Corvette Performance - AFR jump and surge, all rpm's

Posted this on another forum also. A bit long.

Hello everyone.

Started tuning a few months ago.

I have always looked to the forums for help in tuning and have found almost every answer for each problem I come across.
Now I have one I can't seem to tune out.

03 Z06, 408ci, ported 243 heads, headers, no cats, comp cams 459 cam, 190 degree thermosat, FIC 50 lb modified stock injectors, Shaner ported stock throttle body, heads are shaved to 63 cc's, have stock ls9 head gaskets, .051 thickness. New set of TR5's gapped at .047.

tuned ve, then WOT, idle, rechecked ve, tuned MAF
40 kpa at idle

Checked for intake leaks. Sprayed everything, MAP to MAF with ether and carb cleaner.
Nothing.
Did the exhaust/O2 bungs with soapy water and held foot on tailpipe.
No leaks.

Clutch in or out rpms/AFR go up and down under all conditions.
Not as much above 3200.

While checking for intake leaks again, pulled the oil filler cap and found out it was sucking air. Suction increased to a certain point while holding palm over opening. Could it be an intake gasket I can't spray/check underneath close to the valley cover?

Secondly, and I think it might have to do with the above, the engine idled great at 12.9 to 1 when commanded with VCM controls. Little to no surge.

Car really pulls hard under WOT.
Made 2 passes at Bristol Dragway.
12.202 at 120 mph was best but no traction in 1st or 2nd gear. With 295 DR's
Launching at 3000.

Drove to Gatlinburg, 104 miles south, got 23 mpg.
Surged the whole way.

Has new GM O2 sensors and seemed to idle smoother.

What am I doing wrong?

Please help.
Thank you.

Almost a hundred views and no reply. :(

Ran a new tune and scan I did yesterday afternoon.

Also at 8 to 10 percent throttle, surge is worse driving or sitting still clutch in or out and throttle follower is active just slightly. .001 to .003

Sitting still it's hard to keep throttle at 8 to 10 percent.
Always wants to stay below or jump to 11 percent.

Opinions?

I wonder if you are having problems with the MAP sensor. It's my understanding that the MAP is used less and the MAF more as RPM increases. If you had an intake leak, you would have abnormally high idle airflow and it would be become less of an issue as RPM/load increased. Some people with aftermarket intakes go so far as to relocate the MAP to get it to read correctly.

You mention you have ported factory heads, so another possibility is that the intake rocker bolt may be leaking air into the port. I know when I had ported 241's the intake rocker bolt hole went right into the intake ports. It was necessary to coat part of the intake rocker bolts with RTV to prevent leaking.

Hello 99C5JA,

RTV'ed rocker studs.
Stock LS6 intake.

MAP read fine in scanner.
But surging is less of an issue as RPM increases.

MAF is disabled.

Thanks for the response.

You shouldn't really be having a problem with an LS6 intake and the MAP not seating/reading right. The vacuum through the oil fill location is puzzling. It still makes me think maybe the RTV on the studs isn't getting it sealed. I can't think of what else in there could cause a noticeable vacuum. You could pull the intake and see if any of the runners show any oil seepage from the bolt hole.

I looked at your log real quick. It looks like at low RPM the bank 2 O2 is reading much lower than bank 1 for extended periods of time.