Erratic AFRs

DEJES09

Member
Joined
Mar 8, 2020
Good morning, recently the car has been experiencing what i can best describe as erratic AFR readings. Erratic in that they will just jump all over the place from very low number (6-7) to high 15.9 with the target AFRs around high 12s to low 13s. This happens during idle or driving. Before this started the AFRs would fluctuate but generally stay around the target numbers unless i was giving it gas or decelerating with my foot off the gas. Now it will just jump like crazy but only after the car has had time to get real hot. In the early morning/night or during a cool day the AFRs are close to normal. If im driving during our usual 90-100 degree afternoons and the coolant temps get to over 180s the erratic behavior will start. Its not immediately after i pass that temp but if i reach high 180s and drive around for a little while at those temps it usually starts, with the car also running like crap once it happens. If i get the car home and let it cool off for the night and start it the next day the AFRs tend to be acting closer to normal again. Has anyone ever experienced anything like this? Im running a wideband 02, FAST XFI 2.0, TR6 ignition, car has been checked for leaks and grounds have been looked at. 02 sensor has been changed out 3 times now cause i thought that it may be the cause but it still occurs. Thanks and any ideas will be much appreciated.
 

RED LS1

SENIOR MEMBER
Joined
Dec 31, 2001
This may not have anything to do with it. But check your Alternator voltage. I've had some erratic behavior from the Wideband from that and it made me start replacing sensors and even the gauge until I caught it.
 

DEJES09

Member
Joined
Mar 8, 2020
This may not have anything to do with it. But check your Alternator voltage. I've had some erratic behavior from the Wideband from that and it made me start replacing sensors and even the gauge until I caught it.
Awesome ill look into it. Thanks
 

Frankensteeen

Rebuilt and learning to walk !
Joined
Apr 22, 2021
Awesome ill look into it. Thanks
Also completely check out the battery... my older fast classic acted exactly just like your xfi. The battery tested good at all the local auto parts stores. Then several weeks later no start . And many hard popping backfires took out the cam sensor relucter tab too .

In went the rebuild cam sensor and New Battery. Runs like a champ now. Good luck
 

DEJES09

Member
Joined
Mar 8, 2020
Also completely check out the battery... my older fast classic acted exactly just like your xfi. The battery tested good at all the local auto parts stores. Then several weeks later no start . And many hard popping backfires took out the cam sensor relucter tab too .

In went the rebuild cam sensor and New Battery. Runs like a champ now. Good luck
Will do, thanks again
 
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