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P0306 and P1404 on chuging 3800

cornhusker

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I've got an 01 Pontiac Bonneville with the 3.8. She's got about 195K on it. Up until a week ago everything was running just fine. Then the car start chugging at idle. I have gone through the basics and can't seem to figure this one out. I think that I'm getting the P1404 (EGR vavle error from cylinder 6 misfire P0306 error code). The basics include new champion plugs and wires. New coil pack and fuel filter. I even swapped out fuel injectors from another cylinder. Whats possibly the most alarming about this issue is that not only is the Service Engine Soon light on, but it even flashes at high speeds!

I currently do not hear a motor knock nor do I hear any kind of vacuum leak. I can smell a slight odor of unburned fuel mixed with rotten eggs when the vehicle is idling. This issually suggest cat converter, but its got too many miles for that fix plus why does the issue always seem to follow cylinder 6?

Is it possible I don't have any juice going to the injector on 6? Is it possible I have a stuck valve? How can I check both of these? Any ideas would be appreciated.

Thanks,
 

melsg5

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Have you tried replacing the EGR valve or if you have an advanced scanner running tests on the valve?
 

cornhusker

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I took the EGR valve off and cleaned the ports. I made sure the valve was not stuck. Cleaned it up with Carb/Choke cleaner and reinstalled. How do I run tests of the EGR valve?
 

cornhusker

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Could someone please upload a picture of where the PCV is located. Althouth I do not hear a vacuum leak,tThis may be a good place to check. A picture would help tremendously.
Thanks,
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cornhusker

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I'm really not sure. When I took it off it appeared as though everything looked good. The EGR valve is literally right next to cylinder #6. I'm not sure if that has any bearing on why cyl 6 is having the issue. Please note that I was able to freely move the EGR valve with hardly any pressure.

What about lower intake manifolds? The 3800's are known for having issues with these. Could that result in my misfire? I haven't noticed any disruption in coolant though.

Thanks,
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melsg5

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The lower intake manifolds have coolant leaks, if there is no evidence that's not your problem. Free movement of the EGR has nothing to do with whether it's good or not. It's controlled by the car computer and has to correctly respond to varying signals being sent to it thus the need for a the proper diagnostic scanner to test it. It's location next to 6 just improves the changes of it causing the P0306 code.
 

cornhusker

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I will get an EGR vavle and slap that on there this week. I thought I would mention that the car does blow some white smoke when its cold, but I can't say that it appears to be using any anti-freeze. This weekend I also took the valve covers off to make sure I didn't have a bent pushrod or rocker. Everything looks good there too. I will update after the installation of an EGR vavle.

Thanks,
 

cornhusker

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The EGR valve finally came in today. Not sure why it took 10 days to be delivered. Regardless I will install it tonight and post my results.

Thanks,
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cornhusker

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And yes I replaced the plugs and wires on all the cylinders. I also checked compression and its at 130 which is within 5 percent of the other 5 cylinders.
 

melsg5

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do a hydrocarbon test on the cooling system to check for a leak, you mentioned white smoke on one of your posts
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cornhusker

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Ok, so I took the car to a local mechanic and he can't seem to figure it out either. He checked all the same things that I checked. He even put a new upper intake on.
So far the following has been completed or has been replaced:

Compression is 130
Injector swapped (Cyl 6)
Plugs n wires (all 6 Cyl)
Coil Pack (One for 2 cylinders)

He suggested that the Cat Converter might be the culprit or the lower intake. Can a bad cat converter really cause a cylinder misfire for the same cylinder everytime? If the converter was clogged wouldn't I see issues with multiple cylinders? As far as the lower intake I have sprayed carb cleaner all around every gasket and the motor doesn't smooth out or run any better.

Since it has compression can I still have a bad/stuck valve or a head that's warped.

Any more information would be appreciated.

Thanks
 

melsg5

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Disconnect the cat and see if it runs better but that shouldnt cause 1 cylinder to misfire. If you have good compression on 6 not a valve issue. If you are still getting the same codes related to the EGR I would find a shop with a Tech II scanner that can run a diagnositc on the EGR valve, I know it's new, but the wire harness or PCM may have an issue controlling the EGR.
 

G6superman

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I have a 99 monte/lumina exact same issue. Was the problem ever solved. I have done plugs and wires all o.e. factory parts. Plug 6 was fouled but the gap was only. 005 from the required .060. Although plugs 3 and 5 were significantly off .080 from .060 and they ran fine. Im going to order a egr valve because they are relatively cheap. I erased the codes and p0306 came back (this is what prompted the plugs and wires change). No vacuum leaks I can find. Was substantial oil build up, assuming this is from 2 years ago when the starter went out exposing a leak, that was fixed. After plugs/wires the car was still missing on 6 round 23-2500 rpms, but seemed to smooth out after driving but still noticeable. Any advice. Exhaust is riddled with small hole and mechanic did say mufflers were shot. Help, attached photo is from 6received_2229578653772981.jpeg
 

melsg5

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Maybe its the picture but the gap seems excessive, are you using a wire gap gage?
The other thing is those are not the same type of plug, or again it's the picture, the one on the left has an extended center insulator compared to the one on the right. Use the correct AC-Delco plug for whichever engine you have 3.1 or 3.8.
Try swapping the coil for that cylinder with another to see if the P0306 goes away and you get a P030X.
Have you done a compression test?
 
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