold (?) + super rich fuel mix

Posted by femmeDSM, Jan 3, 2006

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  1. femmeDSM

    femmeDSM Proven Member

    864
    62
    Joined Oct 31, 2004
    D/FW, Texas
    Finally got my car running this week ( :rocks: ), and am trying to diagnose some interesting new problems...

    First on the list is a strange noise that seems to be coming from the exhaust manifold at idle/low rpms. It sounds like a quick "knocking" that sounds almost exactly like a lawnmower engine (best I can describe it). Like I said, the noise is only present at idle (car actually idles at 750!), and disappears (or significantly lessens) as the rpms raise past about 1500. The car will vibrate a bit while this noise is occuring, as well. It almost feels/sounds like the car has cams and/or poly motor mounts (super rough & shaky).

    The car is running pig rich, as well, as evidenced by the look of the spark plugs when I remove them (black w/ carbon deposits on plugs 1, 2, and 3. 4 looks relatively normal for some reason???). The car will stall occasionally (maybe every 20 minutes or so, if I leave it at idle).

    The car is missing one exhaust manifold bolt, which managed to back its way out while I was driving, and disappear into the "void" of my engine bay. :rolleyes: All other exhaust mani bolts are tightened to FSM specs. OEM replacement for the missing bolt is on its way.

    Any ideas? Could the noise and rich fuel mixture be connected in any way? Just trying to get a complete list of everything I should be checking here....I've got the fuel system memorized ( :toobad: ...See my other posts about this. LOL), now I'm just moving on to the next problem :)

    Edit: Forgot to mention that the car runs smoothly once it gets going, and boosts great. I have been trying to keep it out of boost until I can fix all the little gremlins, but the few times I have let her stretch her legs, she has responded quite happily.

    Thanks in advance for any help, as usual :)
     
  2. femmeDSM

    femmeDSM Proven Member

    864
    62
    Joined Oct 31, 2004
    D/FW, Texas
    Just received a video link from another member and thought I would post it up. This is *almost* exactly what the car is sounding like:

    http://video.google.com/videoplay?do...03436320945976

    Also, I believe I have traced the rich fuel mix and random misfire/stalling problem to faulty wiring at the coolant temp sensor. Seems the previous owner decided to connect the wires to the sensor with electrical tape, which has since worn off. The little clip that goes into the sensor is toast, too (someone had the bright idea of shoving a bunch of RTV sealant into the connector holes), so it looks like I have some wire splicing ahead of me. :toobad:

    Whoever owned this car before me should be ashamed of themselves. WTF
     
  3. xveganxcowboyx

    xveganxcowboyx Proven Member

    1,214
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    Joined May 15, 2005
    St. Paul, Minnesota
    Seeing as how nobody has responded, I'll trhow out my guess. It's possible there is a leak in your exhaust manifold (whether from the bolt or not I don't know). This could cause noise (usually it gets louder as you accelerate though). It could also introduce enough fresh air to fool the O2 sensor into giving you a richer mixture. Seems like a lon shot, but you never know.
     
    femmeDSM likes this.
  4. femmeDSM

    femmeDSM Proven Member

    864
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    Joined Oct 31, 2004
    D/FW, Texas
    Thanks, that sounds like it could be a possibility. I do occasionally notice a puff of smoke coming from around the exhaust manifold gasket area on startup. I guess this is as good an excuse as any to go ahead and get that EVOIII exhaust manifold that I've had my eye on. Couldn't hurt. :sneaky:
    I will be able to tell w/ more accuracy when I Seafoam my intake, I guess.

    I think the rich fuel situation is directly related to the coolant temp sensor, though. Like I said, when I went down to the car last night and wiggled the connector, the wires just came off in my hand. :rolleyes: I don't think they were ever connected properly. Poor car.

    The car came with the Christmas Light Display (i.e. AF gauge), and it pretty much stays on the richest setting possible at lower rpms (sometimes doesn't even register at all), then gradually goes up to Stoich once I hit like 3K. I get a CEL after the car has been on for a few minutes, but no codes will come up, so I can't clear it. From what I've read, this is a telltale sign of the coolant temp sensor taking a crap.

