ditto. same here.

 

good info thanks! yeah i was running no cats for a couple years but now i am going to be running them again partly because i want to be 'cleaner' and partly because its a challenge to make power through stock cats plus it smells better LOL
I'm glad to know others aren't having issues though, I would think a big cam would be the first tell your car definately isn't stock which would leave to further checking but if not thats great!

 

Bringing this back from the dead. I have a 1995 pickup with a 5.3 that I put a comp cam in. It's a 215/223 on a 112+5. I didn't think I would have any issues, but I failed DEQ. Since it's a 95 it gets sniffed. Anybody swapped an OBD2 engine into an OBD1 vehicle in oregon? Were you able to tell the state that and have them plug in? That would make this WAY easier for me.

 

no we just put a single cat on them about 3' after the turbo, and run them right at stoich

 

Thanks for the reply. I am worried that the overlap is what's causing the issue. I'll do some more tuning before I go back to DEQ to make sure I am as close to stoich as possible.

 

what exactly are you failing? NOx or CO(1 or 2) ? post a pic of the test if you can.

do you have a cat? even with overlap things can be done, retarding the timing to get a hotter more complete burn at idle...but you gotta be careful too much will create more oxides of nitrogen than a single cat can handle.

I street tune and trouble shoot for portland and vancouver guys. The ls1 pcm flashing ad on craigslist is me.

 

Its failing for high hydrocarbons. First time i took it it was 4X the limit for both idle and 2500 rpm (880). Then it got a tune update and it brought the HC down to 3X the limit for both. I put a few gallons of e85 in and drove it around for it to adjust and that brought the idle HC to about 330 and 2500 RPM HC to about 440. The limit is 220.

Wouldn't retarding the timing mean the spark comes later? Did you mean advance the timing? Please correct me if I am wrong. I have recently started learning how to tune. I have access to efilive and am in process of getting my wideband setup to read serial data to the V2 flashscan. I just put the cable together today, but didn't get a chance to set up the V2.

The timing is currently at about 40° at idle, I would need to check what it is at 2500. This is from the log I took a couple days ago. For street tuning do you advance timing until there is KR and back it off 2 or 3 degrees? I think I need to work on the VE and MAF tables first and see if that helps. I have a feeling they're not fully there yet.

Thanks for the reply! I'll try to get pictures of them up tomorrow.

 

Pictures of the latest 2 attempts at DEQ from the post above.

Attempt after remote tune update with log and no WBO2 data


Attempt after a few gallons of E85 without any tune adjustments.

 

advance = more degrees BTDC

retard = fewer degrees BTDC

generally I run most LS engines around 20º at idle. I'll retard it to 18º to help keep the engine temp up on vehicles with cold plugs (turbo or supercharger) 40º seems odd to me.

That you're failing for high hydrocarbons makes me think you're running rich, or the cats are not getting hot enough.

tell me more about your combo, are your o2's functioning?

 

Oh ok, interesting that you retard timing to increase temps.

​I have a 5.3 from a 2001 yukon with 243 heads milled .030" to get compression back up, comp cam lsr 54-455-11 (215/223 .604" .61" 112+5 LSA), 8.1L truck injectors (part number 25343789), 2008 truck intake, Holley 90 mm drive by cable throttle body, 08 returnless fuel rail, corvette fuel filter, long tube headers, and 2006 silverado efans. The vats, egr, evap, and rear O2s were all deleted. This is in a 95 C1500 with a 6 speed manual (98 Fbody T56). The rear end will now have 4.88 gears and I will be running a 29" tires.​​​​​​

I am running 2 cats, one on each side a few inches after the header collector in the y pipe. They are the "high flow" spun cats, I guess I hadn't thought about the fact that the cats might not be functioning as well as a regular cat would or that half of the exhaust would heat it enough. The way I had to run my Y pipe, a single cat would be 2 to 3 feet away from the header collector and I thought it be better to run them right after the collector. Here's a link to the cat:
​https://www.summitracing.com/parts/mpe-59929​​​​​​

Thanks for the reply! I appreciate it!

 

I'm not very familiar with the efi live stuff, but once you get it up and running let me know what your afr and timing is at idle. I can then point you towards which was to go to pass.

yes retarding the timing increases the exhaust gas temps at idle and low load.

lucky for us we dont have to run that way all the time. we can pick and choose exactly how much spark we want vs engine load.


pm me if you dont see me in this forum. I only ever come in here once in a while.

 

Thanks for the info! I will grab a lot today with the updated VE and MAF tables and let you know what I find.