valve job?

[89 jeep]

Hi everyone
89 Cherokee is lacking power. Changed the plugs and #3 plug is black with soot, not wet or oily. Changed them about a week later, still only #3 is black with soot. Compression is fine on all cylinders. During hard take-off, engine has a kinda muffled pop and does not take off like before. Do some of you think i need a valve job.
Thanks yall

 

[old_man]

Valve job is the last thing I would think of. A compression check will tell the tale. Running rich can be caused by a multitude of causes.

O2 sensor
Air Charge Sensor
Map Sensor
Clogged CAT
Bad TPS.
Injector

 

[89 jeep]

Compression is running 140-150 on all cylinders. Engine is lacking power.

 

[DanMan2k06]

Do an injector balance test, check the voltage of your tps, check all o2 sensors, fuel pressure regulator...

 

[old_man]

Compression is running 140-150 on all cylinders. Engine is lacking power.

Compression is good. That pretty much rules out rings and valves.

My guess would be either O2 sensor or clogged CAT.

You can somewhat check the CAT by doing a vacuum reading at idle. If the vacuum is low, your cat is probably clogged.

Just a long shot, but is your air filter clogged?

 

[89 jeep]

Hmmm. Ill check those things and get back.
Thanks

 

[89 jeep]

It was a bad injector. Runs great, idles smooth.
Thanks yall