DP + CAT Question. Failing emissons in CO

[Jonnymkiii]

I have a question about a DP/CAT combo, similar to the stock set up. I am failing emissions hard (High HC and CO) and about the only new thing I can try is to get a temporary DP and couple it with an additional CAT. Already have a new O2 sensor, CAT and inspected and cleaned all the emissions components.

I am having a difficult time locating a stock DP+CAT and think it may be easier to buy a cheap aftermarket DP (2.5" or so) and have a muffler shop modify it to fit a 2nd CAT for emissions. Once I pass emissions, I can put my 3" DP back on.

Anyone see a problem with this approach? I just want to make sure this is feasible before I commit to buying parts. Thanks!


Jonny

 

[jetjock]

You should post numbers when asking for emissions help but if the CO is high the problem isn't going to be fixed with a DP/cat.

 

[hvyman]

My car passed with a full 3in exhaust and high flow cat....

 

[Nick M]

You should post numbers when asking for emissions help but if the CO is high the problem isn't going to be fixed with a DP/cat.

I haven't live there since 2003, but we were on the IM240 at the time. I suspect he still is. He can scan the trace, it is quite complete.

 

[jetjock]

Yes, I'm aware Colorado is IM240. My point was high CO indicates a lack of fuel control, something the addition of a small catalyst is very unlikely to resolve. Put simply his car is broken and he's trying to band-aid it because he thinks "it's the only new thing I can try".

 

[Nick M]

Yes, I'm aware Colorado is IM240.

I wasn't sure myself.

 

[Jonnymkiii]

Yes, I'm aware Colorado is IM240. My point was high CO indicates a lack of fuel control, something the addition of a small catalyst is very unlikely to resolve. Put simply his car is broken and he's trying to band-aid it because he thinks "it's the only new thing I can try".

My apologies for the general post; my intent was to see if there was anything wrong with installing a CAT in the DP. My initial thought is it is how the car came stock and I saw several posts while searching where folks have done that, so I thought why not give it a go. You don't like that idea, so please allow me to provide some additional details and if you have any advice, I'm all ears.

Here is what I've done so far. I've had the car since 1992 and the engine was rebuilt in 2006; see Sig for mods, etc. I recently performed a compression test and everything was in spec. Over the last couple of months I've installed a brand new wiring harness, installed a new factory O2 sensor, installed a new 3" Random Technology high-flow cat, tore down the entire intake/emissions system for inspection, cleaning and gasket replacement. The vacuum hoses were replaced and I performed several boost leak tests and there are no leaks. I don't see any issues with the ignition;I have the HKS Twin Power ignition amplifier installed with NGK plugs 1 degree cooler and the gap is set to .028.

The vacuum holds steady at -15psi at idle, so I do not believe there is a vacuum leak either. I also just had the car tuned [MAP-ECU].. by professionals, not me. Last weekend I rebuilt the CPS (Internal leak) and the timing is fine (10 BTDC - w/ diag box jumper), so I don't think it's timing either.

Here is what I registered:
HC 10.74 Fail
CO 70.49 Fail
NOx 2.60 Pass

Both HC and CO are VERY high and I am at a loss as to why. When I said I couldn't think of anything new to try, I wasn't trying to take any short cuts; I literally can not think of anything else to test or try. As I said, I am all ears for any ideas. Thanks -


Jonny

 

[mecevans]

High HC

Rich
Misfire
ignition timing
Low compression

High CO

Rich
Intake restriction

Things like boost leaks, leaky injectors, high fuel pressure, faulty ignition system and feedback control is what you need to look at.

 

[Bleakvoid]

CO will grow exponentially the farther from the stoichiometric ideal of 14.7 AFR your tune is at the specific loads emissions testing is done at; this is because a cat is designed to catalyze at maximum efficiency at stoichiometric parameters or slightly leaner (ie, cruising speed). Hydrocarbons will follow if it's failing CO by running rich. If you have a wideband, hook it up and see where your AFRs are at test conditions, usually 15mph and 25mph, probably in first or second. Might be RPMs where you live, YMMV.

