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Old 11-18-2011   #1  
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Default Lacking power after head rebuild

So I just went through the well documented spark plug issue. I will spare you the typical rant and get straight to the point.
The driver side head had to come off to get #s 7 & 8 out. I farmed this work out because I didn't have time and my knuckles were beat up enough just trying to get the stinkers out.
I got it back today and it just doesn't seem to have the same oomph. It feels like a 30+ hp loss. If this thing weren't computer controlled I'd say the ignition timing is retarded. Otherwise it is running smooth and no other problems to report. Is there any way to confirm this and have it reprogrammed if need be? I suppose I could be imagining things.
The mechanic says to drive it a few days and see if it improves- the computer may be going through some reprogramming on the fly. That doesn't sound right to me, but they're not equipped with any reprogramming tools anyhow; so I'd have to take it to the dealer for this I guess.
I don't doubt his skill as a mechanic and have no reason to think anything was assembled incorrectly. I guess I'm here to confirm that.
TIA, Bryan
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Old 11-18-2011   #2  
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I'd give it a few days. It's not uncommon for the ECM to go through some stabilization after engine work. After a few days and it still feels the same, I would take it to the dealer and have them run a diagnostic on it.
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Old 11-18-2011   #3  
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Possible, be sure to take it back if it doesn't improve.
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Old 11-19-2011   #4  
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I didn't think it would take that long to configure. That is very encouraging news. Thanks guys.
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Old 11-20-2011   #5  
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Either the valve timing is off on the bank that was repaired, or the VVT (Variable Valve Timing) isn't working.
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Old 11-20-2011   #6  
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it still doesn't feel right. there has been a slight improvement, but the torque i am used to just isn't there. is the VVT a programmable thing, or a mechanical thing that would require more disassembly?
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Old 11-20-2011   #7  
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Quote:
Originally Posted by Bryan M View Post
it still doesn't feel right. there has been a slight improvement, but the torque i am used to just isn't there. is the VVT a programmable thing, or a mechanical thing that would require more disassembly?
There are electrical connections to oil control solenoids that control the oil flow in the cam phasers. Electrical signals from the PCM to these solenoids changes the
Cam phase, changing the valve timing. So, there are several things that could
have been screwed up on re-assembly.
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Old 11-20-2011   #8  
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what's involved in the repair?
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Old 11-20-2011   #9  
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what's involved in the repair?
The first thing I would do is look at the cam phase (valve timing) on each bank with
the datalog function using a scan tool. This will verify that the VVT isn't working.
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Old 11-20-2011   #10  
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oh well. i was hoping it was something i could do myself. all i have is a code reader. i doubt the mechanic i went to has this type of equipment, so i guess that means i'll have to go to the dealer.

thanks for your input. i have a feeling this is it. at partial throttle it feels "normal". if i step on it from a stop there is a flat spot around 2000 rpms, sort of feels normal (but not quite) until if shifts to 2nd. then it is a hard jump into 2nd.
if i step on it at highway speeds, there isn't much pull at all.
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