what should my AFR be at idle

[Mchlgrrsn]

Originally Posted by dan0617

If your sensor is behind the cats it will be very steady and in the mid 14's. if it is in front of the cats it will oscillate, and you will see upper 13's to mid 15's. These are part throttle numbers of course. Sensor needs to be in front of cats to be accurate.

What if you don't have cats ?

[JHall651]

I have the ADM gauges and my sensor is after the cat and it bounces around 17 to 19 during light cruising or just maintaining pretty much any normal speed. Problem is I have SLP S/C with SLP handleheld tune and they will not let me re-tune or it will void their warranty. I'm not sure what to do about it. When I go WOT it will drops instantly to 10.5 and holds steady its just the cruising AFR that concerns me. I also have gotten a few lean fuel trim CELs lately. I guess I need to call SLP.

[dan0617]

Post cat sensor won't change reading much but it will make it VERY slow to react. You are lean at cruise for sure. Vacuum leak?

[JHall651]

Well, I had the RX breather on and just pulled that off and replace hose and oil cap. Seeing if that will take care of CELs. Talked to Tracy from RX and he said sometimes "canned tunes" don't like the breather. But even with breather off cruising AFR is still staying same. Still waiting to see if P0171 and P0174 will pop again. They seem to do it when they want so only time will tell. They pop sometimes at idle, sometimes at cruising, sometimes after 50 miles, and sometimes after 250 miles. I've checked every hose and can't see any places there could be a vacuum leak. Weird thing is these CELs didn't start until like 2000 miles after S/C and RX can w/ breather install. No idea why they just started happening. I have changed nothing with the engine since they were installed and other than S/C and RX I am stock except for cat back Borla exhaust.

[Mchlgrrsn]

17 to 19 while on the gas is lean. 10.5 is rich. The breather helps keep oil out of your throttle body. With the amount of mods you have I would defiantly get a custom tune and keep the breather on.

Oops My bad it will keep oil out your catch can. I don't have one yet so it ends up in my throttle body.

[dan0617]

I ended up taking an open breather and built a large Pcv valve into it. It will let air out but not in. Any breather that lets any air in is a vacuum leak, metered or not. Your tune may or may not be able to compensate for it, but either way it isn't right. Needs tuned for, or better yet, find a way like I did to let air out but not in so there is no vacuum leak. Getting it to work without throwing codes and getting it right are 2 totally different things.

Is your AFM turned off in that canned tune? If not, that might make the lean wideband readings.

10.5 at WOT is rich but most canned tunes are, for any car not just ours. But by you telling us this it would appear your wideband is pretty accurate.

[dan0617]

Originally Posted by Mchlgrrsn

17 to 19 while on the gas is lean. 10.5 is rich. The breather helps keep oil out of your throttle body. With the amount of mods you have I would defiantly get a custom tune and keep the breather on.

Oops My bad it will keep oil out your catch can. I don't have one yet so it ends up in my throttle body.

The breather allows blow-by out of the crankcase during wot to keep from pressurizing the crankcase and blowing out seals. The catch can system needs properly installed check valves. To be right it also needs a check valve in the breather.

[SC2150]

dan0617, where are you getting the filtered make up air for the crankcase from? The RX breather has a flow controlling checkvalve only letting the filtered air in the PCM is able to adapt to within parameter....and maintains a closed system to meet emmissions rules. an open breather allows excess unmetered air in and will be difficult to tune for unless doing a SD tune.

The best is the 1LE clean side separator as that does a pretty good job of separating the clean side oil AND maintains a closed and 100% metered system.

[dan0617]

I have an L99 so no valley port. I have the port on the passenger valve cover plugged. Port from drivers side rear valve cover has line going to vacuum port on intake located under passenger side of throttle body. In that line is a 1 way check valve and an oil catch can. Pulls in crankcase vapors through catch can and check valve and creates vacuum in crankcase during normal driving, but under boost the check valve closes and doesn't allow crankcase to pressurize. Breather also has check valve so it won't let air in but will let air out. It allows crankcase to be vacuum during normal driving but with blow-by At wot, if necessary, it will let air out. Seems to work perfect.

What make-up air are you talking about? Should my crankcase not have vacuum at normal part throttle driving?

[dan0617]

If someone wants open breather on valve cover they could run a line from crankcase to check valve to catch can to supercharger inlet. I have thought about this myself.

Doing it this way the unmetered air coming through the breather and then crankcase is pulled in preMAF so it does get metered.

[05SilverStreak]

Originally Posted by Unobtainium

Just don't go into the 10's very much or for very long. It is bad for cylinder lubrication to go too low. Stay above 11.0 and all is happy. Most like 11.5.

A little backwards here.....10's is pig rich, but safe. I agree with 11.0 - 11.5. Anything near 12 is ok for like a quarter mile pass but will make heat quickly if you stay there for too long after that.

[Mchlgrrsn]

Originally Posted by dan0617

If someone wants open breather on valve cover they could run a line from crankcase to check valve to catch can to supercharger inlet. I have thought about this myself.

Doing it this way the unmetered air coming through the breather and then crankcase is pulled in preMAF so it does get metered.

You have my interest. My car just got done its build. A few little issues I'm mopping up. 1 is this whole breather thing. I don't have a catch can. According to my boost gauge I'm making a ton of vacuum. Oil is getting into my throttle body. I put a breather on and it has appeared to slow down or stop. Still too soon to tell. I'm going back into the shop next week for a cog drive and fuel rails. Any suggestions for this blow by. I know a catch can will keep it out of my throttle body but that seems like a band aid. I m new to FI I drive the car hard. Wot is common place.

[dan0617]

You need a catch can for sure.

[Mchlgrrsn]

Originally Posted by dan0617

You need a catch can for sure.

I'm surprised I didn't get the deadly " do a search buddy". Reading about oil separators now. I know about them. I don't know about vacuum. How much is normal ? I'm getting 10 at idle and as much as 20 driving normal. Like I said before going back to shop next week just doing my homework.