    Thanks for the help :)
     
  5. dsmsucks

    dsmsucks Proven Member

    607
    4
    Joined May 14, 2005
    Rochester, New York
    Okay change the exhaust mainfold bolt that your missin. That CAN cause the noise your hear. Pig rich, have you changed the o2 sensor. Chech if you have boost leaks to. Leaks can cause a rich mixture!
    Back to the noise, my car was making the same sound but only when I shut the car off. Pop......5second...... pop.......5seconds.....pop. This happened right after I installed the 550cc and 2g mas combo
     

    325  0

    1990 Mitsubishi Eclipse GST
    manual · 1G DSM
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    femmeDSM likes this.
  6. 99gst_racer

    99gst_racer Moderator

    9,060
    867
    Joined Apr 5, 2003
    Coloma, Michigan
    Sounds like an exhaust leak to me.

    Also, if your blinky AF gauge is not bouncing back and forth, then your O2's aren't cycling. You might have a bad O2 sensor.
     

    Street Build 7K  67

    1999 Mitsubishi Eclipse GST
    609.8 whp · 541.2 lb/ft · 2G DSM
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  7. femmeDSM

    femmeDSM Proven Member

    864
    62
    Joined Oct 31, 2004
    D/FW, Texas
    The lights on the AF gauge do bounce back & forth, just seem to like staying all the way on the Rich side. They will start bouncing normally once the RPMs get past 2.5K-3K or so. Could this still be an O2 sensor on its way out?

    Also, figured I would mention that I have run quite a bit of starter fluid through the engine in the past week or so, during my fuel system troubleshooting. I know that alcohol injection/race gas will temporarily kill an O2 sensor, but might ether/starter fluid do the same thing? Just a thought.
     
  8. femmeDSM

    femmeDSM Proven Member

    864
    62
    Joined Oct 31, 2004
    D/FW, Texas
    Quick update....Seafoamed the intake tonight, and a good amount of white smoke came out of the exhaust mani. :( Oh well, I guess I have an excuse to get that EVOIII manifold now. haha. :|
     
  9. beatshack

    beatshack Proven Member

    180
    4
    Joined May 19, 2005
    Edmonton,
    I have a leak at the exhaust manifold gasket (manifold to block).. it sounds like lifter tick, only louder. The stupid thing is I didn't get the leak until I ran an entire can of combustion chamber cleaner (like seafoam) through it.
     
  10. femmeDSM

    femmeDSM Proven Member

    864
    62
    Joined Oct 31, 2004
    D/FW, Texas
    Yeah, depending on how many miles you've got on the car, it's possible to "break loose" some crud that was sticking to the gasket. Good that you found it now, though, before it got bigger/worse.

    I assume you changed your oil after the Seafoam...Sometimes that can help a little with problems that arise during/after Seafoam treatments.
     
  11. beatshack

    beatshack Proven Member

    180
    4
    Joined May 19, 2005
    Edmonton,
    Yeah, changed my oil directly after a quick hard run. My oil still gets dirty fast (syntec) after 3 oil changes after running that stuff through!
     
  12. unclesam099

    unclesam099 Proven Member

    144
    1
    Joined Aug 4, 2004
    SE PA, Pennsylvania
    My friend's old '94 Mustang GT had aftermarket headers and the bolts worked themselves loose. The headers were leaking at the flange, and it sounded like a loud ticking and increased as the RPMs did. You already confirmed it with seafoam, tho.
     
  13. laserspeeddemon

    laserspeeddemon Proven Member

    1,789
    40
    Joined Jul 26, 2002
    Fredericksburg, Virginia
    Exhaust leaks are a small problem most mechanics (even myself) over look, but can greatly affect performance.

    If they sound is pulsating its most likely the cause of your noise. The fact that you've lost a turbo bolt is also key. I'm working on a 95 TSi AWD right now, and that is one of the MANY problems it has.
     

    1K  0

    1992 Plymouth Laser RS Turbo AWD
    manual · 1G DSM
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