Billiumss

iTrader: (11)

I just recently tuned a 1999 Camaro SS M6 with 105k over the weekend and all though the A/F is good, maybe a tad on the rich side, something weird is going on. Didn't want to tweak the A/F anymore until we find out more info to whats going on. VE and MAF were tuned with HP Tuners. Car pulls fine, feels very strong. Air temp was about 60 in the dyno shop with around 40% humidity or so.

Car mods are:

PRC STG 2 Heads with dual springs
226 226 112lsa cam
QTP LT, no cats
Lid
Stock MAF
LS6 Intake
38# injectors
True Duals before axle

When I was scanning the car, my WB 02 readings are about .2 leaner than the dynos, dyno guys stuck the sniffer at the end of the tail pipe. There was NO knock anywhere but I did notice a slight dip in the MAF freq at around 5,800ish RPMs which reflects on the graph but the A/F didn't move. As for the wavyness before the "big" dip, everything in the scan looks normal, MAF, MAP smooth as it should be when RPMs are rising.

This was done on a Dynojet. What do you guys think? Issue with the dyno?

John02SS

iTrader: (47)

It looks like valvetrain to me. On my dyno I've had a few cars do that and each time it was valve float and always at 5800 rpm. Wierd it always does it at 5800 though. Most of these guys had aftermarket rockers and when we put stock rockers on it went away. Even with the small cam and double springs, it still picks up a bad harmonic right there. Good luck with it!

John

Slowhawk

iTrader: (12)

The top looks like valve float but the graph indicates a harmonic. Try unplugging the KR sensor harness and make a few pulls.Just because you don't read KR doesn't mean it isn't affecting it.(I've seen it on a few cars)

Could be a plug/wire problem too. Or even too much oil in the intake.

A few idea's for you