Little to no timing at speed, knocking like crazy! Help! - Pontiac G8 Forum: G8 Forums - G8Board.com
 
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post #1 of 8 (permalink) Old 01-11-2017, 09:31 AM Thread Starter
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Little to no timing at speed, knocking like crazy! Help!

So we've been having an issue where the car has been knocking like crazy up top and now more recently a report that the car had 2 degrees of timing at 45 mph. We have exhausted just about all possibilities that we could think of that would cause this issue, and now have turned to you guys. So the back story.....

Changed tuners and cam's, when the last cam was pulled, we discovered the car had a bent valve and a nice little impression in the top of the piston, however, the car ran completely fine with in that condition with the last cam. After the new cam was swapped in, troubles started. Decently rough idle and of course the knock up top (3-7 degrees at 4500 rpm and up). I'm not understanding how it ran fine, bent valve and all with the last cam but with the new cam, were getting headache. Any ideas?

New Cam specs 223/231 .625/.622 111+0
About .025-0.030 clipped off of the heads, stock LS3 valves.

2009.1 MSM G8 GT: R.I.P April-2014
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post #2 of 8 (permalink) Old 01-11-2017, 09:57 AM
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after the tear down on the first time finding the bent valves ,was there a piston to valve clearance check? and I would have checked the piston to valve clearance on the new cam for sure ,,,, I wouldn't run it to long in its current condition , due to more damage

kook 1 7/8 long tubes, ls3 cam,dod delete,tuning school transmission tune,cai,corsa exhaust,lowered 1",staggered wheel set 19x8.5 19x9.5 breyton gts av
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post #3 of 8 (permalink) Old 01-11-2017, 10:11 AM Thread Starter
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We should have done so, but did not, we figured it ran fine before tearing it apart, so we put it back together as is. What baffles me is the tuners comment of him seeing only 2 degrees of timing at 45 MPH, I cant put that together of how that could happen.

2009.1 MSM G8 GT: R.I.P April-2014
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post #4 of 8 (permalink) Old 01-11-2017, 11:14 AM
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Was the cam that you swapped out also aftermarket? Or was this the first cam job you've done on the car?

If it was a previous swap, did you degree it in? Did you degree the new cam in?

Always need to be sure to replace known damage parts, and new valves generally require a valve job especially when the sucker was struck and bent.

Until you properly fix your valve problem and verify that your cam meets spec and is installed properly, you can't otherwise observe to detect additional potential problems. You may want to price a full valve job to see how much it would be per cylinder. I would rather not do a single cylinder anyways, but with a single damaged seat you can probably get away with it as long as the other valves are fine.

There is no evidence of other problematic valves?

'09 G8 GT - Mods Planned: Stage 1C Livernois, Fender Well CAI, Kooks Mids, Solo Axle back (Already have the X Pipe), GXP Trans Cooler, 2800 Circle-D Stall Converter, Differential (Max 3.45), Suspension mods (Bushings, sway bars, etc)

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post #5 of 8 (permalink) Old 01-11-2017, 11:49 AM
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So many variables here.

Is there audible knock?
Can you post the tune file and or the log file?
Plugged fuel injectors?
Low fuel pressure?
Plugged cats?

Lots of variables here

PBM G8 GXP M6-Self flex fuel tune,OBX LTs, Kooks A/B, Monster Stg 3 clutch, LSA S/C, cam, fuel system, stock block and stock heads. Best e.t 10.81/ best mph 135
2007 TBSS-Self tune, bolt ons 13.06@106.7, 2,200 D.A
1991 GMC Syclone- Self tune/catback 12.8@104, 4,200ft D.A

2002 Bonneville SSEi- Self tune, 3.4" pulley, FWI. The beater
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post #6 of 8 (permalink) Old 01-11-2017, 11:57 AM Thread Starter
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Fueling is fine, though fuel pressure hasn't been logged, i think my tuner would have pointed out anything else out of the ordinary. It is not necessarily an audible knock, but you can hear the car "breaking up" through the exhaust in the higher rpm's. What specifically would you like to see in the log? I can screen shot and post it up, I appreciate the help.
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post #7 of 8 (permalink) Old 01-11-2017, 12:07 PM
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Okay, it sounds like an ignition problem, and an ignition problem WILL cause KR.

Scan for current misfires on each cylinder using the Hp Tuners scan tool. Make sure the misfire tables in the tune are set to stock before doing this or the misfires will not be detected in the log!!

Keep us posted

PBM G8 GXP M6-Self flex fuel tune,OBX LTs, Kooks A/B, Monster Stg 3 clutch, LSA S/C, cam, fuel system, stock block and stock heads. Best e.t 10.81/ best mph 135
2007 TBSS-Self tune, bolt ons 13.06@106.7, 2,200 D.A
1991 GMC Syclone- Self tune/catback 12.8@104, 4,200ft D.A

2002 Bonneville SSEi- Self tune, 3.4" pulley, FWI. The beater
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post #8 of 8 (permalink) Old 01-11-2017, 02:27 PM Thread Starter
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Quote:
Originally Posted by STAGEUP View Post
Okay, it sounds like an ignition problem, and an ignition problem WILL cause KR.

Scan for current misfires on each cylinder using the Hp Tuners scan tool. Make sure the misfire tables in the tune are set to stock before doing this or the misfires will not be detected in the log!!

Keep us posted
Stock tables on both "Cylinder mode" and "SCD mode" correct? And great idea by the way, I didnt think of this.

2009.1 MSM G8 GT: R.I.P April-2014
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