Knocking Issue While holding RPM's
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TECH Enthusiast
Joined: Jun 2010
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From: Illinois
Knocking Issue While holding RPM's Alright before I start tearing into the motor, I had an ls1 motor with an ls6 head/cam/intake set up. The tune was set up for that motor as it had all the bolt ons. I recently just upgraded to an lq9 and still have all the same bolt ons etc and after a few other issues getting sorted out, i finally decided to take the car for a long drive. As soon as I got on the highway and was cruising along at 70mph, the car started making a knocking sound and sounded a lot like a lifter. I idled it back home and the sound seemed to go away.
I started it up again and there were no sounds, took it for a drive through the neighborhood and still no sounds. As soon as i took it for a long drive it started making the taping sound and i had to idle it back again.
So my question is, could the change in displacement cause a need to have the car retuned? Or would there be some other issues? I changed the injectors, fuel filter is new, fuel pump is new etc.
Just wanted to get an idea if a tune is needed before I go and spend the $400 to get the car tuned.
I started it up again and there were no sounds, took it for a drive through the neighborhood and still no sounds. As soon as i took it for a long drive it started making the taping sound and i had to idle it back again.
So my question is, could the change in displacement cause a need to have the car retuned? Or would there be some other issues? I changed the injectors, fuel filter is new, fuel pump is new etc.
Just wanted to get an idea if a tune is needed before I go and spend the $400 to get the car tuned.
Well, changing displacement without changing the tune
will jack the speed density side of things. But 5.7 to 6.0
is a minor error, like 5% (so 14.7:1 becomes 15.5:1).
Closed loop ought to take that out, if you do run closed
loop. I would not expect cruise ping out of it unless your
prior tune ate up all the timing margin.
Now putting 243 heads on a LQ9 might have raised CR
as well. That could aggravate spark knock. But I'd
expect that to be covered up by KR in steady state,
and to sound different than a mechanical problem.
will jack the speed density side of things. But 5.7 to 6.0
is a minor error, like 5% (so 14.7:1 becomes 15.5:1).
Closed loop ought to take that out, if you do run closed
loop. I would not expect cruise ping out of it unless your
prior tune ate up all the timing margin.
Now putting 243 heads on a LQ9 might have raised CR
as well. That could aggravate spark knock. But I'd
expect that to be covered up by KR in steady state,
and to sound different than a mechanical problem.
Thread Starter
TECH Enthusiast
Joined: Jun 2010
Posts: 611
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From: Illinois
the 243's were on the 5.7 as well. So my compression would go from roughly 10.5:1 to 11.0:1. It sounds a lot like a lifter, but only does it while driving at higher RPM's (highway driving). For instance, I drove to and from the train station in it today which is roughly 20 miles there and back. This was city driving where there was stop and go and speeds of up to 55 (I speed a little bit). However, there wasn't a single sound since the RPM's stay relatively low in OD at that speed.
So main changes would be the .3 increase in displacement and the high of a point bump in compression. I appreciate the answer btw. What did you mean by KR?
So main changes would be the .3 increase in displacement and the high of a point bump in compression. I appreciate the answer btw. What did you mean by KR?
