engine swap failed emissions

[dosamstr]

Hi,

I had a 94 prizm with a 1.6L

long story short, I had to swap the engine.

The new engine is a 97 corolla 1.6L


The car fails low idle hydrocarbons (HC)

I replaced the entire ignition system from the rotor to the plugs (still failed)

Ran a tank of guaranteed to pass. Failed worse than with just new ignition parts. (may have had up to a quarter tank left before refilled the tank, so some may still be in there)


My question is, (aside from how to fix the damn thing) its a 97 motor, if it were in a 97 car they would just plug in to the computer and say, ok no codes, no check engine light, PASS

or since it doesn't have a 96+ computer is that moot? .... could I go get a 97 computer from a junk yard?



details of the fail:

Low idle only, 330-380 HC when standard is 220. Other standards have never been a problem, passes high idle HC from 90 to 150 ( ranges are based upon the 3 tests)

[REN69]

Could be a bad O2 sensor... or a Cat, lol... can't remember which one influences the HC's

[kickfli12]

Originally Posted by REN69

Could be a bad O2 sensor... or a Cat, lol... can't remember which one influences the HC's

O2 measures nox and the cat burns off the excess fuel reducing the ammount of hydrocarbons coming out of the tail pipe if im not mistaken.

[Bitter]

No, O2 measures oxygen in the exhaust which is an indicator of the air/fuel mixture that was burnt. The amount of O2 left over tells if more or less fuel is needed and the computer uses the O2 sensor to make adjustments in the mixture, always playing catch up with what's already happened.

A weak cat could cause high HC, so could a cold one. Before you get to the test go for a good hard drive, then keep the engine running fast in neutral while you're waiting. Hold it around 2000RPM for a few minutes before you test.

[Hiro Protagonist]

Originally Posted by kickfli12

O2 measures nox and the cat burns off the excess fuel reducing the ammount of hydrocarbons coming out of the tail pipe if im not mistaken.

Complete opposite - the O2 or Lambda sensor measures the air-fuel ratio of the exhaust and tells the ECU whether to richen or lean the mixture - ideally the air-fuel ratio will be ~14:1 (called stoichiometric) and will result in complete combustion (minimising carbon monoxide) whereas a rich mixture will increase result in incomplete combustion and excess carbon monoxide and hydrocarbons in the exhaust. The cat gets rid primarily of NOx through a redox reaction as well as excess carbon monoxide and hydrocarbons through an oxidation reaction. Older cats used to only deal with the carbon monoxide and hydrocarbons in the exhaust, but they've been obsolete since the early 80s when the three-way (NOx, CO, HC) cats became standard (same kind of time that unleaded fuel came out, which made cats standard in most places in the world as 3-ways can't run on leaded fuel.

[PhatRoyale]

Looks like you need a new catalytic converter.