----- Original Message ----- From: "Bill Putney" Newsgroups: alt.autos.ford,alt.autos.honda,alt.autos.nissan,alt.autos.toyota,alt.trucks.chevy Sent: Tuesday, June 10, 2008 5:42 PM Subject: Re: Repeatedly Running On A Low Tank?
Your car was running in open loop mode during the test. If the car is not in closed loop mode, the PCM is running the engine on a stored lookup table (the amount of fuel injected is determined by the engine rpm, TPS reading, MAF reading). Older systems did not do a particularly good job of "learning" parameters at idle. Still, the air filter, unless really dirty, should not have kept the car from passing. At idle the air flow through the filter is relatively low, meaning the pressure drop across the filter was also low. I suppose the combination of the lower atmospheric pressure at high altitude and a dirty filter could have resulted in an air flow vs. sensor relationship that was not addressed in the PCM's look-up table, resulting in too much fuel for the air flow, causing you to fail the test. Still, if the car was warmed up, the converter should have been able to mask any excess fuel condition. Did it fail because of high hydrocarbons, or high carbon monoxide readings? Was the car originally sold with a high altitude calibration (back then cars sold in high altitude areas often got a different set of parameters loaded to the PCM).
Ed