I have an annoying problem. I recently moved to Flagstaff Arizona, about 7000ft ele. I have an 86 IROC with an LB9 about (I know) 215,000mi. I did many bolt ons, including shorty headers. When I cold start the car it runs very poorly, seems to load up, and occasionally pop through the intake on accel. I scanned the computer, MAF, coolant temp sender, etc all read fine. The only thing I can think of is maybe since I put headers on the car and the O2 sensor is moved further away from the exhaust ports, and not getting to temp. I was thinking of upgrading to a 3 wire sensor to heat it up sooner. I really don't know. I am in the process of building a nasty 355 with AFR heads and a full roller valvetrain, but for now, the 305 doesn't use oil or smoke and isnt costing too much money. Any help I would greatly appreciate it.

 

The O2 sensor is ignored on startup, but a heated O2 might be good for normal stop and go driving anyway....but most likely not your problem.

Was the car originally from Flagstaff? I seem to recall reading soemwhere that GM had "High Altitude" EPROM programming to lean the mixture accordingly, might be worth looking into?

 

The car is originally from Phoenix (about 5600ft. lower in elevation) I thought about the chip, thing and it sounds about right. I just had to help my friend put smaller jets, and metering rods in his Blazer, cuz it was tunning too rich. Tomorrow I am going to lower the fuel pressure, and see if it helps. If not, I'm gonna look into that chip, or force feed it with a blower.

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1986 IROC TPI 305
Comp Cams cam, 1.6 rockers. Ported base and plenum, Hughes 700r4, 2500 stall lockup conv. Jet Hot coated Heddman headers, random tech. Cat, Flowmaster 3in cat back, 7.75 BW rear (out of 88 GTA) 3.27 gear. Full poly bushings, Bilstien shocks struts, Kenny Brown strut tower brace, and subframe connectors.

Future upgrades 355, GMPP forged steel crank, ARP main studs, and fastners, ZZ-9 cam, Comp cams Roller lifters, rockers, and pushrods. Vigalante conv, 1LE brakes, and driveshaft.