Stuck in 4 cyl mode - Pontiac G8 Forum: G8 Forums - G8Board.com
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post #1 of 25 (permalink) Old 02-21-2013, 02:39 PM Thread Starter
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Stuck in 4 cyl mode

So this morning as I'm taking my girlfriend to work, the car get stuck in 4 cylinder mode. No loud noises from from the engine. Spark is present to all 8 cylinders. Any ideas of what may have caused this? Its at the stealership right now. Just wondering what they may find.
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post #2 of 25 (permalink) Old 02-21-2013, 03:42 PM
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No idea, but what was it like to drive? Acceleration, fuel economy if you drove it much like that? I'd love to be able to force 4 cylinders active with more throttle than currently programmed.

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post #3 of 25 (permalink) Old 02-21-2013, 03:44 PM Thread Starter
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It sucks. Shifts hard and a lot of vibration. Not good at all!!
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post #4 of 25 (permalink) Old 02-21-2013, 03:55 PM
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post #5 of 25 (permalink) Old 02-21-2013, 04:00 PM Thread Starter
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So they just called and said it was some purge cylinder and both front o2 sensors and over $500 to fix. I just replaced both o2 sensors exactly 1 week ago with bosch when doing header install.
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post #6 of 25 (permalink) Old 02-21-2013, 04:03 PM
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^ Next time you get on here to ask for help, information like "Hey I did a header install last week" would be a good idea to disclose.

It never threw one single CEL? Do you have an aftermarket tune?




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post #7 of 25 (permalink) Old 02-21-2013, 04:14 PM Thread Starter
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Sorry. It does have a tune but it was before the headers so it was throwing the rear o2 cel. But I don't see how both brand new o2's can die exactly 1 week after they were installed.
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post #8 of 25 (permalink) Old 02-21-2013, 04:47 PM
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It's actually pretty common to have an 02 sensor fail right after putting on headers if you run it without a tune for a week or so. Just happened to 2 buddies of mine with gto's after their header install. They had no problems for a week and then both cars started throwing codes.

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post #9 of 25 (permalink) Old 02-21-2013, 05:05 PM
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I had issues with the Bosch sensors I tried on my car. They were slower than the stockers and the computer didn't like them..I went back to the stock ones.

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post #10 of 25 (permalink) Old 02-22-2013, 11:28 AM Thread Starter
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So maybe it is the o2's. I thought the dealership was just yanking my chain by saying the front o2's were bad. I'm gonna have them save em for me and return them to AutoZone when I get the car back. Thanks for all the help guys. Will update when I get the car back (hopefully today).
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post #11 of 25 (permalink) Old 02-22-2013, 06:26 PM Thread Starter
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Just got word from the dealership that whatever they thought was wrong with it did not fix it. They replaced the o2's and whatever purge cylinder they talked about and its still doing the same thing. Im wondering about the dod solenoid thats under the intake. Would that throw up a specific code for the solenoid if it had gone bad? Again, Thanks for the help.
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post #12 of 25 (permalink) Old 02-22-2013, 08:09 PM
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I sure hope your not paying for these *did not solve the problem* shotgun parts there throwing at you. There are 4 solenoids (one for each cylinder) in that DOD system. They are hot all the time, and get there grounds when the ECM says so, and in the correct sequence, to make the transition as smooth as can be.
It sounds like all 4 ground return wires *from the 4 solenoids*, have found a way to be grounded all the time (instead of when the ECM OKs it).
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post #13 of 25 (permalink) Old 02-22-2013, 08:16 PM Thread Starter
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I do plan to tell the dealership to jump in a lake if they try to charge me for it. I'm thinking of just pulling it out of the dealership and doing the DoD delete myself. I don't like that they did 2 things to it and it didn't fix anything.
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post #14 of 25 (permalink) Old 02-22-2013, 10:01 PM
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Because its at the dealers service dept., does that *for sure* mean that they know that all 8 plugs and all 8 fuel injectors are operating correctly. You know that if fuse F35-20A is blown, it wipes out the 4 odd fuel injectors and 4 ignition coils. Or that if fuse F29-20A is blown, it will wipe out all the even injectors and coils. That equals a very crummy running (valves still cycling) condition. If you *can not* get proof from them about the condition of those fuses and take your car back, you could check that out for yourself. They are located in your underhood fuse box.
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post #15 of 25 (permalink) Old 02-22-2013, 11:02 PM Thread Starter
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All 8 coils were firing. And the cylinders not working are the same 4 that cut off for dod. I know the outer 2 cylinders on the drivers side and inner 2 on the passenger side are the 4 that aren't working.
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post #16 of 25 (permalink) Old 02-25-2013, 08:50 AM
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Originally Posted by bmw78586 View Post
I do plan to tell the dealership to jump in a lake if they try to charge me for it. I'm thinking of just pulling it out of the dealership and doing the DoD delete myself. I don't like that they did 2 things to it and it didn't fix anything.
Did you make any more decisions about the G8 over the weekend?

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post #17 of 25 (permalink) Old 02-25-2013, 08:57 AM Thread Starter
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Nope. Waiting for my local dealership to get back to me today. If they haven't found anything today, I'm going to pull it out of there and just do the DoD delete kit myself.
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post #18 of 25 (permalink) Old 02-25-2013, 12:34 PM
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Nope. Waiting for my local dealership to get back to me today. If they haven't found anything today, I'm going to pull it out of there and just do the DoD delete kit myself.
Completely understandable, please let me know how things are going.

Michelle, GM Customer Service

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post #19 of 25 (permalink) Old 02-25-2013, 01:06 PM Thread Starter
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So they called and said apparently an o2 sensor harness melted on the header. Gonna pick it up and see how it runs. Will keep posted.
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post #20 of 25 (permalink) Old 02-25-2013, 01:20 PM
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Did you forget to push it back in its mount?


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