Hi guys, I have an 86 IROC w/305 TPI. Well I am asking this question because in the morning when I start her up and she is nice and cold, it seems like it has more power than when the temp hits above 165 for the first time. Oil pressure also drops from like 45 to 30 at this time also (at speed). Is that closed-loop? How come when it is warmed up it feels like I lost some Juice? I thought it is supposed to be the other way around? What gives? Thanks to any responses. Sorry for the wierd question, but my SOTP readings told me this

 

Your O2 sensor is probably wore out. When the engine is cold (open loop) the O2 sensor doesn't do anything. When the coolant temp sensor hits 160-170 degrees and the O2 sensor gets to 600 degrees, then the ECM goes into closed loop operation. At this point the ECM is either adding or subtracting fuel to compensate (can't remember which it would be with a weak signal at the O2) ... this additon or subraction of fuel is why your performance is "sluggish" after warm-up.

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1986 Trans AM
355 TPI
4 Wheel Disc Brakes
9 bolt Borg Warner Rear (2.77's....oh joy) :P
6" rods, approx. 9.7:1 Compression, Stock TPI (soon to be ported), 24#/hr LTI injectors (cleaned and flowmatched by Cruizin Performance), Hedman Shorty Headers, 3" exhaust with 80 series flowmaster, SBC 993 heads completely redone and modified for 1.6 RR, 1.52 RR (for now), Comp Cams XE262-14 TPI Cam, Holley AFPR, TPIS airfoil, MSD wires, MSD 6-AL Ignition, Hypertech 53,000 volt coil.

Track times to come.

 

Just wanted to say that I havwe noticed the same thing in both the TA's I have owned. The one I drive now has a new o2 sensor. I think it just has more to do with the cold air and more fuel being dumped to warm the car up. I could be wrong though. My car feels twice as strong. Hope this helps.

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14.48@93.72mph 2.03 60 ft
After Pulley's 14.31@95.18, 2.14 60 ft

 

mine feels that way also, maybe its because the air coming in is nice and cold and we are getting alot better combustion and probably are running more rich then usual.

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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series Muffler added to Unkown CatBack, Ported Intake

http://www.geocities.com/david_angel_16

 

That's another possibility. During open loop operation the ECM is less involved with the operation of the vehicle. Damn ECM :P

 

I live in a cold climate area. One hour it can get +15c and next -10c in winter and what a difference the cold air makes on a properly tuned TPI.

Colder air = dense air = more oxygen molecules = filling cylinders more = more power

Whatever you do, make your engine suck the cold air and it will make the difference you can feel.



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89Iroc, 305 TPI, WC T5, 3.08 Posi, Headers, Hooker Y-Pipe, 3 inch over the axle, Flowmaster 80, No Cat, Aluminium Driveshaft, Ported Plenum, Air Foil, K&N, AFPR, All free mods,