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Old 05-06-2010, 11:52 AM   #1 (permalink)
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3.4L misfire

2000 basic 3.4L, engine running *rough*, happened all of a sudden like. Stopped by Autozone and they read the code (the check engine light was flashing) and the code said (I forget the exact number) #3 cylinder was misfiring. I put new plugs and wires on last month and it was running perfectly until this misfire thing. I replace the coil block on a whim, but that didn't change anything. The other two possibilities are vacuum leak and fuel injector. I can't rule out a vacuum leak except to say nothing is disconnected and all the hoses seem to be in good shape. I'm thinking I'm going to change the #3 injector, so, it looks like I need to remove the TB and UIM. Is there a gasket kit for the manifold? or do I need some secret agent gasket compound? I would appreciate your thoughts.

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Old 05-06-2010, 12:02 PM   #2 (permalink)
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have you pulled the #3 plug to check it's condition first? And what kind of plugs are you using?

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Old 05-06-2010, 12:26 PM   #3 (permalink)
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Originally Posted by wanderson75 View Post
have you pulled the #3 plug to check it's condition first? And what kind of plugs are you using?
I've just pulled the #3 plug. It's black with carbon, so it appears to be fouled. All the plugs are one month old, AC-Delco 41-940's.

Even though I've changed the coil block, I don't know if this plug wire is good even though it's brand new, and I'm not sure how to check it.

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Old 05-06-2010, 12:34 PM   #4 (permalink)
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Check the other plugs as well. It's very possible that the bad coil caused that plug to foul out. But I'd look at the others as well just to doubly check.

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in·sane   /ɪnˈseɪn/ Show Spelled[in-seyn] Show IPA
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2. of, pertaining to, or characteristic of a person who is mentally deranged: insane actions; an insane asylum.
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4. Swapping a 3.8V6 Supercharged into an 05 Base Impala.
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Old 05-06-2010, 12:46 PM   #5 (permalink)
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Well, the #3 spark plug is firing, I turned the engine over and watched the plug fire. I'm not sure if that is scientific or not. I'm pulling the other plugs just to see how they look. Thanks.

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Old 05-06-2010, 01:11 PM   #6 (permalink)
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Well, obviously the 'normal' things are never what's wrong for me. I've gone about as far as I can go with troubleshooting. Every cylinder is firing except #3, it's not intermittent, it's all the time. The spark plug wires are good, the plugs are good. I wonder what the most 'probable' thing would be? I think this one's heading to the shop next week.

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Old 05-07-2010, 05:57 AM   #7 (permalink)
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Go cheap and work your way up. Replace plug #3 as well as the wire. A cat that is starting to go bad can also cause misfires on the #3 as well. You can have a shop do a back pressure test.

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in·sane   /ɪnˈseɪn/ Show Spelled[in-seyn] Show IPA
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1. not sane; not of sound mind; mentally deranged.
2. of, pertaining to, or characteristic of a person who is mentally deranged: insane actions; an insane asylum.
3. utterly senseless: an insane plan.
4. Swapping a 3.8V6 Supercharged into an 05 Base Impala.
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Old 05-07-2010, 06:03 AM   #8 (permalink)
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I'll replace the plug and wire today, I guess I don't need to assume that the new parts are any good :~) Hopefully luck will be with me. I hate to think of replacing the cat, I hear that is very expensive.

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Old 05-12-2010, 07:02 AM   #9 (permalink)
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wanderson75, just wanted to say thanks for your help. I probably would have spent some unecessary money, I never in a million years would have thought the new plug wire was bad. I replaced the #3 wire and all is well now.

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Old 05-12-2010, 07:25 AM   #10 (permalink)
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Good to hear it man.

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in·sane   /ɪnˈseɪn/ Show Spelled[in-seyn] Show IPA
–adjective
1. not sane; not of sound mind; mentally deranged.
2. of, pertaining to, or characteristic of a person who is mentally deranged: insane actions; an insane asylum.
3. utterly senseless: an insane plan.
4. Swapping a 3.8V6 Supercharged into an 05 Base Impala.
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Old 05-13-2010, 09:16 AM   #11 (permalink)
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I had 8psi of back pressure when my cat plugged...

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