cherokee513

98 Cherokee 4L straight 6

Can anyone explain fuel trim banks. My ODB software is showing long and short term fuel trim banks 1 and 3 and no data for 2 and 4.

Are banks a group of cylinders?


Thanks

James

Madman

I have the same question

JD Cravin

I didnt think the straight 6 had more than one bank. A V8 would show 2 banks, but I guess not?????

Radi

I"m guessing the trim number for bank 3 is some wildly odd number compared to #1? If so, it's a phantom reading which some scanners seem to do. There's only one bank on the 4.0.
The only inline 6 I know of with more than 1 fuel bank is BMW...with three banks of two.

Madman

This guy is good

rrich

I've seen that screen but never really delved into it.

98 was the tail end of the transition to the more modern system. It went from 2 O2 sensors to 4, with 2 pre-cats. Both were OBDII.

If you had an O2 sensor failure on the upstream sensor just below the front 3 cylinders, the code would be "Upstream O2 senor Bank 1."
If it was the other upstream sensor, it would be "Upstream Bank 2." So JEEP considers they have 2 banks of 3 cylinders each.

The front 3 are Bank 1, the rear 3 are Bank 2.
Each bank has it's own O2 sensors, pre and post cat.

Your screen is indicating the "trim" for both banks, but your software is ahead of itself. It's ready for a system with 4 banks, not just 2. So it's putting the information in the 1 and 3 slots, leaving the other 2 blank. Not a problem.

You must be using a data link with a laptop PC. The software you have is generic, not specifically made for Jeep. I don't think there is one specifically made for Jeep. You'll find a few other places where they had to use "poetic license" too, it just looks strange at first. I have several brands/types of software for laptop/data link - all of them have their own quirks.

The idea of "banks" dates back to at least the 50's. ie: a Chevy 283 had 2 banks of 4 each - 1,4,6,7 was bank 1, every other one in the firing order, all fed by the left side of the carburetor.
The other 4 was Bank 2 - fed by the carb's right side.
You'd kill each bank in turn, noting the RPM drop, then adjust the carb so both banks were the same - "balancing" the carb for peak performance.

4's, 6's, even straight 8's and v12's all had similar "banks" just rarely called banks.