Guys replaced the head on my 01 with a head from a 99. Used the header from the 99. The 01 has 4 O2 sensors and the 99 had none other than one in front exhaust pipe. Any ideas what to do?

 

Bad news. The 01 needs all 4 sensors to run the engine. Older ones only used one, but you don't have an older one.

EDIT TO ADD: Oh, slap me with a dead fish! I forgot the most important thing! Welcome to the forum!

 

They had to do a lot more than that....the 99 header/ exhaust manifold will not mate with the down pipe/ crossover pipe from an 01 its about 4 inches too short ...plus all 4 o2 sensors on an 01 are built into the exhaust manifold/ header..
if you take that out you have 0 sensors where they are supposed to be. It can be done but you have to have 4 o2 bungs welded in....2 in the header, hopefully one in each main collector...123 and 456... then you need 2 put in after the resonator / 2nd cat and you have to run wires to make them all fit. Those guys are idiots and screwed you

 

You could also take the PCM and harness out of the 99.

So what exactly is in there now? Is it running or half-done? COP or distributor?

Did you mean

or

 

Will the 2001 exhaust header not bolt up to the 99 block? That seems the simplest solution.

 

No it will not, the ports are smaller on the 01 head and the manifolds dont mate properly....supposedly there is an adapter plate that will allow you to use the 99 head with the 01 manifolds but I dont have the numbers...

 

https://jeepexhaustadapter.com/

 

If you are going to keep the 2000 cali emissions ecu you can use the 99 style exhaust. A bung will need to be welded in. Be sure not to position one of the bank 1 sensors directly down stream of the first sensor. You can extend the bank 1 sensor 2 and bank 2 sensor 2 to the stock 99 location. Use spacers to simulate the cat or install one.

 

THe 01 he has needs 4 sensors not to throw codes...i ran 4 when i put a 98 into my 01...2 o2 bungs welded into the 98 exh manifold ...one in each main collector so nbr 1 reads plugs 1 -2-3. And the second reads 4-5-6. Just have to angle them right so they dont hit the motor mounts..Then inbetween the resonator and the muffler i put 2 more bungs so the computer sees all 4....no codes. I also had to cut the stock 01 crossover pipe because it didn't reach the 99 exh manifold flange and have them bend me a new crossover and weld it in...nice work but it was not mandrel bent so it gets a little small right where it bends down and over...I wouldnt really worry but im stroked and im sure its a little restricted there...a project for some other day. i had to splice in 10 feet of wire on both rear o2 sensors so they would reach the connectors way up front...no issue until i need too change out a sensor.. it can be done without extreme effort but im really happy to get rid of that POS 0331