switched 36s to 72s, now mostly 15.94...

[S351 R]

After switching to 72s the car starts rather well, idles "ok" with only a little hunting, cruising is about the same as before, start-off and gear changes are plenty jerky but can keep her going.

Problem is that most of the above is happening with 15.94 AFRs or at least on the high end of 14+. Idle VEs are 78 and it takes 90 in those cells to get the reading down from the 15.94. When I set closed loop, seeing 20-24% correction at highway cruise.

The only thing I changed was the Fuel Calc to show 72's. I verified that the #3145 SiemanDeka were in fact '72s. I also switched sides for the 02 sensor to rule out a bad injector - both sides acted the same. Car was fully warm for all this. The 36# tune wasnt perfect, but did fine for driveablity yesterday.

So, first, is it really possible for my car to to have behaved as good as it did (albeit pretty jerky) with such a lean reading?
And second, what should I look at first before making my VE tables all 90 and up for the cruise/idle cells?

Thanks for any thoughts on this.

 

[S351 R]

Well, raised the FP from 40psi to around 55 and this did help, but am still using VE's of 75 to idle at low 14 AFR. Driveability is a little less jerky and still runs ok. Still starts like a champ too. Maybe spray pattern/pulse width at such a low fuel demand may be causeing droplets of fuel not to get burnt, thereby giving a lean reading.

Higher up in the 2500-3000 with some med load (scared to do any wot) it behaves more sensibly with decent AFR vs O2 corr with VE's of 80 or so.

What is strange is that it gets leaner hotter it gets. Now mind you it behaves properly for awhile even after coolant is up to temp, but I guess the more the motor gets heat saturated, then there is a noticeable increase in lean reading. Any enrichment or fuel add is done by 145* or so.

Do I simply have to dial in a large injector to a currently mild motor (351W, S-trim, Performer heads, mild cam) or is something not right? Or do I need to be worried about high VE #'s or simply continue to give it what it wants.

FWIW, my 'real-time' cursor in the VE table, and Spark table hovers between the 400 and 800 rpm column when it is actually at 1000 rpms. ??? The datalog playback feature puts the curson where it is supposed to be though...

 

[Ricky Trussell]

I believe your cursor issue is with your dash selection. You need to have scaled rpm or rpm in the dash with base fuel map.
(I think)

 

[S351 R]

Thanks for the reply, looks like i already had the rpm option used on the VE and Spark tables dash. Not sure what else it might be, but it works in everything else fine.

As far as the lean issue, Im going to try increasing the Injector Opening time from 1.0 to 1.3 to help those big injectors out during such low demand. I'll post the results