Exhaust leaks and the changes in AFR

JaredKaragen · Post by **JaredKaragen** » Fri Feb 29, 2008 7:19 pm

When there is an exhaust leak in a manifold or exhaust, I know the AFR is atrifically leaned out; my question is, does anyone have a figure on how much leaner it actually makes it? I know the size of the leak means alot to this, but lets put this in a general 2 areas: leak between the downpipe flange and turbo open WG (no dump) What have you seen on dynos when it comes to AFR's and such things? The reason I bring this up is because my WG placement is different; and I am having a bitch of a time getting to be able to trust my AFR's under boost. on the new setup there is more of a clear path for air rushing by to get into the EG compared to the last setup, but I doubt a 12:1 AFR turning into a 16:1 steady AFR under boost has to be wrong; Adding shitloads of fuel to the boost tables (mainly in VTEC) has had little effect to the AFR readout on my WB. Wrightfully so; I took an old tune; that was pig-ass rich before, and it made no dramatic AFR changes compared to my old tuned map; (back to talking about my current tune) The funny thing is I will still see spots of 12:1, and 13:1 when not in boost and in the untuned portions of the map so I know the WBo2 is working, and I also verified this by revving and flooring the throttle while shutting the motor off to pump clean fresh air into the cylinders/exhaust; and the WBo2 pinged out lean like it should have....

z31 · Post by **z31** » Fri Feb 29, 2008 9:58 pm

Instead of guessing how much fudge room there is, you need to sort it out and fix the problem. No two leaks are going to be the same so there's really no way to ballpark it. That's just my two cents...so take it for what it's worth. How is your wastegate placed since you said it's oddly placed? Also if you know there's a leak, why can't you fix it correctly? Is there no room to weld another bung further down if you think the wastegate is causing turbulance across the sensor?

JaredKaragen · Post by **JaredKaragen** » Fri Feb 29, 2008 11:51 pm

not oddly placed but the opening in it is more in an airstream into the engine bay compared to the last setup; I have noticed a significant AFR change between setups with no exhaust leaks except a small one at the outlet flange where the last setup was (same DP flange used). I can say this; I believe I might know whats going on; I need to try a new MAP sensor and see where it puts me; My datalogs show weird things happening, like logging only in col 1 and 2 under VTEC, and hitting a max of 2PSI in low-cam when my boost gauge says .5bar very annoying; plus the datalogs show the 6PSI, and also show it's eading from the correct cells; but it's not.... frikken weird.

JaredKaragen · Post by **JaredKaragen** » Sat Mar 01, 2008 2:09 am

replaced the MAP; problem gone; maybe this explains a few things. on another note; my base ignition does not need a +12.5 degree modifier... so things are definately telling me there was a problem with my old distributor (replaced a week ago) AFR's are acting funny; I need to do some more investigating

Boosted K20 · Post by **Boosted K20** » Tue Mar 04, 2008 8:17 am

also double check to make sure ur fuel pressure is not dropping in the higher rpms. if u add tons of fuel with little change to the a/f ratio, thats a sign that either the regulator or pump took a shit on u and pressure is dropping up top

Post by **calvin** » Tue Mar 04, 2008 11:48 am

Boosted K20 wrote:also double check to make sure ur fuel pressure is not dropping in the higher rpms. if u add tons of fuel with little change to the a/f ratio, thats a sign that either the regulator or pump took a shit on u and pressure is dropping up top

x2

JaredKaragen · Post by **JaredKaragen** » Tue Mar 04, 2008 3:39 pm

calvin wrote:
Boosted K20 wrote:also double check to make sure ur fuel pressure is not dropping in the higher rpms. if u add tons of fuel with little change to the a/f ratio, thats a sign that either the regulator or pump took a shit on u and pressure is dropping up top
x2

Here's something funny; Everything kinda poped back to normal; I think it is something with the car honestly because things with this thing have been bugging the crap out of me... but I was more concerned about people noticing AFR differences between open and closed WG, alone with small exhaust leaks to compare.