Math Wizzards - BEN Factor IAT correction

[SSpdDmon]

Well, if spark advance has an effect on your AFR, wouldn't it make sense that higher IAT temps where timing is being pulled will have an effect on your BEN's? My IAT's don't start pulling timing until mid-90*F. Thanks to my Austin Ram Air and the Michigan weather, I rarely see temps in excess of 93*. Maybe that's why I don't notice this so much when I tune?

[Black02SS]

I notice the same effects. I have my IAT's zero'd out so there is no difference in timing.

[TAQuickness]

I think I know what it is... I just need some time to figure out how to explain it.

[TAQuickness]

The attached screen shots are 4 logs taken over the last 2 days with no tuning changes between logs. This is an apples to apples comparison.

In chronological order:

Afternoon1:
AVG IAT: 100* F - 37.7* C
AVG ECT: 194* F - 90* C
AVG BARO: 30.0 inHg - 101.6 kPa

Morning1:
AVG IAT: 84* F - 28.8* C
AVG ECT: 188* F - 86.6* C
AVG BARO: 30.1 inHg - 101.9 kPa

Afternoon2:
AVG IAT: 101* F - 38.3* C
AVG ECT: 199* F - 92.7* C
AVG BARO: 30.1 inHg - 101.9 kPa

Morning 2:
AVG IAT: 84* F - 28.8* C
AVG ECT: 192* F - 88.8* C
AVG BARO: 30.5 inHg - 103.3 kPa

In each screen shot, the first grid represents Cell Count, the second grid represents my AVG BEN factor, the third grid represent my AVG RPM, and the fourth grid represents my AVG MAP kPa. All data has been filtered to remove values below 178* F ECT, and to remove values where TPS changes more than 5% in less than 100ms.

[GMPX]

I too have been tearing my hair out with this issue.
Before I go into why I think this happens basically you just need to be aware of the problem and try to tune with consistant IAT values, sometimes that can't be done so just filter out any data above say 25 degC IAT, sorry, I know most of you talk in degF, but I am used to degC, besides, the PCM's own calculations are in DegC

I am currently running SD mode of course and I have found that between IAT values of 20degC and 40degC there is a big change in AFR's at low airflow (idle etc). Changing the Charge Temp tables does not seem to have the desired results of correcting this problem. :cry:
I have seen the AFR at idle almost locked on 14.63 in open loop, yeah, my BEN factor at idle is like 1.00 , but then at 40degC these AFR's can drift to high 15's, not good. Again, this only seems to be at idle.

What I have done is allow the PCM to go into closed loop at idle and part throttle only, no good for tuning, but once the VE is mapped in open loop, I've enabled closed loop just under those conditions and this problem of IAT AFR drift has gone. This makes me think, perhaps the PCM is only factoring in the IAT compensation in closed loop?, I really don't know.
The problem of AFR drift does not appear to effect WOT AFR's, they have been spot on on every log I've done hot or cold IAT's.

Cheers,
Ross

[SinisterSS]

...besides, the PCM's own calculations are in DegC

That doesn't mean it's right. :P

[bink]

GMPX,

Have you tried bumping the "Open Loop Lean Limit (Idle)" value {B3607}. Stock is 1.00 (Eq Ratio).

Cheers,
joel

[GMPX]

GMPX,

Have you tried bumping the "Open Loop Lean Limit (Idle)" value {B3607}. Stock is 1.00 (Eq Ratio).

Cheers,
joel

That would affect the commanded AFR only, the thing is the PCM is still commanding 14.63, problem is it does not realise the actual is in the 15's when in Open Loop without any O2 feedback.

Cheers,
Ross

[GMPX]

...besides, the PCM's own calculations are in DegC

That doesn't mean it's right. :P

You guys :lol: :lol:

I guess I better learn imperial before we all head over for SEMA, I don't want a units interpreter on the stand!!.

Another idea, Paul, can you put a 'bug' in the software to force metric only, then you guys might just see the light :wink:

Cheers,
Ross

[bink]

GMPX,

Have you tried bumping the "Open Loop Lean Limit (Idle)" value {B3607}. Stock is 1.00 (Eq Ratio).

Cheers,
joel

That would affect the commanded AFR only, problem is the PCM is still commanding 14.63, problem is it does not realise the actual is in the 15's.

Cheers,
Ross

Yes, I understand. It was near 100*F here over the weekend. I bumped the {B3607} value to 1.13 and it helped. 1.30 and it was pretty stable. My point being -> could a commanded idle AFR below 14.68 put it in a range that the PCM is better able to compensate??

Cheers,
joel