catalytic converter blues

[tdr1919]

No joy up here in NY when it comes to inspection time for my 86. Last year we made it thru emissions after an hour long battle with the f$#&%
machine.
This year Im feelin' real froggy, car is running dynamite after finding a few vac. leaks, everything as far as safety, spot on. Ready to go see the man!
One & a half grueling hours and the damn thing wont pass the emissions, my friend mechanic is spitting at the machine, jumping up and down. The
long and short is to get my co down it looks like I need a new converter.
MY QUESTION IS:
do you think I can change the rear converter only or do I really need to do the pre-cats up front which I know will be a bitch and a half to get out.
singin' those ol' cata-lytic blues, oh yeah
Thanks - Tom

 

[Schrade]

If the burn is good, the cat probably won't make much difference, EVEN IF IT HAS EXTREME FOULING, from running rich and out of tune for too long. It will only restrict exhaust flow, and have little effect on emission, unless the burn is still not correct.

Can you post up the scan of the data? How's the other reads? Don't buy cats til you know if the burn is right...

 

[tdr1919]

If the burn is good, the cat probably won't make much difference, EVEN IF IT HAS EXTREME FOULING, from running rich and out of tune for too long. It will only restrict exhaust flow, and have little effect on emission, unless the burn is still not correct.

Can you post up the scan of the data? How's the other reads? Don't buy cats til you know if the burn is right...

Schrade, Il try to upload the file

 

[tdr1919]

Schrade I sent you a PM,
Tom

 

[Schrade]

Where's Tom here? I didn't get the scan. Maybe post it up here - there's a few people here who probably know more than me with scans without lookin' up the data...

 

[tdr1919]

I gave you guys some bad info, I failed on HC not CO, although CO was in by only the slightest margin. HC's were almost double the limit.
I failed for NOX three years ago, a new EGR fixed that. High CO was an issue due to a bad solenoid in the AIR system.
Last year I passed emissions
Tom

 

[Schrade]

I gave you guys some bad info, I failed on HC not CO, although CO was in by only the slightest margin. HC's were almost double the limit.
I failed for NOX three years ago, a new EGR fixed that. High CO was an issue due to a bad solenoid in the AIR system.
Last year I passed emissions
Tom

That DEFINITELY means get the burn right, before buying a new cat. Too high HC's WILL foul a cat, and no reason putting on a new one till the burn is right. In fact, you can gut the cat, and if the burn is right, the cat (or the inspector) will NEVER know, unless there's evidence of removal. If it's clogged, I suggest you do that...

Too high HC's could be due to poor fuel atomization, from poor injector spray quality (bad atomization = bad burn, too many HC's passing). O2 sees this as too much fuel, and lowers the pulsewidth to try to decrease fuel, but that's not the fix.

Could also be low fuel pressure, which is prevents high-pressure spraying - fuel dribbles out of injector.

Bad fire in one or more holes lets fuel pass unburned - plug, wire, distributor, opti, ???

Low temp thermostat makes warm-up take longer, cold motor will not burn well, especially since fuel is maxing when cold / open loop...

Dump some grain alcohol into the tank, to pass the test. Formula for gas / alcohol mix is posted around here somewhere, including exact HC results, +/- a few points...

 

[tdr1919]

That DEFINITELY means get the burn right, before buying a new cat. Too high HC's WILL foul a cat, and no reason putting on a new one till the burn is right. In fact, you can gut the cat, and if the burn is right, the cat (or the inspector) will NEVER know, unless there's evidence of removal. If it's clogged, I suggest you do that...

Too high HC's could be due to poor fuel atomization, from poor injector spray quality (bad atomization = bad burn, too many HC's passing). O2 sees this as too much fuel, and lowers the pulsewidth to try to decrease fuel, but that's not the fix.

Could also be low fuel pressure, which is prevents high-pressure spraying - fuel dribbles out of injector.

Bad fire in one or more holes lets fuel pass unburned - plug, wire, distributor, opti, ???

Low temp thermostat makes warm-up take longer, cold motor will not burn well, especially since fuel is maxing when cold / open loop...

Dump some grain alcohol into the tank, to pass the test. Formula for gas / alcohol mix is posted around here somewhere, including exact HC results, +/- a few points...

Schrade,
Did you look at my test resuts? did it make any sense?
I have FIC rebuilt and flow tested BoschIII (i thought they were II's) injectors.
I pulled my plugs (5,000 miles) and they are light tan in color, my wires cap and rotor 10 k miles. I havent tested my fuel pressure while driving, but running at rest (idle) pressure is around 38 lbs.

 

[nelson84]

Move to another state that doesn't test your car. Where I live they don't check, My 85 vette has no cat, and is to old to test anyways.

 

[Schrade]

Hey Tom - the scan file came through as a .uni (media) format file; couldn't open it in Windows OR Linux.

Does the scanner have a 'Print to file' key? You can then save as a .txt, or other simple format...