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post #1 of 12 (permalink) Old 02-23-2012, 04:34 PM Thread Starter
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Hey everybody, new to the forum.

I have an '05 Cobalt. It has been flagging Fuel Trim and Misfire codes for over a year. I have made some repairs that seemed successful. Replace the coil pack for the misfires. Fixed it at the time but came back a few months later.

I started checking for intake leaks and found one good sized at the intake manifold between cyl #3 and cyl #4. Looked like an intake manifold seam leak so I replaced the manifold. Still leaking. You can actually here it hiss. So I pulled it back off and made sure I didn't do anything wrong. Looked good. Checked the cyl head ports for straightness. Ok, no issue seen.

I am stuck. Has anyone been through this?

Help. Please.
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post #2 of 12 (permalink) Old 02-24-2012, 06:01 AM
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Probably a dumb question, but you did replace the gasket, right?

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post #3 of 12 (permalink) Old 02-24-2012, 05:13 PM Thread Starter
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Not a dumb question. Any question could lead to a conversation that leads to an answer for my problem.

I did replace the gasket. The new manifold came with gaskets.
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post #4 of 12 (permalink) Old 02-24-2012, 05:17 PM
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post #5 of 12 (permalink) Old 02-24-2012, 05:31 PM
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you torque it down?

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post #6 of 12 (permalink) Old 02-24-2012, 06:14 PM
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If you hear a hiss it's not leaking between head and manifold it would be between throttlebody and manifold or the crank case vent hose. Make sure throttle body collar is sealed tight. Are you still getting misfire codes? Probably not. But U will get lean code or mixture code anytime you have air entering head that is not metered by MAF sensor. If you hear a hiss it should be easy enough to find. Have U tried the propane trick?

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post #7 of 12 (permalink) Old 02-24-2012, 09:19 PM
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You know, If you had a misfire issue, then it ended up been the coil pack, once replaced, it solved your issue, but the problem re-occurs, it could be as simple as bad spark plugs, replace your spark plugs with better ones, do not get the Boshe platinum 4s, use simple regular spark plugs, I have gone through 2 coil packs, I have been told those kind of spark plugs cause your coil to burn out your coil pack because they are too hot, I'm not a mechanic, but since I started using the regular ACDelco spark plugs (Yes, they are $6 each) I have had no issues with my coil pack. Try that before doing anything drastic, obviously, if your coil pack is already damaged, you will need to replace it too.

As for your manifold leak, read the above posts...
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post #8 of 12 (permalink) Old 02-25-2012, 05:44 AM Thread Starter
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I did not try the propane trick, I used a smoke machine. It looked like it was coming from between the manifold and the head but I could not be sure. When you say throttle body you mean the one on top of the intake. Correct? I did not replace any gasket for that. I will to be safe.

Which crank hose are you referring too? That could be it. The leak looks like it comes from the under side of the manifold. There may be a hose I just don't see clearly.

Misfire is gone now. I do not have Delco plugs but if you guys think I should stick with them I will get them.

This is my sisters car who travels back and for to college. I need to sort this out. She will be back in a week and I will have the car for a week. Hopefully I will get to the bottom of this.

Great stuff so far, thank you for the input.
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post #9 of 12 (permalink) Old 02-25-2012, 05:59 AM
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If it was a leak between head and manifold it would make more of a pulsating piss,piss sound. If it is a constant hiss it is before intake manifold. If you removed throttle body make sure that gasket isn't cracked. The hose in question goes from intake to valve cover. Can't remember if it is a straight hose or if there is a PCV in line. The spigget at the intake has been known to crack around where hose connects so check for leak there also.
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Last edited by Coby7; 03-01-2012 at 05:50 AM. Reason: Wrong wording
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post #10 of 12 (permalink) Old 02-26-2012, 06:41 PM
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if you switched the manifold you switched over your sensors maybe check to see if the seals are ok

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