Ok im a lil confused. The goal is to get a 128 blm across the board right ? But i read some where that if you have a perfect a/f ratio that you will burn up you cats is this true ? I haven't started to adjust them yet just trying to get a better understanding before i try it.

 

i believe the 14.7/1 is for emmissions and functionality of the Cat. the 02 toggles over the 14.7 and is calibrated to fuction along with a Cat. i have no Cat so i can run a diff A/F ratio in CL if i wish. i plan on doing that this spring if i can fiqure this all out. in PE i plan on running 12.8/1 again if i can nail the tune. today lean. since in PE not all that often dont think it will hurt Cat if a bit lean. not sure on that. my PE comes at 50% TPS. stock may be 75%. not sure on that either.

 

Deviation from 14.7:1 is what hurts cats. If you have the tune dead on 128, the cat will be as happy as it can be (unless you have a big cam causing false lean readings at idle, etc.)

AFR is never really "perfect." There's a range in which the engine will run, an area for peak power, another area for peak efficiency, etc. You tune for the compromise that you and the engine like best. Tuning for peak power will shorten cat life, as the mixture will be a bit more rich than 14.7:1.

Tuning by BLM with a stock O2 will only get you 14.7:1. Tuning for other AFRs will require other tools, i.e. the WBO2, or trial and error guessing.

 

i tuned for 128 blms and when on dyno WB my commanded 12/1 PE showed 12/1 on WB. since blms were close it fell in line nicely on PE. not so for AE it was way off!

 

ok i kinda get it better now

 

Let me try to set things straight.
1) A cat will get quite hot with 14.7:1. This is where it operates with great efficiency in converting all emissions to nil. This means that it will be hotter than the exhaust itself (it is "burning" the emissions on its surface area).

2) At WOT, there is a lot of flow going through the cat, and if you were to keep it at 14.7:1, the extra heat that the cat generates from the emissions (along with high exhaust temps, and flow rate) will quickly lead it to an overheating situation which will destroy the washcoat and eventually melt the substrate. The way around this is to reduce the efficiency of the cat. The best way to do this is to richen the mixture (eliminate the O2 that is required to catalyze the CO and HC). This will put the cat to sleep and will basically keep it at the exhaust temperature (rather than overheat on its own).

3) The worst thing you can do to a cat is transition from hot cat (even a little rich) to air (dfco). That air will cause the temperature to skyrocket in a blink of an eye (as the oxidizing atmosphere will suck up all unburnt fuel on the catalyst, etc...). So, if you were to take a catalytic converter equipped car around a road coarse for a while, you're likely to cause some catalyst damage (but it'll mainly be washcoat damage).

4) The other (even more) worst thing you can do - disconnect a few (1 or 2) spark plug wires or introduce a nice vacuum leak to a few cylinders. The extra air and fuel that reaches a hot cat will basically start on fire and literally consume the cat (especially if you drive it that way for awhile). Once all the substrate melts and blows into the muffler, it will obviously no longer reduce emissions (and tends to reduce the flow through the muffler - we did that to a Jetta and tested the exhaust back pressure, hehe).

5) Worst thing again: Disabling DFCO will send tons of misfired fuel and air into the cat, just like in #4. Combustion isn't stable at overrun (add to that the injectors don't fire consistently at low PW's).

I know this because I've done the tests to prove it with thermocouples in the catalyst substrate (I'm an EFI engineer and have to make emissions compliant calibrations, yay).

 

To add to this, the longer you're in PE and close to stoich the hotter the cat will be. Extended PE load like on a load dyno can cause cats to melt if the tune is being held high RPM high load. So you'll notice in newer cars that the AFR in 1st gear will be higher than 2nd which will in turn be higher than 3rd to control cat temps AND do more in cylinder cooling to prevent detonation. Detonation is misfire and I won't repeat what RednGold just said about misfires cause that's all dead on.

RednGold, there's just one thing that I disagree with, slightly. DFCO and decel enlean isn't going to hurt the cat for the same reason you gave for 2) . During DFCO the throttle is closed and the volume of air going into and out of the motor is VERY low. Also the old style injectors are a little odd at small pulse widths but the newer delphi style are like P&H ranges. The biggest thing with injectors is the voltage, it's extreamely important with the saturated injectors but I've found them to handle low pulse widths very well so long as they get more than 12v. If you've got under-drive pulleys or a weak alt/battery then your idle pulse widths might be flaky, but in DFCO the voltage should be stable enough.
If it's not much trouble, could you send me some data where you've logged the cat temps? I've got one more daq channel and think the cat temp would be really nice to watch.

 

DFCO isn't bad, it's the transition to DFCO from a high load that will do it (full throttle snapped shut) and it's only the transition that I'm talking about (fuel (misfuel, walls drying, etc..) and then air reach the hot cat). Good decel enlean minimizes the effect.

Also, even with good injectors, the engine itself has a hard time getting good consistent combustion at overrun. Opening the IAC some will help though (throttle follower). If you have an exhaust gas analyzer, any time you see HC spikes, you'll see cat temp spikes.

I don't have any cat temp logs on the two computers that I have with me. I'm in China right now debugging our new computer's algorithms and software before we begin a Euro 3 calibration for an OEM here. When we get to the point of testing cat temps, I'll be glad to send you some data.

The correct place to measure the catalyst temperature is to drill a hole 1" back from the front face of the front brick, and insert the thermocouple such that the tip is in the middle of the exhaust flow. That is the critical temperature. You may also want to measure inlet and outlet and second brick temperatures, but if you only have 1 channel, go with what I said above.

Cats start to thermally degrade above 800-900 C, but that (and higher temps) usually can't be totally avoided, but should be minimized. The cat will start to work in the neighborhood of 350-400 C (from direct contact with exhaust). Once it lights off, it will usually sustain its own temperature as long as the inlet and ambient temps are reasonable.

Sorry for the hijack 91. Yes, you do usually try to get the calibration perfect with 128's everywhere (both BLM and Integrator). PE enabled will ignore BLM's below 128 (and it will use 128 in that case, so don't be fooled). PE disables closed loop feedback, also. A wideband will help calibrate WOT PE (which you'll want to achieve in the neighborhood of 12.5:1 A/F).