needed advise from the pros!

[geofffinlay]

Hi Oldman,
Don't feel too bad. Lots of experienced techs don't REALLY know what they're doing either in that department. OBDII is a VERY complex system. Anyone that says they know it all is fudging the truth. Even the best trained dealership techs have to go to their manuals to follow complex diagnostic routines occasionally.

I have specialized in scan tools and emissions and driveability diagnostics since the early 80s. I've trained many experienced trainers and college instructors as well as literally thousands of regular working technicians. I've been hired for companies like Snap On, MAC and OTC to train their people and Customers and throughout it all, I only met a handful of techs at any level that were REALLY impressive.

Most of the better ones are content with their basic knowledge, knowing that they have to go find the information as they need it and there's nothing wrong with that. It takes a huge sacrifice to take the time to study things that you may only need once every couple of years. In my position, I've had to know enough to answer questions in both seminar and live hands-on situations. I had no choice but to make that time to keep at least a couple of steps ahead. I DON'T know everything about OBDII, but I do know that as each technician discovers that there's far more to OBDII than they thought, it's a real eye-opener for them.

I really don't know what kind of shop you need to go to for a diagnosis, if there isn't an emissions specialist in your area. I think that maybe you need to call your local GM dealer and ask them how much they want to do a diagnosis on your O2s and Cat. Maybe if you tell them in advance that you're going to take it to your local repair shop for the actual repair, they'll make sure they're accurate. Keep in mind that they'll want to get the work themselves and knowing that they could be second guessed will keep them honest as well as accurate.

I really can't comment on removing the cat & resonator. Aside from it being illegal - even in your none-test state, (Google EPA for tampering rules & schedule of fines) it may actually damage the engine without the appropriate amount of exhaust backpressure. Your fuel consumption will never improve as long as a code is stored (C/E light on) by the PCM. The PCM is programmed to run a little richer, with the ignition timing less advanced with most emissions related codes stored (that's pretty much all of them).

If the C/E light is on continuously and a second issue occurs (likely), you won't know what the second (or third) problem is. My PROFESSIONAL advice is to fix it.

Best of Luck

Geoff

[1fatcat]

What you need to do is find out if your new converter is a two or three way converter. You need a three way. There are a lot of two way converters on the aftermarket, as well as a lot of three ways. If the manufacturer doesn't specify or know, then it's probably two way.

Someone once told me that by installing a spark plug anti-fouler between the exhaust and the rear o2, you can trick the computer to believe all is good by moving the sensor out of the main stream of exhaust flow. If caught, it is punishable by fine and/or jail time (depending on who is doing it and how often I would imagine). I have never tried it, but it stands to reason that it could work?

[1fatcat]

Here is some good reading for ya. http://en.wikipedia.org/wiki/Catalytic_converter

[00Beast]

Could get one of those ZZP plug things where it emulates the rear 02 sensor, so it tricks the PCM into thinking it's all fine. Not sure if that will pass emissions, though.

[1fatcat]

LOL, I just image googled spark plug anti fouler. The pictures tell all! http://images.google.com/images?hl=en&s ... =&aql=&oq=

[geofffinlay]

I know zip about aftermarket tricks to fool the PCM, but I can't imagine any of them being able to emulate the changing voltage signal that the rear O2 supplies. The PCM is continuously testing every component remotely related to emissions.

There are 3 Continuous Monitors, (and usually 6/7 Non-Continuous Monitors),they're working all the time. One of them is called the Comprehensive Component Monitor, which is awake 24/7 looking for stuff to happen. It continuously looks at everything from shift solenoids to sensor response times and even Evap related temp/pressure changes when the vehicle is parked overnight.

There are separate Oxygen Sensor & Cat Monitors that continually track/report all O2 activity. If an O2 isn't responding the way the PCM expects, the Task Manager (that's Chrysler's name for it) issues orders for the PCM to run a specific routine to force the O2 to respond with an expected value change.

A typical routine for a rear O2 that's reading 0.00v for too long, would be to open the Evap Purge Valve for a couple of seconds and monitor the O2 (front & rear) response. That would generate a report that you can find in Mode #6 of a "real" scan tool.

The aftermarket trick would have to read the PCM's mind to supply the voltage from the (rear?) O2 it is replacing. It's not impossible to make such a device, it's just that it would be cheaper to fix the car.

Currently, Canada is 1 up on Russia........ gotta go

Geoff

[1fatcat]

GM runs the same check. The PCM will induce a rich and lean condition and watch the o2's, looking for a change to verify that they are reading within the window. If they are out of limit, a code sets. The two way converters do not satisfy the PCM if a three way converter if called for.

[geofffinlay]

'95 and earlier vehicles are 1st gen OBD(I). There was no rear O2 sensor, and no facility in the PCMs/ECMs to read the cat's efficiency. Those systems were/are extremely simple relative to OBDII vehicles in terms of programming and diagnosis, especially self-diagnosis. They didn't run complex self tests, just basic routines based on a few parameters.

Not just GM, every car & light truck sold in North America after Jan 1 '96 is OBDII equipped imports, domestics and everything else light duty that's sold here. They ALL run the same basic tests, or they can't be certified for sale, (check out Federal Test Procedures/EPA). Some systems are more complete than others, but I don't believe any of them can be fooled and stay legal.

OBDII computers are programmable (that's part of the OBDII spec), and it's absolutely possible to reprogram a PCM so it "ignores" certain conditions, but if the EPA don't know about it and don't approve it, it isn't legal and it is VERY costly if you're caught.

I'm just a guest here, but I would never condone modifying a DD if those mods reduced the effectiveness of the designed-in emission controls. It's probably not really relevant, but every kit or home built car I've been involved in could/can pass ANY emissions program easily; that's why I'm so keen on FI over carbs. I would only want to see carbs on a race car that needs to keep its revs in a relatively confined range where the carbs can be finely tuned. For me, carburetion on a street car is a cruel joke.

But that's me

Geoff