tuning out the smell of a bigger cam... tips on a $DA2?

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dizwiz24
Posts: 55
Joined: Mon Jun 29, 2009 6:15 pm

tuning out the smell of a bigger cam... tips on a $DA2?

Post by dizwiz24 »

I have a 224/234 114 LSA cam on my supercharged 93 vette ($DA2).

I dont run cats to minimize exh backpressure to maximize supercharger performance.

There is a nasty exhaust smell at idle that im having a tough time getting rid of.

BLM's sometimes split (and then come back together), but usually are always in the 108 range on both sides. If datalogs show BLM splits, its always the Left side is around 108 and the right side is aroudn 122 or so.
But then they will come back togetherr...always on the low side of 128.

Recently, Ive heard someone say the combination of greater intake duration and lobe separation (which 114 isnt really that bad) cause overlap.

The O2 sensors see excess O2 from the overlap phase and start throwing fuel at it - which is undesireable.

Can I tune this smell out by lowering VE values around idle and the appropriate MAP sensor range?

What about eliminating the O2's and just running in open loop all the time (ie. setting the tune so it never goes into closed loop)?

Is that recommended or can that cause me fueling issues if Im at different altitudes / temps. Or can I use the open loop fuel adder tables to provide the proper adj for different temps?

Id also like to gain some MPG back. I lost some with this cam change.
If the O2's are dumping fuel un-needingly (due to overlap), it seems like eliminating them and running open-loop could be the ticket.

What do you all think?
JP86SS
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Post by JP86SS »

Split BLM at idle might get better playing with IAC air flow. distribution issues seem to play a big role in that.
http://www.thirdgen.org/techboard/diy-p ... -blms.html
Also read "Vern's tale on post #8.

Idle stink can get better by lowering the o2 constants by small amounts until you find the happy spot. Finding it at idle with split BLM will be more difficult I think.
There are three tables for idle use in $8D, not sure what you have in DA2.
I came down around 50 mV on the readings and there was a noticable difference but not sure on the boosted app how that will perform.
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JP86SS
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Post by JP86SS »

I forgot to mention,
Adjusting the VE tables will not work because the O2 constants (for idle) and the other o2 tables for part throttle operation will drive the fuel right back in.
Changing the o2 values to run in the range you want is the only way in CL to do it.
Open loop is always an option but that would be up to you to go that way.
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Six_Shooter
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Post by Six_Shooter »

JP86SS wrote:Split BLM at idle might get better playing with IAC air flow. distribution issues seem to play a big role in that.
http://www.thirdgen.org/techboard/diy-p ... -blms.html
Also read "Vern's tale on post #8.

Idle stink can get better by lowering the o2 constants by small amounts until you find the happy spot. Finding it at idle with split BLM will be more difficult I think.
There are three tables for idle use in $8D, not sure what you have in DA2.
I came down around 50 mV on the readings and there was a noticable difference but not sure on the boosted app how that will perform.
Can you elaborate a bit more on exactly what you did with the constants, and what constants they were. I'd like to clean up the idle a bit on a friend's car, but his is open loop right now, and large cam, and a bunch of other things playing against us. We want to turn closed loop back on, but only if I can get the same quality of idle (as smooth, not smell wise) as we have now. Last time we tried CL there was noticeable surging.
dizwiz24
Posts: 55
Joined: Mon Jun 29, 2009 6:15 pm

Post by dizwiz24 »

JP86SS wrote:Split BLM at idle might get better playing with IAC air flow. distribution issues seem to play a big role in that.
http://www.thirdgen.org/techboard/diy-p ... -blms.html
Also read "Vern's tale on post #8.

Idle stink can get better by lowering the o2 constants by small amounts until you find the happy spot. Finding it at idle with split BLM will be more difficult I think.
There are three tables for idle use in $8D, not sure what you have in DA2.
I came down around 50 mV on the readings and there was a noticable difference but not sure on the boosted app how that will perform.
So I should see if I can change the threshold from:

< 500mV : Lean = command Add Fuel

to

< 450 mV : lean = command Add Fuel
JP86SS
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Joined: Thu Apr 22, 2004 5:49 pm
Location: Strongsville, Ohio
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Post by JP86SS »

Sorry I didn/t see your reply.
Yes drop them by 50 mV to start with in all 3 constants.
8498 = 465=Idle O2 Rich/Lean Slow Zero Error Lower
8497= 500=Idle O2 Rich/Lean Slow Zero Error Upper
8496 = 500= Idle O2 Rich/Lean Threshold Fast
These are the $8D locations with my current values.
I need to tweak the values now that I have a 406/new cam momotor, they worked really nice with my 350 roller with 224/230/112 cam.
idle smell improved a bunch from the stock settings.

For adjusting the CL values of the O2 in CL I recommend using the spreadsheet I created that shows the relationships between the o2 tables.
I included it in the S_AUJP V4 package or its available on TGO.
Explaination of the spreadsheet use... http://www.thirdgen.org/techboard/diy-p ... sheet.html
O2 table explaination thread and link to where the sheet was (link doesn't work anymore)
Send me a PM with your e-mail if you want a copy or DL the S_AUJP V4.
http://www.thirdgen.org/techboard/diy-p ... oints.html

The original post on o2 adjustment about idle smell
http://www.thirdgen.org/techboard/diy-p ... tants.html
HTH
JP
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decipha
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Location: New Orleans, LA

Post by decipha »

The o2s are not going to be accurate at low loads if you have a mechanical overlap causing a false lean condition

The best approach I've found is to disable closed loop at the lower rpm and airmass range, just allow closed loop in the upper ranges

Also to rid the fuel smell at idle you'll want to fire the injectors later to prevent being scavenged, I always fire the injectors on the closed intake valve, I don't know if your pcm is sequential or batch so it may not apply

The most effective method for dialing in idle is with a vac gauge, give her the fuel and spark where she pulls the most vac and lock it in

Good luck
dizwiz24
Posts: 55
Joined: Mon Jun 29, 2009 6:15 pm

Post by dizwiz24 »

I know its ben a year, but i wanna chime back in

I put different headers on (arh 1 7/8" vs. Tpis) and there is less split blm issue.

the new headers have the 02 bungs in a slightly different location.

I like the suggestion on playing with fuel/spark to get the most idle vacuum. Thats how we used to do it with carbs. Though i wonder if the fuel changes would just get negated by the computer once it goes into closed loop at idle

if worse comes to worse, i will disable closed loop idle and run open loop idle.

Btw. My 93 vette is speed density $da2
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