Removed Catalytic Questions

In reply to Curtis73 (Forum Supporter) :

Modern emissions controlled vehicles operate at stoich even under load.  Some turbo engines run stoich into the double digits of boost pressure, and the big deal with the Ford 7.3 is that it was engineered to run stoich all the time, no power enrichment.

Basically anything made in the last 20-30 years that isn't a rotary or a TBI setup runs stoich 99% of the time.

Curtis73 (Forum Supporter) said:

Paul_VR6 (Forum Supporter) said:

Keith Tanner said:

In reply to L5wolvesf :

No, it's the tang of HC for me. I'm pretty sure that's what it is.

Pretty sure it's NOx as HC and CO should be low around stoich/idle. I also agree just throw some cats on there to take the edge off and be a good steward of the planet if you plan to road drive it.

Yes, it happens during rich operation, like WOT.  But modern emissions-controlled vehicles rarely operate at stoich.  They're close to it at cruise (13s) but pretty rich at WOT (in the 11s).  This is to keep cylinder temps down and reduce NOx.  The whole thing is a trade-off for manufacturers.  In order to get them to conform to max allowed outputs of the three main parameters, they end up pushing the HC (running a bit rich) to mitigate NOx.  That's why so many of the commonly available plug-in tuners can get you 10-15 hp by leaning out the fuel map and adding a little timing advance - things that OEMs can't do without risking failing the NOx part of the testing process.

You mean they almost always run at stoich, right?  Even the F150 in question will run stoich pretty much all of the time.  With catalysts, the need to run a little rich to lower the NOx isn't really needed, more so when the engine has EGR (which is far more effective of a device and can actually add fuel economy when done right).   Besides, the main feedback sensor- the basic O2 sensor- is only really accurate at stoich- so all of that switching happens right around that.

And most spark advance is done at best possible spark, for fuel economy and/or power reasons.  That best spark is either right under the knock limit or at MBT.  

WOT in this era would be a little rich to keep the exhaust temps down- but not optimized because of a lack of a exhaust temp model at the time- it was very much in development in '94, let alone when this truck was developed years before that.

Curtis73 (Forum Supporter) said:

L5wolvesf said:

Lots of input re “the smell”. Are you referring to the sulfur smell? My impression regarding the sulfur smell is/was it came from a cat that was going bad for some reason. Is that not correct?

Referring to the lack of sulfur smell.  Running without a cat can make it smell like an old 60s muscle car running rich.

OK now I got (smell) it

I am not asking about the cats to avoid pollution measures. I was born and raised (not necessairily grown up) in Los Angeles so I’ve experienced the UNpleasant aspects of pollution firsthand. OTOH, I’m a fully addicted internal combustion car guy. I cruised Van Nuys, ran Mulholland, autoX’d and raced. So I’ve created some of it myself.

I am asking to 1) determine if a vehicle without cats is problematic, 2) establish if I need to spend additional money on the vehicle which effectively raises its price.

Thank you for the input so far

Maybe brand spanking new cars, and we can agree to disagree, but in 7 years of running repair shops and hundreds of times troubleshooting on an OBD2 scanner or during a smog test, I have never once seen any stock-tuned car run stoich except maybe at idle.  Ever.  Not one.

WOT in my 2006 van is 12.7 ish until it passes about 4000 rpm.  Cruise is 13.9-14.3 depending on other parameters like coolant temp.  I should also mention that it is spot on with the fuel map.  It's what the fuel map commands, it's what the injectors deliver, and it's what the O2 sensors read.

My Impala SS LT1 was in the high 11s, low 12s at WOT.  I recurved the fuel to be stoich everywhere except WOT where I left it at around 13.5 because I didn't really want to have to buy 93 octane for the last 3 hp.

In reply to Curtis73 (Forum Supporter) :

2004-05 Mazdaspeed Miata actually tries to hang on to stoich too long when it goes into boost, causes a driveability problem. We have a doodad that smooths it out by getting the car to react just a little faster. But it's very much trying to run at stoich in closed loop. With a narrowband O2 sensor, that's all it can really do. 
 

WOT and idle - are there other throttle positions? ;)

In reply to Curtis73 (Forum Supporter) :

Really? I have never seen a car not run stoich and hang onto it for as long as possible.  Even when you mat the throttle they will stay stoich for a few seconds.  If they didn't, emissions would skyrocket.

80s GM ECMs even had an "economy mode" (that got nulled out after the EPA said you can't do that) that was the opposite of their PE schemes: it would find stoich and then subtract fuel to run at around 16-17:1 under cruise, periodically bumping back up to re-find where stoich was.  

Production engines are engineered to be able to run stoich most of the time.  The only real exceptions are the aforementioned rotaries, which do not like to idle that lean, and some TBI implementations for the same reason.  That is where they hung an airpump on it to give the converter something to work with.  But under any load and they run stoich...

In reply to Curtis73 (Forum Supporter) :

I did vehicle calibration for almost 30 years, and the last 25 or so was focused on emissions.  I'm 100% sure that OBDII era cars have to run stoich to just meet the standard.  Maybe a slight bias one way or another, based on how the rear sensor is reading.  But the whole idea of switching the O2 sensor is around stoich.  

Of all of the vehicles you have worked on, which one does not have the front NB O2 sensor switch?  Because if they do, that is around stoich, even the system says that it's running rich.  

If the engine isn't cycling around stoich, something fishy is going on.

And the richness at high loads is first for best power and then once things get hot enough, then you go richer to keep some component from overheating.

The other interesting thing is that GM calibrates for 14.2:1 as stoich... since that is the stoichiometric ratio for E10.

Really, all the computer knows is lambda, the "air fuel ratio" is the number the computer spits out to you whenever it sees stoich from the O2 sensor.  (I think GM uses an equivalency ratio, not lambda, which is the same concept but reversed)

In reply to Pete. (l33t FS) :

We use 14.3.

But yea, that's pretty irrelevant- it's what the O2 and the WBO2 sensor says for Lambda or Phi.  

GameboyRMH said:

(If you really want to put it back, good aftermarket units are available from companies like Random Tech and Magnaflow)

So this kinda got me to thinking (a somewhat different kind of smell). The question that came to me is – is a cat just a cat? Besides the pipe diameter would any cat do the job? Using the 94 F150 as an example; could I take a used (not used up) cat from another vehicle (Honda, Chevy, BMW, etc) install it and be good?

In reply to L5wolvesf :

A cat isn't a cat- especially over design time, the core designs changed a lot, and even more, the catalyst formulations changed a lot- more metal and more effective combinations of metals.  (this isn't a statement on how they age, but how they were designed)

First, it depends on the year, but given the availability of catalysts older than your truck, the highest possibility that you will find is it will probably be better than the original one.

Second, I would try to find a similar flow engine.  If it's a single catalyst for both banks, then you probably need a pretty big one to keep the flow up.  If it's a catalyst for each bank, then a large 4 cyl engine should flow just fine.

That being said, if you got 2 catalysts from a +2000 4 cyl honda, they will likely be better designed than the brick in your original truck.  For the most part, try to find the front one, as the rear ones generally have not much metal on them (they don't have to do much, and we reduce them by 1/7 to 1/10 of the front brick).

So that's a really long answer that, yea, pretty much any modern catalyst should work.