 

[Jonnymkiii]

Thanks for the feedback; I'll have another look at the tune... sounds like that may have more to do with it.

 

[3p141592654]

If you measure the Vf signal on the diagnostics box, and it is pegged at 0V then it is running open loop, and if it is at 5V then it is adding fuel to try and fix a perceived lean condition. In any case, your mixture is way out of whack. If you post your complete emission profile (O2, CO, CO2, HC, NOx) we can tell you precisely how out of whack it is.

 

[jetjock]

What those guys said. The engine is obviously not in fuel control. It's running rich. NOx is low because O2 is low. O2 is low because CO is high. Do whatever it takes to get the O2 sensor cross counting (I'm guessing the MAP tune is bad) and hope NOx doesn't rise past the cut point.

 

[Jonnymkiii]

Thanks for the feedback guys! I've spoken to the tuning shop and am working on an appointment to get back to fix the tune; y'all are right, its running rich. The shop also said they didn't think the Random Tech CATs were good at removing emissions and that could be part of the problem too... anyone else hear tale of that?


3P, as requested, all the emission numbers are as follows:


GAS-------Reading-----Limit
HC------->10.47------>2.5
CO-------> 70.50----->20.0
CO2------> 450.54
NOx------> 2.60------->4.0

I'll check the vf signal and see what that is saying once I get home. Thanks again for the help and feedback!


Jonny

 

[jetjock]

Odd, one would think the tuning shop would have used a 5 gas or at least a wideband. Assuming the problem is the tune they should be called on the carpet for giving the car back to you like that.

Vf can also be used to check the O2 sensor when the system is in diag mode and the engine is off idle. Vf then becomes an emulation of the O2 sensor. At 2500 rpm you want a minimum of 8 cross counts per 10 seconds with an average (a couple of minutes will suffice) voltage of 2.5

On an IM240 it may not be enough to pass though because such tests require tuning that produces good results across the drive cycle. The cat is important on these tests because it picks up the slack.

 

[3p141592654]

Need O2 as well, and what sort of units are they using?

 

[Nick M]

The vacuum holds steady at -15psi at idle, so I do not believe there is a vacuum leak either. I also just had the car tuned [MAP-ECU].. by professionals, not me. Last weekend I rebuilt the CPS (Internal leak) and the timing is fine (10 BTDC - w/ diag box jumper), so I don't think it's timing either.

Timing is likely irrelevant if not mentioned. My Supra in Denver that ran good only had 16" of vacuum and passed easily. I find it hard to believe it is anything other than the tune on the MAP ECU. Unless you have an injector with a mechanical fault, and that isn't likely.

I have sigs shut off so I don't know your mods. But I think somebody would have already brought up any issue in it.

 

[jetjock]

IM240 drive cycle test Jon. Not steady state like Cali's ASM. The results are in grams per mile.

 

[Nick M]

IM240 drive cycle test Jon. Not steady state like Cali's ASM. The results are in grams per mile.

In the StL, the inspector sees that the MIL is not on, and then plugs in to see that readiness was not reset. It is a state controlled system. OBDII only of course. OBDI is safety check only.

 

[87targa]

HC mainly has to do with how the fuel is burning so a cat will help lower that...what ever didn't burn in the cylinder should burn away in the cat....your high flow should work fine since I too have a random tec cat and passes HC. CO has mainly to do with your fuel. first lean it out to stoich like everyone here has said then run it again. it should pass then. if not try the simple stuff like putting in new spark plugs that are the stock heat range.

 

[3p141592654]

As you can see from the chart below, you need to have excess oxygen to reduce the HC in the exhaust stream, so a cat won't help you if you are running rich. See the chart below.

Ahh, grams per mile, thanks JJ. I guess that can be converted to an average mixture for the run.