JekyllandHyde

iTrader: (3)

Ok, I was reading the article on the PROM guide book on changing O2 constants for cams with big overlap to account for the extra air in the exhaust stream going past the O2 sensor. Now I'm not a cam expert by any means, but how much overlap should one have before needing to change the O2 constant? For example I have a TPIS ZZ-409 cam, and the LSA is 112 which is supposed to be easy to tune for EFI, but has an overlap of about 3.9 degrees. I swapped out the original 91 L98 camshaft in there that had a 114 LSA, and I have no idea how much overlap it had. Would this cam be enough to warrant changing the O2 constants?

Dominic Sorresso

Did you mean 39d overlap? When you do change O2 constants, it's really for idle and to reduce the "rich" condition. Outside of idle, I haven't found a need to modify O2 constants. I had a roller cam in my 84 Xfire with 53d overlap. Did same with larger intake cams for my LT-5.

JekyllandHyde

iTrader: (3)

Sorry, I meant to say 61 degrees of overlap. I dunno where I got that 3.9d number from. But yes, it's a bigger camshaft than stock obviously. I'm reading 160 BLMs at idle only. Anything above that and BLMs kick in and read on or close to 128.

I re-read the article and changed the following constants:

Idle O2 rich/lean slow zero lower
Idle O2 rich/lean slow zero upper
Idle O2 rich/lean threshold fast

I did just these three for a little experimentation. So what I did was, I kept richening up my idle VE cells until the idle would start dropping down to 128 and the car was idling pig rich and you could smell it out of the exhaust. I tried adjusting the three settings above lower as per the article in the PROM tuning handbook on O2 constants, but it produced no change in the BLMs? Was there another setting I was missing?

Ronny

iTrader: (1)

I dont believe that is the correct one. Is there one that says "median" in your def file?

Dominic Sorresso

Should be either a constant or or could be a table using O2 mv. Not fast or slow O2

Orr89RocZ

iTrader: (20)

I did alittle playing on MAF cars with these constants and they did appear to work. I had a fairly big cam in my 383 and it idled well but BLM always said it was way off from 128. I tuned a 360" motor with a big 280XFI cam in it and it idled rock steady at a lean 16's to 1 air fuel, BLM was also way off 128 but the car was steady so we left it at that and did not change o2 constants.

Keep playing around with it and see what happens. Your basically targeting a different air fuel ratio when moving the o2 constants around. Usually in those tables you start to see 450-500 mv at higher airflow/higher rpm ranges where overlap has less effect and at idle you see 600mv or so to compensate for additional air in the exhaust due to overlap. Also suppose to compensate for A.I.R systems on stock cars with no overlap based cams.

I'd tune the motor til it was idling well and gave best vacuum at idle. Monitor plugs to see how the burn looks and note the BLM at the best idle condition. Then try to adjust o2's til the BLM is closer to 128 I guess. the upper and lower table i think is correct but I thought there was 1 more.

Ronny

iTrader: (1)

I think the table is like: 02 mvolt threshold high
median (.45)
low
I moved mine 10% up. To achieve richer than stoich. Now WB shows stoich 1.0 vs leaner prior to making change.

JekyllandHyde

iTrader: (3)

Thanks for the responses. At this point, the car still has issues idling so I'm going to lock it into open loop later night and tune by smell and plug readings.

Ronny, what ECM and mask are you using? I should have stated earlier, I'm using 730 ECM and the 8D mask. I'm also using an AUJP bin to start off with as well. Since my engine is reading leaner when it's probably not, I'd have to move the constants lower to account for the extra air in the exhaust due to overlap no?

Ronny

iTrader: (1)

EBL-ECU same on .bin and mask. I too idle OL. Last I looked was idleing at about 13/1 on WB. 224/230 @114 LSA. (TBI).

JekyllandHyde

iTrader: (3)

Well, I fooled around with it tonight. I turned on the car and let it warm up until it hit closed loop and then shut down and pulled plugs 1,3,5,7. They all looked pretty normal, you can even say a little lean. Goes against what I was originally thinking since blm 160 would mean that the car is dumping fuel right? I was expecting to see fouled plugs. I set timing to around 23*in the idle cells of the VE table and added fuel over the stock AUJP ve in the idle cells. Which leads me to my next stupid question. We removed the AIR system but left the smog pump and hard pipes on the headers in place with the intention of putting the AIR system back in since I still have cats. We did not plug the holes on the air pipes at the headers but thought we would be ok because the have check valves. The air system was left off because we need to adjust the rockers again. Could it be possible that air is leaking into the exhaust stream through the unplugged AIR pipe check valves and affecting my readings?

Dominic Sorresso

I would cap AIR inlets. Check valves go bad.

Ronny

iTrader: (1)

When I first moddded engine and first began tuning I too saw BLMs at 160. I believed it to be my tune so I kept adding fuel. turned out it was a significant leak at header collector flange to exhaust flange. Seems probable you too have exhaust leak/fresh air infiltration driving the max BLM.

branz28

Deleted, I knew i shouldn't have posted so late at night.

gta324

did a 6E tune last year on a 383 with a big cam.
Not easy, hade to put O2 around 150mV just to get a decent idle and the low rpms where tricky....

This year I swapped to a 730ECM and 8D code in it.

Running the S_aujpv4 and tuned idle idle in open loop, soo much easier

Currently its running in open loop all the time but will test CL later, but the owner is so happy with how its running so dont know when it will happen.

The point: Get S_AUJP V4 and tune idle in Open loop........