dizwiz24

ive been at wits end for this for years.
ever since i dumped cats (for the racetrack) and put in a hotcam, the exhaust stinks on my 93.

its been explained to me that any aftermarket cam has more overlap. so some unburned o2 is going past the o2 sensors causing it to falsely run rich.

that makes sense

what doesnt make sense is i have now made pe mode any cell below 1200 rpm and have zeroed out all the open loop afr fuel adders (at the kpa and coolant temp range my idle is at)

so only the only fuel adder is the ve tables (and any long term blm corrections from before i locked my idle into open loop)...i keep pushing those ve numbers lower and lower - without seeing any change on my wideband. i still see 13.2-13.8 at 850 rpm idle.

i may try raising the idle to see if that changes afr.

note that when im drivng the car (in closed loop), afr is around 14.5-14.9. where it should be. i dont notice any stink ever when the car is driving (of course airflow is carrying exhaust away, but.....ive never once had an objectionable smell)...

what gives !!! is this just a speed density /cam issue that i will never get fixed?

the car is a vert and i dont like stink smell sticking to my clothes in the pits.

FrankieD

if you're trying to get rid of the smell it will never happen without cats even if you lean it out to 14.5 or higher.
I just tuned my VE all round to run in open loop full time and not just in idle. Perhaps that's the way to go.

bjankuski

Have you zeroed out the PE change to fuel are ratio vs RPM at the idle positions? What about your minimum pulse width under constants, is that set to zero? One thing about the LT1 intake is that it has poor air distribution at idle and your WB is only reporting an average reading of all eight or four cylinders. The latter 1994 LT1 had quite a bit of difference in the pulse widths for the LT1 at idle and you may be running into that issue. It seems strange to me that the O2 sensor in closed loop cannot correct for this problem. The hot cam is not that large and GM was going to release it for the 1996 grand sport but then changed in the end to the milder cam. It also seems strange to me that you cannot get the car to run leaner when you reduce the VE it should get leaner. Attach your bin and I could look it over and see if anything jumps out.

dizwiz24

the problem isnt at any condition other than idle. so there is no benefit to open loop all the time, only at idle

at speed, highway, etc. my afrs are right around 14.7:1. no smell issue etc.

tequilaboy

Check/reduce the min pulse width and default pw settings as already mentioned by Brian.

Other things that will help: Reduce idle rpm as low as possible...try 650-700 rpm and retard the ign timing a bit to reduce idle torque which will add IAC counts (more air per rev which will allow more fuel to burn). This should also reduce the residual exhaust gas and put more heat into the exhaust. Suggest around 10-12 degrees spark advance at idle.

RWDsmoke

I have a hotcammed 86 with no cats. When I try to run closed loop idle the exhaust will burn your eyes. Now in open loop My wideband still shows mid 13's for a smooth idle. Any leaner and I get missfires which makes the exhaust really stink. It idles best at 750 rpm's and 27 degrees advance. Now it is no worse than any car without cats. At cruise it's happy with 14.6 - 16 AFR.

I just read an article on how GM ECM'S control fuel using feedback from the o2 sensor. The author's opinion was there is no reason to run closed loop if you do not have cats. I run open loop all the time now and after data logging and tuning, my car has never run better.

cv67

idling too lean can stink and burn your eyes, too