Rough idle after head and cam replacement
 

So, here is the run down I have a 2WD 98 4.0 XJ with 341,816 miles on the original motor I developed a really bad lifter tick, so I figured since I gotta get a new cam, and lifters I would go with Comp Cams 68-301-5 cam along with new timing chain, lifters, push rods, and rockers. I also went with edelbrock's aluminum 4.0 head and a new distributor, because the old one had a ton of play in it. Got it back together and the cam broken in, but then I got a P0204 code put a noid light on it and it's firing. I pulled the plug and it had spark I also checked compression which was 175ish hot. So I moved the number 4 injector to the number 3 spot and vice-versa with no change. I unplug the front o2 sensor and it didn't help, also i hooked up a test light and i have constant power on the + side of the harness when its running, and a pulshing light on the negitive side when its running as well. Any ideas on where to look next?

If I raise the idle it pops intermittent out of the exhaust.

Fuel pressure is 46psi at idle

Guess it time to start throwing parts at it....

Did it run right during the cam break in? Or was it misbehaving from the get go?

Assuming you didn't have that code until you did the cam/head etc I would look long and hard at all the injector wiring, connectors , grounds etc.
Very possible something got messed up when you were working on it.

it hard to say, because as soon as it started it was ran at 2000-2500rpms for 30 minutes and then shut down to change the oil.

I have taken the harness completely out unwrapped it and checked every wire I didn't find anything.

Is it possible the P0204 code was pre-existing? The 4.0 is really touchy when it comes to valve train tolerance (forgive me if I'm being captain obvious) because there is no adjustment. How did you pick push rod lengths? Also, if you still have the old distributor cap, you can cut a window in it and see if your indexed correctly. See Cruiser54 tip 13: Distributor Indexing | cruiser54
By chance, did you install Harland Sharp roller rockers?

After making sure as mentioned above that the new distributor is in correctly.
if that doesn't solve the problem put the old distributor with the old pickup back is and try it.
We're back to the crummy replacement parts problem.

(BTW Although you didn't mention it I'm assuming that when you threw all these part àt the thing you replaced the plug wires,)

No, it ran great other then the horrible lifter knock. As for the push rods I just used factory length push rod with factory lifters and factory rockers, i figured since the cam isn't to aggressive I wouldn't need custom length push rods. I don't have the old distributor cap, but I did mark #1 spot on the base to make sure the rotor was slightly off #1 when installed.

I've tried two sets of used plug wires and have a new set on order.

Did you do all the stuff in Codak's thread?

Speaking of which wonder if he solved his issue...

From what you have said , before you, for whatever reason, put a cam and an aluminum head on an engine with 340k on it it ran fine with no codes. Only problem was the lifter noise.

Now:as I understand it:
1) it idles bad and sometimes backfires out the exhaust
2 it's setting an injector code on cylinder 4, but swapping injectors around doesn't move the code. The noid light doesn't show a problem
3) it has NOT set a misfire code, which is interesting.

I have no idea what's wrong with the thing but pretty clearly it occurred after all parts were replaced. Compression is ok, fuel pressure is ok, I really wonder if timing ( ignition or injector) is off on cylinder 4. Put the old distributor AND the old pickup back in and see what happens. There have been a lot of horror stories about replacement distributors having the gear 180 off, who knows what else could be wrong with it.
(Also,btw. You did all this work because of "horrible lifter knock" how did you confirm the noise was actually lifter knock and which cylinder was it?)

I not aware of Codak's issue, but to be honest ive looked at so many threads i might have seen it and not know. Which one is it?