Dyno/Tune experts, please step in..

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Nov 13, 2005 | 03:40 PM

BlkSS1755

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From: Long Island, NY

Dyno/Tune experts, please step in..

had my car dynoed over the week.. the car seems to fall everytime it reaches ~5300 RPMS all 3 pulls for just a bit. same time, same drop same RPM.. mainly in 4th gear.. on the highway, if i stand on it in 4th, when i reaches ~5300 RPMS, it feels like i took my foot off the gas..bogs pretty bad...but 1st, 2nd, 3rd pull to 6000 RPMS with no problem. no check engine lights. car runs 26 spark.. and about 2.7 knock retard at that RPM..

it's a 2000 FRC w/ 30K miles

mods:
-halltech stinger
-Z06 intake maifold
-Z06 ti's
-Kooks 1 3/4" w/ 3x3 cats
- NGK TR55 gapped @ .045 w/ Z06 wires

the car has NO tune as of now. is this more of a tuning problem, or should i start looking at somewhere else? valve float? other than that problem, the car runs fine.

thanks in advance,
vinnie

Nov 13, 2005 | 04:22 PM

technical

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From: Fat Chance Hotel

When was the last time you performed maintenance on the vehicle?

*fuel filter*

Nov 13, 2005 | 07:48 PM

Redline-Motorsports

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I don't think 2.7 degrees of KR would drop that much power as is shown. I also don't think that AFR is much of a problem either.

Valve float would flatten out the whole end of the curve. Your "dip" goes back to where it should be. I would think you would feel that on the street. Is there an issue with the dyno?? I've seen this happen when the wheels break loose on the dyno but you don't have that kind of power.

Nov 13, 2005 | 08:01 PM

ArcticZ28

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Wow, that's really weird. The dip in the graph does look like it has little to no effect on everything once it recovers. I'm interested in finding out what this is.

Nov 13, 2005 | 08:16 PM

BlkSS1755

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From: Long Island, NY

Quote:

Originally Posted by ArcticZ28

Wow, that's really weird. The dip in the graph does look like it has little to no effect on everything once it recovers. I'm interested in finding out what this is.

someone responed that i he had the same problem.. he swapped out LS6 springs and it fixed the problem. any thoughts?

thanks

Nov 13, 2005 | 08:25 PM

Nickn20

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From: Bay Area, CA

typically valve float doesnt recover, It almost looks like a an electrical problem of some kind, it doesnt look like fuel as it recovers and a fuel flow problem wouldnt, an air flow problem like valve float doesnt either, an intermitent spark problem could be it, maybe a wire in the harness has rubbed on something grounding out your injector circuit or coil packs, check for lose grounds, inspect the wiring harness for breaks or wires rubbing on stuff, maybe a bad crank postion sensor or cam postion sensor.

one more thing this may sound really stupid, but check your plugs and wires, just throw away the ones in there now, put in a brand new set of TR55s, and test your plug wires with a ohm meter.

factory wires ~700 ohms is GM spec MSD, taylors should be 0-50. other brands I am not sure should be around there. plug gap at .050 - .055 should be good also.

Last edited by Nickn20; Nov 13, 2005 at 08:31 PM.

Nov 13, 2005 | 08:30 PM

Redline-Motorsports

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Because the curve after the dip appears to be in line with the curve prior to the dip, I don't see that valve springs are the issue. Once valve float starts it doesn't recover. The motor would just flatten out.