Idle’s good, missing under load

[DavisRanger]

I just recently did a complete rebuild on my 2.9L. Almost everything under the hood is new.

The truck idles great, but when under a load it’s missing at low speeds (lower rpm), but doesn’t miss at higher RPM’s.
I removed the cats because they were clogged and put in a straight pipe. Never reconnected my O2 sensor, but I wouldn’t think that it would cause that kind of issue.

Got the timing nailed down and have made sure all of my vacuums and sensors are plugged in (minus the O2).

I replaced the MAP sensor and now I’m thinking it could be my IAC. I pulled the codes and this is what I got.

the engine was not running when I pulled these codes.

Code 221 (if I remember right this has to do with timing, and I believe that this is from when I was setting it.)
Code 51
Code 41

Any help would be much appreciated.

 

[RonD]

Nice looking rebuild

1988 PCM(computer) uses 2 digit codes only, they can be seen here: https://www.therangerstation.com/tech_library/2digitcodes.shtml

So not sure where 221 would come from, and its not even a listed 3 digit code?

Put back on your O2 sensor and hook it up

O2 is only used after COLD engine has been running for 3 minutes or so
O2 is not used at idle or WOT(wide open throttle)

So your misfires can be caused by lack of O2 feedback

Also distributor and spark system can be RPM range specific

 

[DavisRanger]

Thank you! Much appreciated, I’ll throw it back on and go from there.