Has anyone ver passed emissions with no cats?

[Qualitywires.com]

I was wondering if you could pass emissions without cat if you leaned out your fuel....I think if you did that and didn't go into boost you would be okay....am I wrong for thinking that?

Or maybe it wouldn't work due to the car being in closed loop and it having a mind of it's own?

 

[Joseph Dell]

The O2 sensors (rear) are designed to check whether the temp behind the cats is HOTTER than the temp in front of them. It is that simple. no manipulation of fuel will impact that. hence the need for O2 sims...

JD

 

[BOMBOVIPER93]

i've been passing emissions w/o cats since 1996, but my 1993 only has (2) O2 sensors I believe. Its kinda funny to watch the inspectors search for them with their mirrors and then make me sit there and wait while the call the Dodge dealership to see if i'm bull*hiting by telling them they are tucked up into the body.

 

[ggc]

I tried to pass E-Check in Ohio without cats, but after three tries, I just put Hi Flow cats on.

 

[Tom F&L GoR]

The rear O2 sensors don't check for temperature, in fact, they are probably electrically heated for quicker light off. They look for oxygen also and their signal should be a function of the upstream O2 sensor, but with less swing in O2 deviation and delayed in response time. The system checks for O2 variations, so a fixed voltage won't fool the system, and "excuses" excursions due to full throttle enrichment.

A tailpipe test is only performed in closed loop, so the fuel system would (try to) adjust for any leaning you might try with the fuel. Basically you are hoping that changing from "gasoline" to "gasohol" with 2.7% oxygen will make a difference, but the engine is smart enough to adjust for it when warm.

In New York, up until now, many counties used a "visual" inspection for emissions. Stuff had to be there, but there was no test for performance. Otherwise, it would be highly unusual for a non-catalyst engine to meet the tailpipe standards.

 

[Joseph Dell]

So does this mean that w/ O2 sims on a car instead of rear O2 sensors, the O2 heater will never "pass" because it will always show "not ready" to the OBDII?

JD

 

[Cudaman]

I thought this post had something to do with putting the neighbor's cat in your Viper and driving around ...we have not had vehicle or emisions testing since the early 70's. I guess we in Florida don't know what we are missing.


Cudaman

 

[Joseph Dell]

How about state tax?

 

[Tom F&L GoR]

Joe, the not ready message is to prevent a battery-disconnect "fix" for a check engine light. There have to be enough successful start & warmup cycles to make the engine management believe everything is normal the system to feel "ready."

The front O2 sensors need to be operational within 20-30 seconds of starting because otherwise those few extra moments of open loop will cause the engine to fail the emissions test the OEMs have to pass. Therefore the front O2 sensors will be heated. The rear O2 sensors are there to provide a passive catalyst monitoring system. The rear O2 won't provide that information until the catalyst is warmed up and reaches it's own "light-off" temperature. Therefore the rear O2 doesn't need to hurry up and be heated to provide an accurate signal, since it has to wait for the catalyst to warm up.

 

[Jack B]

Tom:

I believe the rear O2's are heated, there is a fuse in the engine compartment for that purpose. If you don't heat them the moisture from combustion will render them inoperative at some point. As a clarification - aren't they merely looking for a delta O2 less then the forward O2's, if not they alarm and hence the service engine light. My guess is that a SIM keeps the voltage in the feed-back circuit at approximately 750 mV, therefore, with the front O2's flopping up and down the PCM is fooled by the constant 750mV.

 

[Tom F&L GoR]

Jack, it seems overkill, since they wouldn't provide a useful signal regarding catalyst efficiency until the catalyst lights off. And so far catalysts aren't electically heated... But a quick search shows rear O2s are heated. Thanks, I learned something.

I am pretty sure that the control system needs to see perturbations in the rear O2 signal to ensure it is functioning. Otherwise you could use a Radio Shack voltage generator in their place, and I don't think that works.

Some systems look at switching rates of the front and rear sensors.
http://autorepair.about.com/library/faqs/bl736h.htm

Some systems also drive the fueling rich or lean just to test the rear O2 sensor.
http://www.wellsmfgcorp.com/counterpoints/counterp_v6_i2_2002.pdf

 

[Ulysses]

The rear O2's in a Viper are heated. The Catalyst checks aren't run until certain parameters are met, one of which is reaching a predetermined drive time. By then, hopefully, the cats are at operating temperature. The use of a heated sensor allows the engine controller to switch to closed loop control more quickly. The reason for heating them is so that the readings are accurate. Below a certain temperature, the readings are not valid.

Tom is right on when he says that the PCM needs to see perturbations in the rear O2's. One of the O2 checks is to count the number of threshold crossings and another is to count the rate of change. If the SIM were steady, you would never pass these operational checks, and trip the CEL.

A good SIM must switch (a simple oscillator), though at a much slower frequency than the upstream O2s, but it must also be able to pass other "rationality" and "functional" checks. Heater performance being one of them.

Hopefully that all made sense, it's pretty late and it's getting hard to think straight.

 

[Joseph Dell]

This is all making sense. So the real question is, with O2 sims (and presumable these are good ones b/c they are from Roe), will I ever pass the O2 heater test? I'll be doing a long drive today, so that will give me a chance to check afterwards. But it's been close to 200 miles so far and EVAP and HO2 are still "not ready"...

Thanks for all the tips y'all!

JD

 

[Ulysses]

Depends on if the SIMS were designed to emulate a passing series of voltage levels when the Heater Test is performed (after shut down). You'll have to ask Sean.

Your EVAP DTC is a bit worrying.