HELPPP>>>> while using cruise control afr goes from 16 to 13 with no reason....

[djv86]

while on flat ground with cruise control set at 65mph the afr goes from commanded 16 to commanded 13. there is a very quick drop in timing instantly before the afr is commanded to 13 then timing goes right back to where it was but yet the afr does not change unless i made a big change in throttle or speed. abuse management some how getting activated ???

]NOTE frame 800-810 is the concern.

attached is the tune file in the truck and the data log from that tune file.

vehicles mods >>>> tbss intake manifold with the 88mm truck tb, xlink, long tubes, sloppy stg 1.5 cam. no dtcs.
comanding too much fuel under cruise.efi
new tune.ctz

[ChipsByAl]

This log is very unusual. Did you start with a file that ran well in the past? Looks like something erratic is going on in the PCM or the tune file.
Al

[djv86]

This log is very unusual. Did you start with a file that ran well in the past? Looks like something erratic is going on in the PCM or the tune file.
Al

i have played with the lean cruise before. although this time the lean cruise data is zeroed but maybe i need to fully turn it off and try again. ive been doing the calc.vet setup in the truck to clean the fuel trims and this was a drive home after making some adjustments.

[djv86]

bump for anyone's thoughts ? is there some type of emissions tests that the pcm could some how perform without knowing it does it.

[nonnieselman]

bump for anyone's thoughts ? is there some type of emissions tests that the pcm could some how perform without knowing it does it.

It is probably the rear oxygen sensor test for catalytic converters. Its common on the Gen 3 PCMs.
Some say that you cant do anything about it.

[djv86]

i have never noticed it do it before until ive put headers on it and removed the rear o2s from the exhaust. although ive had the cats removed for 8 months now and never noticed it before as well. although the truck has a RPO NU4 which is california level 2 plus for emissions. i wonder if a federal emissions calibration from the same year would help ?

[nonnieselman]

i have never noticed it do it before until ive put headers on it and removed the rear o2s from the exhaust. although ive had the cats removed for 8 months now and never noticed it before as well. although the truck has a RPO NU4 which is california level 2 plus for emissions. i wonder if a federal emissions calibration from the same year would help ?

Plug your rear oxygen sensors in zip tie them to the frame or something. Then after a couple days datalog it and see if it does it again.